JournalTOCs

Seismological Research Letters
Journal Prestige (SJR): 2.008

Citation Impact (citeScore): 3
Number of Followers: 12

Full-text available via subscription

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ISSN (Print) 0895-0695 - ISSN (Online) 1938-2057
Published by GeoScienceWorld

[17 journals]

Nominations for the Next Joyner Lecturer Due 30 June
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  PubDate: Fri, 31 May 2024 00:00:00 GMT
Follow the Trace: Becoming a Seismo‐Detective with a Campus‐Based
Raspberry Shake Seismometer
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  Abstract: Seismic signals, whether caused by earthquakes, other natural phenomena, or artificial noise sources, have specific characteristics in the time and frequency domains that contain crucial information reflecting their source. The analysis of seismic time series is an essential part of every seismology‐oriented study program. Enabling students to work with data collected from their own campus, including signals from both anthropogenic and natural seismic sources, can provide vivid, practical examples to make abstract concepts communicated in classes more concrete and relevant. Data from research‐grade broadband seismometers enable us to record time series of vibrations at a broad range of frequencies; however, these sensors are costly and are often deployed in remote places. Participation in the Raspberry Shake citizen science network enables seismology educators to record seismic signals on our own campuses and use these recordings in our classrooms and for public outreach. Yale University installed a Raspberry Shake three‐component, low‐cost seismometer in the Earth and Planetary Sciences department building in Summer 2022, enabling the detection of local, regional, and teleseismic earthquakes, microseismic noise, and anthropogenic noise sources from building construction, an explosive event in a steam tunnel, and general building use. Here, we discuss and illustrate the use of data from our Raspberry Shake in outreach and education activities at Yale. In particular, we highlight a series of ObsPy‐based exercises that will be used in courses taught in our department, including our upper‐level Introduction to Seismology course and our undergraduate classes on Natural Disasters and Forensic Geoscience.
  PubDate: Tue, 28 May 2024 00:00:00 GMT
On the Provenance of Field Reports of the 1886 Charleston, South Carolina,
Earthquake: A Seismo‐Historical Whodunnit
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  Abstract: AbstractMuch of what is known about the effects of the 1886 Charleston, South Carolina, earthquake throughout the epicentral region can be attributed to meticulous field investigations by an individual with training in geology and engineering, Earle Sloan (Clendenin, 1926). In a recent study, Bilham and Hough (2024) undertook a detailed analysis of the effects of the earthquake on railroads in the Charleston region, drawing heavily from Sloan’s reports. This exercise identified several inconsistencies in Sloan’s field reports, including understandable measurement imprecision, inferred data entry mistakes, and transcription errors. The study also begged the question, where was Sloan at the time of the mainshock and over the following week' And to what extent did he draw from secondhand information in compiling his reports' On this question Sloan’s reports were sometimes enigmatic, lending themselves to misinterpretation in contemporaneous as well as modern interpretations. Beyond the details that were germane for, and briefly summarized by, the studies of Bilham and Hough (2023, 2024), in this report we don our historical seismologist caps to chronicle Sloan’s activities following the earthquake. We summarize our inferences here for the benefit of future scholars who might attempt to retrace either Sloan’s footsteps or our own. This study also serves to highlight Sloan’s singular contributions to earthquake science, which were never published separately.
  PubDate: Thu, 09 May 2024 00:00:00 GMT
New Empirical Source‐Scaling Laws for Crustal Earthquakes Incorporating
Fault Dip and Seismogenic‐Thickness Effects
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  Abstract: AbstractNew global source‐scaling relations for the aspect ratio and rupture area for crustal earthquakes that include the width‐limited effect and a possible free‐surface effect are derived using a global dataset of finite‐fault rupture models. In contrast to the commonly used scaling relations between moment magnitude (M), fault length (L), width (W), and area, we built self‐consistent scaling relations by relating M to the aspect ratio (L/W) and to the fault area to model the change in the aspect ratio once the rupture width reaches the down‐dip width limit of the fault. The width‐limited effect of large‐magnitude earthquakes depends on the fault dip and a regional term for the seismogenic thickness. The magnitude scaling of the aspect ratio includes a break in the magnitude scaling that is dip angle dependent. This dip angle‐dependent magnitude scaling in the magnitude–area relation is modeled by a trilinear relation incorporating a dip‐related transition range. The effect of the free surface was observed using a normalized depth term and parameterizing the source by the depth of the top of the fault rupture; it is more apparent in the area scaling relation. The scaling differences are related to the fault geometry, not to the rake angle, as commonly assumed. Finally, the corresponding L and W scaling relations obtained by converting the area and aspect ratio models to L and W models not only show good agreement with the previous regional scaling laws on average but also provide better fault‐specific application due to the inclusion of a fault‐specific dip angle and seismogenic thickness.
  PubDate: Fri, 26 Apr 2024 00:00:00 GMT
Cyclic Injection Leads to Larger and More Frequent Induced Earthquakes
under Volume‐Controlled Conditions
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  Abstract: AbstractAs carbon storage technologies advance globally, methods to understand and mitigate induced earthquakes become increasingly important. Although the physical processes that relate increased subsurface pore pressure changes to induced earthquakes have long been known, reliable methods to forecast and control induced seismic sequences remain elusive. Suggested reservoir engineering scenarios for mitigating induced earthquakes typically involve modulation of the injection rate. Some operators have implemented periodic shutdowns (i.e., effective cycling of injection rates) to allow reservoir pressures to equilibrate (e.g., Paradox Valley) or shut‐in wells after the occurrence of an event of concern (e.g., Basel, Switzerland). Other proposed scenarios include altering injection rates, actively managing pressures through coproduction of fluids, and preinjection brine extraction. In this work, we use 3D physics‐based earthquake simulations to understand the effects of different injection scenarios on induced earthquake rates, maximum event magnitudes, and postinjection seismicity. For comparability, the modeled injection considers the same cumulative volume over the project’s operational life but varies the schedule and rates of fluid injected. Simulation results show that cyclic injection leads to more frequent and larger events than constant injection. Furthermore, with intermittent injection scenario, a significant number of events are shown to occur during pauses in injection, and the seismicity rate remains elevated for longer into the postinjection phase compared to the constant injection scenario.
  PubDate: Fri, 19 Apr 2024 00:00:00 GMT
Imaging the Sedimentary and Crustal Structure of the Luoyang Basin,
Central China, Using a Dense Nodal Seismic Array
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  Abstract: AbstractThe Luoyang basin lies in the southern margin of the North China block, separating the trans‐North China orogen to the north and the Qinling‐Dabie orogen to the south. Determining how the basin formed is important for understanding the history of the North China block and its evolution during the Mesozoic and Cenozoic times. Based on the teleseismic data recorded by a dense nodal seismic array, we used the receiver function method to image the sedimentary and crustal structures in the Luoyang basin. Common conversion point stacking images show that the Moho is at a depth of ∼35 km on the south and west sides and slightly uplifted to ∼30 km below the northeastern basin. Two sets of P‐to‐S conversions are imaged in the shallow crust, separating the near‐surface sediments into consolidated, semiconsolidated, and unconsolidated layers. The top of the consolidated sedimentary layer is close to the surface at the southern basin and present at a depth of ∼2 km beneath the central basin, then deepens to a depth of ∼3 km below the northern basin. The discontinuous interface in the sediments indicates that the sedimentary layer was truncated by some blind north‐dipping normal faults. The northeastward thinning crust, thickening sedimentary layers, and dipping normal faults together indicate that the Luoyang basin evolved in association with the deep crustal extension response to the lithospheric thinning of the North China block. By superimposing the deep crustal extension, we propose that the present‐day landform of the Luoyang basin was also shaped by fluvial erosion at the surface, which was accompanied by the expansion of Yihe and Luohe riverbeds during the Quaternary.
  PubDate: Wed, 17 Apr 2024 00:00:00 GMT
The Potential of Crowdsourced Data for the Rapid Impact Assessment of
Large Earthquakes: The 2023 M 7.8 Kahramanmaraş‐Pazarcık, Türkiye,
Earthquake
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  Abstract: AbstractReliable and rapid impact assessment for large earthquakes is a challenge because it is difficult to rapidly determine the fault geometry and thus the spatial distribution of shaking intensities. In this retrospective study of the M 7.8 Kahramanmaraş‐Pazarcık, Türkiye, earthquake, we evaluate how eyewitness observations crowdsourced through the LastQuake system can improve such assessments. These data consist of felt reports describing the local level of shaking or damage and manually validated geolocated imagery. In the first part of this study, the methods used to derive macroseismic intensity values from felt reports, particularly for high values, are validated by comparison with independently determined intensities. This comparison confirms that the maximum intensity that can be derived from felt reports does not generally exceed VIII. A fatality estimate of 3000 could be made within a few hours by evaluating the number of people exposed to high intensities using the felt reports and assuming a point source. However, this estimate was known to be an underestimate because of the point‐source approximation; this underestimate was also confirmed by the geolocated imagery showing high levels of damage at epicentral distances well beyond those predicted by circular isoseismals. However, improved estimates could have been derived from the event’s ShakeMaps using the U.S. Geological Survey Prompt Assessment of Global Earthquakes for Response (PAGER) fatality loss‐modeling system, either by incorporating the felt reports into the ShakeMaps computation or using, in addition, a finite‐source (here line‐source) model derived from the felt reports using the Finite‐fault rupture Detector software. The inclusion of fault geometry would have resulted in a fatality estimate with data collected within 10 min of the origin determination, which was consistent with the final PAGER alert level and the reported death toll that were both only known days later. Although more work would be helpful to assess the reliability of the derived fault geometry, in regions where they are collected in large numbers, felt reports collected within 10 min of the earthquake can be used to substantially improve current fatality estimates.
  PubDate: Fri, 12 Apr 2024 00:00:00 GMT
Magnitude m b : Reducing Processing‐Related Variability
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  Abstract: AbstractIt is well known that magnitude mb shows a large variation between different stations and agencies for the same event. In this study we investigate the various causes of this variation and we have found that apart from the regional variation caused by the Earth’s 3D structure, a major contribution to the variation is the way the data are processed: automatic or manual determination of amplitude and period is different for the same signal at different agencies or processing systems and/or there are errors in the amplitude measurements when correcting the signal from the simulated World Wide Standard Seismic Network Short Period (WWSSN‐SP) response. Part of the problem to objectively investigate the causes for the variation is that few agencies use the International Association of Seismology and Physics of the Earth’s Interior standard for reporting the observations. To get less variability in mb, a standardized way of reading amplitude and period must be developed and used.
  PubDate: Fri, 12 Apr 2024 00:00:00 GMT
Double‐Vergent Plate Boundary Faults and Triggered Coseismic Rupture of
the 2022 Chihshang Doublet Earthquake Occurred in Eastern Taiwan
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  Abstract: AbstractThe earthquake doublet of Mw 6.5 and 6.9 occurred along the west‐dipping Central Range fault (CRF) adjacent to the east‐dipping creep segment of the Longitudinal Valley fault in eastern Taiwan on 17–18 September 2022. The faulting model derived from the Interferometric Synthetic Aperture Radar and Global Positioning System observation suggests that the west‐dipping CRF rupture is responsible for the two mainshocks. Meanwhile, the two major earthquakes resulted in ∼100 km of fault slip along the double‐convergent plate boundary faults near the Longitudinal Valley in eastern Taiwan. The 2022 Chihshang earthquake sequence filled the seismic gap of the CRF located between the 2006 ML 6.1 Taitung earthquake and the 2013 ML 6.1 Ruisui earthquake. Finally, the 2022 Chihshang earthquake sequence increased the Coulomb failure stress in the southernmost segment of the CRF, which may cause a higher seismic potential in the future.
  PubDate: Wed, 10 Apr 2024 00:00:00 GMT
Direct Evidence for Diverse Source Complexity in Small Earthquakes ( M w
3.3–5.0) Obtained from Near‐Source Borehole Seismic Data
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  Abstract: AbstractSmall earthquakes (Mw <5) may have a similar degree of complexity as large earthquakes. However, their seismic waveforms are strongly distorted during wave propagation, making their complexity challenging to resolve. In many cases, the source parameters of small events are determined based on models that assume their source patterns are simple. In this study, to directly examine the source complexities in small events, we examined high‐quality near‐source (<8 km) seismic waveforms recorded by two excellent downhole sensors in Japan. The results show that the P waveforms of microearthquakes (Mw <2) are always simple at the sensors and agree well with the synthetic waveforms based on a 1D structure up to 20 Hz. The microearthquake waveforms in this frequency band essentially represent path effects besides the static source effect, suggesting that the contribution of structural inhomogeneity to the observed waveforms is small. Taking advantage of this, we inferred the moment rate functions of 164 Mw 3.3–5.0 events from the shapes of the direct P waves. They showed diversity in their complexity, and even conservatively estimated, 25% of the events had multiple subevents. The results suggest that methods that account for complexity, rather than those that assume a simple source pattern, are required to characterize even small events.
  PubDate: Wed, 10 Apr 2024 00:00:00 GMT
SKHASH: A Python Package for Computing Earthquake Focal Mechanisms
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  Abstract: AbstractWe introduce a Python package for computing focal mechanism solutions. This algorithm, which we refer to as SKHASH, is largely based on the HASH algorithm originally written in Fortran over 20 yr ago. HASH innovated the use of suites of solutions, spanning the expected errors in polarities and takeoff angles, to estimate focal mechanism uncertainty. SKHASH benefits from new features with flexible input formats and allows users to take advantage of recent advances in constraining focal mechanisms for small magnitude or poorly recorded earthquakes. The 3D locations of earthquakes and the velocity models used are varied when finding acceptable solutions. As a result, source–receiver azimuths are reflective of errors from the earthquake locations and velocity models, in addition to the takeoff angles. Users can consider weighted P‐wave first‐motion polarities derived from traditional or machine‐learning picks, cross‐correlation consensus, and/or imputation techniques using SKHASH. Focal mechanism solutions can also be further constrained using traditional, machine learning, and/or cross‐correlation consensus S/P amplitude ratios. With improved reporting of individual and collective P polarity and S/P amplitude misfits, users can better evaluate the success of the solutions and the quality of the measurements. The reporting also makes it easier to identify potential issues with metadata, including incorrectly reported station polarity reversals. In addition, by leveraging vectorized operations, taking advantage of an efficient backend Python C Application Programming Interface, and the use of a parallel environment, the Python SKHASH routine may compute mechanisms quicker than the HASH routine.
  PubDate: Wed, 10 Apr 2024 00:00:00 GMT
Modern Approaches for Historical Seismograms: Moment Tensor Inversion of
the 1947 Squillace Basin, South Italy, Earthquake
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  Abstract: AbstractThe scientific community has become increasingly aware of the importance of preserving and recovering historical seismic data, also because of their possible use in combination with modern techniques of analysis. Seismograms coming from the analog recording era cover more than 100 yr of seismic activity and may have a great relevance, especially for seismic risk evaluations in regions struck by destructive events in the past centuries but characterized by minor activity in the last decades. In this study we used analog seismograms to investigate an earthquake of presumed magnitude 5.7 that occurred in 1947 in central Calabria, south Italy, a high‐seismic risk region framed in a complex geodynamic setting led by northwest‐trending Nubia–Eurasia convergence and southeastward Ionian slab rollback. According to seismic catalogs, the 1947 is the only M > 5.5 earthquake instrumentally recorded in an area where the presence of the lateral edge of the Ionian slab has been suggested and an intense debate is still open concerning possible existence, and proper location, of a subduction‐transform edge propagator (STEP) fault zone. To study this earthquake, we selected 15 medium‐ to long‐period analog seismograms with related instrumental parameters, and we proceeded with vectorization process and proper waveform corrections. A technique specifically developed for time‐domain moment tensor computation through waveform inversion of analog seismograms has been applied to the digitized recordings. The moment tensor solution estimated for the 1947 earthquake indicates strike‐slip mechanism, focal depth of 28 km and Mw 5.1. The obtained hypocentral depth and left‐lateral kinematics on about west‐northwest–east‐southeast‐oriented fault fit well with the local seismotectonic framework and are compatible with STEP fault activity in central Calabria, furnishing a new seismological constraint to the debate concerning slab edge kinematics. Moreover, the presented analysis is useful for sharing with the scientific community new data and methodological issues related to historical seismogram management.
  PubDate: Mon, 08 Apr 2024 00:00:00 GMT
HD‐TMA: A New Fast Template Matching Algorithm Implementation for Linear
DAS Array Data and Its Optimization Strategies
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  Abstract: AbstractDistributed acoustic sensing (DAS) technology, combined with existing telecom fiber‐optic cable, has shown great potential in earthquake monitoring. The template matching algorithm (TMA) shows good detection capabilities but depends on heavy computational cost and diverse template events. We developed a program named HD‐TMA (high‐efficiency DAS template matching algorithm), which accelerates computation by 40 times on the central processing unit platform and 2 times on the graphic processing unit platform. For linear DAS array data, we introduced a fast arrival‐picking algorithm based on the Hough transform to pick the time window of template waveform. The HD‐TMA was successfully applied to the 2022 Ms 6.9 Menyuan earthquake aftershock sequence recorded by a DAS array, and the DAS data result was compared with a collocated short‐period seismometer data’s result. Two optimization strategies were discussed based on this data set. (1) Using signal‐to‐noise ratio in choosing the location and aperture of the subarray and the time window of the template waveform. (2) Considering the decrease in template events’ marginal utility, we proposed applying a neural network to build a template event library, followed by the HD‐TMA scanning. Such strategies can effectively reduce computational cost and improve detection capability.
  PubDate: Wed, 03 Apr 2024 00:00:00 GMT
SSA2py: A High‐Performance Python Implementation of the
Source‐Scanning Algorithm for Spatiotemporal Seismic Source Imaging
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  Abstract: AbstractThis article introduces the first version of SSA2py (v.1.0)—an open‐source package designed to implement the source‐scanning algorithm (SSA). SSA2py is a Python‐based, high‐performance‐oriented package that incorporates the SSA method, which has been effectively applied to numerous earthquakes for imaging the spatiotemporal behavior of the seismic source. The software supports a wide range of data and metadata resources. These include the International Federation of Digital Seismograph Networks Web Services, the SeedLink protocol, and others, ensuring optimal access to waveforms and station metadata. Furthermore, the code may evaluate the quality of accessible waveforms using signal analysis methods, allowing for the most appropriate data selection. The SSA method has been computationally optimized using multiprocessing techniques for efficient central processing unit and graphic processing units executions, enabling considerably accelerated computational processes even for large‐scale grid searches. The program is also designed to provide statistical and methodological uncertainties for the executed cases through jackknife, bootstrap, and backprojection array response function tests. After appropriate tuning by the user, SSA2py can be used for detailed earthquake source studies that backprojection technique typically serves as a complementary output to the source inversion result or as a near‐real‐time tool for successful and quick identification of the style and complexity of the earthquake rupture. With a wide and flexible configuration, the user has complete control over all calculating aspects of SSA2py. This article provides a detailed description of the structure and capabilities of this new package, and its reliability is demonstrated through targeted applications to the 2004 Mw 6.0 Parkfield and 2019 Mw 7.1 Ridgecrest earthquakes. Furthermore, the computational efficiency of SSA2py is validated through rigorous performance tests.
  PubDate: Fri, 29 Mar 2024 00:00:00 GMT
Temporary Seismic Network in the Metropolitan Area of Rome (Italy): New
Insight on an Urban Seismology Experiment
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  Abstract: AbstractThis study presents data and preliminary analysis from a temporary seismic network (SPQR), which was deployed in the urban area of Rome (Italy) for three months in early 2021. The network was designed to investigate the city’s subsurface while evaluating the feasibility of a permanent urban seismic network, and consisted of 24 seismic stations. Despite significant anthropogenic noise, the SPQR network well recorded earthquake signals, revealing clear spatial variability referable to site effects. In addition, the network’s continuous recordings allowed the use of seismic noise and earthquake signals to derive spectral ratios at sites located in different geological and lithological settings. During the experiment, there were periods of activity restrictions imposed on citizens to limit the spread of COVID‐19. Although the observed power spectral density levels at stations may not show visible noise reductions, they do cause variations in calculated spectral ratios across measurement sites. Finally, a statistical noise analysis was conducted on continuous seismic station data to evaluate their performance in terms of detection threshold for earthquakes. The results indicate that all network stations can effectively record earthquakes with a good signal‐to‐noise ratio (≥5 for P and S phases) in the magnitude range of 1.9–3.3 at distances of 10 km and 80 km, respectively. In addition, the network has the potential to record earthquakes of magnitude 4 up to 200 km, covering areas in Central Italy that are far from the city. This analysis shows that it is possible to establish urban observatories in noisy cities such as Rome, where hazard studies are of particular importance due to the high vulnerability (inherent fragility of its monumental heritage) and exposure.
  PubDate: Wed, 27 Mar 2024 00:00:00 GMT
A New Spatial Variation Model for Ground‐Motion Intensities Combined
with Correlation and Coherency
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  Abstract: AbstractRegional seismic risk or loss assessments generally require simulation of spatially distributed ground motions using multiple intensity measures. Hence, in this study, ground‐motion model estimation is performed with a spatial correlation. Previously, many researchers have analyzed spatial correlations and developed empirical models using ground‐motion recordings. In this study, ground motions occurring in California between 2019 and 2023 were used to analyze spatial correlations using semivariograms for the peak ground acceleration and pseudospectral acceleration in various spectral periods. Based on the analysis results, two aspects need to be revised in the conventional correlation model: (1) the empirical exponential model cannot reasonably reflect the target spatial correlation at a separation distance <10 km, and (2) the variation in the spatial correlation ground‐motion intensity cannot be described at a small separation distance <1 km. Owing to these limitations, we revised the fitting model of the semivariogram to better characterize the spatial correlation. In the model, another function called coherency, replaced the spatial correlation to characterize the variation in the Fourier phase rather than the intensity within a separation distance <1 km. This research shows that the spatial variation in any region can be analyzed by combining the coherence and correlation functions for practical seismic‐risk or loss assessment problems.
  PubDate: Mon, 25 Mar 2024 00:00:00 GMT
Reliable Earthquake Source Parameters Using Distributed Acoustic Sensing
Data Derived from Coda Envelopes
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  Abstract: AbstractA challenge in fully using distributed acoustic sensing (DAS) data collected from fiber‐optic sensors is correcting the signals to provide quantitative true ground motion. Such corrections require considering coupling and instrument response issues. In this study, we show via comparison with geophone and broadband seismometer data that we can use coda envelope calibration techniques to obtain absolute moment magnitudes and source spectra from DAS data. Here, we use DAS and nodal geophones deployed as part of a geothermal monitoring experiment at Brady Hot Springs, Nevada, and on a 20 km long dark fiber of the ESnet’s Dark Fiber Testbed–a U.S. Department of Energy user facility, in Sacramento, California. Several DAS line segments with colocated geophone stations were used to compare the amplitude variation using narrowband S‐wave coda envelopes. The DAS coda envelope decay at each point showed remarkable similarity with coda envelopes from different events in each narrow frequency range examined. The coda envelopes are used to determine Mw magnitudes and source spectra from regional stations without any major scatter. Because coda waves arrive from a range of directions, the azimuthal sensitivity of DAS is somewhat ameliorated. We show that the openly available seismic coda calibration software toolkit can be used for straightforward and faster processing of large DAS datasets for source parameters and subsurface imaging.
  PubDate: Mon, 25 Mar 2024 00:00:00 GMT
Novel Phase‐Sensitive Full‐Waveform Tomography for Seismic
Imaging
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  Abstract: AbstractFull‐waveform tomography (FWT) is increasingly recognized as a pivotal technique for delineating high‐resolution subsurface properties. Despite its significant potential, practical applications of FWT encounter persistent challenges, particularly in dealing with local minima and cycle‐skipping problems. These difficulties often arise and are intensified by the least‐squares (L2) norm’s intrinsic insensitivity to phase mismatches. To address these challenges, we have redefined the traditional L2 norm misfit function by incorporating a time shift within the synthetic waveform. This shift is determined by the temporal discrepancies between the observed and synthetic waveforms, identified through a cross‐correlation technique. This approach, termed phase‐sensitive FWT, integrates phase differences into the new misfit function, thus significantly mitigating the cycle‐skipping problem. Numerical experiments demonstrate that PSFWT reduces dependence on the initial model and achieves more accurate inversion results compared with the traditional L2 norm method, highlighting its potential for enhancing the precision and reliability of seismic imaging.
  PubDate: Mon, 25 Mar 2024 00:00:00 GMT
Weighted Compressive Sensing Applied to Seismic Interferometry: Wavefield
Reconstruction Using Prior Information
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  Abstract: AbstractSeismic interferometry is widely used for passive subsurface investigation using seismic noise. The technique requires much storage for long noise records to suppress interferometric noise, which consists of spurious arrivals that do not correspond to the inter‐receiver surface waves. Such long recordings may not be available in practice. Compressive sensing (CS), which is a wavefield reconstruction technique operating on incomplete data, may increase the availability, and reduce storage limitations of long noise time series. Using a numerical example of a linear array surrounded by sources and the Fourier basis for a sparse transform, we show that inter‐receiver wavefields can be recovered at the locations where seismometers are unavailable, reducing the storage required for interferometry. We propose and develop a weighted CS algorithm that helps suppress the spurious arrivals by incorporating a priori information about the arrivals of surface waves that can be expected.
  PubDate: Mon, 25 Mar 2024 00:00:00 GMT
Strengthening the Development and Use of “Deep” Seismic Event
Catalogs
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  Abstract: T he development of seismic event catalogs has undergone a revolution due to the combination of increasingly available continuous waveform data with advanced methods for detecting events and phase arrival times. This began with template matching but has accelerated and generalized with the development of deep learning methods for detecting phase arrival times. Some of the most popular deep learning models for detecting phase arrival times (Zhu and Beroza, 2019; Mousavi et al., 2020) have been applied to a range of applications from quickly delivering refined catalogs of aftershocks after a major event (Liu et al., 2020; Kato, 2024) to very large‐scale studies reporting hundreds of thousands of events (Tan et al., 2021; Park et al., 2022) that in each case resulted in a multifold increase in event count and improved locations compared to those from routine monitoring. The continuing advances in these tools and the introduction of user‐friendly packages (Woollam et al., 2022) are making them more accessible such that they are emerging as a new standard approach.
  PubDate: Mon, 25 Mar 2024 00:00:00 GMT
Tracking Seismic Velocity Perturbations at Ridgecrest Using Ballistic
Correlation Functions
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  Abstract: AbstractWe present results based on data of a dense nodal array composed of 147 stations, deployed in 2022 near the epicenter of the 2019 Mw 7.1 Ridgecrest earthquake to investigate characteristics of the seismic wavefields. Through array analyses, we identified two primary components. First, we observed far‐field P waves dominating the 0.5–1.2 Hz frequency range, which are likely primarily generated by wind‐driven oceanic swell activity. Second, we detected near‐field body waves resulting from anthropogenic activities in the frequency range 2–8 Hz. We examined noise correlation functions derived from data of the dense deployment and regional stations to explore fault‐zone seismic velocity changes using ballistic arrivals, with a focus on velocity perturbation shortly before and after the Ridgecrest earthquake sequence. Our findings exhibit distinct behavior compared to results obtained through standard coda‐wave interferometry. Particularly, we observed a decrease in P‐wave travel time on certain station pairs prior to the 2019 earthquake sequence. Supported by detailed investigation of the local seismic wavefields, we interpret the decreasing P‐wave travel time as likely caused by a velocity increase away from the fault, possibly related to fluid migration. However, additional information is necessary to verify this hypothesis.
  PubDate: Wed, 20 Mar 2024 00:00:00 GMT
Ukrainian Seismic Network: Current Status and Challenges
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  PubDate: Mon, 18 Mar 2024 00:00:00 GMT
Anisotropic Characterization of the Chukchi Boardland Based on
Ocean‐Bottom Seismic Experiment during N11‐CHINARE
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  Abstract: AbstractThe current research focus at Chukchi Boardland (CB) revolves around sediment stratification and crustal structure, but investigations into deep stress fields and mantle dynamics are limited. This article presents a study on the anisotropic characteristics of the CB. Shear‐wave splitting measurements were conducted using the transverse energy minimization at six stations recovered from the 11th Chinese National Arctic Research Expedition. The observation period for these six stations ranged from 2 August 2020 to 8 September 2020. The results demonstrate significant anisotropy within the CB, with the fast shear‐wave polarization direction ranging from N60°E to N70°E. The time delays between fast and slow shear waves were found to be ∼0.7 s. By comparing the anisotropy observed at the CB with that at land stations in Arctic Alaska, this study suggested that the genesis of anisotropy beneath the CB was related to the formation of the Amerasian basin. The tectonic processes of rifting during basin evolution and midocean ridge spreading led to the development of anisotropy in the lithosphere beneath the CB during expansion.
  PubDate: Thu, 14 Mar 2024 00:00:00 GMT
Along‐Strike Variation of Rupture Characteristics and Aftershock
Patterns of the 2023 M w 7.8 Türkiye Earthquake Controlled by Fault
Structure
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  Abstract: AbstractOn 6 February 2023, an Mw 7.8 earthquake occurred along the East Anatolian fault zone (EAFZ) in southeastern Türkiye, representing the strongest earthquake in the region in nearly 80 yr. We investigate rupture characteristics and aftershock patterns of the earthquake through focal mechanism calculation, backprojection analysis, and finite‐fault inversion. The results show bilateral rupture propagation of the mainshock with transient supershear speed in the southwest portion of the EAFZ, as well as shallower coseismic slip and abundant normal‐faulting aftershocks in the same portion. We attribute these earthquake behaviors to the along‐strike variation of fault structure of the EAFZ, which features a more complex fault geometry accompanied by numerous short normal faults in the southwest portion. These results shed light on fault segmentation, rupture speed variation, and slip partitioning along the EAFZ, advancing our understanding of fault structural control on earthquake behaviors in a complex multisegment fault system.
  PubDate: Thu, 14 Mar 2024 00:00:00 GMT
Shake to the Beat: Exploring the Seismic Signals and Stadium Response of
Concerts and Music Fans
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  Abstract: AbstractLarge music festivals and stadium concerts are known to produce unique vibration signals that resemble harmonic tremor, particularly at frequencies around 1–10 Hz. This study investigates the seismic signals of a Taylor Swift concert performed on 5 August 2023 (UTC) as part of a series at SoFi Stadium in Inglewood, California, with an audience of ∼70,000. Signals were recorded on regional seismic network stations located within ∼9 km of the stadium, as well as on strong‐motion sensors placed near and inside the stadium prior to the concert series. We automatically identified the seismic signals from spectrograms using a Hough transform approach and characterized their start times, durations, frequency content, particle motions, radiated energy, and equivalent magnitudes. These characteristics allowed us to associate the signals with individual songs and explore the nature of the seismic source. The signal frequencies matched the song beat rates well, whereas the signal and song durations were less similar. Radiated energy was determined to be a more physically relevant measure of strength than magnitude, given the tremor‐like nature of the signals. The structural response of the stadium showed nearly equal shaking intensities in the vertical and horizontal directions at frequencies that match the seismic signals recorded outside the stadium. In addition, we conducted a brief experiment to further evaluate whether the harmonic tremor signals could be generated by the speaker system and instruments, audience motions, or something else. All evidence considered, we interpret the signal source as primarily crowd motion in response to the music. The particle motions of the strongest harmonics are consistent with Rayleigh waves influenced by scattered body waves and likely reflect how the crowd is moving. Results from three other musical performances at SoFi in summer 2023 were similar, although differences in the signals may relate to the musical genre and variations in audience motions.
  PubDate: Wed, 13 Mar 2024 00:00:00 GMT
Complex Rupture Features and Triggering during the 2022 Chishang
Earthquake Sequence in Eastern Taiwan Estimated by InSAR, GPS, Strong
Motion, and Teleseismic Waveform Evidence
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  Abstract: AbstractThe most recent 2022 Chishang earthquake sequence broke a long‐time seismic quiescence on the Central Range fault (CRF), attracting lots of attention to the seismic behaviors and fault interactions of the Longitudinal Valley zone (LVZ), eastern Taiwan orogeny. However, detailed rupture features of both the foreshock and mainshock are still scarce. Here, available static displacements (i.e., Interferometric Synthetic Aperture Radar [InSAR], Global Positioning System [GPS], and strong motion [SM]) and kinematic waveform evidence (i.e., high‐frequency GPS, strong motion, and teleseismic data) are used to delineate the rupture behaviors of both the foreshock and mainshock in this sequence. Our results indicate that the static displacements derived from strong‐motion sites rival the high precision of GPS observations, replenishing the near‐field constraints on the hanging wall together with InSAR and GPS. The optimal uniform slip models exhibit that both the foreshock and mainshock generally ruptured the west‐dipping CRF along the south‐southwest‐striking direction with a steep dip angle >65°. The slip distribution models revealed that the rupture of foreshock and mainshock nearly ruptured a total length of CRF within 65 km from the Guanshan to Ruisui at a depth of above 14 km, and their slips are concentrated within one asperity and two asperities, respectively. The spatial evolution of this sequence’s ruptures exhibits a discontinued and separated pattern, and is well consistent with the local seismicity. Considering that the mainshock was initialed in a weak slip and negative static Coulomb stress region caused by the foreshock, the 2022 sequence occurrence is in favor of a preslip triggering mechanism. The rupture region of the 2022 sequence filled the “seismic gap” along the western flank of the LVZ and will promote the potential seismic hazard in this region.
  PubDate: Wed, 13 Mar 2024 00:00:00 GMT
How Accurately Are MERMAID Seismograms Located'
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  Abstract: AbstractFloating seismographs (Mobile Earthquake Recorder in Marine Areas by Independent Divers project “MERMAIDs”) record the data at depth at a location that is determined by linearly interpolating between the Global Positioning System positions when surfacing, assuming a constant drift velocity at depth. We study the influence of a changing drift velocity between surfacings and of a curvature of the drift trajectory. We separate localizations that directly follow a triggered ascent from those that are interpolated later. The first ones have on average a mislocation of 99 m due to curvature of the drift, against 685 m for interpolated localizations. Mislocations due to nonconstant velocity are somewhat smaller. Equivalent time errors have a distribution with heavier tails than Gaussian. The halfwidth of the 95% interval for equivalent arrival‐time errors is smaller than 27 ms if the seismogram recording triggers an immediate ascent. If the recording is transmitted at a later surfacing, the interpolation is less precise with a 95% confidence interval halfwidth of 222 ms, but 67% of the errors are below 44 ms. We conclude that the localization errors have no significant impact on the accuracy of picked arrival times.
  PubDate: Wed, 13 Mar 2024 00:00:00 GMT
Background Seismic Noise Levels among the Caribbean Network and the Role
of Station Proximity to Coastline
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  Abstract: AbstractThe amplitude and frequency content of background seismic noise is highly variable with geographic location. Understanding the characteristics and behavior of background seismic noise as a function of location can inform approaches to improve network performance and in turn increase earthquake detection capabilities. Here, we calculate power spectral density estimates in one‐hour windows for over 15 yr of vertical‐component data from the nine‐station Caribbean network (CU) and look at background noise within the 0.05–300 s period range. We describe the most visually apparent features observed at the CU stations. One of the most prominent features occurs in the 0.75–3 s band for which power levels are systematically elevated and decay as a function of proximity to the coastline. Further examination of this band on 1679 contiguous USArray Transportable Array stations reveals the same relationship. Such a relationship with coastal distance is not observed in the 4–8 s range more typical of globally observed secondary microseisms. A simple surface‐wave amplitude decay model fits the observed decay well with geometric spreading as the most important factor for stations near the coast (<∼50 km). The model indicates that power levels are strongly influenced by proximity to coastline at 0.75–3 s. This may be because power from nearshore wave action at 0.75–3 s overwhelms more distant and spatially distributed secondary microseism generation. Application of this basic model indicates that a power reduction of ∼25 dB can be achieved by simply installing the seismometer 25 km away from the coastline. This finding may help to inform future site locations and array design thereby improving network performance and data quality, and subsequently earthquake detection capabilities.
  PubDate: Fri, 08 Mar 2024 00:00:00 GMT
Microseismic Event Location with Dual Vertical DAS Arrays: Insights from
the FORGE 2022 Stimulation
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  Abstract: AbstractWe investigate the resolvability of a microseismic event location given a recording array composed of vertical distributed acoustic sensing (DAS) boreholes. We use a modified source‐scanning algorithm that takes into account both P and S waves. We transform the brightness maps it produces into probability density functions (PDFs), over which we carry out a resolution and uncertainty analysis. We apply this approach to microseismic events recorded by two vertical DAS boreholes as part of the Frontier Observatory for Research in Geothermal Energy (FORGE) project. We show that for the specific acquisition geometry in FORGE, the horizontal location of the events cannot be determined, but their depth can, similar to results obtained with a single borehole. Using synthetic examples, we show that the recording array’s geometry is the limiting factor in the determination of the horizontal location. We investigate various possible recording geometries composed of idealized DAS‐like vertical boreholes with varying locations and depths. We find that, besides the number of recordingd boreholes, their depth is the main factor influencing the location estimation uncertainty. The number and position of the boreholes mainly influence the spatial distribution of the PDF, whereas the boreholes’ depth mainly influences its size. Despite the simplicity of our analysis, it highlights the influence of the monitoring array design for microseismic events’ locating using vertical DAS arrays.
  PubDate: Fri, 08 Mar 2024 00:00:00 GMT
Which Global Moment Tensor Catalog Provides the Most Precise
Non‐Double‐Couple Components'
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  Abstract: AbstractThe availability of digital seismic waveform data enabled compilation of seismic moment tensor catalogs that provide information about earthquake source processes beyond what could be derived from earlier methods that assume double‐couple sources representing slip on planar faults. This additional versatility involves additional complexity. Moment tensors are determined by inversions minimizing the misfit between observed and synthetic waveforms, and depend on the specifics of the data inverted, the inversion algorithm, and the Earth structure assumed. Hence, substantial uncertainties arise in moment tensors and quantities derived from them, which can be assessed by comparing moment tensors from multiple global and regional catalogs using different data and inversion procedures. While the double‐couple (DC) components of moment tensors are generally determined with greater certainty, non‐double‐couple (NDC) components for the same earthquake sometimes differ significantly between catalogs. This observation raises questions about the reliability of their determination and hence their geological significance. Using the correlation between NDC components in different catalogs, we quantify the reliability of NDC components in moment tensor catalogs through the determination of the effects of unmodeled and inaccurately modeled effects contained in them. We determine that the NDC components in the Global Centroid Moment Tensor catalog are, on average, more precise than in other catalogs, and thus studies on NDC components should be based on this catalog. Furthermore, their uncertainties are largely unrelated to uncertainties in the DC components. Therefore, the reliability of fault angles derived from a moment tensor is largely independent from the reliability of its NDC components.
  PubDate: Wed, 06 Mar 2024 00:00:00 GMT
The 6 February 2023 Earthquakes in Southern Türkiye: When Geoscience
Meets Public Concern
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  PubDate: Thu, 29 Feb 2024 00:00:00 GMT
Cause of Enigmatic Upper‐Mantle Earthquakes in Central Wyoming
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  Abstract: AbstractEarthquakes deeper than 60 km generally occur in subducting slabs. However, on 21 September 2013 two earthquakes (M 4.8 and 3.0) occurred at ∼71 to 75 km depths in the upper mantle beneath central Wyoming in the stable North American continent, where there is no actively subducting slab at present. The cause of the two events is still unclear. Here, we present detailed 3D P‐wave isotropic and anisotropic tomography down to 750 km depth under Wyoming and adjacent areas. Our result shows that the two Wyoming events took place within a high‐velocity (high‐V) body at 0–160 km depths, which may be part of dense continental lithosphere. Another high‐V body exists at ∼300 to 500 km depths, which may reflect a remnant of the subducted Farallon slab. A significant low‐velocity (low‐V) zone appears at ∼200 to 300 km depths between the two high‐V bodies, and the low‐V zone exhibits seismic anisotropy that VP is greater in the vertical direction than that in the horizontal direction. The low‐V zone may include ascending fluids from dehydration of the subducted slab remnant, which was promoted by the nearby hot Yellowstone plume. It is highly possible that the ascending fluids induced the 2013 Wyoming upper‐mantle earthquakes.
  PubDate: Thu, 29 Feb 2024 00:00:00 GMT
Generalization of Deep‐Learning Models for Classification of Local
Distance Earthquakes and Explosions across Various Geologic Settings
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  Abstract: AbstractAlthough accurately classifying signals from earthquakes and explosions at local distance (<250 km) remains an important task for seismic network operations, the growing volume of available seismic data presents a challenge for analysts using traditional source discrimination techniques. In recent years, deep‐learning models have proven effective at discriminating between low‐magnitude earthquakes and explosions measured at local distances, but it is not clear how well these models are capable of generalizing across different geological settings. To address the issue of generalization between regions, we train deep‐learning models (convolutional neural networks [CNNs]) on time–frequency representations (scalograms) of three‐component earthquake and explosion signals from eight different regions in the continental United States. We explore scenarios where models are trained on data from all regions, individual regions, or all but one region. We find that although CNN models trained on individual regions do not necessarily generalize well across different settings, models trained on multiple regions that include diverse path coverage generalize to new regions, with station‐level accuracy of up to 90% or more for data sets from unseen regions. In general, CNN‐based discrimination models significantly outperform models based on uncorrected P/S ratio (measured in the 10–18 Hz frequency band), even when CNN models are tested on data from entirely unseen regions.
  PubDate: Thu, 29 Feb 2024 00:00:00 GMT
Fiber Seismic Network on the Moon
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  Abstract: AbstractInternal structures of the Moon are key to understanding the origin and evolution of the Earth–Moon system and other planets. The Apollo Passive Seismic Experiment detected thousands of lunar seismic events and vastly improved our understanding of the Moon’s interior. However, some critical questions like the state and composition of the core remain unsolved largely due to the sparsity of the Apollo seismic stations and the strong scattering of seismic waves in the top layer of the Moon. In this study, we propose the concept of a fiber seismic network on the Moon and discuss its potential in overcoming the challenges in imaging deep Moon structures. As an emerging technique, distributed acoustic sensing (DAS) can provide a cost‐efficient solution for large‐aperture and dense seismic network deployment in harsh environments. We compute lunar synthetic seismograms and evaluate the performance of DAS arrays of different configurations in retrieving the hidden core reflected seismic phase ScS from the strong scattered waves. We find that, compared to a sparse conventional seismic network, a fiber seismic network using tens of kilometers of cable can dramatically increase the chance of observing clear ScS by array stacking. Our results indicate that DAS could provide new opportunities for the future lunar seismic surveys, but more efforts and further evaluations are required to develop a space‐proof DAS.
  PubDate: Wed, 28 Feb 2024 00:00:00 GMT
Imaging Urban Hidden Faults with Ambient Noise Recorded by Dense Seismic
Arrays
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  Abstract: AbstractThe identification of preexisting near‐surface faults represents a piece of crucial information needed to correctly assess the seismic hazard of any area. The mapping of these structures is particularly challenging in densely populated and heavily urbanized areas. We use ambient seismic noise recorded by a dense array in Seal Beach, California, to image shallow fault lines via a reflected surface‐wave analysis. Our results highlight the presence of previously unknown shallow faults that correlate remarkably well with shallow seismicity and active survey images.
  PubDate: Fri, 23 Feb 2024 00:00:00 GMT
A Practical Approach to Automatic Earthquake Catalog Compilation in Local
OBS Networks Using Deep‐Learning and Network‐Based Algorithms
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  Abstract: AbstractIn land‐based seismology, modern automatic earthquake detection and phase picking algorithms have already proven to outperform classic approaches, resulting in more complete catalogs when only taking a fraction of the time needed for classic methods. For marine‐based seismology, similar advances have not been made yet. For ocean‐bottom seismometer (OBS) data, additional challenges arise, such as a lower signal‐to‐noise ratio and fewer labeled data sets available for training deep‐learning models. However, the performance of available deep‐learning models has not yet been extensively tested on marine‐based data sets. Here, we apply three different modern event detection and phase picking approaches to an ∼12 month local OBS data set and compare the resulting earthquake catalogs and location results. In addition, we evaluate their performance by comparing different subcatalogs of manually detected events and visually revised picks to their automatic counterparts. The results show that seismicity patterns from automatically compiled catalogs are comparable to a manually revised catalog after applying strict location quality control criteria. However, the number of such well‐constrained events varies between the approaches and catalog completeness cannot be reliably determined. We find that PhaseNet is more suitable for local OBS networks compared with EQTransformer and propose a pick‐independent event detection approach, such as Lassie, as the preferred choice for an initial event catalog compilation. Depending on the aim of the study, different schemes of manual repicking should be applied because the automatic picks are not yet reliable enough for developing a velocity model or interpreting small‐scale seismicity patterns.
  PubDate: Fri, 23 Feb 2024 00:00:00 GMT
Study on the Heterogeneity of the Stress Field in the Maduo Earthquake
Fault Zone
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  Abstract: AbstractThe 2021 Maduo earthquake sequence occurred on the Jiangcuo fault zone in Qinghai, China. However, the earthquake sequence did not occur along a straight fault. Aftershocks in the southeast section deflected the aftershocks in the southeast section to the east, when the aftershocks in the northwest section bifurcated. To investigate the relationship between these eastward deflections, aftershock bifurcations, and fault activity, 150 focal mechanism solutions of the Maduo earthquake sequence are collected and processed, and then the stress fields in the subregion and whole region are subsequently determined by partitioning the sliding window from southeast to northwest. The results show that the overall tectonic stress field of the Maduo earthquake sequence exhibits northeast–southwest compression and northwest–southeast extension due to the northward compression of the Indian plate, causing rupture of the Kunlunshankou‐Jiangcuo fault, which straightened the curved Maduo‐Gander fault. The stress field at the deflection of the southeastern section of the source area differs significantly from the overall stress field. The plunge angle of the extensional stress axis in the southeastern deflection area is close to vertical, which is speculated to be due to the effect of the crack tip and the adjustment of local stress after the earthquake. The extensional stress axis at the bifurcated distribution of aftershocks in the northwestern section of the source area is slightly greater than of the overall stress field, indicating that the activation of the bifurcated hidden fault was triggered by the high rupture intensity and the adjustment of local stress. The reactivation of the hidden bifurcated fault results in local stress and causes decreasing seismicity west of the bifurcation area.
  PubDate: Wed, 21 Feb 2024 00:00:00 GMT
Seismic Reflection and Borehole Constraints on the Tectonic Activity of
the North Branch of the Lintong–Chang’an Fault: Implications for the
Seismic Hazards near the Megacity of Xi’an, Central China
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  Abstract: AbstractActive faults that develop in urban regions pose significant seismic hazards to cities with densely concentrated populations and wealth, as demonstrated by several destructive earthquake events in the recent decades. Lintong–Chang’an fault is a known active fault, which comprises multiple branches and traverses the urban area of Xi’an in Weihe Graben—a prominent Chinese megacity with a rich 3000‐year‐old civilization and a population of 13 million. High‐resolution seismic reflection profiles and borehole transects, combined with Quaternary strata dating, reveal that: (1) to the south of Shenhe Loess Tableland, two northern branches of the fault zone follow the trend of the middle part and extend to the front of the Qinling mountains in the SW240° direction; (2) the strata since the late Middle Pleistocene on the borehole transect have been offset, with the vertical displacement of the ∼216 ka layer measured at 5.9 ± 0.3 m, the ∼118 ka layer at 3.8 ± 0.3 m, and 41 ka layer at 1.0 ± 0.1 m, indicating an average vertical slip rate of 0.02–0.04 mm/yr for the individual branch at the study site. Notably, the slip rate of the entire fault zone could be two to three times that of a single branch. Despite the relatively low‐slip rate, the fault traverses the megacity of Xi’an, is situated in the relay zone of two large, strongly active basin boundary normal faults (Huashan and Qinling Piedmont faults) and is responsible for the formation of Xi’an ground fissures. Hence, it is necessary to pay special attention to this fault.
  PubDate: Thu, 15 Feb 2024 00:00:00 GMT
Unraveling the Complex Interplay: Exploring the Relationships between
Seismic and Volcanic Activities in the Colca River Area Using the Coulomb
Stress Transfer
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  Abstract: AbstractThe Colca River area is affected by shallow small‐to‐moderate earthquakes due to the activity of normal and strike‐slip crustal faults on the overriding South American plate. In addition, volcanic activity from the Sabancaya volcano has been recorded. However, the complex relationship between seismic and volcanic activities and the factors that trigger them are poorly understood. To better understand the factors that influence seismic and volcanic activity and their potential connection, it is crucial to characterize the interactions between subsequent earthquakes and assess the impact of magmatic inflation on seismic events. In this study, we analyzed the static Coulomb stress transfer caused by the selected largest earthquakes from 1991 to 2022. We focused on both the assumed source faults and the receiver faults. Furthermore, we examined the Coulomb stress change due to magmatic inflation in 2013–2022 on nodal planes of the selected earthquakes. The results confirm the tectonic source for most earthquakes in the Colca region. Commonly, the magmatic source enhanced the stress change induced by the tectonic source. Although the Coulomb stress change caused by the significant earthquakes had a greater impact than the one resulting from the magmatic inflation, the Coulomb stress transfer seems not to be a dominant factor determining the occurrence and location of earthquakes in this area. The results indicate that most source faults of the analyzed earthquakes were not brought closer to failure due to a positive Coulomb stress transfer caused by seismic activity or magmatic inflation.
  PubDate: Thu, 08 Feb 2024 00:00:00 GMT
Development of a GIS‐Based Predicted‐ V S 30 Map of Türkiye Using
Geological and Topographical Parameters: Case Study for the Region
Affected by the 6 February 2023 Kahramanmaraş Earthquakes
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  Abstract: AbstractThe time‐averaged shear‐wave velocity in the upper 30 m of a site (VS30) is virtually essential in characterizing local soil conditions for multiple purposes, including estimation of site effects, anticipated ground‐motion levels, seismic hazards, and the shape of design spectra. Considering the significance of this proxy and that a number of the Disaster and Emergency Management Presidency of Türkiye (AFAD) strong ground‐motion stations across Türkiye lack assigned VS30 values, a comprehensive study was performed herein to develop empirical equations for estimating VS30 values in Türkiye based on relationships between 432 VS30 measurements at the AFAD stations, geologic units, and topographic data. Initially, units in the geological digital maps were reclassified into four geological periods. Statistical relationships between geological period classes and VS30 samples were interpreted to determine the VS30 boundaries for each period class. Second, VS30 estimations with topographic parameters by utilizing a 2D trend surface analysis method were performed. The resultant two‐parameter polynomial coefficients were associated with VS30 according to the least squares principle, leading to the development of topographic functions for VS30 estimation under each geological period class (R2=0.601). Thereby, digital VS30 estimation maps were produced in grid (90 m) format that may be queried in a Geographic Information Systems environment. Moreover, the quantile regression method was also utilized to determine the coefficients of the envelope curve corresponding to a given exceedance probability (p) for the worst case scenario. Finally, to evaluate the accuracy of the proposed equations, the verifications performed with the VS30 data at the selected AFAD stations in the region affected by the 6 February 2003 earthquakes have also presented successful outcomes. Considering the availability of VS30 maps derived from digital elevation data in the literature, this study offers novel equations that take into account geological units and provide crucial background data for the regional seismic hazard‐based risk assessments in Türkiye, especially for site effect studies using VS30 as a regional site classification parameter.
  PubDate: Thu, 08 Feb 2024 00:00:00 GMT
Long‐Term Infrasound Sensor Calibration and Characterization
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  Abstract: AbstractPrevious testing has shown that infrasound sensors deployed in the field can exhibit notable deviations from their nominal, lab‐based calibrations. These variations may be due to changes in environmental conditions, long‐term sensor drift, or other unresolved features. In early 2018, we installed two identical infrasound elements with five infrasound sensors at each element (Chaparral M50A, Chaparral M64LN, CEA/Martec MB2005, CEA/Seismowave MB3a, and Hyperion IFS‐5113A). These sensors were accepted or under consideration for use in the International Monitoring System network of the Comprehensive Nuclear‐Test‐Ban Treaty. Each element had all sensors connected to a single digitizer and port to the atmosphere. We also recorded instrument enclosure air temperature and humidity and external air temperature. Using the MB2005 as the reference, we examine the relative sensor response (both magnitude and phase) as a function of time and frequency and compare it with quarterly laboratory calibrations and environmental conditions. We find that the magnitude response for all sensors exhibits some variability in both the lab and field, with the amplitude variations often >5%. The field‐based variations are more severe and occur on both long‐term (months) and short‐term (hours) timescales. Short‐term variability correlates with changes in environmental conditions and is considerable (up to 25%) for the Chaparral M50A and noticeable (∼5%) for the French Alternative Energies and Atomic Energy Commission (CEA) MB3a. Long‐term magnitude variability for the Chaparral M50A was up to 50% and does not clearly correlate with environmental conditions. The other sensors show some long‐term magnitude offsets, but they have relatively stable responses in the conditions we examined. The MB3a also displays some frequency‐dependent magnitude variability and shows a minor dependence on temperature. Phase estimates are stable and near zero for all sensors tested. These results strongly suggest sensor response and variability due to environmental conditions should be considered in future infrasound data interpretation and sensor selection and development.
  PubDate: Tue, 06 Feb 2024 00:00:00 GMT
Recalibration of the Intensity Prediction Equation in Italy Using the
Macroseismic Dataset DBMI15 Version 2.0
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  Abstract: AbstractWe recompute the coefficients of the intensity prediction equation (IPE) in Italy using the data of the DBMI15 version 2.0 (v.2.0) intensity database and the instrumental and combined (instrumental plus macroseismic) magnitudes reported by the CPTI15 v.2.0 catalog. We follow the same procedure described in the previous article, consisting of a first step in which the attenuation of intensity I with respect to the distance D from macroseismic hypocenter is referred to the expected intensity at the epicenter IE and a second step in which IE is related to the instrumental magnitude Mi, the combined magnitude Mc, the epicentral intensity I0, and the maximum intensity Imax using error‐in‐variable (EIV) regression methods. The main methodological difference with respect to the original article concerns the estimation of the uncertainty of IE to be used for EIV regressions, which is empirically derived from the standard deviation of regression between IE and Mi and also used for the regressions of IE with Mc, I0, and Imax. In summary, the new IPE determined from DBMI15 v.2.0 is I=IE−0.0081(D−h)−1.072[ln(D)−ln(h)], in which D=R2+h2, h = 4.49 km, and IE can be calculated from the intensity data distribution of the earthquake. If the intensity data distribution is not available, IE can be calculated from the following relationships IE=−2.578+1.867Mw, IE=I0.
  PubDate: Tue, 06 Feb 2024 00:00:00 GMT
Distributed Acoustic Sensing for Crowd Motion and Firecracker Explosions
in the Fireworks Show
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  Abstract: AbstractUrban seismology has recently emerged as a vibrant scientific field, driven by the growing interest in seismic signals generated by major public events, sports gatherings, and transportation services. However, deploying dense traditional seismometers in economically active, densely populated urban areas with heavy traffic poses significant challenges. In this study, we conducted a field experiment utilizing distributed acoustic sensing (DAS) technology during a fireworks display in Guangzhou on 5 February 2023. About 572 m of optical fiber was turned into 286 seismic sensors and deployed on LingShan Island to monitor various vibration signals generated during the fireworks show. Our analysis revealed substantial correlations between crowd motions during different phases of the event and ambient noise features recorded by DAS. Moreover, the cross‐correlation functions of the ambient noise with its dispersion characteristics pointed to near‐field pedestrian activity as the primary noise source. Real‐time heat maps of human crowd motions were reconstructed from DAS recording, offering significant insights into the variations of activity intensity across different locations. Discerning fireworks events on the DAS array is more effective than on a scattered seismometer array, because it is easier to ensure that the same event is picked for all the sites in the DAS dense linear configuration. The DAS data inspection allowed us to pick up a total of 549 firecracker explosions in comparison to the seismometer data that only allowed us to detect 116 firecracker events. The heights of fireworks were located by the grid‐search method and predominantly distributed at 75–300 m, closely aligning with actual fireworks explosion locations. Our findings underscore that the DAS technology can monitor crowd motion and detect vibration signals in the air, bridging the gap between fundamental earth science research and human social activities.
  PubDate: Fri, 02 Feb 2024 00:00:00 GMT
Correlation between Strain Rate and Seismicity in Different Tectonic
Settings
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  Abstract: AbstractGeodetic strain rate characterizes present‐day crustal deformation and therefore may be used as a spatial predictor for earthquakes. However, the reported correlation between strain rates and seismicity varies significantly in different places. Here, we systematically study the correlation between strain rate, seismicity, and seismic moment in six regions representing typical plate boundary zones, diffuse plate boundary regions, and continental interiors. We quantify the strain rate–seismicity correlation using a method similar to the Molchan error diagram and area skill scores. We find that the correlation between strain rate and seismicity varies with different tectonic settings that can be characterized by the mean strain rates. Strong correlations are found in typical plate boundary zones where strain rates are high and concentrated at major fault zones, whereas poor or no correlations are found in stable continental interiors with low strain rates. The correlation between strain rate and seismicity is also time dependent: It is stronger in seismically active periods but weaker during periods of relative quiescence. These temporal variations can be useful for hazard assessment.
  PubDate: Fri, 02 Feb 2024 00:00:00 GMT
Earthquake Disaster Fatality Data: Temporally Stable Power Law Behavior
and Effects of Underreporting
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  Abstract: AbstractWe investigate changes in the global reported fatalities from earthquake disasters in the global Emergency Events Database (EM‐DAT). Drawing parallels with the Gutenberg–Richter frequency–magnitude analysis, in terms of disaster frequency versus the number of casualties, we see a significant overlap of the curves and improving levels of completeness over six 20‐year periods. This implies a decrease in underreporting with time. We find that the apparent strong upward trend in the number of (reported) earthquake disasters in EM‐DAT is caused by a gradually improved reporting primarily of events killing fewer than 10 people. Our findings imply that the true (reported and unreported) number of earthquake disasters, according to the EM‐DAT definition, has been surprisingly constant over, at least, the last 100 yr. We also show that the average annual number of people killed in earthquake disasters is relatively unaffected by spurious trends in reporting and has remained remarkably constant despite population increase. This implies an impressive reduced mortality risk roughly proportional to population increase since 1900. However, there is no indication in the data that the risk of future mega‐disasters is negligible, and further major reductions in vulnerability should be actively pursued.
  PubDate: Fri, 02 Feb 2024 00:00:00 GMT
Operational Earthquake Forecasting in Japan: A Study of Municipal
Government Planning for an Earthquake Advisory or Warning in the Nankai
Region
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  Abstract: AbstractA team of social scientists from the United States and Japan has conducted a study exploring the extent to which municipal governments in Japan have developed plans for response to an operational earthquake forecast from the Japan Meteorological Agency (JMA), indicating that seismic activity in the Nankai trough region has elevated the short‐term probability that a major earthquake may occur. Employing both survey research and in‐depth interviews, the team explored various aspects of the history and science behind the alerting system, guidance from the national government of Japan, and planning by local jurisdictions for a possible future Nankai trough major earthquake. The survey included questions regarding planning actions included in response plans for receipt of “special earthquake warning information” as well as questions regarding challenges in the planning process, expectations that an earthquake would follow the issuance of an alert, and whether planning would reduce the number of fatalities and injuries. We also conducted in‐depth interviews that explored the scientific basis for the alerting system and asked working disaster managers in the Nankai region what they had done to plan and the reasons for not planning if plans had not been developed. We received 469 responses from a total of 736 jurisdictions that comprise the Nankai region—a response rate of 63.7%. We conducted a total of 17 in‐depth interviews. In general, we found that a majority of jurisdictions have response plans for receipt of an alert from the JMA; however, the plans lacked a number of planning elements considered important from a disaster management perspective. In addition, many smaller jurisdictions lacked the staffing, resources, and guidance to form comprehensive response plans. Our report identifies both the strengths and weaknesses of existing plans, and outlines a program for improving planning in the region.
  PubDate: Tue, 30 Jan 2024 00:00:00 GMT

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