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Seismological Research Letters
Journal Prestige (SJR): 2.008  Citation Impact (citeScore): 3 Number of Followers: 12  Subscription journalISSN (Print) 0895-0695 - ISSN (Online) 1938-2057 Published by GeoScienceWorld  [17 journals]
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- An Additional Perspective on “Is the Long‐Term Probability of the
Occurrence of Large Earthquakes along the Nankai Trough Inflated'
Conflict between Science and Risk Management”—By Manabu Hashimoto-
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Authors: Goltz JD.
Abstract: I would like to comment on the Hashimoto (2022) opinion article published in a recent issue of SRL on Nankai’s long‐term earthquake probabilities from the disciplinary perspective of disaster management and social science rather than seismology. My comments are not so much a disagreement with Hashimoto’s view that the long‐term probabilities for the Nankai trough may be inflated but instead to provide a somewhat contrasting perspective on why this region should continue to be an area of concern and focused planning, preparedness, and hazard mitigation. We recently commemorated the tenth anniversary of the Great East Japan Earthquake and Tsunami, a disaster that claimed the lives of 18,000 people, displaced hundreds of thousands, caused widespread damage in the Tohoku region, and raised reasonable concern regarding the southern areas of the subduction zone, where there is also a lengthy history of major earthquakes and far greater population exposure and critical infrastructure at risk.
PubDate: Wed, 08 Jun 2022 00:00:00 GMT
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- Evaluation of the Event Detection Level of the Cuban Seismic Network
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Authors: Diez Zaldivar ER; Priolo E, Sandron D, et al.
Abstract: AbstractThe detection level of a seismic network is a measure of its effective ability to record small earthquakes in a given area. It can vary in both space and time and depends on several factors such as meteorological conditions, anthropic noise, local soil conditions—all factors that affect the seismic noise level—as well as the quality and operating condition of the instruments. The ability to estimate the level of detection is of tremendous importance both in the design of a new network and in determining whether a given network can recognize seismicity consistently or needs to be improved in some of its parts. In this article, we determine the detection level of the Cuban seismic network using the empirically estimated seismic noise spectral level at each station site and some theoretical relationships to predict the signal amplitude of a seismic event at individual stations. The minimum local detectable magnitude thus depends on some network parameters such as the signal‐to‐noise ratio and the number of stations used in the calculation. We also demonstrate the effectiveness of our predictions by comparing the estimated detection level with those empirically determined from one year of data (i.e., the year 2020) of the Cuban seismic catalog. Our analysis shows, on the one hand, in which areas the current Cuban network should be improved, also depending on the regional pattern of faults, and, on the other hand, indicates the magnitude threshold that can be assumed homogeneously for the catalog of Cuban earthquakes in 2020. Because the adopted method can use current measurements of the seismic noise level (e.g., daily), the proposed analysis can also be configured for continuous monitoring of network state quality.
PubDate: Thu, 02 Jun 2022 00:00:00 GMT
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- Ground‐Motion Observations and Probabilistic Seismic Hazard:
Frequently Asked Questions-
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Authors: Iervolino I.
Abstract: AbstractObserved exceedances of ground‐motion intensity from probabilistic seismic hazard analysis (PSHA), in countries where it is used for structural design, spark significant public attention, rekindle scientific debates, and are sometimes discussed in trials about the accountability for structural failures and other earthquake‐related losses. This short article addresses, in a question‐reply format, some recurring issues and related research findings that should be carefully taken into account by those who author or face these reasonings. It considers Italy as a reference, yet the discussed issues are common to several other countries worldwide and thus may be interesting at an international level. The arguments provided, mainly stemming from the fact that observed cases of exceedance should not necessarily be considered a failure of PSHA, can possibly help in gaining a more informed perception of seismic hazard assessment and structural design as implemented in building codes.
PubDate: Wed, 01 Jun 2022 00:00:00 GMT
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- SSA News and Notes
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PubDate: Thu, 26 May 2022 00:00:00 GMT
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- Erratum to Efficacy and Usefulness of an Independent Public Earthquake
Early Warning System: A Case Study—The Earthquake Network Initiative in
Peru-
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Authors: Fallou L; Finazzi F, Bossu R.
Abstract: In the original version of the article, authors’ first and last names were inverted. This version contains the corrected authors’ names.
PubDate: Thu, 26 May 2022 00:00:00 GMT
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- Site Amplification at High Spatial Resolution from Combined Ambient Noise
and Earthquake Recordings in Sion, Switzerland-
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Authors: Perron V; Bergamo P, Fäh D.
Abstract: AbstractEarthquake site effects have a major impact on the seismic hazard. However, evaluating the site response over a broad frequency range and with a high spatial resolution remains difficult. Therefore, there is a high demand from the engineering seismology community in having cost‐effective and reliable approaches to evaluate the site response. Empirical site effect assessment has shown good reliability up to high frequencies but relies on earthquake recordings that require long station deployments. In contrast, seismic ambient noise can be rapidly recorded anywhere at any time. The hybrid standard spectral ratio (SSRh) combines both the spectral ratio from earthquake recordings at a few sites and the spectral ratio from ambient noise recordings at many sites from short duration deployments. The objective of our study is to evaluate the applicability of the SSRh to a large urban area. Our studied area is the Rhône valley around the city of Sion (Switzerland), which is prone to complex 2D and 3D site effects in a broad frequency range caused by the soft, thick, and variable sedimentary deposit of the Rhône river. We benefit from four permanent and five long‐term seismic stations present in the area, and we performed 299 short ambient noise measurements on a regular 300 m side grid. At the permanent stations, we find good agreement between the SSRh and the empirical amplification function estimates using earthquake observations, and we observe a good stability of the SSRh over time, frequency, and space, despite the strong variability of the ambient noise. Based on that, we estimate the SSRh for every ambient noise recording point in the area to compute a high‐resolution amplification model and subsequently a site‐specific seismic hazard model for the Sion area. Our models are in good agreement with the geological information.
PubDate: Wed, 25 May 2022 00:00:00 GMT
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- S ‐Wave Velocity Structure of the Crust and Upper Mantle beneath the
North China Craton Determined by Joint Inversion of Rayleigh‐Wave Phase
Velocity and Z/H Ratio-
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Authors: Xu X; Li G, Ding Z, et al.
Abstract: AbstractThe North China craton (NCC) is one of the oldest craton in the world. Since the Cenozoic, the NCC has undergone severe lithospheric thinning, accompanied by extensive crustal deformations and volcanic activities. To better understand the mechanisms of the crustal and lithospheric deformations and intraplate volcanisms, we construct a high‐resolution 3D S‐wave velocity model for the NCC by jointly inverting Rayleigh‐wave phase velocity dispersion and Z/H ratio measurements. Across the NCC, our model reveals significant lateral variations. In the shallow crust, prominent low‐velocity anomalies associated with thick sediments are resolved in the Bohai Bay basin, and the Ordos basin and its surrounding grabens. Meanwhile, our model also shows that sediments are thin or even missing in the southeast of the Ordos basin and other orogens in the study area. The sedimentary structures of the Bohai Bay basin and the surrounding grabens of the Ordos basin may be the superficial response to the subduction of the Pacific plate and the northeastward push of the Tibetan plateau, respectively. Under the Datong volcano, our model reveals an integrated low‐velocity anomalies from the mid‐to‐lower crust to the mantle, which verifies that the Datong volcano has a deep origin. Besides, the low‐velocity zone beneath the eastern NCC (ENCC) connects to the low‐velocity anomalies under the Datong volcano in the upper mantle. Combining the previous studies, we further propose that the asthenospheric upwelling of the Datong volcano and the subduction of the Pacific plate may jointly contribute to the lithospheric thinning of the ENCC.
PubDate: Wed, 25 May 2022 00:00:00 GMT
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- Yield Estimation and Event Discrimination of the 4 August 2020 Beirut
Chemical Explosion-
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Authors: Zhang L; Zhao L, Xie X, et al.
Abstract: AbstractWe investigate the 4 August 2020 Beirut accidental chemical explosion based on regional seismic data recorded at both on‐ and off‐shore stations. The Lg‐wave body‐wave magnitude is mb(Lg)=3.30±0.46 for the Beirut explosion. The explosive yield obtained using an empirical magnitude‐yield relation based on a fully buried explosion source model is only 0.112 kt. Alternatively, the yield estimated using an empirical relation between the yield and crater size is 1.22 kt, with the uncertainties between 0.48 and 2.3 kt. The latter is closer to reality. The P/S spectral amplitude ratios, including Pg/Lg, Pn/Lg, and Pn/Sn, are calculated for the Beirut explosion and nearby natural earthquakes. We find the P/S spectral ratios are effective in discriminating the explosion from earthquakes in the Northwestern Arabia plate. By comparing the spectral ratios of large open‐pit explosions, including the Beirut, Xiangshui, and Tianjin explosions, with those from historical nuclear explosions, buried small chemical explosions, and natural earthquakes, we further investigate the detailed differences of network‐averaged P/S spectral ratios between different source types.
PubDate: Wed, 25 May 2022 00:00:00 GMT
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- UNIBRA/DSEBRA: The German Seismological Broadband Array and Its
Contribution to AlpArray—Deployment and Performance-
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Authors: Schlömer A; Wassermann J, Friederich W, et al.
Abstract: AbstractThe German Seismological Broadband Array (Deutsches Seismologisches Breitband Array [DSEBRA]) comprises 100 mobile seismological stations and can be deployed as a stand‐alone network or in conjunction with other stations to build an even larger array. The first mission of DSEBRA was in the framework of the European AlpArray initiative. The aim of the project is to understand the deep structure, mantle dynamics, plate tectonics, its linkage to surface processes, and seismic hazard of the Alps–Apennines–Carpathians–Dinarides orogenic system. DSEBRA, purchased in the framework of the German Priority Program Mountain Building Processes in 4D, contributed to one‐third of the temporary AlpArray seismic network (AASN). The stations are currently deployed in the Alpine foreland of Germany and Austria, in the high Alps of Austria and Italy, and in the Pannonian basins of Hungary. The stations are equipped with state‐of‐the‐art technology, thus allowing to acquire high‐quality broadband data in real time. In this article, we present the current station deployment within the AASN, describing the equipment and its handling. Furthermore, we discuss the data quality and perform noise analyses. In conclusion, DSEBRA stations provide excellent data and are very well suited for deployment in national or international seismological experiments.
PubDate: Wed, 25 May 2022 00:00:00 GMT
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- Sensitivity of Tsunami Data to the Up‐Dip Extent of the July 2021 M w
8.2 Alaska Earthquake-
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Authors: Mulia IE; Gusman A, Heidarzadeh M, et al.
Abstract: AbstractA large tsunamigenic earthquake of magnitude Mw 8.2 occurred on the Alaska‐Aleutian subduction zone in July 2021. To reveal the characteristics of the event, we first applied spectral and wavelet analyses to the induced tsunami recorded both at the local and Pacific‐wide sea level observation networks. Because the earthquake was relatively deep (∼30 km), the resultant maximum tsunami amplitudes were only ∼5 and ∼50 cm in the open ocean and coastal area respectively. However, owing to the unique geological feature of the region, the tsunami had dominant periods of 57–73 min, which are longer than that typically generated by similar‐size megathrust earthquakes. Furthermore, we compared multiple source models inferred from various data sets and evaluated their performances in reconstructing the observed tsunami waveforms. The comparison results suggest that the up‐dip limit of the rupture area must be restricted at depth of ∼20 km to accurately reproduce the observed tsunami waveforms. Shallower slips beyond the prescribed limit led to an overestimation of the tsunami amplitude. This implies that the earthquake was unlikely to rupture the plate interface on the near trench section.
PubDate: Thu, 19 May 2022 00:00:00 GMT
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- 2019 M w 5.9 Mirpur, Pakistan Earthquake: Insights from Integrating
Geodetic, Seismic, and Field Observations-
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Authors: Barkat A; Javed F, Joe Tan Y, et al.
Abstract: AbstractOn 24 September 2019, an Mw 5.9 earthquake struck near the Mangla reservoir in northeastern Pakistan and resulted in 39 fatalities and 746 serious injuries, making it the deadliest earthquake in the region since the 2005 Mw 7.6 Kashmir earthquake. Here, we integrate geodetic, seismic, and field observations to characterize the source properties and impact of the Mirpur earthquake as well as investigate whether it might be a reservoir‐induced event. From inverting Interferometric Synthetic Aperture Radar data, we find that a fault with strike ∼310°, dip ∼6°, and rake ∼117° is the optimal source, with slip concentrated between 5 and 6 km depth. This is consistent with our relocated aftershocks depth distribution and the lack of surface rupture observed in the field. Therefore, we infer that the earthquake ruptured the Main Himalayan Thrust (MHT). The event’s shallow depth might explain the extensive damage caused despite its moderate magnitude, with a maximum shaking intensity of VIII based on our field survey. The survey also revealed extensive damages associated with earthquake‐induced liquefaction. Our modeling shows that loading due to increased reservoir water level in the three months before the Mirpur earthquake led to Coulomb stress increase of ∼7–10 kPa on the rupture plane. However, this effect is ∼10 times smaller than the Coulomb stress increase due to the 2006 Mangla earthquake, and the Mirpur earthquake only occurred ∼1–2 weeks after peak water level. These suggest that pore pressure diffusion contributed to promoting the fault rupture at a time when it is close to failure due to accumulated stress from inter‐seismic loading. Because the Mirpur earthquake resulted in a stress increase of >0.2 MPa on the surrounding sections of the MHT and nearby faults, future rupture of these faults is a significant hazard and proper management of reservoir operations is necessary to prevent further elevating the seismic risk.
PubDate: Thu, 19 May 2022 00:00:00 GMT
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- Estimating Explosion Yields Using Moment Tensor Solutions and Seismic
Moment-
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Authors: Pasyanos ME.
Abstract: AbstractSeismic moment, a measurable and well‐understood quantity of seismic sources, is used to estimate the yield of explosions. Application of such a method in the past, as in the manner of mb‐derived yields, has been complicated by the effect of variations in the explosion working point, depth, and secondary source effects (such as spalling and tectonic release) on the observed moment. We start using the full (six‐element) moment tensor solution, which can capture the relevant source physics and, at least in theory, better isolate the primary explosion source. The moment‐to‐yield ratio is then estimated using an explosion source model which, provided with emplacement conditions, can relate the two parameters. We discuss the major sources of uncertainty associated with the method, and calibrate it with chemical and nuclear explosions at the Nevada National Security Site. We then apply the method to published moment tensor solutions for the six declared North Korean nuclear explosions that occurred between 2006 and 2017. The results are mostly consistent with other yield estimates made using a variety of high‐frequency methods. This technique is a new approach to estimating explosive yield and simple to implement, as much of the complexity is captured by the source models.
PubDate: Wed, 11 May 2022 00:00:00 GMT
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- Seismicity around Southern Lake Erie during 2013–2020 in Relation to
Lake Water Level-
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Authors: Yao D; Huang Y, Xue L, et al.
Abstract: AbstractThe water level change in the Great Lake region can modulate stresses in the nearby fault system and potentially induce earthquakes. We perform a systematic analysis of local seismicity around southern Lake Erie during 2013–2020 to investigate the relation between seismicity and lake water level change. We obtain a newly detected catalog of tectonic earthquakes, which reveals 20–40 M > 0 earthquakes/yr before 2019. The peak seismicity rate in 2019 is dominated by active aftershocks following the 2019 ML 4.0 Ohio earthquake. The clustering analysis reveals both clusters with multiple events and stand‐alone events that might represent isolated zones of crustal weakness in this region. The absolute location analysis identifies a group of earthquakes around the epicenter of the 1986 M 5 earthquake, which might be linked to the nearby injection activities. To evaluate the potential interaction with changing water loading of Lake Erie, we then model the coulomb stress change (ΔCSC) caused by elastic lake‐water loading and find that ΔCSC strongly depends on effective friction coefficient (μ′). Considering the geometry of the receiver fault, higher lake water level results in positive ΔCSC and would promote failure when μ′≤0.3, and leads to negative ΔCSC and would discourage rupture when μ′>0.3. Further analysis indicates a lack of temporal correlation between long‐term seismicity and water level variations before the 2019 Ohio sequence, suggesting that water level fluctuations do not modulate long‐term seismicity. However, we cannot fully rule out the impact of increasing water level on reactivating the fault that hosted the 2019 Ohio earthquake sequence because of the uncertainty of μ′. Our results highlight the necessity of denser and closer monitoring of lake seismicity to further investigate the impact of changing water loading on reactivating shallow faults in this region.
PubDate: Mon, 09 May 2022 00:00:00 GMT
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- Design, Modeling, and Evaluation of a Class‐A Triaxial Force‐Balance
Accelerometer of Linear Based Geometry-
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Authors: Germenis N; Dimitrakakis G, Sokos E, et al.
Abstract: AbstractA new class‐A force‐balance accelerometer (FBA) is designed, simulated, and evaluated. The focus of this work was to design a low‐cost but high‐performance instrument. The FBA has output voltage proportional to ground acceleration, flat response from direct current to 200 Hz, output range ± 10 V differential (40Vpp, peak‐to‐peak) and sensitivity 2.5 V/g, which provides a ± 4g range. Unlike other well‐established designs with rotational pendulum systems and single‐coil actuators that present partially nonlinear performance, the proposed design is based on a linear motion spring‐mass mechanism with two parallel leaf springs and a double symmetrical magnet‐coil force actuator. This architecture ensures that the displacement transducer’s response is linear and that an acting force on the seismic mass is not disturbed by any cross‐axial motion. This force depends on displacement only, as imposed by the electronic control circuit, which is implemented on a small high‐density printed circuit board (PCB) mounted on top of the mechanical construction. The plates of the variable capacitance displacement transducer consist of ordinary PCBs for cost efficiency. The coils of the force actuator are placed on each side of the moving plate of the capacitive transducer and the magnets are placed on the aluminum rigid frame of the device. The central moving plate of the variable capacitor and the attached force actuator coils, along with some extra aluminum mass, consist the accelerometer’s seismic mass. The performance of the accelerometer is evaluated in terms of earthquake data records and in comparison of its response with that of a commercial FBA with corresponding specifications. The instrument’s self‐noise was also measured over a long period of operation and proved to comply with typical FBA application requirements and commercial product standards.
PubDate: Thu, 05 May 2022 00:00:00 GMT
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- Hierarchical Bayesian Modeling for Improved High‐Resolution Mapping of
the Completeness Magnitude of Earthquake Catalogs-
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Authors: Feng Y; Mignan A, Sornette D, et al.
Abstract: AbstractAssessing the completeness magnitude Mc is essential for most seismicity studies. However, when studying the spatial variation of Mc in a region, the conventional methods that compute Mc based on the frequency–magnitude distribution (FMD) tend to give gaps and large uncertainties of Mc in subregions of low seismicity, thus rendering high‐resolution Mc mapping infeasible. To address the limitations of the FMD‐based methods, the Bayesian magnitude of completeness (BMC) method was proposed a decade ago to incorporate a priori information about Mc derived from its empirical relationship to the seismic network spatial configuration Mc=f(d), with d being the distance to the kth (typically k = 4 or 5) nearest seismic station at each node in space. Although widely used, the BMC method has several critical shortcomings that have long been neglected. In this study, we propose a hierarchical Bayesian model that inherently overcomes these shortcomings of the BMC method for high‐resolution Mc mapping coined hierarchical Bayesian magnitude of completeness (H‐BMC), which provides a unified and more appropriate approach to the integration of a priori information and local observations concerning Mc. We use an earthquake catalog from the Taiwan region to demonstrate that, compared with the FMD‐based methods based solely on observed magnitudes, the proposed H‐BMC method effectively utilizes a priori information via prior distributions and thereby gives complete and more reliable high‐resolution Mc mapping in terms of gap filling and uncertainty reduction. We also highlight that the H‐BMC method for Mc mapping serves as a generic and flexible modeling framework for logically combining imprecise information about Mc from different sources.
PubDate: Thu, 05 May 2022 00:00:00 GMT
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- Seismic and Infrasound Data Recorded at Regional Seismoacoustic Research
Arrays in South Korea from the Six DPRK Underground Nuclear Explosions-
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Authors: Stump B; Hayward C, Golden P, et al.
Abstract: AbstractFive seismoacoustic research arrays and one infrasound research array located across the southern Korean peninsula have been installed, maintained, and are cooperatively operated by Southern Methodist University and Korea Institute of Geoscience and Mineral Resources. The seismoacousitc arrays are each composed of 1–5 broadband seismometers spaced from 0.5 to 1.5 km and 4–16 infrasound sensors spaced from 0.1 to 1.5 km. The arrays—BRDAR, CHNAR, KSGAR, KMPAR, TJIAR, and YPDAR—have recorded regional seismic and infrasound signals from the six underground nuclear explosions conducted by Democratic People’s Republic of Korea. These seismoacoustic data are being made available for researchers interested in studying and quantifying the explosion source functions of these events as well as wave propagation effects in the solid earth and atmosphere as constrained by seismic and infrasound observations at regional distances.
PubDate: Thu, 28 Apr 2022 00:00:00 GMT
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- The 2014 Zigui Earthquake Sequence near the Three Gorges Dam in China
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Authors: Huang R; Zhu L, Xu Y, et al.
Abstract: AbstractSeismicity in the Three Gorges Reservoir (TGR) region increased noticeably as the water level of the reservoir rises, since the Three Gorges Dam (TGD) was built in 2003. Here, we determined moment tensors of six earthquakes in the 2014 Zigui earthquake sequence (ZGS) in the TGR region using local and regional broadband seismic waveform data. We also determined the focal depth of the mainshock using its teleseismic waveform data and then relocated the epicenter using its travel times at local stations. High‐precision locations of 64 events in the sequence were obtained by combining the double‐difference relative location result and the mainshock’s absolute location. The event locations and moment tensor solutions indicate that the ZGS occurred between depth 5 and 9 km on a previously unknown fault striking southwest and dipping ∼80° to the northwest. The event depth distribution and coulomb stress change estimation suggest that the ZGS were not induced directly by the reservoir water but triggered by the stress change from the annual reservoir water level variation. We estimated that the newly found fault has the potential for a magnitude 5.7 earthquake for which ground motion has a 16% probability to exceed the designed maximum intensity level at the TGD, though it would take more than 100 yr to accumulate the needed amount of slip.
PubDate: Thu, 28 Apr 2022 00:00:00 GMT
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- Reply to “Comment on ‘The 373 B.C. Helike (Gulf of Corinth, Greece)
Earthquake and Tsunami, Revisited’ by Stiros (2022) ” by Dora
Katsonopoulou and Ioannis Koukouvelas-
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Authors: Stiros SC.
Abstract: AbstractThis reply is a response to a comment criticizing a recent article proposing a new scenario for the 373 B.C. earthquake, derived from ancient texts. This earthquake and a following tsunami are reported to have destroyed Helike and Boura, two ancient Greek towns, which then were found submerged into the Gulf of Corinth, punished by Poseidon, an ancient Greek god. The comment contested the new scenario that these ancient texts reflect a later legend, of Roman times. The comment is unsubstantiated, because (1) ruins of the two towns, invisible till recently, have been found in archaeological excavations, without any signs of a marine regression, while no significant marine regression is derived from sedimentological data; (2) Helike and Boura were town–states consisting of smaller villages, located at elevations above 20 and 500 m, respectively, and their subsidence into the sea was impossible; (3) ancient authors writing shortly after 373 B.C. ignore the loss of Helike and Boura; and (4) ancient texts reporting the loss are much later, of Roman times (>200 yr after 373 B.C.), and they reflect a local legend and manipulated or forged ancient texts, for example by pseudo‐Aristotle. The scenario proposed in Seismological Research Letters represents the only realistic explanation for the ancient texts referring to the 373 B.C. earthquake.
PubDate: Thu, 28 Apr 2022 00:00:00 GMT
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- Comment on “The 373 B.C. Helike (Gulf of Corinth, Greece) Earthquake
and Tsunami, Revisited” by Stiros (2022)-
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Authors: Katsonopoulou D; Koukouvelas I.
Abstract: AbstractWe are writing this comment because the presentation and the conclusions reached by Stiros (2022) regarding the catastrophic Helike earthquake of 373 B.C. neglect significant historical sources and scientific data from longstanding geoarchaeological work and excavations in the Helike region and offer an incomplete picture of the knowledge acquired about this famous earthquake of Classical Greece. In particular, the attempted re‐examination of ancient sources is incomplete and subjective, serving the author’s a priori view that accounts of the 373 B.C. earthquake are later fabrications from Roman times. To this end, Stiros neglects published archaeological data dated from soon after the 373 B.C. catastrophe and wrongly concludes that the area did not experience repeated earthquake phenomena. Furthermore, his proposal that the Helike and Aigion faults are identical is an evident geological error. Instead, the two faults are 5 km apart, and their seismological evolution and tectonic geomorphology are quite different.
PubDate: Thu, 28 Apr 2022 00:00:00 GMT
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- P ‐Wave Velocity Structure of the Lower Crust and Uppermost Mantle
beneath the Sichuan–Yunnan (China) Region-
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Authors: Wei Z; Zhao L.
Abstract: AbstractWe conduct a tomographic inversion for the 3D P‐wave velocity structure in the lower crust and uppermost mantle of the Sichuan–Yunnan region in the southeastern margin of the Tibetan Plateau. A total of 43,450 reliable arrival times of P waves are picked from over 300,000 regional seismic records using an automatic algorithm based on deep learning. A two‐stage iterative inversion process in which events are relocated, leading to a significant reduction in travel‐time residuals, is adopted. A statistical resolution matrix analysis suggests that our model has an optimal spatial resolution length of ∼0.4° in the lower crust and ∼0.2° in the uppermost mantle. Our 3D model shows that both the lower crust and uppermost mantle in the region are characterized by strong lateral heterogeneities. The unusually low velocities in the lower crust may indicate the existence of lower crustal flow, whereas the high‐velocity anomalies in the uppermost mantle in and around the Sichuan–Yunnan Rhombic block (SYRB) may be an important factor in preventing the ductile materials in the lower crust from moving eastward. Our model also indicates a coupling between the surface deformation and the material flow in the lower crust. Finally, the lower crustal flow may influence the materials in the shallow part of the uppermost mantle beneath the SYRB, and the crust–mantle transition zone beneath the Songpan–Ganzi block may be influenced by weak materials from both the uppermost mantle and the lower crust.
PubDate: Wed, 27 Apr 2022 00:00:00 GMT
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- Crustal Structure across the West Antarctic Rift System from
Multicomponent Ambient Noise Surface Wave Tomography-
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Authors: Dylan Mikesell T; Mordret A, Xu Z, et al.
Abstract: AbstractApproximately 2 yr (2010–2011) of continuous seismic records from a subset of the Antarctic component of the Polar Earth Observing Network (POLENET‐ANET) seismic network deployed in West Antarctica are used to compute the nine components of the correlation tensor between each pair of stations in the network. Rayleigh wave velocity information from the vertical and radial components was extracted in the form of group and phase velocity dispersion curves, whereas the transverse component provided complimentary Love wave velocity information. The multicomponent Rayleigh wave measurements (ZZ, RR, ZR, and RZ) were averaged and used to infer the measurement uncertainties. The Rayleigh and Love wave group and phase velocities were then regionalized in space using a 2D deterministic tomography. A transect that spans the West Antarctic rift system was extracted from the tomography at individual periods between 7 and 60 s for the four types of surface wave velocities (i.e., Rayleigh and Love phase and group velocities). A transdimensional Bayesian joint inversion algorithm was used to invert these four datasets for a 1D model of isotropic shear‐wave velocity versus depth at each point along the transect. In this way, surface wave dispersion curves from multicomponent noise correlations were used to build a 2D isotropic shear‐wave velocity model down to ∼55 km depth. In this model, the top of the large low‐velocity zone beneath Marie Byrd Land was imaged (up to a 5% decrease in velocity at ∼50 km depth), which provides further evidence for a mantle hot spot beneath the crust that supports the high topography in this region. We also observed a large velocity contrast in the lower crust beneath Marie Byrd Land at a depth where previous long‐period seismicity has been observed. This strong contrast occurs more shallow than in previous crustal models, which compared to our model identify a deeper Moho (∼5–10 km deeper) beneath Marie Byrd Land. This new model has implications for interpreting earthquake locations in this region and perhaps necessitates that we revisit past hypocenter estimation studies using updated velocity models for the region.
PubDate: Wed, 27 Apr 2022 00:00:00 GMT
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- Near‐Source Attenuation and Spatial Variability of the Spectral Decay
Parameter Kappa in Central Italy-
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Authors: Castro RR; Colavitti L, Vidales‐Basurto CA, et al.
Abstract: AbstractWe study the spectral decay parameter κ using S‐wave recordings from the central Italy dense regional array. The data set used consists of 266 earthquakes, 353 stations, and 13,952 observations of κ with a mean value of 0.0412 ± 0.0177 within the distance range of 7.1–168.8 km. We model the variation of κ with hypocenter distance r as κ(r)=κ0+κs+κ˜(r), in which κ0 and κs represent the near‐site and the near‐source decay parameters, respectively, and κ˜(r) the average κ along the S‐wave source‐station paths. We first determine κ˜(r) with a nonparametric inversion approach and then we solved for κ0 and κs with a second inversion. We found that κ˜(r) increases with distance within the whole distance range analyzed (9.2–80.6 km). The near‐source decay parameter takes values in the range 0.0<κs≤0.026 with a mean value of 0.003 ± 0.006, which represents 7.52% of the mean value of the observed κ. The values of the near‐site decay parameter vary in the range 0.0035≤κ0≤0.0823 with a mean value of 0.0298 ± 0.0133, that is, 72.28% of the mean value of the κ observed. We conclude that most of the high‐frequency attenuation takes place near the site, because κ˜(r) contributes with only 20.2% of the spectral decay. We also investigate the spatial variability of κ by determining κ˜(r) within four quadrants that divide the studied region taking as a reference axis the Apennines chain orientation. We found higher values of κ˜(r) in the southern quadrants, where seismicity and faulting are more active, and less attenuation in the more stable northeast quadrant.
PubDate: Wed, 27 Apr 2022 00:00:00 GMT
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- Nodal Seismic Experiment at the Berkeley Section of the Hayward Fault
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Authors: Taira T; Dreger DS, Allam AA.
Abstract: AbstractThe Hayward fault (HF) in the San Francisco Bay area of California is one of the most hazardous faults of the San Andreas fault system with a total length of 70 km. In November 2020, we conducted a dense array experiment that deployed 182 three‐component nodal sensors for about a five‐week period at the Berkeley section of the HF. Our primary goal of this experiment was to image the seismic velocity structure in the upper crust of this area to better understand the fault‐zone structure and its elastic properties. A linear array (10 stations with 5–10 m spacing) was deployed on the north side of University of California, Berkeley Memorial Stadium where the HF runs underneath, together with 27 stations that were installed surrounding the stadium. Here we detail our scientific motivation, station metadata, and quality of seismic waveforms. We also show initial results of fault‐zone guided waves observed from the linear array and provide first‐step results of Green’s functions between nodal stations obtained by an ambient noise cross‐correlation analysis.
PubDate: Tue, 26 Apr 2022 00:00:00 GMT
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- The Surface Process and Seismogenic Structure of the 2021 M s 6.1 Biru,
Central Tibet Earthquake-
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Authors: He Z; Li Y, Li Y, et al.
Abstract: AbstractOn 19 March 2021, the Ms 6.1 Biru earthquake occurred in central Tibet. Because of the limited number of stations, researchers have different understandings of the epicenter and the focal mechanism. In addition, when the earthquake occurred in a key location at the intersection of the strike‐slip structure and the extensional structure in the Tibetan plateau, no seismogenic fault is associated with this earthquake, according to the known active faults. In this article, the focal mechanism solution, the meizoseismal area, the orientation of the long axis of the isoseismal lines, and the spatial distribution and geometric characteristics of earthquake fissures were obtained based on the Interferometric Synthetic Aperture Radar coseismic deformation field, inversion of the focal mechanism solution, and field investigation. The macroscopic epicenter was located approximately 13.17 km southeast from the instrumental epicenter, and the earthquake occurred in the seismotectonic background of south–north extrusion, east–west extension, and a mixture of strike‐slip and normal faulting. The focal mechanism solution is the normal fault rupture of the northeast‐trending main nodal plane. The earthquake caused regularly arranged coseismic ground fissures and damaged a myriad of buildings. The maximum intensity was VIII. The long axis of the isoseismal lines was in the northeast–southwest direction, thus showing a distinct hanging‐wall effect. The seismogenic structure was a newly discovered northeast‐trending normal fault with a partial sinistral component. The newly discovered seismogenic normal fault, together with the normal faults that have been identified in adjacent areas, is vital to the crustal deformation of the central Tibetan plateau.
PubDate: Fri, 22 Apr 2022 00:00:00 GMT
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- CGFDM3D‐EQR: A Platform for Rapid Response to Earthquake Disasters
in 3D Complex Media-
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Authors: Wang W; Zhang Z, Zhang W, et al.
Abstract: AbstractEarthquake disasters cause serious losses of human life and property. A rapid response platform for earthquake disasters can provide scientific suggestions for real‐time postearthquake rescue deployment, reducing losses. We developed an earthquake response platform named CGFDM3D‐EQR that quickly provides earthquake intensity for evaluating complex earthquake disasters. The intensity evaluations are derived from strong ground motion simulations that couple 3D complexities in elevation, medium structure, and earthquake source. The curved grid finite difference method (CG‐FDM), which can accurately resolve 3D complexities during earthquake simulation, is adopted in this platform. We developed a CG‐FDM parallel algorithm for strong ground motion simulation based on central processing unit (CPU) and graphical processing unit (GPU) heterogeneous architectures. With these characteristics, the platform can simulate strong earthquake ground motions and provide seismic intensity assessments in less than 30 min using our cluster. To verify the platform, we performed four simulations, and the results show that our platform is reliable and efficient. Owing to its user‐friendly features and high efficiency, the CGFDM3D‐EQR platform can play essential roles in seismic hazards responses, scenario earthquake evaluations, and related applications.
PubDate: Wed, 20 Apr 2022 00:00:00 GMT
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- Validation of the Probabilistic Seismic Hazard Assessment by the Taiwan
Earthquake Model through Comparison with Strong Ground Motion Observations
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Authors: Gao J; Tseng Y, Chan C.
Abstract: AbstractTo validate the probabilistic hazard assessment proposed by the Taiwan Earthquake Model (TEM), we compared it with the strong ground motion observations. We accessed the Taiwan Strong Motion Instrumentation Program (TSMIP) database and reported the maximum ground shaking of each strong‐motion station. Comparing the TSMIP observations and the TEM hazard model reveals similar spatial patterns. However, some records indicate significantly higher shaking levels than the model does due to the occurrence of some large events, for example, the 1999 Mw 7.6 Chi‐Chi earthquake. Such discrepancies cannot be explained by model parameter uncertainties but by unexpected events in the given short observation period. We have confirmed that, although each seismogenic structure in Taiwan is unlikely to rupture within a short period, the summarized earthquake potentials from all of the structures are significant. In addition, we discuss the impacts of some model parameters, including epistemic uncertainties of source parameters, truncation of standard deviation for ground‐motion prediction equations, the Gutenberg–Richter law for area source, and the time‐dependent seismicity rate model. The outcomes of this study provide not only crucial information for urban planning on a city scale and building code legislation on a national scale but also suggestions for the next generation of probabilistic seismic hazard assessment for Taiwan as well as other regions.
PubDate: Wed, 20 Apr 2022 00:00:00 GMT
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- Ambient Infrasound Noise, Station Performance, and Their Relation to Land
Cover across Alaska-
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Authors: Macpherson KA; Coffey JR, Witsil AJ, et al.
Abstract: AbstractThe addition of 108 infrasound sensors—a legacy of the temporary USArray Transportable Array (TA) deployment—to the Alaska regional network provides an unprecedented opportunity to quantify the effects of a diverse set of site conditions on ambient infrasound noise levels. TA station locations were not chosen to optimize infrasound performance, and consequently span a dramatic range of land cover types, from temperate rain forest to exposed tundra. In this study, we compute power spectral densities for 2020 data and compile new ambient infrasound low‐ and high‐noise models for the region. In addition, we compare time series of root‐mean‐squared (rms) amplitudes with wind data and high‐resolution land cover data to derive noise–wind speed relationships for several land cover categories. We observe that noise levels for the network are dominated by wind, and that network noise is generally higher in the winter months when storms are more frequent and the microbarom is more pronounced. Wind direction also exerts control on noise levels, likely as a result of infrasound ports being systematically located on the east side of the station huts. We find that rms amplitudes correlate with site land cover type, and that knowledge of both land cover type and wind speed can help predict infrasound noise levels. Our results show that land cover data can be used to inform infrasound station site selection, and that wind–noise models that incorporate station land cover type are useful tools for understanding general station noise performance.
PubDate: Tue, 19 Apr 2022 00:00:00 GMT
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- The 1620 and 1644 Earthquakes in Alcoy and the Eastern Region of Spain
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Authors: Buforn E; Udías A.
Abstract: AbstractThe 2 December 1620 earthquake, which caused considerable damage to the town of Alcoy in eastern Spain, and the seismic sequence of June 1644 in the region from Alcoy to the coast of the Mediterranean Sea are studied using contemporary sources. Focal parameters are determined for the 1620 shock and the three mainshocks of the 1644 sequence on 15, 19, and 26 June. The distribution of damage and casualties from the 1620 earthquake in Alcoy leads to the assignment of maximum intensities of VIII–IX. A solution is presented for problems concerning dates, locations, and sizes of the three largest shocks of the 1644 sequence given in previous catalogs and studies.
PubDate: Tue, 19 Apr 2022 00:00:00 GMT
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- Numerical Study on the Characteristics of Abyssal T ‐Wave Envelopes
Controlled by Earthquake Source Parameters-
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Authors: Yun S; Lee W, Dziak RP, et al.
Abstract: AbstractHydroacoustics has been successfully applied to detect and locate small‐to‐intermediate submarine tectonic activities infrequently recorded in land‐based seismic arrays. However, to extend the utilization of T waves to extract other important earthquake source parameters, such as source strength, the roles of earthquake focal mechanisms, and source depths in T‐wave envelopes must be thoroughly understood. We performed 3D numerical modeling considering anisotropic source radiation and realistic scattering in the oceanic crust for two focal mechanisms (normal and strike‐slip faults) and three depths (5, 10, and 15 km) to investigate the effect of source radiation and focal depth on abyssal T waves. By analyzing the synthetic T‐wave envelopes, we showed that stronger SV‐energy radiation from a normal‐fault earthquake event generates higher‐intensity T waves of the same source magnitude. The anisotropic source radiation of a double‐couple source causes azimuthal changes in the shapes of T waves, and deeper earthquakes cause gentle‐sloped envelopes; however, the slopes also vary with respect to the azimuths of receivers and focal mechanisms. Temporal changes in the slopes of T‐wave envelopes of magmatic swarm events near Wordie Volcano, Bransfield Strait, Antarctic Peninsula, imply that the depth dependency can be utilized to determine relative depths for hydrothermal‐vent events or sequenced earthquakes.
PubDate: Tue, 19 Apr 2022 00:00:00 GMT
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- Moving beyond S Minus P Earthquake Locations as “THE” Lab in
Seismology Education-
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Authors: Hubenthal M; Taber J.
Abstract: AbstractLocating earthquakes is an important activity that underpins both seismological research and seismology education broadly. The seismology community tends to view the earthquake location process as a fundamental element of the field, and locating earthquakes is arguably the most common seismology education activity that middle school through introductory college students encounter. As a result, nearly all students’ first, and primary, exposure to the field of seismology consists of paper seismograms, drawing compasses, and 2D maps. This occurs in an era of computers available for every student, high‐speed Internet, publicly available digital waveforms, complex algorithms to solve for earthquake locations, and the Next Generation Science Standards driving public education. This article explores the origins of the S minus P location method both as a scientific solution and as an educational activity in Earth Science classrooms, and reflects on technical, pedagogical, and curricular aspects of common implementations, underpinning beliefs, and their implications. From this reflection, three opportunities are identified for the seismology community to expand the seismological horizons of Earth Science students and instructors. These include working with instructors across a range of educational levels to correct the record on how earthquakes are located, to rethink both the content and pedagogy used both to teach about the process of earthquake locations, and to define several key ways the seismology community might lead geoscience educators to move beyond earthquake locations as “THE” seismology lab used with students.
PubDate: Thu, 14 Apr 2022 00:00:00 GMT
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- Testing Earthquake Nucleation Length Scale with Pawnee Aftershocks
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Authors: Wu BS; McLaskey GC.
Abstract: AbstractThe interpretation of precursory seismicity can depend on a critical nucleation length scale h*, yet h* is largely unconstrained in the seismogenic crust. To estimate h* and associated earthquake nucleation processes at 2–7 km depths in Oklahoma, we studied seismic activity occurring prior to nine M 2.5–3.0 earthquakes that are aftershocks of the 3 September 2016 M 5.8 Pawnee, Oklahoma, earthquake. Four of the nine M 2.5–3.0 aftershocks studied did not have detectable seismicity within a 2 km radius of their hypocenters in the preceding 16 hr time windows. For the other five events, which did exhibit foreshock sequences, we estimated the static stress changes associated with each event of each sequence based on precise earthquake relocations and magnitude estimates. By carefully examining the spatiotemporal characteristics, we found all five of these M 2.5–3.0 aftershocks, and 70% of our studied events were plausibly triggered via static stress transfer from nearby earthquakes occurring hours to seconds earlier, consistent with the cascade nucleation model and a small h* in this region. The smallest earthquakes we could quantitatively study were M −1.5 events, which likely have 1–2 m rupture dimensions. The existence of these small events also supports a small nucleation length scale h*≤1 m, consistent with laboratory estimates. However, our observations cannot rule out more complicated earthquake initiation processes involving interactions between foreshocks and slow slip. Questions also remain as to whether aftershocks initiate differently from more isolated earthquakes.
PubDate: Thu, 14 Apr 2022 00:00:00 GMT
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- Data Quality Analysis of China Permanent Seismic Network by Repeating
Earthquakes-
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Authors: Chai X; Zhang P, Wang C, et al.
Abstract: AbstractHighly similar waveforms recorded from repeating earthquakes can be utilized to evaluate the data quality of a seismic station. We used a hypothesis testing method to establish a data quality detection model based on repeating earthquakes. The model effectiveness was verified by using waveforms of a pair of repeating earthquakes, which occurred in northeastern Japan on 20 March 2021 (Mw=7.0) and 1 May 2021 (Mw=6.9), from 109 stations in the Global Seismographic Network. A total of 842 permanent broadband stations in mainland China were evaluated using this model. Eighteen anomalies were found mainly attributed to calibration, instrument noise, mass recentering, and regional long‐period interference. We found that most of the stations function well. Moreover, utilizing repeating earthquakes to analyze the waveform quality can circumvent the need for extensive forward calculations, as well as greatly reduce the influence of source parameter uncertainties and structural complexity on the seismogram. Additionally, the need for detection in other datasets in different regional networks has broadened the scope of these applications.
PubDate: Wed, 13 Apr 2022 00:00:00 GMT
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- BSPASS: A Beam Search‐Based Phase Association and Source Scanning
Earthquake Location Method-
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Authors: Wang C; Liang C.
Abstract: AbstractWe propose a novel phase association and source scanning method by incorporating the norm‐grid search and a beam search technique together to associate seismic phases, and to determine the accurate location of a particular event simultaneously. The method is called the beam search‐based phase association and source scanning (BSPASS). Using synthetic travel times for two seismic networks with different station spacings, we examine the practicability and accuracy of the BSPASS method. The results show that BSPASS could constrain event location with high precisions, if the standard deviation of travel‐time errors is less than 0.4 s. The method works well even for those earthquakes located at the network boundary. We applied the BSPASS method to the beginning day of the 2018 Purcell mountains earthquake swarm. Two times more events are detected automatically, and similar spatiotemporal distribution of these earthquakes is recognized by our method compared to the U.S. Geological Survey catalog. We also investigate the flexibility and robustness of the BSPASS method by adding Gaussian noises to phase arrivals. With the increasing of noise levels, the location errors grow accordingly. Based on our tests, we suggest that there might be an upper limit of phase picking errors for a particular source array configuration, for example, 0.4 s in this study, above which the global optimization procedure fails to resolve a better source location under the constraint of travel‐time residuals than that of the norm‐grid searching.
PubDate: Wed, 13 Apr 2022 00:00:00 GMT
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- Working with Dynamic Earthquake Rupture Models: A Practical Guide
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Authors: Ramos MD; Thakur P, Huang Y, et al.
Abstract: AbstractDynamic rupture models are physics‐based simulations that couple fracture mechanics to wave propagation and are used to explain specific earthquake observations or to generate a suite of predictions to understand the influence of frictional, geometrical, stress, and material parameters. These simulations can model single earthquakes or multiple earthquake cycles. The objective of this article is to provide a self‐contained and practical guide for students starting in the field of earthquake dynamics. Senior researchers who are interested in learning the first‐order constraints and general approaches to dynamic rupture problems will also benefit. We believe this guide is timely given the recent growth of computational resources and the range of sophisticated modeling software that are now available. We start with a succinct discussion of the essential physics of earthquake rupture propagation and walk the reader through the main concepts in dynamic rupture model design. We briefly touch on fully dynamic earthquake cycle models but leave the details of this topic for other publications. We also highlight examples throughout that demonstrate the use of dynamic rupture models to investigate various aspects of the faulting process.
PubDate: Wed, 13 Apr 2022 00:00:00 GMT
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- Revisiting Operational Aftershock Forecasting in the Eastern Intermountain
West-
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Authors: Mesimeri M; Pankow KL.
Abstract: AbstractWe present a magnitude‐dependent aftershock model for the eastern Intermountain West (IMW) that can be used to inform and improve reliability of initial U.S. Geological Survey (USGS) operational aftershock forecasts (OAFs). The model is derived after considering recent M ≥ 5.0 aftershock sequences in the eastern IMW, and careful identification of M < 5.0 aftershock sequences from regional earthquake catalogs (western Montana, Utah). We propose a workflow for M < 5.0 earthquake sequences that consists of: (1) spatiotemporal analysis of magnitude of completeness, (2) application of multiple declustering–clustering algorithms, (3) discrimination between mainshock–aftershock sequences (MS‐AS) and earthquake swarms, and (4) synthesizing the results to determine the final list of MS‐AS. In addition, we examined separately aftershock sequences with 5.0 ≤ M < 6.0 and M ≥ 6.0 and find a notable difference in earthquake productivity. Our results show that the proposed model for IMW differs from the one used in the USGS OAF, and highlights the need for region‐specific aftershock modeling. This study validates the hypothesis that earthquake sequences following large surface‐faulting earthquakes in the eastern IMW, and perhaps generally in the Basin and Range Province, behave fundamentally differently than those following moderate‐size earthquakes.
PubDate: Wed, 13 Apr 2022 00:00:00 GMT
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- Is the Long‐Term Probability of the Occurrence of Large Earthquakes
along the Nankai Trough Inflated'—Scientific Review-
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Authors: Hashimoto M.
Abstract: AbstractThe Earthquake Research Committee (ERC), the Headquarters for Earthquake Research Promotion, Japan, issued a new report on long‐term evaluation of the occurrence of large earthquakes along the Nankai trough, southwestern Japan, in 2013, which was made along the line of the revision of national earthquake counter measures according to the 2011 Great Eastern Japan Earthquake Disaster. The central issue was the 30‐yr probability, but the method to estimate probability was not changed from the previous one issued in 2001 based on the time‐predictable model, which led to a 60%–70% chance of M ≥ 8 event during the coming 30 yr. However, there are several drawbacks in this evaluation such as neglect of errors in uplift data, inconsistency between uplift rate and geodetic and geomorphological data, mechanical interpretation of time‐predictable model, and contradiction between the assumptions in Brownian passage time model and time‐predictable model. Because ERC calculates probability with average recurrence intervals for other subduction and active fault zones, the same scheme should be adopted to the Nankai trough.
PubDate: Mon, 11 Apr 2022 00:00:00 GMT
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- Low‐Noise Optical Accelerometers: Bridging the Gaps among Geophones,
Accelerometers, and Broadbands in a Deep Borehole-
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Authors: Hopp C; Taira T, Robertson M, et al.
Abstract: AbstractEarthquakes and other seismic sources produce waves with frequency content spanning many orders of magnitude. Recording a broader frequency band of interest has historically required deploying multiple instruments designed to work the best within limited, overlapping frequency ranges. Here, we detail a 300 m deep borehole deployment of a sensor package, including three new optical accelerometers that can potentially replace many dedicated instruments with a single, low‐noise sensor. These instruments are designed with a flat frequency response from 0.005 to 1500 Hz, spanning the flat response segments of broadband sensors and geophones, as well as a low‐noise floor and high sensitivity. The sensors have been functioning normally for over four years, fully grouted at depths of >100 m. Year‐long power spectral density (PSD) profiles show that the optical accelerometers have a lower noise floor than a colocated geophone for all frequencies, with 20 dB noise reduction at 250 Hz. PSD comparisons to a broadband sensor installed at the surface show a 5–30 dB noise reduction for the optical accelerometer above 1 Hz, although this is likely due, in part, to the broadband sensor being subjected to much higher surface noise. At periods >5 s, the broadband sensor shows up to 20 dB lower noise than the optical accelerometer, which in turn has up to 50 dB lower noise floor than the colocated geophone. Finally, modeling the Brune displacement spectrum for theoretical seismicity within 1 km of the borehole shows that the optical accelerometers could potentially deliver a detection threshold improvement of one magnitude unit relative to the colocated geophone.
PubDate: Mon, 11 Apr 2022 00:00:00 GMT
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- Rupture Process of the 2017 M w 6.3 Earthquake in Jinghe, Northwest
China, Constrained by GNSS, InSAR, and Teleseismic Waveforms-
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Authors: Xiao Z; Wang J, Xu C, et al.
Abstract: AbstractThe Jinghe, Xinjiang, earthquake on 8 August 2017 is not only one of the largest events that happened along the north Tien Shan but also the first Mw>6 event that received adequate seismic and geodetic observations in this region, providing a rare chance to gain insights into the faults that bound the Tien Shan. A previous rupture model (Zhang et al., 2020) was built based on a hypothesis of a north‐dipping seismogenic fault, but field geological mapping suggests the fault to be south dipping. Different fault geometry would result in different rupture scenarios. Here, we reconstructed the coseismic ground deformation with Global Navigation Satellite Systems (GNSS) observations and Sentinel‐1A interferograms, modeled the rupture process on the geologically consistent fault plane with constraints from GNSS, Interferometric Synthetic Aperture Radar data, and teleseismic P waveforms. Our results demonstrate that this earthquake occurred on a ramp fault buried under the foothills of the north Tien Shan, with strike of 86.8° and dip of 46°. The unidirectional coseismic rupture extended 20 km along strike and down to a depth of 20 km with an average rupture velocity around 1.9 km/s. Primary slip occurred within 3–7 s after the rupture initiation with a peak of 0.38 m. This event released 3.78×1018 N·m seismic moment, corresponding to Mw 6.31. Modeling the interseismic deformation shows that the seismogenic fault of the 2017 Jinghe event absorbs about 5.2 ± 1.0 mm/yr crustal shortening between the Junngar basin and the north Tien Shan. The recurrence interval for earthquakes of the same magnitude as the 2017 Jinghe earthquake is estimated to be 73 ± 14 yr based on the coseismic slip and interseismic slip rate.
PubDate: Fri, 08 Apr 2022 00:00:00 GMT
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- Is the Long‐Term Probability of the Occurrence of Large Earthquakes
along the Nankai Trough Inflated'–Conflict between Science and Risk
Management–-
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Authors: Hashimoto M.
Abstract: In October 2019, a Japanese newspaper—the Chunichi Shimbun—published a series of articles on the 30 yr probability of the occurrence of earthquake along the Nankai trough, southwest Japan, entitled with “Inside Story of 80% of the Nankai Trough” (Ozawa, 2019a). These articles cast doubt on the estimate and criticized the process of issuance of probability, reporting that “probability is inflated” (Ozawa, 2019a).
PubDate: Thu, 31 Mar 2022 00:00:00 GMT
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