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The Leading Edge
Journal Prestige (SJR): 0.386

Citation Impact (citeScore): 1
Number of Followers: 1

Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1070-485X
Published by Society of Exploration Geophysicists

[3 journals]

Multidimensional EMD with marginal Hilbert-Huang spectrum applications for
engineering geophysics — Technical tutorial and field example
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  Authors: Chen C; Jeng Y.
  Abstract: Spectral analysis is vital in solving various engineering problems. Conventional methods like fast Fourier transform and wavelet transform are effective, but they have difficulties dealing with the nonlinear and nonstationary data frequently encountered in engineering geophysics. A newer methodology, Hilbert-Huang transform (HHT), has been developed as a remedy. In this article, a systematic review and technical tutorial on the evolving advanced data processing method, multimarginal HHT spectral analysis, which is derived from HHT, will be the main theme. A field example to indicate the possible application to engineering geophysics follows. Basic but important issues related to conventional methods are also discussed.
  PubDate: Sun, 01 May 2022 00:00:00 GMT
A new DAS sensor prototype for multicomponent seismic data
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  Authors: Takekawa J; Mikada H, Xu S, et al.
  Abstract: We present a novel type of multicomponent sensor prototype that uses distributed acoustic sensing (DAS) technology. A prototype of the new sensor has three individual parts consisting of optical fiber wound around a polyvinyl chloride frame. We deployed the sensor prototype at a test site and recorded seismic waves generated by a wooden hammer. A geophone array was also set for comparison purposes. The data observed with the new DAS sensor prototype show good agreement with the conventional geophone. The particle motion of waveforms obtained by the DAS sensor prototype shows ellipsoidal motion, the propagating velocity of which coincides with the velocity of the Rayleigh waves estimated by the dispersion curve based on the geophone data. We introduced a simple string model to explain the dynamic behavior of the sensor. The analysis results of the string model can explain features of recorded seismic data. These results indicate that the DAS sensor prototype records seismic waves via lateral vibration of the string. The present study shows a new possibility of the multicomponent sensor with the DAS technology.
  PubDate: Sun, 01 May 2022 00:00:00 GMT
An airborne micro-TEM and physics deep learning solution to near-surface
corrections in sand-covered areas
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  Authors: Colombo D; Türkoğlu E, Sandoval-Curiel E.
  Abstract: Sand-covered areas, such as desert environments, pose challenges to seismic imaging for resource exploration and monitoring. Aeolian sand dunes provide extreme variations of elastic parameters causing, among other effects, nonlinear velocity gradients proportional to compaction. Description and correction for sand velocities is typically performed through empirically derived sand curve functions. Shallow drilling with uphole traveltime measurements represents another established technique for characterizing the thickness of the sand layer. This defines a basal depositional surface across the investigated area to apply the sand correction for seismic processing operations. The accurate definition of the unconformable base of sand is crucial for the application of robust near-surface corrections. An airborne transient electromagnetic solution is proposed, where the acquisition instrumentation, acquisition parameters, and inversion strategies are tuned to the ultra-shallow depth of the target (2–20 m). The data inversion component makes extensive use of a recently introduced physics-driven DL inversion scheme. It enables boosted depth resolution in the resistivity model using all of the available data while achieving an acceptable data misfit to honor the propagation of the electromagnetic radiation. The imaged resistivity boundary provides an excellent match to the existing uphole data and indicates the presence of long-wavelength mismatch from the previously interpreted base of sand.
  PubDate: Sun, 01 May 2022 00:00:00 GMT
A field experiment of a temperature-tolerant distributed acoustic sensor
in deep geothermal reservoir prospecting
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  Authors: Kasahara J; Hasada Y, Kuzume H, et al.
  Abstract: Seismic exploration technologies with distributed acoustic sensing (DAS) are investigated to acquire seismic waves in high-temperature environments and locate supercritical geothermal reservoirs deeper than the brittle-ductile transition boundary in Japan. We conducted a seismic reflection survey in the Mori-Nigorikawa geothermal field in the Nigorikawa caldera basin. An optical fiber system and an array of geophones were installed to 2100 m depth in F-01, a little-deviated high-temperature geothermal production well, and along a road for about 1.2 km on the surface. Numerous reflectors appear to gather at a depth between 2000 and 3000 m, corresponding to the production zone of the well. Although the production zone is located mainly within the Nigorikawa volcanic conduit estimated in the past geothermal analysis, the reflectors are also distributed outside the conduit. The DAS waveforms show distinct traveltime discontinuity at 1060 m depth. Our traveltime tomography and forward-simulated synthetic DAS waveforms could indicate the existence of a water layer 250 m long and 50 m thick at 1060 m depth. The Mori Geothermal Power Plant reinjects wastewater at this depth through a reducing well. The use of high-temperature-tolerant fiber enables the deployment of seismic sensors much closer to the deep target and may investigate effective fluid circulation through production and reducing wells.
  PubDate: Sun, 01 May 2022 00:00:00 GMT
Fast and efficient void detection in carbonates by combined ERT and
borehole data: A case study from Chania Airport in Greece
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  Authors: Economou N; Kritikakis G, Manoutsoglou E, et al.
  Abstract: A typical approach for karstic carbonate risk assessment is to utilize integrated geophysical research and calibrate the data with either pre- or postmeasurement acquisition borehole information. Here, we present a case study of a time-demanding investigation on the detection of subsurface areas prone to new building foundation stability at a site rich in karstic structures belonging to the Trypali Unit (Triassic-Jurassic). During excavation and construction to expand the airport in Chania, Crete, Greece, a large karstic void was revealed, which triggered an alert that led to an immediate work stoppage and the demand for an investigation of the subsurface of the whole area. The scope was to detect weak zones or voids larger than 0.5 m with a fast and timely approach because the costs of a long project stop are high. To meet the time demands with an efficient approach, we utilized the electrical resistivity tomography method, which guided a fast postacquisition borehole program and was supplemented by in-borehole video recordings, aiding in the direct detection of karstic structures. The 3D inversion of the electrical data provided electrical resistivity tomography images of the subsurface, which characterized the area as highly karstified and fractured and detected voids with sizes ranging from 0.5 to 6 m.
  PubDate: Sun, 01 May 2022 00:00:00 GMT
In-situ physical properties of reclaimed lands in Singapore
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  Authors: Niu Y; Li Y, Chian S, et al.
  Abstract: Reclaimed land construction is crucial for sustainable development of the land-scarce city-state of Singapore. To characterize the physical properties of two different types of reclaimed lands — one with well-sorted sands and the other with municipal solid waste — we conduct both active and passive seismic surveys at the sites and compare them with natural geologic formations. From the multichannel surface wave analysis, we observe more complex features related to mode kissing, mode jump, and mode loss on the dispersion spectra of the reclaimed lands, indicating complex subsurface structures. To utilize multiple orders of Rayleigh waves for inversion, we design a quantitative procedure to optimize the mode-order assignment. Seismic data and inverted results show that an older municipal solid waste landfill is more heterogeneous and stronger in its shear strength compared to the younger landfill. The reclaimed land filled with sand is more homogeneous and weaker in shear strength than the natural sedimentary rock formation. The contrast of physical properties at the four sites suggest a significant acceleration in soil hardening when landfill materials are chemically reactive with each other and with the environment. These in-situ measurements are crucial for civil engineering constructions and redevelopment of reclaimed lands in the future.
  PubDate: Sun, 01 May 2022 00:00:00 GMT
Characterizing shallow subsurface using 3D seismic while drilling with a
downhole pilot
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  Authors: Aldawood A; Almarzoug M, Silvestrov I, et al.
  Abstract: Seismic while drilling (SWD) can provide high-resolution subsurface information and characterize near-surface geology. We present a case study of SWD analysis using a data set from a desert environment acquired over a complex overburden. The data were acquired with a system composed of wireless surface geophones as well as top-drive and downhole sensors. The drill-bit noise data were reprocessed using a specialized workflow with two essential elements. First, a downhole pilot from a near-bit sensor was used for deconvolution, which led to improved data quality, particularly in the shallow subsurface. Second, nonlinear beamforming leveraged the 3D carpet of geophones to enhance signal quality and enable picking 3D traveltimes. A simple workflow for building a 1D velocity model used 3D traveltimes from an offset of 180 to 500 m. We vertically projected and averaged all 3D traveltimes to obtain a robust checkshot profile for the section from 190 to 1855 m. For the shallow subsurface (0–800 m), we further applied an advanced workflow with 3D traveltime inversion that more accurately handled mid- and far-offset data using a ray-tracing engine. More than 100,000 offset traveltime picks were inverted for a 1D velocity model. The model closely ties with the geology of the near surface, namely the formation tops associated with major impedance and lithologic contrasts. Amplitude signatures of 3D SWD gathers also correlate with the velocity model and lithologic changes, showing weak energy associated with soft formations and higher-energy first-arrival waveforms associated with compacted formations. Finally, we used the data extracted from a 2D line to reconstruct a migrated image of the back-propagated drill-bit sources. Joint use of kinematic and dynamic signatures helps characterize markers associated with loss circulation zones and target layers.
  PubDate: Sun, 01 May 2022 00:00:00 GMT
Introduction to this special section: Engineering geophysics
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  Authors: Grobbe N; Tosti F.
  Abstract: In the context of our growing population, new paradigms are required for, e.g., the monitoring and management of infrastructure and buildings and the use of the subsurface and its resources. Increasing energy demands entail continuous improvement of imaging techniques to better understand subsurface resources and to maximize production in an environmentally safe manner. Climate change, in combination with rapid population growth, puts increasing pressure on freshwater resources, groundwater systems, and urban living environments. Many subdisciplines and areas within geophysics, including engineering geophysics, are increasingly involved in tackling these global challenges.
  PubDate: Sun, 01 May 2022 00:00:00 GMT