P- and S-wave reflection profiling for near-surface investigation of glacial sediments

Expressions of ductile, soft-sediment deformations induced by ground movements due to past earthquakes are difficult to recognize in near-surface soils. We have carried out shallow S-wave reflection studies in a seismically active area located northeast of metropolitan Lisbon, Portugal. Identifying shallow disturbed zones and hidden fault segments in this area is important but quite difficult because of small vertical slips due to earthquakes, the Holocene alluvial cover hiding the fault segments, and a high rate of surficial sedimentation. We have performed S-wave reflection profiling at two sites — Vila Franca Xira and Castanheira de Ribatejo. We detected different but interrelated evidence of soft-sediment deformation in the seismic data. This evidence includes sharp lateral changes in the S-wave velocity field; changes in the reflection horizons in stacked sections; aligned diffractions in unmigrated sections; discontinuities in common-offset gathers; and discontinuities, backscattered, and diffracted arrivals in common-source gathers. Though not equally clear everywhere, this evidence is recognizable at many locations where earthquake-motion-induced disturbed zones are interpreted. To confirm these interpretations, we have performed synthetic modeling of a seismic wavefield using the same acquisition geometry as in the field experiments, and with multiple disturbed zones present as vertical emplacements through horizontally lying soil layers. The modeling results resemble the observations in field data. It is possible to confirm the signatures of soft-sediment deformation in the shallow S-wave reflection data. The approach that we used will be useful in many seismically active, soil-covered areas in the world.

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Intergrated Well‐Log, VSP, and Surface Seismic Analysis of Near‐Surface Glacial Sediments: Red Lodge, Montana

10.4133/1.3614212 ◽

2011 ◽

Author(s):

Jingqiu Huang ◽

Robert Stewart ◽

Joe Wong ◽

Carlos Montana

Keyword(s):

Seismic Analysis ◽

Well Log ◽

Near Surface ◽

Glacial Sediments

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Tunnel detection at Yuma Proving Ground, Arizona, USA — Part 1: 2D full-waveform inversion experiment

Geophysics ◽

10.1190/geo2018-0598.1 ◽

2019 ◽

Vol 84 (1) ◽

pp. B95-B105 ◽

Cited By ~ 5

Author(s):

Yao Wang ◽

Richard D. Miller ◽

Shelby L. Peterie ◽

Steven D. Sloan ◽

Mark L. Moran ◽

...

Keyword(s):

Surface Wave ◽

Waveform Inversion ◽

Velocity Profiles ◽

Infinite Length ◽

Full Waveform Inversion ◽

S Wave ◽

Near Surface ◽

Tunnel Detection ◽

Full Waveform ◽

Wave Methods

We have applied time domain 2D full-waveform inversion (FWI) to detect a known 10 m deep wood-framed tunnel at Yuma Proving Ground, Arizona. The acquired seismic data consist of a series of 2D survey lines that are perpendicular to the long axis of the tunnel. With the use of an initial model estimated from surface wave methods, a void-detection-oriented FWI workflow was applied. A straightforward [Formula: see text] quotient masking method was used to reduce the inversion artifacts and improve confidence in identifying anomalies that possess a high [Formula: see text] ratio. Using near-surface FWI, [Formula: see text] and [Formula: see text] velocity profiles were obtained with void anomalies that are easily interpreted. The inverted velocity profiles depict the tunnel as a low-velocity anomaly at the correct location and depth. A comparison of the observed and simulated waveforms demonstrates the reliability of inverted models. Because the known tunnel has a uniform shape and for our purposes an infinite length, we apply 1D interpolation to the inverted [Formula: see text] profiles to generate a pseudo 3D (2.5D) volume. Based on this research, we conclude the following: (1) FWI is effective in near-surface tunnel detection when high resolution is necessary. (2) Surface-wave methods can provide accurate initial S-wave velocity [Formula: see text] models for near-surface 2D FWI.

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Fault Zone Guided Wave generation on the locked, late interseismic Alpine Fault, New Zealand

10.26686/wgtn.13818791.v1 ◽

2021 ◽

Author(s):

JD Eccles ◽

AK Gulley ◽

PE Malin ◽

CM Boese ◽

John Townend ◽

...

Keyword(s):

Fault Zone ◽

Plate Boundary ◽

Guided Wave ◽

S Wave ◽

Low Velocity ◽

Catchment Scale ◽

Near Surface ◽

Low Velocity Zone ◽

Alpine Fault ◽

Velocity Zone

© 2015. American Geophysical Union. All Rights Reserved. Fault Zone Guided Waves (FZGWs) have been observed for the first time within New Zealand's transpressional continental plate boundary, the Alpine Fault, which is late in its typical seismic cycle. Ongoing study of these phases provides the opportunity to monitor interseismic conditions in the fault zone. Distinctive dispersive seismic codas (~7-35Hz) have been recorded on shallow borehole seismometers installed within 20m of the principal slip zone. Near the central Alpine Fault, known for low background seismicity, FZGW-generating microseismic events are located beyond the catchment-scale partitioning of the fault indicating lateral connectivity of the low-velocity zone immediately below the near-surface segmentation. Initial modeling of the low-velocity zone indicates a waveguide width of 60-200m with a 10-40% reduction in S wave velocity, similar to that inferred for the fault core of other mature plate boundary faults such as the San Andreas and North Anatolian Faults.

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Investigating Near Surface S-Wave Velocity Properties Using Ambient Noise in Southwestern Taiwan

Terrestrial Atmospheric and Oceanic Sciences ◽

10.3319/tao.2014.12.02.05(eosi) ◽

2015 ◽

Vol 26 (2-2) ◽

pp. 205 ◽

Cited By ~ 6

Author(s):

Chun-Hsiang Kuo ◽

Kuo-Liang Wen ◽

Che-Min Lin ◽

Strong Wen ◽

Jyun-Yan Huang

Keyword(s):

Wave Velocity ◽

Ambient Noise ◽

S Wave ◽

Near Surface ◽

Southwestern Taiwan

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3D elastic full-waveform inversion of surface waves in the presence of irregular topography using an envelope-based misfit function

Geophysics ◽

10.1190/geo2017-0081.1 ◽

2018 ◽

Vol 83 (1) ◽

pp. R1-R11 ◽

Cited By ~ 24

Author(s):

Dmitry Borisov ◽

Ryan Modrak ◽

Fuchun Gao ◽

Jeroen Tromp

Keyword(s):

Surface Wave ◽

Objective Function ◽

Surface Waves ◽

Large Scale ◽

Body Wave ◽

Waveform Inversion ◽

Full Waveform Inversion ◽

S Wave ◽

Near Surface ◽

Full Waveform

Full-waveform inversion (FWI) is a powerful method for estimating the earth’s material properties. We demonstrate that surface-wave-driven FWI is well-suited to recovering near-surface structures and effective at providing S-wave speed starting models for use in conventional body-wave FWI. Using a synthetic example based on the SEG Advanced Modeling phase II foothills model, we started with an envelope-based objective function to invert for shallow large-scale heterogeneities. Then we used a waveform-difference objective function to obtain a higher-resolution model. To accurately model surface waves in the presence of complex tomography, we used a spectral-element wave-propagation solver. Envelope misfit functions are found to be effective at minimizing cycle-skipping issues in surface-wave inversions, and surface waves themselves are found to be useful for constraining complex near-surface features.

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Shallow velocity structure and poisson's ratio at the Tarzana, California, strong-motion accelerometer site

Bulletin of the Seismological Society of America ◽

10.1785/bssa0860061704 ◽

1996 ◽

Vol 86 (6) ◽

pp. 1704-1713 ◽

Cited By ~ 2

Author(s):

R. D. Catchings ◽

W. H. K. Lee

Keyword(s):

Urban Areas ◽

Velocity Structure ◽

Strong Motion ◽

P Wave ◽

S Wave ◽

Near Surface ◽

Velocity Models ◽

Wave Velocities ◽

Poisson's Ratios ◽

Poisson’S Ratios

Abstract The 17 January 1994, Northridge, California, earthquake produced strong ground shaking at the Cedar Hills Nursery (referred to here as the Tarzana site) within the city of Tarzana, California, approximately 6 km from the epicenter of the mainshock. Although the Tarzana site is on a hill and is a rock site, accelerations of approximately 1.78 g horizontally and 1.2 g vertically at the Tarzana site are among the highest ever instrumentally recorded for an earthquake. To investigate possible site effects at the Tarzana site, we used explosive-source seismic refraction data to determine the shallow (<70 m) P-and S-wave velocity structure. Our seismic velocity models for the Tarzana site indicate that the local velocity structure may have contributed significantly to the observed shaking. P-wave velocities range from 0.9 to 1.65 km/sec, and S-wave velocities range from 0.20 and 0.6 km/sec for the upper 70 m. We also found evidence for a local S-wave low-velocity zone (LVZ) beneath the top of the hill. The LVZ underlies a CDMG strong-motion recording site at depths between 25 and 60 m below ground surface (BGS). Our velocity model is consistent with the near-surface (<30 m) P- and S-wave velocities and Poisson's ratios measured in a nearby (<30 m) borehole. High Poisson's ratios (0.477 to 0.494) and S-wave attenuation within the LVZ suggest that the LVZ may be composed of highly saturated shales of the Modelo Formation. Because the lateral dimensions of the LVZ approximately correspond to the areas of strongest shaking, we suggest that the highly saturated zone may have contributed to localized strong shaking. Rock sites are generally considered to be ideal locations for site response in urban areas; however, localized, highly saturated rock sites may be a hazard in urban areas that requires further investigation.

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Near-surface glaciotectonic structures in the sediments of an overdeepened glacial valley revealed by a shallow 3D seismic survey

10.5194/egusphere-egu21-8195 ◽

2021 ◽

Author(s):

David Tanner ◽

Hermann Buness ◽

Thomas Burschil

Keyword(s):

Seismic Reflection ◽

P Wave ◽

Seismic Survey ◽

Small Scale ◽

Academic Press ◽

Near Surface ◽

Glacial Sediments ◽

Area Source ◽

Terminal Moraine ◽

Rhine Valley

Glaciotectonic structures commonly include thrusting and folding, often as multiphase deformation. Here we present the results of a small-scale 3-D P-wave seismic reflection survey of glacial sediments within an overdeepened glacial valley in which we recognise unusual folding structures in front of push-moraine. The study area is in the Tannwald Basin, in southern Germany, about 50 km north of Lake Constance, where the basin is part of the glacial overdeepened Rhine Valley. The basin was excavated out of Tertiary Molasse sediments during the Hosskirchian stage, and infilled by 200 m of Hosskirchian and Rissian glacioclastics (Dietmanns Fm.). After an unconformity in the Rissian, a ca. 7 m-thick till (matrix-supported diamicton) was deposited, followed by up to 30 m of Rissian/W&#252;rmian coarse gravels and minor diamictons (Illmensee Fm.). The terminal moraine of the last W&#252;rmian glaciation overlies these deposits to the SW, not 200 m away.We conducted a 3-D, 120 x 120 m&#178;, P-wave seismic reflection survey around a prospective borehole site in the study area. Source/receiver points and lines were spaced at 3 m and 9 m, respectively. A 10 s sweep of 20-200 Hz was excited by a small electrodynamic, wheelbarrow-borne vibrator twice at every of the 1004 realized shot positions. We recognised that the top layer of coarse gravel above the till is folded, but not in the conventional buckling sense, rather as cuspate-lobate folding. The fold axes are parallel to the terminal moraine front. The wavelength of the folding varies between 40 and 80 m, and the thickness of the folded layer is on average about 20 m. Cuspate-lobate folding is typical for deformation of layers of differing mechanical competence (after Ramsay and Huber 1987; &#181;1/&#181;2 less than 10), so this tell us something about the relative competence (or stiffness) of the till layer compared to the coarse clastics above. We also detected small thrust faults that are also parallel to the push-moraine, but these have very little offset and most of the deformation was achieved by folding.Ramsay, J.G. and Huber, M. I. (1987): The techniques of modern structural geology, vol. 2: Folds and fractures: Academic Press, London, 700 pp.

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