Discontinuity of the Mozumi–Sukenobu fault low-velocity zone, central Japan, inferred from 3-D finite-difference simulation of fault zone waves excited by explosive sources

2004 ◽  
Vol 378 (3-4) ◽  
pp. 209-222 ◽  
Author(s):  
Yutaka Mamada ◽  
Yasuto Kuwahara ◽  
Hisao Ito ◽  
Hiroshi Takenaka
Keyword(s):  
Finite Difference ◽  
Fault Zone ◽  
Low Velocity ◽  
Central Japan ◽  
Low Velocity Zone ◽  
Velocity Zone ◽  
Fault Zone Waves

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

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.

scholarly journals 14C Ages of Wood Remains from the Hirayu Low Velocity Zone, Abo Tunnel, Central Japan.

1991 ◽  
Vol 30 (2) ◽  
pp. 103-106
Author(s):  
Shoji FUJII ◽  
Toshio NAKAMURA ◽  
Toyoaki SAWADA
Keyword(s):  
Low Velocity ◽  
Central Japan ◽  
Low Velocity Zone ◽  
Velocity Zone

An eigenfunction representation of deep waveguides with application to unconventional reservoirs

Geophysics ◽  
2021 ◽  
Vol 86 (6) ◽  
pp. T509-T521
Author(s):  
Owen Huff ◽  
Bin Luo ◽  
Ariel Lellouch ◽  
Ge Jin
Keyword(s):  
Finite Difference ◽  
Energy Distribution ◽  
Wave Energy ◽  
High Frequency ◽  
Guided Waves ◽  
Guided Wave ◽  
Low Velocity ◽  
Eagle Ford ◽  
Low Velocity Zone ◽  
Velocity Zone

Guided waves that propagate in deep low-velocity zones can be described using the displacement-stress eigenfunction theory. For a layered subsurface, these eigenfunctions provide a framework to calculate guided-wave properties at a fraction of the time required for fully numerical approaches for wave-equation modeling, such as the finite-difference approach. Using a 1D velocity model representing the low-velocity Eagle Ford Shale, an unconventional hydrocarbon reservoir, we verify the accuracy of the displacement eigenfunctions by comparing with finite-difference modeling. We use the amplitude portion of the Green’s function for source-receiver eigenfunction pairs as a proxy for expected guided-wave amplitude. These response functions are used to investigate the impact of the velocity contrast, reservoir thickness, and receiver depth on guided-wave amplitudes for discrete frequencies. We find that receivers located within the low-velocity zone record larger guided-wave amplitudes. This property may be used to infer the location of the recording array in relation to the low-velocity reservoir. We also study guided-wave energy distribution between the different layers of the Eagle Ford model and find that most of the high-frequency energy is confined to the low-velocity reservoir. We corroborate this measurement with field microseismic data recorded by distributed acoustic sensing fiber installed outside of the Eagle Ford. The data contain high-frequency body-wave energy, but the guided waves are confined to low frequencies because the recording array is outside the waveguide. We also study the energy distribution between the fundamental and first guided-wave modes as a function of the frequency and source depth and find a nodal point in the first mode for source depths originating in the middle of the low-velocity zone, which we validate with the same field data. The varying modal energy distribution can provide useful constraints for microseismic event depth estimation.

The Multiscale Structure of the Longmen Shan Central Fault Zone from Local and Teleseismic Data Recorded by Short-Period Dense Arrays

2020 ◽  
Vol 110 (6) ◽  
pp. 3077-3087
Author(s):  
Yafen Huang ◽  
Hongyi Li ◽  
Xin Liu ◽  
Yuting Zhang ◽  
Min Liu ◽  
...  
Keyword(s):  
Fault Zone ◽  
Receiver Functions ◽  
Seismic Array ◽  
Trapped Waves ◽  
Low Velocity ◽  
Surface Rupture ◽  
P Waves ◽  
Low Velocity Zone ◽  
Short Period ◽  
Velocity Zone

ABSTRACT The Longmen Shan fault zone (FZ), which consists of the back-range, the central, and the front-range faults, acts as the boundary between the Sichuan basin and eastern Tibet. In this study, local and teleseismic waveforms recorded by a 2D small aperture seismic array (176 temporary short-period seismometers) deployed by China University of Geosciences (Beijing) from 22 October to 20 November 2017 and a dense linear seismic array of 16 stations deployed by Geophysical Exploration Center, China Earthquake Administration during July 2008 are used to study the FZ structure by analyzing FZ-trapped waves (FZTWs), the radial-to-vertical amplitude ratio, and travel-time delays. Based on power density spectra analysis, FZTWs from local events with larger amplitudes and longer wavetrains are clearly observed at stations 6002–6003, 6013–6025, and W025–W032. The dispersion measured from trapped waves is quite weak. The near-surface shear velocity structure estimated from the radial-to-vertical amplitude ratios of local initial P waves shows a low-velocity zone around the surface rupture trace. The slight time delay of direct P waves examined from local and teleseismic events indicates a relatively shallow slow structure beneath the arrays. Through the comprehensive analysis of the central FZ, our results suggest a shallow low-velocity zone with a width of ∼150–160  m along the surface rupture trace. Moreover, our P-wave receiver functions reveal that the Moho depth beneath the Longmen Shan FZ is approximately 45 km, and receiver functions at stations located within the surface rupture zone show more complicated waveforms than those off the surface rupture.

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

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.

Partial melting and the low-velocity zone

1970 ◽  
Vol 4 (1) ◽  
pp. 62-64 ◽  
Author(s):  
Don L. Anderson ◽  
Hartmut Spetzler
Keyword(s):  
Partial Melting ◽  
Low Velocity ◽  
Low Velocity Zone ◽  
Velocity Zone

Nature of the low velocity zone in Cascadia from receiver function waveform inversion

2012 ◽  
Vol 337-338 ◽  
pp. 25-38 ◽  
Author(s):  
Ralf T.J. Hansen ◽  
Michael G. Bostock ◽  
Nikolas I. Christensen
Keyword(s):  
Receiver Function ◽  
Waveform Inversion ◽  
Low Velocity ◽  
Low Velocity Zone ◽  
Velocity Zone
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