scholarly journals Joint inversion of surface wave velocity and gravity observations and its application to central Asian basins shear velocity structure

2009 ◽  
Vol 114 (B2) ◽  
Author(s):  
Monica Maceira ◽  
Charles J. Ammon
Keyword(s):  
Surface Wave ◽  
Wave Velocity ◽  
Velocity Structure ◽  
Joint Inversion ◽  
Shear Velocity ◽  
Central Asian ◽  
Surface Wave Velocity

scholarly journals Using ambient seismic noise to study temporal and spatial surface wave velocity structures and ambient noise field characteristics of central South Island, New Zealand

2021 ◽  
Author(s):  
◽  
Rachel Heckels
Keyword(s):  
New Zealand ◽  
Surface Wave ◽  
Wave Velocity ◽  
Seismic Noise ◽  
Shear Velocity ◽  
Southern Alps ◽  
Ambient Seismic Noise ◽  
Near Surface ◽  
Surface Wave Velocity ◽  
Velocity Changes

<p>Ambient seismic noise is used to examine the spatial and temporal surface wave velocity structures and ambient seismic noise fields in the vicinity of different fault zone environments. This study focuses on two distinct regions of central South Island, New Zealand. The Canterbury Plains is a sedimentary basin with many minor faults, which was considered to have low seismic hazard prior to the 2010 – 2011 Canterbury earthquake sequence. We focus on the time period immediately following the 2010 Darfield earthquake, which ruptured the previously unmapped Greendale Fault. The second region of interest is the central Southern Alps. The locked portion of the Alpine Fault currently poses one of the largest seismic hazards for New Zealand. The wealth of data from both permanent and temporary seismic deployments in these regions make them ideal areas in which to assess the effectiveness of ambient noise for velocity modelling in regions surrounding faults at different stages of their seismic cycles.  Temporal velocity changes are measured following the Mw 7.1 Darfield earthquake of 4 September 2010 in the Canterbury Plains. Nine-component cross-correlations are computed from temporary and permanent seismic stations lying on and surrounding the Greendale Fault. Using the Moving-Window Cross-Spectral method, surface wave velocity changes are calculated for the four months immediately following the earthquake until 10 January 2011, for 0.1 — 1.0 Hz. An average increase in seismic velocity of 0.14 ± 0.04 % is determined throughout the region, providing the first such estimate of postseismic relaxation rates in Canterbury. Depth analyses further showed that velocity changes are confined to the uppermost 5 km of the subsurface and we attribute this to postseismic relaxation via crack-healing of the Greendale Fault and throughout the surrounding region.  Rayleigh and Love wave dispersion is examined throughout the Canterbury region. Multi-component cross-correlation functions are analysed for group and phase dispersion curves. These are inverted using frequency-time analysis for 2-D phase and group velocity maps of Rayleigh and Love waves. A high-velocity zone to the southeast of the region coincides with volcanic rocks of Banks Peninsula. Dispersion curves generated from the surface wave tomography are further inverted for one-dimensional shear velocity profiles. These models show a thin, low-velocity near surface layer consistent with the basin sediments, which thins towards the foothills of the Southern Alps. A near-surface damage zone is identified along the length of the Greendale Fault, with consistent reduced Vs velocities to depth of up to 5 km.  Surface and shear wave velocity maps are computed for the central Southern Alps to image the seismic structure of the region. Tomographic surface maps at periods of 5 – 12 s are produced from dispersion measurements of three-component cross-correlation functions. At periods of 5 – 8 s a strong NE-SW trending velocity contrast highlights the Alpine Fault. One-dimensional shear velocity models, computed from the surface wave maps, are in agreement with previous models produced by other conventional methods. An analysis of surface wave amplitudes through signal-to-noise ratios of cross-correlations reveals strong directional effects. Calculated signal-to-noise ratios are up to eight times higher for surface waves travelling north-west than for waves travelling to the south or east. We attribute this to a combination of more energetic ocean wave signals from the Southern Ocean compared to the Tasman Sea.</p>

scholarly journals Using ambient seismic noise to study temporal and spatial surface wave velocity structures and ambient noise field characteristics of central South Island, New Zealand

2021 ◽  
Author(s):  
◽  
Rachel Heckels
Keyword(s):  
New Zealand ◽  
Surface Wave ◽  
Wave Velocity ◽  
Seismic Noise ◽  
Shear Velocity ◽  
Southern Alps ◽  
Ambient Seismic Noise ◽  
Near Surface ◽  
Surface Wave Velocity ◽  
Velocity Changes

<p>Ambient seismic noise is used to examine the spatial and temporal surface wave velocity structures and ambient seismic noise fields in the vicinity of different fault zone environments. This study focuses on two distinct regions of central South Island, New Zealand. The Canterbury Plains is a sedimentary basin with many minor faults, which was considered to have low seismic hazard prior to the 2010 – 2011 Canterbury earthquake sequence. We focus on the time period immediately following the 2010 Darfield earthquake, which ruptured the previously unmapped Greendale Fault. The second region of interest is the central Southern Alps. The locked portion of the Alpine Fault currently poses one of the largest seismic hazards for New Zealand. The wealth of data from both permanent and temporary seismic deployments in these regions make them ideal areas in which to assess the effectiveness of ambient noise for velocity modelling in regions surrounding faults at different stages of their seismic cycles.  Temporal velocity changes are measured following the Mw 7.1 Darfield earthquake of 4 September 2010 in the Canterbury Plains. Nine-component cross-correlations are computed from temporary and permanent seismic stations lying on and surrounding the Greendale Fault. Using the Moving-Window Cross-Spectral method, surface wave velocity changes are calculated for the four months immediately following the earthquake until 10 January 2011, for 0.1 — 1.0 Hz. An average increase in seismic velocity of 0.14 ± 0.04 % is determined throughout the region, providing the first such estimate of postseismic relaxation rates in Canterbury. Depth analyses further showed that velocity changes are confined to the uppermost 5 km of the subsurface and we attribute this to postseismic relaxation via crack-healing of the Greendale Fault and throughout the surrounding region.  Rayleigh and Love wave dispersion is examined throughout the Canterbury region. Multi-component cross-correlation functions are analysed for group and phase dispersion curves. These are inverted using frequency-time analysis for 2-D phase and group velocity maps of Rayleigh and Love waves. A high-velocity zone to the southeast of the region coincides with volcanic rocks of Banks Peninsula. Dispersion curves generated from the surface wave tomography are further inverted for one-dimensional shear velocity profiles. These models show a thin, low-velocity near surface layer consistent with the basin sediments, which thins towards the foothills of the Southern Alps. A near-surface damage zone is identified along the length of the Greendale Fault, with consistent reduced Vs velocities to depth of up to 5 km.  Surface and shear wave velocity maps are computed for the central Southern Alps to image the seismic structure of the region. Tomographic surface maps at periods of 5 – 12 s are produced from dispersion measurements of three-component cross-correlation functions. At periods of 5 – 8 s a strong NE-SW trending velocity contrast highlights the Alpine Fault. One-dimensional shear velocity models, computed from the surface wave maps, are in agreement with previous models produced by other conventional methods. An analysis of surface wave amplitudes through signal-to-noise ratios of cross-correlations reveals strong directional effects. Calculated signal-to-noise ratios are up to eight times higher for surface waves travelling north-west than for waves travelling to the south or east. We attribute this to a combination of more energetic ocean wave signals from the Southern Ocean compared to the Tasman Sea.</p>

scholarly journals Surface wave velocity structure of the western Himalayan syntaxis

2013 ◽  
Vol 194 (3) ◽  
pp. 1866-1877 ◽  
Author(s):  
A. C. Hanna ◽  
D. S. Weeraratne
Keyword(s):  
Surface Wave ◽  
Wave Velocity ◽  
Velocity Structure ◽  
Surface Wave Velocity

scholarly journals Joint Body‐ and Surface‐Wave Tomography of Yucca Flat, Nevada, Using a Novel Seismic Source

2019 ◽  
Vol 109 (5) ◽  
pp. 1922-1934 ◽  
Author(s):  
Liam D. Toney ◽  
Robert E. Abbott ◽  
Leiph A. Preston ◽  
David G. Tang ◽  
Tori Finlay ◽  
...  
Keyword(s):  
Surface Wave ◽  
Phase Velocity ◽  
Wave Velocity ◽  
Velocity Structure ◽  
Joint Inversion ◽  
P Wave ◽  
S Wave ◽  
Surface Wave Dispersion ◽  
Velocity Models ◽  
Phase Velocity Dispersion

Abstract In preparation for the next phase of the Source Physics Experiments, we acquired an active‐source seismic dataset along two transects totaling more than 30 km in length at Yucca Flat, Nevada, on the Nevada National Security Site. Yucca Flat is a sedimentary basin which has hosted more than 650 underground nuclear tests (UGTs). The survey source was a novel 13,000 kg modified industrial pile driver. This weight drop source proved to be broadband and repeatable, richer in low frequencies (1–3 Hz) than traditional vibrator sources and capable of producing peak particle velocities similar to those produced by a 50 kg explosive charge. In this study, we performed a joint inversion of P‐wave refraction travel times and Rayleigh‐wave phase‐velocity dispersion curves for the P‐ and S‐wave velocity structure of Yucca Flat. Phase‐velocity surface‐wave dispersion measurements were obtained via the refraction microtremor method on 1 km arrays, with 80% overlap. Our P‐wave velocity models verify and expand the current understanding of Yucca Flat’s subsurface geometry and bulk properties such as depth to Paleozoic basement and shallow alluvium velocity. Areas of disagreement between this study and the current geologic model of Yucca Flat (derived from borehole studies) generally correlate with areas of widely spaced borehole control points. This provides an opportunity to update the existing model, which is used for modeling groundwater flow and radionuclide transport. Scattering caused by UGT‐related high‐contrast velocity anomalies substantially reduced the number and frequency bandwidth of usable dispersion picks. The S‐wave velocity models presented in this study agree with existing basin‐wide studies of Yucca Flat, but are compromised by diminished surface‐wave coherence as a product of this scattering. As nuclear nonproliferation monitoring moves from teleseismic to regional or even local distances, such high‐frequency (>5  Hz) scattering could prove challenging when attempting to discriminate events in areas of previous testing.

scholarly journals Crustal surface wave velocity structure of the east Albany-Fraser Orogen, Western Australia, from ambient noise recordings

2017 ◽  
Vol 210 (3) ◽  
pp. 1641-1651 ◽  
Author(s):  
C. Sippl ◽  
B.L.N. Kennett ◽  
H. Tkalčić ◽  
K. Gessner ◽  
C.V. Spaggiari
Keyword(s):  
Surface Wave ◽  
Wave Velocity ◽  
Western Australia ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Surface Wave Velocity

scholarly journals Imaging the subsurface using induced seismicity and ambient noise: 3-D tomographic Monte Carlo joint inversion of earthquake body wave traveltimes and surface wave dispersion

2020 ◽  
Vol 222 (3) ◽  
pp. 1639-1655
Author(s):  
Xin Zhang ◽  
Corinna Roy ◽  
Andrew Curtis ◽  
Andy Nowacki ◽  
Brian Baptie
Keyword(s):  
Surface Wave ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Joint Inversion ◽  
Body Wave ◽  
Source Parameters ◽  
Wave Dispersion ◽  
Inversion Method ◽  
Surface Wave Dispersion ◽  
Wave Data

SUMMARY Seismic body wave traveltime tomography and surface wave dispersion tomography have been used widely to characterize earthquakes and to study the subsurface structure of the Earth. Since these types of problem are often significantly non-linear and have non-unique solutions, Markov chain Monte Carlo methods have been used to find probabilistic solutions. Body and surface wave data are usually inverted separately to produce independent velocity models. However, body wave tomography is generally sensitive to structure around the subvolume in which earthquakes occur and produces limited resolution in the shallower Earth, whereas surface wave tomography is often sensitive to shallower structure. To better estimate subsurface properties, we therefore jointly invert for the seismic velocity structure and earthquake locations using body and surface wave data simultaneously. We apply the new joint inversion method to a mining site in the United Kingdom at which induced seismicity occurred and was recorded on a small local network of stations, and where ambient noise recordings are available from the same stations. The ambient noise is processed to obtain inter-receiver surface wave dispersion measurements which are inverted jointly with body wave arrival times from local earthquakes. The results show that by using both types of data, the earthquake source parameters and the velocity structure can be better constrained than in independent inversions. To further understand and interpret the results, we conduct synthetic tests to compare the results from body wave inversion and joint inversion. The results show that trade-offs between source parameters and velocities appear to bias results if only body wave data are used, but this issue is largely resolved by using the joint inversion method. Thus the use of ambient seismic noise and our fully non-linear inversion provides a valuable, improved method to image the subsurface velocity and seismicity.

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