Significant Effects of Shallow Seismic and Stress Properties on Phase Velocities of Rayleigh Waves Up to 20 s

Yang, Chenhao; Li, Guoliang; Niu, Fenglin; Ben‐Zion, Yehuda

doi:10.1007/s00024-018-2075-7

Cited by 12 publications

(10 citation statements)

References 36 publications

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“…This is consistent with our observations on velocity reductions in the top 22 m associated with weak ground motion. Rubinstein and Beroza () showed that temporal changes of S wave velocities caused by the 2004 Parkfield earthquake concentrate in the top 100 m. Modeling results from Yang et al () suggest that temporal changes of seismic velocities in the top 1–3 km can produce observable changes in analyses using Rayleigh waves with periods of 5–20 s. Therefore, resolving the depth range of temporal changes based on sensitivity kernels of Rayleigh waves can be subjected to large uncertainties without information (e.g., from borehole data) on changes in the shallow crust.…”

Section: Discussionmentioning

confidence: 99%

Imaging and Monitoring Temporal Changes of Shallow Seismic Velocities at the Garner Valley Near Anza, California, Following the M7.2 2010 El Mayor‐Cucapah Earthquake

Qin

Ben‐Zion

Bonilla³

et al. 2020

JGR Solid Earth

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Seismograms from~700 local earthquakes recorded at various depths (0, 6, 15, 22, 50, and 150 m) by sensors of the Garner Valley Downhole Array in Southern California are used to analyze the shallow velocity structure and temporal changes of seismic velocities after the 2010 M7.2 El Mayor-Cucapah (EMC) earthquake. The direct P and S wave travel times between surface and borehole stations reveal very low shear wave velocities (178-259 m/s) and very high V p /V s ratios (6.2) in the top 22 m. Temporal changes of seismic velocities after the EMC earthquake are estimated using autocorrelations of data in moving time windows at two borehole stations (22 and 50 m) and seismic interferometry between multiple station pairs of the Garner Valley Downhole Array. The S wave velocity in the top 6 m drops abruptly by 14.3 ± 3.3%, during the passage of surface waves from the EMC event with a peak ground acceleration of 39 Gal, and recovers in~236 s. The average velocity reductions decrease with depth and are 10.9 ± 3.1%, 8.5 ± 2.1%, 6.3 ± 2.1%, and 4.5 ± 2.0% in the top 15, 22, 50, and 150 m, respectively. Comparisons of seismic interferometry results between sensor pairs at 0-22 and 22-150 m indicate that statistically significant velocity changes are limited at the site to the top 22 m. Pore pressure data are in phase with the surface displacement and reach maxima when the highest velocity drop occurs, suggesting fluid effects contribute to the observed velocity reductions. Key Points:• The top~20 m at the site has very low seismic velocities and very high V P /V S ratios • Moderate PGA produces large coseismic S wave velocity reductions in the top~20 m • The coseismic changes are followed by rapid recoveries in less thañ 240 s Supporting Information:• Supporting Information S1

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Section: Discussionmentioning

confidence: 99%

Imaging and Monitoring Temporal Changes of Shallow Seismic Velocities at the Garner Valley Near Anza, California, Following the M7.2 2010 El Mayor‐Cucapah Earthquake

Qin

Ben‐Zion

Bonilla³

et al. 2020

JGR Solid Earth

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“…We used the velocity model from ( 21 ) for depths greater than 500 m below the surface. Since the sensitivity kernels of surface waves can be significantly affected by the shallowest structure ( 51 ) and earthquake tomography is relatively insensitive to these depths, we used a generic velocity model for the shallow velocity structure at volcanoes ( 52 ) for the top 500 m. The coarseness of our velocity model at very shallow depths limits the resolution of the kernels that we calculate in the highest frequency bands.…”

Section: Methodsmentioning

confidence: 99%

Crustal seismic velocity responds to a magmatic intrusion and seasonal loading in Iceland’s Northern Volcanic Zone

et al. 2019

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“…4 and 5 ). A recent study 37 showed that shallow (1-3 km) changes in rock fabrics (including the closure of fractures) can significantly impact phase velocity and attenuation at surface-wave periods up to 10 s, characterized by much deeper sensitivity peaks. This means that, even if closing at a very shallow depth 38 , 39 , fluid-filled fractures are still a valid explanation for our observations.…”

Section: Discussionmentioning

confidence: 99%

Rayleigh-wave attenuation across the conterminous United States in the microseism frequency band

Magrini

Boschi

Gualtieri

et al. 2021

Sci Rep

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Mapping variations in the attenuation of seismic energy is important for understanding dissipative mechanisms in the lithosphere, and for modeling ground shaking associated with earthquakes. We cross-correlate ambient seismic signal recorded across the EarthScope Transportable Array in the 3–15 s period range. We apply to the resulting cross correlations a new method to estimate lateral variations in Rayleigh-wave attenuation, as a function of period, beneath North America. Between 3 and 6 s, our maps are dominated by a strong eastward decrease in attenuation. This pattern vanishes at longer periods, confirming early observations based on regional earthquakes. Attenuation maps and phase-velocity maps are anti-correlated at periods between 3 and 6 s, but the anti-correlation is also largely lost at longer periods. This corresponds to the attenuation coefficient decreasing with period more rapidly in the west than in the east, while the change in phase velocity with period is more uniform across the continent. Our results point to a transition in the properties of upper-crustal materials with depth, probably related to the closure of fluid-filled cracks and pores, and imply that measures of attenuation from seismic noise carry significant information on crustal rheology.

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Significant Effects of Shallow Seismic and Stress Properties on Phase Velocities of Rayleigh Waves Up to 20 s

Cited by 12 publications

References 36 publications

Imaging and Monitoring Temporal Changes of Shallow Seismic Velocities at the Garner Valley Near Anza, California, Following the M7.2 2010 El Mayor‐Cucapah Earthquake

Imaging and Monitoring Temporal Changes of Shallow Seismic Velocities at the Garner Valley Near Anza, California, Following the M7.2 2010 El Mayor‐Cucapah Earthquake

Crustal seismic velocity responds to a magmatic intrusion and seasonal loading in Iceland’s Northern Volcanic Zone

Rayleigh-wave attenuation across the conterminous United States in the microseism frequency band

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