Estimating deep S-wave velocity structure in the Los Angeles Basin using a passive surface-wave method

Hayashi, Koichi; Martin, Antony; Hatayama, Ken; Kobayashi, Takayuki

doi:10.1190/tle32060620.1

Cited by 20 publications

(6 citation statements)

References 6 publications

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“…We estimated dispersion characteristics of Rayleigh wave phase velocities in the lower frequency range using continuous microtremor and event data. We applied the two-site SPAC (2sSPAC) method (e.g., Morikawa et al 2004;Hayashi et al 2013) for the microtremor data, assuming that the microtremor wave-field around the area is spatially and temporally uniform. We selected four sensor pairs around the heavily damaged zones (S6-S8: 167 m, S5-S8: 201 m, S3-S6: 238 m, and S3-S5: 349 m) for the data processing.…”

Section: Rayleigh Wave Phase Velocitymentioning

confidence: 99%

Subsurface velocity structure and site amplification characteristics in Mashiki Town, Kumamoto Prefecture, Japan, inferred from microtremor and aftershock recordings of the 2016 Kumamoto earthquakes

Hayashida

Yamada

et al. 2018

Earth Planets Space

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In order to investigate the seismic velocity structure in the region of concentrated severe damage during the 2016 Kumamoto earthquake sequence, we conducted continuous seismic observations in the central area of Mashiki Town, Kumamoto Prefecture. During 4 days of observations at eight temporary sites, 2 months after the mainshock, recordings from 30 aftershocks (1.7 ≤ M j ≤ 4.3, 1.9 km ≤ depth ≤ 13.5 km) were obtained. The aftershock data showed that site amplifications at approximately 1 Hz are dominant in a zone where almost no buildings were damaged along the Akitsu riverside, whereas site amplifications at higher than 3 Hz are observed in the heavily damaged zones. Our data also showed that the peak acceleration and velocity amplitudes, as well as seismic intensities for the small events in the less damaged zone, are clearly larger than those in the damaged zones, implying that the damage distribution is inconsistent with site response based on linear site amplifications. The estimated phase velocities of Rayleigh waves using the aftershock and microtremor data show dispersive characteristics in the lower frequency range (0.26 ≤ f ≤ 1.27 Hz), but the values are substantially smaller than those derived from the P-S logging model at the nearest KiK-net strong-motion observation station KMMH16. The derived microtremor horizontal-to-vertical spectral ratios and earthquake radial-to-vertical (R/V) spectral ratios show common distinct peaks at around 0.4 Hz, which are possibly related to the response of deep sedimentary layers beneath the area. The refined velocity structure model that better accounts for both the phase velocity and common dominant peak indicates that the values of S wave velocity (Vs) above the bedrock layer (Vs = 2700 m/s) are smaller than those inferred from the logging model and the depth to the bedrock layer could be much deeper (about 600 m) in comparison with the logging model (234 m). The derived R/V spectral ratio at station KMMH16 also shows a distinct peak at 0.4 Hz, suggesting that there is no large difference of deep sedimentary structure between the observation area and station KMMH16. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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Section: Rayleigh Wave Phase Velocitymentioning

confidence: 99%

Subsurface velocity structure and site amplification characteristics in Mashiki Town, Kumamoto Prefecture, Japan, inferred from microtremor and aftershock recordings of the 2016 Kumamoto earthquakes

Hayashida

Yamada

et al. 2018

Earth Planets Space

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“…Numerical hydrological models exist for the Los Angeles basin (Reichard et al, 2003). Some detailed borehole information is available for the Los Angeles basin (Hayashi et al, 2013) and the Santa Clara Valley (Newhouse et al, 2004;O'Connell and Turner, 2011;Wentworth et al, 2015). Three-dimensional numerical calculations (Roten et al, 2014) would be needed to confirm that the modified fluid pressure did not inadvertently increase shaking from other types of seismic waves.…”

Section: Overpressured Aquifermentioning

confidence: 99%

Nonlinear Attenuation of S Waves by Frictional Failure at Shallow Depths

Sleep

Nakata

2017

Bulletin of the Seismological Society of America

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Strong S waves produce dynamic stresses, which bring the shallow subsurface into nonlinear anelastic failure. The construct of coulomb friction yields testable predictions about this process for strong-motion records. Physically, the anelastic strain rate increases rapidly with increasing dynamic stress, and dynamic stress is proportional to the difference between total strain and anelastic strain. Nonlinear models of vertically propagating S waves in layered media confirmed and illustrated analytical inferences. The effective coefficient of friction bounds (clips amplitude) the resolved horizontal acceleration normalized to the acceleration of gravity. There is a tendency for the random signal from vertically propagating S waves to become transiently circularly polarized at the maximum (clipped) resolved acceleration, as the acceleration component perpendicular to the current acceleration adds weakly the resolved acceleration. Frictional attenuation does not preferentially suppress high-frequency signal; it cannot be modeled by increasing ordinary linear attenuation. In addition, an effect of shallow cohesion is to allow brief pulses of strong high-frequency acceleration to reach the surface. Frictional attenuation within deep overpressured aquifers suppresses shaking recorded at the surface, but does not simply clip amplitude at a given resolved acceleration. The anelastic strain rate increases slowly with stress within shallow muddy sediments. The accelerations from reverberations within such layers can exceed 1g.

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“…The averaged S‐wave velocity in stiffer exhumed sediments is ∼800 m s −1 for averaged sediments in the San Fernando Valley [ Magistrale et al ., ], and locally ∼1000 m s −1 in the Mission Hills anticline in the San Fernando Valley [ O'Connell and Turner , ]. The S‐wave velocity for both accumulating and exhumed sediments in the Los Angeles Basin is ∼400–500 m s −1 at 50 m depth [ Magistrale et al ., ; Hayashi et al ., ]. The computed PGV for 3–4 s Love waves for S‐wave velocity of 400, 500, 600, 800, and 1000 m s −1 is 2.61, 1.67, 1.05, 0.65, and 0.42 m s −1 , respectively (retaining an extra digit for comparison).…”

Section: Application To Greater Los Angelesmentioning

confidence: 99%

Nonlinear attenuation of S-waves and Love waves within ambient rock

Sleep

Erickson

2014

Geochem. Geophys. Geosyst.

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We obtain scaling relationships for nonlinear attenuation of S-waves and Love waves within sedimentary basins to assist numerical modeling. These relationships constrain the past peak ground velocity (PGV) of strong 3-4 s Love waves from San Andreas events within Greater Los Angeles, as well as the maximum PGV of future waves that can propagate without strong nonlinear attenuation. During each event, the shaking episode cracks the stiff, shallow rock. Over multiple events, this repeated damage in the upper few hundred meters leads to self-organization of the shear modulus. Dynamic strain is PGV divided by phase velocity, and dynamic stress is strain times the shear modulus. The frictional yield stress is proportional to depth times the effective coefficient of friction. At the eventual quasi-steady self-organized state, the shear modulus increases linearly with depth allowing inference of past typical PGV where rock over the damaged depth range barely reaches frictional failure. Still greater future PGV would cause frictional failure throughout the damaged zone, nonlinearly attenuating the wave. Assuming self-organization has taken place, estimated maximum past PGV within Greater Los Angeles Basins is 0.4-2.6 m s 21. The upper part of this range includes regions of accumulating sediments with low S-wave velocity that may have not yet compacted, rather than having been damaged by strong shaking. Published numerical models indicate that strong Love waves from the San Andreas Fault pass through Whittier Narrows. Within this corridor, deep drawdown of the water table from its currently shallow and preindustrial levels would nearly double PGV of Love waves reaching Downtown Los Angeles.

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Estimating deep S-wave velocity structure in the Los Angeles Basin using a passive surface-wave method

Cited by 20 publications

References 6 publications

Subsurface velocity structure and site amplification characteristics in Mashiki Town, Kumamoto Prefecture, Japan, inferred from microtremor and aftershock recordings of the 2016 Kumamoto earthquakes

Subsurface velocity structure and site amplification characteristics in Mashiki Town, Kumamoto Prefecture, Japan, inferred from microtremor and aftershock recordings of the 2016 Kumamoto earthquakes

Nonlinear Attenuation of S Waves by Frictional Failure at Shallow Depths

Nonlinear attenuation of S-waves and Love waves within ambient rock

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