Site response across downtown Santa Cruz, California

Cranswick, Edward; King, Kenneth W.; Worley, David M.; Williams, Robert A.; Spudich, Paul; Banfill, Robert

doi:10.1029/gl017i010p01793

Cited by 15 publications

(6 citation statements)

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“…1986;Nixdorf 1986; Plomerova & BabuSka 1988).The other half of the observed average traveltime residuals and almost all of the average amplitude residuals are produced by the near-surface structure in the topmost kilometre. That these shallow structures can play an important role for the magnitude residuals agrees with the observation of strong amplitude effects due to local, near-surface geology(Nakanishi & Motoya 1990;Mori & Frankel 1992; see alsoCranswick 1988;Cranswick et al 1990;Aki 1993).…”

supporting

confidence: 82%

Traveltime and amplitude anomalies at the seismic broad-band may GRF

Weber

1994

Geophysical Journal International

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S U M M A R Y Traveltime and amplitude residuals of P waves from teleseismic events show a positive correlation at the stations of the German seismic broad-band array GRF. Fast arrivals consistently have reduced amplitudes in the four frequency ranges considered (short-period bandpass, WWSSN-SP filter, broad-band velocity and WWSSN-LP filter).With the exception of the WWSSN-LP filter, 40-60 per cent of the average of the relative traveltime and almost 100 per cent of the average of the amplitude residuals at individual stations, with respect to the reference station A l , can be explained by near-surface sediment layers. These shallow structures are known from local and regional geology and are documented in borehole, local refraction and polarization studies. This aximuthal-and distance-independent term (station average) reaches values of up to -0.55 s and -0.15 units in log amplitude (magnitude).Even after the removal of these station averages, which also contain a trend of increasing crustal and uppermost mantle velocity from north to south, large azimuthal-and distance-dependent relative traveltime and magnitude residuals can be observed across the array. These residuals vary between -0.8 and +1.1 s and -0.54 and +0.72 magnitude units. Negative (fast) traveltime residuals are again related to negative magnitude residuals (small amplitudes). The azimuthal-and distance-dependent patterns of these residuals are identical within three distinct clusters of stations. The main features of the residual patterns correlate well with the main fault systems and inhomogeneities near the array, some of which have been postulated previously. The velocity anomalies causing the azimuthal-and distancedependent residuals are located in crust and uppermost mantle under the array and its vicinity.The fact that local effects like sedimentary covers are responsible for 40 per cent or more of the station average residuals demonstrates again that site effects should be removed before tomographic methods are employed. The simple stations corrections usually applied in global tomography might severely underestimate the influence of local and regional velocity anomalies, since even after the removal of the station average residual large azimuthal-and distance-dependent traveltime and amplitude anomalies remain between stations less than 100 km apart. These anomalies due to shallow inhomogeneities might then erroneously be mapped into features at greater depth.

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supporting

confidence: 82%

Traveltime and amplitude anomalies at the seismic broad-band may GRF

Weber

1994

Geophysical Journal International

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“…These strong site effects were the immediate cause of the disaster at the Cypress overpass structure and the Marina district. These strong amplifications had been foreseen (Office of Emergency Preparedness, 1972; Davis et al, 1982), and were verified by recordings of aftershocks (Cranswick et al, 1990); Jarpe et al, 1989). Somerville and Yoshimura (1990) proposed that S waves reflected from the Mohorovicic discontinuity also contributed to higher than expected accelerations in the San Francisco region.…”

Section: Data and Interpretation Of Strong Motion Records Specific Ementioning

confidence: 70%

“…Somerville and Yoshimura (1990) proposed that S waves reflected from the Mohorovicic discontinuity also contributed to higher than expected accelerations in the San Francisco region. Cranswick et al (1990) show strong site response in aftershocks along a profile across an alluvial valley in Santa Cruz.…”

Section: Data and Interpretation Of Strong Motion Records Specific Ementioning

confidence: 99%

Strong Motion Seismology

Anderson

1991

Reviews of Geophysics

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“…In linear scale, it is a coefficient that changes the frequency scale. The algorithm to find this logarithmic shift minimizes the misfit between BSRlinear and BSR as defined in the Equation (2). Note that the misfit is weighted by the logarithmic sampling.…”

Section: Fsp: a New Parameter To Characterize Non-linear Site Behaviormentioning

confidence: 99%

“…It is widely recognized that soft soils can amplify dramatically the seismic motion compared to rock reference site because of seismic waves being trapped in sub-surface sedimentary layers [1][2][3]. The seismic site response depends on the site geometric configuration, the nature of the soil and the incoming ground motion [4].…”

Section: Introductionmentioning

confidence: 99%

A new parameter to empirically describe and predict the non-linear seismic response of sites derived from the analysis of Kik-Net database

Cruz

Régnier²,

Bertrand³

et al. 2020

Soil Dynamics and Earthquake Engineering

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We evaluate the non-linear site response at the stations of the Japanese Kik-Net network by computing the ratio between the Fourier spectra of the recordings at the surface and at the downhole station. When the amplitude of the input signal increases, we observe a shift of the resonance peaks towards lower frequencies, characteristic of non-linear soil behavior. We propose a new parameter called fsp to characterize this shift. We observe that fsp is a good proxy for the shear modulus reduction by comparing fsp and the modulus reduction curve obtain by both laboratory test measurements and numerical approaches. The fsp is used to correct the linear site response and surface ground motion in frequency domain in order to take into account the non-linear soil behavior. We show that the procedure we established reduces the error in predicting the main frequency peak by 50% compared to an elastic evaluation of the site response during the 2016 Kumamoto earthquake (Mw=7.1).

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Site response across downtown Santa Cruz, California

Cited by 15 publications

References 1 publication

Traveltime and amplitude anomalies at the seismic broad-band may GRF

Traveltime and amplitude anomalies at the seismic broad-band may GRF

Strong Motion Seismology

A new parameter to empirically describe and predict the non-linear seismic response of sites derived from the analysis of Kik-Net database

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