Ground Motion Model for the 1989 M 6.9 Loma Prieta Earthquake Including Effects of Source, Path, and Site

1993 ◽  
Vol 9 (2) ◽  
pp. 251-287 ◽  
Author(s):  
John F. Schneider ◽  
Walter J. Silva ◽  
Cathy Stark
Keyword(s):  
Point Source ◽  
Site Response ◽  
Source Model ◽  
Soil Response ◽  
Loma Prieta Earthquake ◽  
Ground Motion Model ◽  
Random Vibration Theory ◽  
Loma Prieta ◽  
Band Limited ◽  
Strong Ground

The objective of this study is to assess the effects of source finiteness, crustal wave propagation, and site response upon recorded strong ground motions from the 1989 Loma Prieta earthquake. Our analysis uses band limited white noise (BLWN) with random vibration theory (RVT) to produce site-specific estimates of peak acceleration and response spectral ordinates for both a point-source and finite-source model. Effects of nonlinear soil response are modeled through an equivalent-linear approach. The point-source model additionally accommodates crustal propagation effects in terms of direct-plus-postcritical reflections.

The Loma Prieta earthquake, ground motion, and damage in Oakland, Treasure Island, and San Francisco

1991 ◽  
Vol 81 (5) ◽  
pp. 2019-2047
Author(s):  
Thomas C. Hanks ◽  
A. Gerald Brady
Keyword(s):  
Ground Motion ◽  
San Francisco ◽  
Strong Ground Motion ◽  
Strong Motion ◽  
Earthquake Ground Motion ◽  
Transverse Motion ◽  
Loma Prieta Earthquake ◽  
Loma Prieta ◽  
Treasure Island ◽  
Strong Ground

Abstract The basis of this study is the acceleration, velocity, and displacement wave-forms of the Loma Prieta earthquake (18 October 1989; M = 7.0) at two rock sites in San Francisco, a rock site on Yerba Buena Island, an artificial-fill site on Treasure Island, and three sites in Oakland underlain by thick sections of poorly consolidated Pleistocene sediments. The waveforms at the three rock sites display a strong coherence, as do the three sedimentary sites in Oakland. The duration of strong motion at the rock sites is very brief, suggestive of an unusually short source duration for an earthquake of this size, while the records in Oakland show strong amplification effects due to site geology. The S-wave group at Treasure Island is phase coherent with the Oakland records, but at somewhat diminished amplitudes, until the steps in acceleration at approximately 15 sec, apparently signaling the onset of liquefaction. All seven records clearly show shear-wave first motion opposite to that expected for the mainshock radiation pattern and peak amplitudes greater than expected for sites at these distances (95 ± 3 km) from an earthquake of this magnitude. While the association between these ground motion records and related damage patterns in nearby areas has been easily and eagerly accepted by seismological and engineering observers of them, we have had some difficulty in making such relationships quantitative or even just clear. The three Oakland records, from sites that form a nearly equilateral triangle about the Cypress Street viaduct collapse, are dominated by a long-period resonance (≃ 1 1/2-sec period) far removed from the natural frequency of the structure to transverse motion (2.5 Hz) or from high-frequency amplification bands observed in aftershock studies. A spectral ratio arbiter of this discrepancy confuses it further. The failure of the East Bay crossing of the San Francisco-Oakland Bay Bridge cannot be attributed to relative displacements of the abutments in Oakland and Yerba Buena Island, but the motions of the Bay Bridge causing failure remain unknown. The steps in acceleration at Treasure Island present unusual strong-motion accelerogram processing problems, and modeling suggests that the velocity and displacement waveforms are contaminated by a spurious response of the filtering operations to the acceleration steps. A variety of coincidences suggests that the Treasure island accelerogram is the most likely strong-motion surrogate for the filled areas of the Marina District, for which no mainshock records are available, but the relative contributions of bad ground, poor construction and truly strong ground motion to damage in the Marina District will never by known in any quantitative way. The principal lesson of all of this is that until a concerted effort is mounted to instrument ground and structures that are likely to fail during earthquakes, our understanding of the very complex relationships between strong ground motion and earthquake damage will, in general, remain rudimentary, imprecise, and vague.

A fault model with variable slip duration for the 1989 Loma Prieta, California, earthquake determined from strong-ground-motion data

1996 ◽  
Vol 86 (1A) ◽  
pp. 122-132
Author(s):  
Stephen Horton
Keyword(s):  
Ground Motion ◽  
Strong Ground Motion ◽  
Propagation Rate ◽  
Fault Model ◽  
Fault Surface ◽  
Loma Prieta Earthquake ◽  
Motion Data ◽  
Finite Fault ◽  
Loma Prieta ◽  
Strong Ground

Abstract A finite-fault model with variable slip duration is inferred from strong-ground-motion data for the Loma Prieta earthquake. Unlike previous models, slip duration is found to be consistent with fault width scaling. Slip duration varies between 1 and 6 sec at points along the fault surface with values between 3 and 6 sec, where slip amplitudes obtain or exceed the average slip of 98 cm. Modest high-frequency modifications of the slip function shape greatly enhance the data fit without significantly changing the inferred static offset or rupture characteristics. This model exhibits bilateral rupture with the propagation rate of the main energy release of 3 km/sec or less. The moment is 2.3 × 1026 dyne-cm, and the largest slip amplitudes occur northwest of the hypocenter. The rake varies with position along the fault from dominantly strike slip in the southeast to dominantly reverse slip in the northwest.

Simulating strong motions of large earthquakes using recordings of small earthquakes: the Loma Prieta mainshock as a test case

1995 ◽  
Vol 85 (4) ◽  
pp. 1144-1160
Author(s):  
Arthur Frankel
Keyword(s):  
Stress Drop ◽  
Site Response ◽  
Strong Motion ◽  
Site Effect ◽  
Corner Frequency ◽  
Simple Method ◽  
Strong Motion Records ◽  
Loma Prieta Earthquake ◽  
Loma Prieta ◽  
Large Earthquakes

Abstract A simple method is developed for predicting ground motions for future large earthquakes for specific sites by summing and filtering recordings of adjacent small earthquakes. This method is tested by simulating strong-motion records for the Loma Prieta earthquake (M 7.0) using aftershocks (M 3.7 to 4.0) recorded at the same sites. I use an asperity rupture model where the rms stress drop averaged over the fault plane is constant with moment. The observed spectra indicate that stress drop remains constant from the M 3 aftershocks up to the M 7 mainshock, about six orders of magnitude in seismic moment. Each simulation sums the seismogram of one aftershock with time delays appropriate for propagating rupture and incorporates directivity and site response. The simulation scales the spectrum in accordance with a constant stress drop, ω−2 source model. In this procedure, the high-frequency energy of the aftershock sum above the corner frequency of the aftershock is not reduced when it is convolved with the mainshock slip velocity function, unlike most previous methods of summation. For most cases, the spectra (0.6 to 20 Hz), peak accelerations, and durations of the simulated mainshock records are in good agreement with the observed strong-motion records, even though only one aftershock waveform was used in each simulation. This agreement indicates that the response of these soil sites is essentially linear for accelerations up to about 0.3 g. The summed aftershock records display the same site-dependent values of fmax as the mainshock records, implying that fmax is a site effect rather than a property of the mainshock rupture process.

Equivalent Point-Source Ground-Motion Model for Subduction Earthquakes in Japan

2021 ◽  
Author(s):  
Behzad Hassani ◽  
Gail Marie Atkinson
Keyword(s):  
Point Source ◽  
Ground Motion ◽  
High Frequency ◽  
Source Model ◽  
Motion Model ◽  
Subduction Earthquakes ◽  
Ground Motion Model ◽  
Equivalent Point ◽  
Back Arc ◽  
Model Approach

ABSTRACT We use an equivalent point-source ground-motion model (GMM) to characterize subduction earthquakes (interface and in-slab) in Japan. The model, which is calibrated using the newly published Next Generation Attenuation (NGA) Subduction database (Bozorgnia et al., 2020), provides a useful complement to the more traditional empirical NGA models developed from the same database. The utility of the point-source model approach lies in its ability to aid in the interpretation of observed trends in the data and to guide modifications to the GMM for application to other regions having fewer data. Key trends in the data that are parameterized with the model include: (a) the enrichment of high-frequency amplitudes for in-slab versus interface events, as modeled by a depth-dependent stress parameter, and (b) attenuation attributes that vary with event type and region, including consideration of fore-arc versus back-arc settings. The developed GMMs of this study are applicable for M 4.5–9.2 for interface events, and M 4–8.5 for in-slab earthquakes, for rupture distances (Drup) from 10 to 600 km, and for 100  m/s<VS30<1500  m/s (time-averaged shear-wave velocity in the top 30 m).

Nonlinear Site Amplification Factors for Constraining the NGA Models

2008 ◽  
Vol 24 (1) ◽  
pp. 243-255 ◽  
Author(s):  
Melanie Walling ◽  
Walter Silva ◽  
Norman Abrahamson
Keyword(s):  
Site Response ◽  
Linear Method ◽  
Site Amplification ◽  
Parametric Models ◽  
Imperial Valley ◽  
Soil Response ◽  
Amplification Factors ◽  
Nonlinear Properties ◽  
Ground Motion Model ◽  
Equivalent Linear Method

Amplification factors computed from the equivalent-linear method using the program RASCALS are used to develop constraints on the nonlinear soil response for possible use by the NGA ground-motion model developers. The site response computations covered site conditions with average VS30 values ranging from 160 to 900 m/s, soil depths from 15 to 914 m, and peak accelerations of the input rock motion ( VS30=1100 m/s) between 0.01 g and 1.5 g. Four sets of nonlinear properties of the soils are used: EPRI, Peninsular Range, Imperial Valley, and Bay Mud. The first two soil models are used for VS30≥270 m/s and the later two are used for VS30≤190 m/s. Simple parametric models of the nonlinear amplification factors that are functions of the PGA on rock and VS30 are developed for the EPRI and Peninsula models.

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