scholarly journals The Effect of Fault Geometry and Minimum Shear Wavespeed on 3D Ground-Motion Simulations for an Mw 6.5 Hayward Fault Scenario Earthquake, San Francisco Bay Area, Northern California

2019 ◽  
Vol 109 (4) ◽  
pp. 1265-1281 ◽  
Author(s):  
Arthur J. Rodgers ◽  
Arben Pitarka ◽  
David B. McCallen
Keyword(s):  
Ground Motion ◽  
San Francisco ◽  
Hanging Wall ◽  
3D Models ◽  
Peak Ground Velocity ◽  
Earth Model ◽  
Fault Geometry ◽  
Bay Area ◽  
Ground Motion Simulations ◽  
Vertical Fault

Abstract We investigated the effects of fault geometry and assumed minimum shear wavespeed (VSmin) on 3D ground-motion simulations (0–2.5 Hz) in general, using a moment magnitude (Mw) 6.5 earthquake on the Hayward fault (HF). Simulations of large earthquakes on the northeast-dipping HF using the U.S. Geological Survey (USGS) 3D seismic model have shown intensity asymmetry with stronger shaking for the Great Valley Sequence east of the HF (hanging wall) relative to the Franciscan Complex to the west (footwall). We performed simulations with three fault geometries in both plane-layered (1D) and 3D models. Results show that the nonvertical fault geometries result in larger motions on the hanging wall relative to the vertical fault for the same Earth model with up to 50% amplifications in single-component peak ground velocity (PGV) within 10 km of the rupture. Near-fault motions on the footwall are reduced for the nonvertical faults, but less than they are increased on the hanging wall. Simulations assuming VSmin values of 500 and 250  m/s reveal that PGVs are on average 25% higher west of the HF when using the lower VSmin, with some locations amplified by a factor of 3. Increasing frequency content from 2.5 to 5 Hz increases PGV values. Spectral ratios of these two VSmin cases show average amplifications of 2–4 (0.5–1.5 Hz) for the lower VSmin west of the fault. Large differences (up to 2×) in PGV across the HF from previous studies persist even for the case with a vertical fault or VSmin of 250  m/s. We conclude that assuming a VSmin of 500  m/s underestimates intensities west of the HF for frequencies above 0.5 Hz, and that low upper crustal (depth <10  km) shear wavespeeds defined in the 3D model contribute most to higher intensities east of the HF.

Deterministic 3D Ground-Motion Simulations (0–5 Hz) and Surface Topography Effects of the 30 October 2016 Mw 6.5 Norcia, Italy, Earthquake

2021 ◽  
Author(s):  
Arben Pitarka ◽  
Aybige Akinci ◽  
Pasquale De Gori ◽  
Mauro Buttinelli
Keyword(s):  
Surface Topography ◽  
Ground Motion ◽  
Seismic Station ◽  
Ground Motions ◽  
Peak Ground Velocity ◽  
Earth Model ◽  
Rupture Directivity ◽  
Epicentral Area ◽  
Near Fault ◽  
Local Topography

ABSTRACT The Mw 6.5 Norcia, Italy, earthquake occurred on 30 October 2016 and caused extensive damage to buildings in the epicentral area. The earthquake was recorded by a network of strong-motion stations, including 14 stations located within a 5 km distance from the two causative faults. We used a numerical approach for generating seismic waves from two hybrid deterministic and stochastic kinematic fault rupture models propagating through a 3D Earth model derived from seismic tomography and local geology. The broadband simulations were performed in the 0–5 Hz frequency range using a physics-based deterministic approach modeling the earthquake rupture and elastic wave propagation. We used SW4, a finite-difference code that uses a conforming curvilinear mesh, designed to model surface topography with high numerical accuracy. The simulations reproduce the amplitude and duration of observed near-fault ground motions. Our results also suggest that due to the local fault-slip pattern and upward rupture directivity, the spatial pattern of the horizontal near-fault ground motion generated during the earthquake was complex and characterized by several local minima and maxima. Some of these local ground-motion maxima in the near-fault region were not observed because of the sparse station coverage. The simulated peak ground velocity (PGV) is higher than both the recorded PGV and predicted PGV based on empirical models for several areas located above the fault planes. Ground motions calculated with and without surface topography indicate that, on average, the local topography amplifies the ground-motion velocity by 30%. There is correlation between the PGV and local topography, with the PGV being higher at hilltops. In contrast, spatial variations of simulated PGA do not correlate with the surface topography. Simulated ground motions are important for seismic hazard and engineering assessments for areas that lack seismic station coverage and historical recordings from large damaging earthquakes.

Ground motion at the San Francisco international airport from the Loma Prieta earthquake sequence, 1989

1991 ◽  
Vol 81 (5) ◽  
pp. 1923-1944
Author(s):  
A. McGarr ◽  
M. Çelebi ◽  
E. Sembera ◽  
T. Noce ◽  
C. Mueller
Keyword(s):  
Ground Motion ◽  
San Francisco ◽  
Epicentral Distance ◽  
Sedimentary Cover ◽  
Low Velocity ◽  
Near Surface ◽  
Loma Prieta Earthquake ◽  
International Airport ◽  
Bay Area ◽  
Loma Prieta

Abstract Following the Loma Prieta earthquake, the U.S. Geological Survey installed four portable digital seismic recorders at the San Francisco International Airport (SFO) for one week to study aftershock ground motion at this important Bay area “lifeline.” This study was motivated largely by the need to anticipate strong ground motion from future major earthquakes affecting the Bay area and, to a lesser extent, by the fact that SFO was shut down for 13 hours owing to damage from the Loma Prieta shock. Accordingly, the recording sites were chosen so as to elucidate the effects of varying thicknesses of low-velocity surficial alluvium on the ground motion. Three large aftershocks with magnitudes ranging from 4.2 to 4.5 each produced ground motion that was recorded at all four SFO stations. One of our stations was collocated with a permanent ground motion recorder that indicated a peak horizontal velocity of 29 cm / sec and a peak horizontal acceleration of 0.33 g during the 18 October mainshock. From the aftershock data and one mainshock record, it is possible to extrapolate approximately the mainshock ground motion to other locations at SFO and, more generally, to assess the effects of low-velocity sedimentary cover, including artificial fill material, on the character of the ground motion. The main-shock ground motion recorded at the permanent station was apparently typical for most of SFO where the near-surface alluvium resulted in peak horizontal ground velocity, in the frequency band 0.1 to 3 Hz, amplified by a factor of about 2.5 relative to that recorded at bedrock sites. Observations, in the epicentral distance range 59 to 95 km, including SFO, of the moho-reflected phases PmP and SmS from the aftershocks support the hypothesis, presented elsewhere, that the phase SmS accounted for much of the peak ground motion throughout most of the San Francisco Bay area.

Engineering evaluation of the EQSIM simulated ground‐motion database: The San Francisco Bay Area region

2021 ◽  
Author(s):  
Floriana Petrone ◽  
Norman Abrahamson ◽  
David McCallen ◽  
Arben Pitarka ◽  
Arthur Rodgers
Keyword(s):  
Ground Motion ◽  
San Francisco ◽  
San Francisco Bay ◽  
San Francisco Bay Area ◽  
Bay Area

Source modelling and strong ground motion simulations for the 24 January 2020, Mw 6.8 Elazığ earthquake, Turkey

2020 ◽  
Vol 223 (2) ◽  
pp. 1054-1068 ◽  
Author(s):  
Daniele Cheloni ◽  
Aybige Akinci
Keyword(s):  
Ground Motion ◽  
High Frequency ◽  
Main Shock ◽  
Peak Ground Velocity ◽  
Coulomb Stress ◽  
Epicentral Area ◽  
Fault Segment ◽  
Ground Motion Simulations ◽  
Finite Fault ◽  
Motion Characteristics

SUMMARY On 24 January 2020 an Mw 6.8 earthquake occurred at 20:55 local time (17:55 UTC) in eastern Turkey, close to the town of Sivrice in the Elazığ province, causing widespread considerable seismic damage in buildings. In this study, we analyse the main features of the rupture process and the seismic ground shaking during the Elazığ earthquake. We first use Interferometric Synthetic Aperture Radar (InSAR) interferograms (Sentinel-1 satellites) to constrain the fault geometry and the coseismic slip distribution of the causative fault segment. Then, we utilize this information to analyse the ground motion characteristics of the main shock in terms of peak ground acceleration (PGA), peak ground velocity (PGV) and spectral accelerations. The absence of seismic registrations in near-field for this earthquake imposes major constraints on the computation of seismic ground motion estimations in the study area. To do this, we have used a stochastic finite-fault simulation method to generate high-frequency ground motions synthetics for the Mw 6.8 Elazığ 2020 earthquake. Finally, we evaluate the potential state of stress of the unruptured portions of the causative fault segment as well as of adjacent segments, using the Coulomb stress failure function variations. Modelling of geodetic data shows that the 2020 Elazığ earthquake ruptured two major slip patches (for a total length of about 40 km) located along the Pütürge segment of the well-known left-lateral strike-slip East Anatolian Fault Zone (EAFZ), with up to 2.3 m of slip and an estimated geodetic moment of 1.70 $\,\, \times $ 1019 Nm (equivalent to a Mw 6.8). The position of the hypocentre supports the evidence of marked WSW rupture directivity during the main shock. In terms of ground motion characteristics, we observe that the high-frequency stochastic ground motion simulations have a good capability to reproduce the source complexity and capture the ground motion attenuation decay as a function of distance, up to the 200 km. We also demonstrate that the design spectra corresponding to 475 yr return period, provided by the new Turkish building code is not exceeded by the simulated seismograms in the epicentral area where there are no strong motion stations and no recordings available. Finally, based on the Coulomb stress distribution computation, we find that the Elazığ main shock increased the stress level of the westernmost part of the Pütürge fault and of the adjacent Palu segment and as a result of an off-fault lobe.

Ground Motion Model for the Vertical-to-Horizontal (V/H) Ratios of PGA, PGV, and Response Spectra

2016 ◽  
Vol 32 (2) ◽  
pp. 951-978 ◽  
Author(s):  
Yousef Bozorgnia ◽  
Kenneth W. Campbell
Keyword(s):  
Ground Motion ◽  
Site Response ◽  
Hanging Wall ◽  
Strong Dependence ◽  
Response Spectra ◽  
Peak Ground Velocity ◽  
Motion Model ◽  
Fault Rupture ◽  
Ground Acceleration ◽  
Ground Motion Model

We present a ground motion model (GMM) for the vertical-to-horizontal (V/H) ratios of peak ground acceleration, peak ground velocity, and 5%-damped pseudo-acceleration response spectra at periods ranging from 0.01 s to 10 s. The V/H GMM includes formulations for the median V/H ratio and for the aleatory within-event, between-event, and total standard deviations. The V/H model is based on the GMMs we have developed for the vertical and “average” horizontal components of ground motion using a mathematical formation that accounts for the correlation between these two components. We validated the V/H model against the NGA-West2 empirical database. We consider our V/H model to be valid for worldwide shallow crustal earthquakes in active tectonic regions for moment magnitudes ranging from 3.3 to 8.5, depending on the style of faulting, and for fault rupture distances ranging from 0 km to 300 km. Our V/H model incorporates period-dependent effects of magnitude saturation, style of faulting, hypocentral depth, fault-rupture dip, geometric attenuation, regionally dependent anelastic attenuation and site response, hanging-wall geometry, and magnitude-dependent between-event and within-event aleatory variabilities. The V/H ratios predicted from the model show a strong dependence on spectral period and site response.

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