Data files for ground-motion simulations of the 1906 San Francisco earthquake and scenario earthquakes on the Northern San Andreas Fault

We built a 3D seismic model of the Po Plain and neighboring regions of northern Italy, covering altogether an area about 600 km by 300 km with an approximately 1 km spaced grid. We started by collecting an extensive and diverse set of geological and geophysical data, including seismic reflection and refraction profiles, borehole logs, and available geological information. Major geological boundaries and discontinuities have thus been identified and mapped into the model. We used kriging to interpolate the geographically sparse information into continuous surfaces delimiting geological bodies with laterally varying thickness. Seismic-wave properties have been assigned to each unit using a rule-based system and, V P , V S , and ρ derived from other studies. Sedimentary strata, although with varying levels of compaction and hence material properties, may locally reach a thickness of 15 km and give rise to significant effects in seismic-wave propagation. We have used our new model to compute the seismic response for two recent earthquakes, to test its performance. Results show that the 3D model reproduces the large amplitude and the long duration of shaking seen in the observed waveforms recorded on sediments, whereas paths outside the basin may be well fit by more homogeneous (1D) hard rock structure. We conclude that the new model is suited for simulation of wave propagation, mostly for T > 3 s, and may serve well as a constraint for earthquake location and further improvements via body-or surface-wave inversion.

Section: Introductionmentioning

confidence: 99%

Development and Testing of a 3D Seismic Velocity Model of the Po Plain Sedimentary Basin, Italy

Molinari

Argnani

Morelli

et al. 2015

“…The 3D velocity model has been used to calculate strong ground motions for scenario earthquakes in the San Francisco Bay Area, including the 1989 Loma Prieta and the 1906 San Francisco earthquakes (e.g., Aagaard, 2006;Graves, 2006;Larsen et al, 2006;Rodgers et al, 2006). Results of these calculations are presented in and Aagaard, Brocher, Dolenc, Dreger, Graves, Harmsen, Hartzell, Larsen, McCandless, et al (2008).…”

Section: Introductionmentioning

confidence: 99%

Compressional and Shear-Wave Velocity versus Depth Relations for Common Rock Types in Northern California

Brocher

2008

This article presents new empirical compressional and shear-wave velocity (Vp and Vs) versus depth relationships for the most common rock types in northern California. Vp versus depth relations were developed from borehole, laboratory, seismic refraction and tomography, and density measurements, and were converted to Vs versus depth relations using new empirical relations between Vp and Vs. The relations proposed here account for increasing overburden pressure but not for variations in other factors that can influence velocity over short distance scales, such as lithology, consolidation, induration, porosity, and stratigraphic age. Standard deviations of the misfits predicted by these relations thus provide a measure of the importance of the variability in Vp and Vs caused by these other factors. Because gabbros, greenstones, basalts, and other mafic rocks have a different Vp and Vs relationship than sedimentary and granitic rocks, the differences in Vs between these rock types at depths below 6 or 7 km are generally small. The new relations were used to derive the 2005 U.S. Geological Survey seismic velocity model for northern California employed in the broadband strong motion simulations of the 1989 Loma Prieta and 1906 San Francisco earthquakes; initial tests of the model indicate that the Vp model generally compares favorably to regional seismic tomography models but that the Vp and Vs values proposed for the Franciscan Complex may be about 5% too high.

“…Aagaard, Brocher, Dolenc, Dreger, Graves, Harmsen, Hartzell, Larsen, McCandless, et al (2008) Compared to observations in the Loma Prieta earthquake, the overestimation in the ground motions was 1-2 modified Mercalli intensity units.…”

Section: Introductionmentioning

confidence: 68%

“…Description of Ground Motions and Aagaard, Brocher, Dolenc, Dreger, Graves, Harmsen, Hartzell, Larsen, McCandless, et al (2008) We use ground motions on an area 250 by 110 km that includes the southern half of the magnitude 7.8 ruptures. We select ground-velocity time histories at sites on several grids, with major urban areas gridded at higher resolutions.…”

Section: Introductionmentioning

confidence: 99%

Long-Period Building Response to Earthquakes in the San Francisco Bay Area

Olsen¹,

Aagaard²,

Heaton³

2008

This article reports a study of modeled, long-period building responses to ground-motion simulations of earthquakes in the San Francisco Bay Area. The earthquakes include the 1989 magnitude 6.9 Loma Prieta earthquake, a magnitude 7.8 simulation of the 1906 San Francisco earthquake, and two hypothetical magnitude 7.8 northern San Andreas fault earthquakes with hypocenters north and south of San Francisco. We use the simulated ground motions to excite nonlinear models of 20-story, steel, welded moment-resisting frame (MRF) buildings. We consider MRF buildings designed with two different strengths and modeled with either ductile or brittle welds. Using peak interstory drift ratio (IDR) as a performance measure, the stiffer, higher strength building models outperform the equivalent more flexible, lower strength designs. The hypothetical magnitude 7.8 earthquake with hypocenter north of San Francisco produces the most severe ground motions. In this simulation, the responses of the more flexible, lower strength building model with brittle welds exceed an IDR of 2.5% (that is, threaten life safety) on 54% of the urban area, compared to 4.6% of the urban area for the stiffer, higher strength building with ductile welds. We also use the simulated ground motions to predict the maximum isolator displacement of base-isolated buildings with linear, single-degree-of-freedom (SDOF) models. For two existing 3-sec isolator systems near San Francisco, the design maximum displacement is 0.5 m, and our simulations predict isolator displacements for this type of system in excess of 0.5 m in many urban areas. This article demonstrates that a large, 1906-like earthquake could cause significant damage to long-period buildings in the San Francisco Bay Area.