Abstract
Kinematic source inversions of past earthquakes in the magnitude range of 6–8 are used to simulate 60 scenario earthquakes on the San Andreas fault. The unilateral rupture scenario earthquakes are hypothetically located at 6 locations spread out uniformly along the southern section of the fault, each associated with two hypocenters and rupture directions. Probabilities of occurrence over the next 30 years are assigned to each of these earthquakes by mapping the probabilities of 10,445 plausible earthquakes postulated for this section of the fault by the Uniform California Earthquake Rupture Forecast. Three-component broadband ground motion histories are computed at 636 sites in the greater Los Angeles metropolitan area by superposing short-period (0.2–2.0 s) empirical Green’s function synthetics on top of long-period (>2.0 s) spectral element synthetics. The earthquake probabilities and the computed ground motions are combined to develop probabilistic estimates of ground shaking in the region from San Andreas fault earthquakes over the next 30 years. The results could be useful in city planning, emergency management, and building code enhancement.
Highlights
The interactions of the north American and the Pacific tectonic plates across much of California have created a network of major and minor active faults in the proximity of major cities such asLos Angeles and San Francisco that are capable of generating earthquakes as large as Mw 8.3 or so.Major north-south trending faults in the vicinity of Los Angeles include the San Andreas fault, the SanJacinto fault, the Elsinore fault, and the Newport Inglewood fault
The simulated ground motions are significantly more intense than the intensities predicted by CB-08, with this difference growing with earthquake magnitude
If we use an Mw 7.28 scenario earthquake to represent this bin in our rupture-to-rafters simulations-based case study, our method would result in a scenario earthquake probability of occurrence of 0.045 over the 30 years
Summary
Los Angeles and San Francisco that are capable of generating earthquakes as large as Mw 8.3 or so. Other yet-to-be discovered blind-thrust faults may be present as well The proximity of these faults to the Los Angeles metropolitan area, the existence of large number of tall steel structures in the region, and the unexpected brittle failures in several steel buildings during the 1994 Northridge earthquake have prompted several investigations of the performance of these types of buildings (mainly of the steel moment frame variety) under hypothetical earthquake scenarios (e.g., [1,2,3,4,5,6,7]). UCERF bases these probabilities on four modeling components: (i) a (fault) model of the physical geometry of known California faults; (ii) a deformation model of slip rates and related factors for each fault section; (iii) an earthquake rate model of the region; and (iv) a probability model It hypothesizes hundreds of thousands of ruptures (referred to as “forecast earthquakes” in this article) on specific seismogenic locations of faults and provides yearly occurrence rates that are most consistent with observations. We should note that the scope of CyberShake is much broader with all known faults being considered, whereas our study is focused on the San Andreas fault
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