We describe Version 2 of the three-dimensional (3D) seismic velocity model of southern California developed by the Southern California Earthquake Center and designed to serve as a reference model for multidisciplinary research activities in the area. The model consists of detailed, rule-based representations of the major southern California basins (Los Angeles basin, Ventura basin, San Gabriel Valley, San Fernando Valley, Chino basin, San Bernardino Valley, and the Salton Trough), embedded in a 3D crust over a variable depth Moho. Outside of the basins, the model crust is based on regional tomographic results. The model Moho is represented by a surface with the depths determined by the receiver function technique. Shallow basin sediment velocities are constrained by geotechnical data. The model is implemented in a computer code that generates any specified 3D mesh of seismic velocity and density values. This parameterization is convenient to store, transfer, and update as new information and verification results become available.

We present a new three-dimensional model of the major fault systems in southern California. The model describes the San Andreas fault and associated strikeslip fault systems in the eastern California shear zone and Peninsular Ranges, as well as active blind-thrust and reverse faults in the Los Angeles basin and Transverse Ranges. The model consists of triangulated surface representations (t-surfs) of more than 140 active faults that are defined based on surfaces traces, seismicity, seismic reflection profiles, wells, and geologic cross sections and models. The majority of earthquakes, and more than 95% of the regional seismic moment release, occur along faults represented in the model. This suggests that the model describes a comprehensive set of major earthquake sources in the region. The model serves the Southern California Earthquake Center (SCEC) as a unified resource for physics-based fault systems modeling, strong ground-motion prediction, and probabilistic seismic hazards assessment.

Abstract. We estimate crustal thickness along an east-west transect of the Baja California peninsula and Gulf of California, Mdxico, and investigate its relationship to surface elevation and crustal extension. We derive Moho depth estimates from P-to-S converted phases identified on teleseismic recordings at 11 temporary broadband seismic stations deployed at -31øN latitude. Depth to the Moho is -33 ( In sections 2-4, we review the geologic setting for the study, describe the station deployment and data analysis, and present the first crustal thickness estimates obtained on the Baja California peninsula. In section 5 we compare the inferred Moho configuration with the related southern California studies and discuss their relationship to surface topography and gulf rifting. The geographical area under discussion straddles the international border to include portions of the state of California, United States, and the state of Baja California, Mfxico. 13,599

Maximum earthquake magnitude (m x ) is a critical parameter in seismic hazard and risk analysis. However, some recent large earthquakes have shown that most of the existing methods for estimating m x are inadequate. Moreover, m x itself is ill-defined because its meaning largely depends on the context, and it usually cannot be inferred using existing data without associating it with a time interval. In this study, we use probable maximum earthquake magnitude within a time period of interest, m p T, to replace m x . The term m p T contains not only the information of magnitude limit but also the occurrence rate of the extreme events. We estimate m p T for circumPacific subduction zones using tapered Gutenberg-Richter (TGR) distributions. The estimation of the two TGR parameters, β-value and corner magnitude (m c ), is performed using the maximum-likelihood method with the constraint from tectonic moment rate. To populate the TGR, the rates of smaller earthquakes are needed. We apply the Whole Earth model, a high-resolution global estimate of the rate of m ≥ 5 earthquakes, to estimate these rates. The uncertainties of m p T are calculated using Monte-Carlo simulation. Our results show that most of the circum-Pacific subduction zones can generate m ≥ 8:5 earthquakes over a 250-year interval, m ≥ 8:8 earthquakes over a 500-year interval, and m ≥ 9:0 earthquakes over a 10,000-year interval. For the Cascadia subduction zone, we include the 10,000-year paleoseismic record based on turbidite studies to supplement the limited instrumental earthquake data. Our results show that over a 500-year period, m ≥ 8:8 earthquakes are expected in this zone; over a 1000-year period, m ≥ 9:0 earthquakes are expected; and over a 10,000-year period, m ≥ 9:3 earthquakes are expected.

We investigate the crustal thickness under the Peninsular Ranges using P‐to‐S converted phases of teleseismic body waves recorded on a temporary broadband seismometer array and isolated by the receiver function method. Ps minus P times at sites west of a compositional boundary that separates the Peninsular Ranges batholith into east and west zones indicate a relatively flat, deep Moho. Ps minus P times at sites east of the compositional boundary decrease eastward, Moho depth estimates (made from the Ps delays and crustal velocities from seismic tomography) indicate a relatively constant 36 to 41 km thick crust in the western zone. In the eastern zone the crust thins rapidly from 35 km thick at the compositional boundary to 25 km at the edge of the Salton trough, a lateral distance of 30 km. The lack of correlation between topography and Moho depths suggests compensation via lateral density variations in the lower crust or upper mantle. We propose that the compositional boundary decouples the eastern and western portions of the batholith, and that the eastern portion has thinned in response to regional Miocene extension, or Salton trough rifting, or both.