Unified Structural Representation of the southern California crust and upper mantle

Abstract

The GTL implemented in the USR was based on Ely et al. (2010) and uses the geology-based Vs30 maps of Wills and Clahan (2006) to specify velocity values at the Earths surface in the voxet. V P , and in turn density, are inferred from surface V S using the scaling laws of Brocher (2005). These values were parameterized to a depth of z T = 350 meters with the following formulations:where z ′ is depth, V ST and V P T are are S-and P-wave velocities extracted from the crustal velocity model at depth z T , P () is the Brocher (2005) P-wave velocity scaling law, andThe coefficient a controls the ratio of surface velocity to original 30 meter average, b controls overall curvature, and c controls near-surface curvature of the velocity profile. The coefficients a = 1/2, b = 2/3, and c = 3/2 were chosen to fit the generic rock profile of Boore and Joyner (1997) while also producing smooth and well-behaved profiles when combined with the underlying basin and crustal velocity models (Ely et al., 2010) ( Figure 7). S2 Model validation, comparison, and uncertaintyThe velocity model (CVM) component of the USR described here is assembled from several different data sets and models, and thus it is challenging to formally assess model resolution and uncertainties. One clear step for the sedimentary basins is to assess the variability in well data that is not represented in the final model. As we discussed, these data measure interval transit times over borehole distances of less than 1 m, whereas the velocity model uses smoothed (25 m sampled) versions of these data. To make this assessment, we compared observations directly with the velocity values represented at 108 well bore locations in the Los Angeles basin. Our analysis shows a standard deviation of 6.5% around a mean of 1.0 for the ratio between compressional wave slowness in logs and the model in a population of ca. 1.1 million samples. This corresponds to a standard deviation in V P of ±99 m/s at 2000 m/s.

Landers 1992 "reloaded": Integrative dynamic earthquake rupture modeling

“…The star marks the epicenter of the 1992 Mw 7.3 Landers earthquake. [Shaw et al, 2015]. Fault surface segments are visualized in white.…”

“…Our model incorporates the 3D velocity structure of the Community Velocity Model-Harvard (CVM-H, version 15.1.0, Shaw et al [2015], available at hypocenter. usc.edu/research/cvmh/15.1.0/cvmh-15.1.0.tar.gz), exemplarily visualized for a cutout in Fig.…”

Higher-mode ambient-noise Rayleigh waves in sedimentary basins

“…The Los Angeles Basin is a typical example of this, where there have been many studies of its structure (Hauksson & Haase 1997;Fuis et al 2001;Süss & Shaw 2003;Tape et al 2009;Lee et al 2014;Shaw et al 2015), using data from both passive and active seismic experiments, as well as well-logs and reflection data from the oil industry. The culmination of these efforts has been the creation of a series of steadily improving Community Velocity Models (Kohler et al 2003;Plesch et al 2011;Shaw et al 2015), which are used among other things, in the simulation of ground motions from scenario earthquakes.…”

The 2015 Fillmore Earthquake Swarm and Possible Crustal Deformation Mechanisms near the Bottom of the Eastern Ventura Basin, California

“…We used the new version of hypoDD that uses a 3D velocity model from traveltime calculations to determine the hypocenters (Waldhauser and Ellsworth, 2000). We resampled the 3D V P and V P =V S model (10 km × 10 km horizontal grid spacing, with 4 km grid spacing in depth down to 32 km depth) described by Shaw et al (2015), which was slightly modified by allowing local seismicity to adjust the model. Finally, by applying a singular-value decomposition technique in hypoDD, we determined the relative errors, which are less than 6 m horizontally and 12 m vertically (Ⓔ Table S1, available in the electronic supplement to this article).…”

“…The cross section shows the modified 3D V P model from Shaw et al (2015) and the approximate locations of late Quaternary faults in the cross section from the Southern California Earthquake Center-Community Fault Model (SCEC-CFM) (Plesch et al, 2007;Marshall et al, 2013;Nicholson et al, 2014). The 1989 and 2015 swarms are plotted in red, and the 2000 swarm is shown in purple in the map view.…”