Teleseismic surface wave study forS-wave velocity structure under an array: Southern California

Abstract

S U M M A R YTeleseismic surface wave data from the dense seismographic network in Southern California (CISN, California Integrated Seismic Network) are used to construct S-wave velocity maps for the region. Surface wave phase velocity measurements are achieved by way of a waveformmatching spectral-domain technique that was developed for use within the CISN array. A two-station phase velocity measurement technique was developed, which takes advantage of the fact that, for surface wave arrivals from any azimuth, there are multiple pairs of CISN stations, which are almost exactly on the same great-circle paths. To ensure the validity of this assumption, particle motions were analysed for measured pairs within the network, showing that the deviation between expected backazimuth from ray theory and observed backazimuths are small enough to be analysed by a simple distance correction. This method was applied to 114 large earthquakes for time periods between 1999 and 2002 and led to the retrieval of phase velocity maps for Rayleigh waves between 20 and 55 mHz and for Love waves between 25 and 45 mHz.Finite frequency effect for propagating surface waves was approximately taken into consideration using a geometrical technique. An ellipse, determined by wavelength and great-circle distance between the source and receiver can describe an influence zone for the finite frequency effect. Phase velocity map reconstructions, using a method which incorporates this effect, show minimal changes in phase velocity maps for our region, but do extend solvable velocity regions.Inversion for S-wave velocity distribution with depth shows that deep structural contrast across the San Andreas extends into the upper mantle. A slow velocity anomaly is evident under the Southern Sierras and the Salton Sea, the latter region indicating the northward extension of tectonic activity in the Gulf of California. Fast velocity roots that reach 60 km are found under the western part of Transverse Ranges and the Northern Peninsular Ranges. Reconstruction of past location of the Western Transverse Range microplate implies that these two ranges may have been adjacent to one another historically. Both the Western Transverse range fast velocity root and the Peninsular range fast velocity root may be a remnant of old oceanic plate.

Testing Waveform Predictions of 3D Velocity Models against Two Recent Los Angeles Earthquakes

“…The crustal structure in CVM-H was improved through 16 iterations of full-3D tomography based on the adjoint-wavefield method (AW-F3DT; Tape et al, 2009Tape et al, , 2010. The latest official release was in November 2011 (CVM-H11.9), which includes a geotechnical layer constrained by the near-surface (V S30 ) shear velocities (Ely et al, 2010), a variable-depth Moho (Yan and Clayton, 2007), and an upper-mantle velocity model determined from finite-frequency teleseismic surface-wave tomography (Prindle and Tanimoto, 2006). CVM-S4.26 is the 26th iterate of a full 3D tomographic (F3DT) inversion procedure (Lee et al, 2013).…”

Full‐3‐D tomography for crustal structure in Southern California based on the scattering‐integral and the adjoint‐wavefield methods

“…The source-receiver paths for earthquake and ambient-noise recordings are highly complementary, together providing a dense and fairly even coverage throughout the entire modeling domain (Figure 1). [2007], and an upper mantle structure from finite-frequency teleseismic surface-wave tomography [Prindle and Tanimoto, 2006]. Notably, CVM-H11.9.1 incorporated the crustal structure obtained by Tape et al [2009Tape et al [ , 2010 from 16 AW-F3DT iterations of low-frequency earthquake waveform data.…”

Rapid Estimation of Damage to Tall Buildings Using Near Real-Time Earthquake and Archived Structural Simulations

“…This model is based on current research, and incorporates tens of thousands of direct velocity measurements that describe the Los Angeles basin and other structures in southern California (Süss and Shaw, 2003;Plesch et al, 2011). The model includes background crustal tomography (Hauksson, 2000;Lin et al, 2007) enhanced using 3D adjoint waveform methods (Tape et al, 2009), the Moho surface (Plesch et al, 2011), and a teleseismic upper mantle wave speed description (Prindle and Tanimoto 2006). Earlier versions of this wave speed model have been used to reliably model the basin response accurately down to a shortest period of approximately 2 s Liu et al, 2004).…”

“…Seismologists have created 3D Earth models (Magistrale et al, 1996;Magistrale et al, 2000;Kohler et al, 2003;Süss and Shaw, 2003;Prindle and Tanimoto, 2006;Tape et al, 2009;Ely et al, 2010;Tape et al, 2010;Plesch et al, 2011) of seismic-wave speeds and density, and thanks to the advent of parallel computing now have the ability to study 3D global and regional seismic-wave propagation using approaches based, for instance, on the finite-element and the finite-difference methods (e.g., Heaton et al, 1995;Olsen et al, 1995;Bao et al, 1998;Graves 1998;Akçelik et al, 2003;Komatitsch et al, 2004;Liu et al, 2004;Komatitsch et al, 2010;Komatitsch, 2011;and similar references). Our approach to numerically propagating seismic waves is based on the spectral-element method (Komatitsch and Tromp 1999;Tromp et al, 2008) and accounts for 3D variations of seismic-wave speeds and density, topography and bathymetry, and attenuation.…”