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

Abstract

We have successfully applied full-3-D tomography (F3DT) based on a combination of the scattering-integral method (SI-F3DT) and the adjoint-wavefield method (AW-F3DT) to iteratively improve a 3-D starting model, the Southern California Earthquake Center (SCEC) Community Velocity Model version 4.0 (CVM-S4). In F3DT, the sensitivity (Fréchet) kernels are computed using numerical solutions of the 3-D elastodynamic equation and the nonlinearity of the structural inversion problem is accounted for through an iterative tomographic navigation process. More than half-a-million misfit measurements made on about 38,000 earthquake seismograms and 12,000 ambient-noise correlagrams have been assimilated into our inversion. After 26 F3DT iterations, synthetic seismograms computed using our latest model, CVM-S4.26, show substantially better fit to observed seismograms at frequencies below 0.2 Hz than those computed using our 3-D starting model CVM-S4 and the other SCEC CVM, CVM-H11.9, which was improved through 16 iterations of AW-F3DT. CVM-S4.26 has revealed strong crustal heterogeneities throughout Southern California, some of which are completely missing in CVM-S4 and CVM-H11.9 but exist in models obtained from previous crustal-scale 2-D active-source refraction tomography models. At shallow depths, our model shows strong correlation with sedimentary basins and reveals velocity contrasts across major mapped strike-slip and dip-slip faults. At middle to lower crustal depths, structural features in our model may provide new insights into regional tectonics. When combined with physics-based seismic hazard analysis tools, we expect our model to provide more accurate estimates of seismic hazards in Southern California.

Structure of the Los Angeles Basin from ambient noise and receiver functions

“…http://gji.oxfordjournals.org/ Downloaded from Lee et al 2014) and have been interpreted as rocks of the Peninsula Ranges batholith (Lutter et al 1999). We also note the depression of the velocity contour in the 3-6 km depth range at 10 km distance.…”

“…The high velocity basement has been previously revealed in V P (Lutter et al 1999;Fuis et al 2001;Lee et al 2014), which can be higher than 7 km s −1 in some locations (Lutter et al 1999; at California Institute of Technology on August 19, 2016…”

“…Another approach was used in Süss & Shaw (2003), where they used P-wave velocity measurements determined from stacking velocities from oil-company reflection surveys and sonic logs from boreholes, along with a basin shape model based on gravity and borehole lithology observations (McCulloh 1960;Yerkes et al 1965). These models have been combined and further enhanced through the use of full waveform inversions (Tape et al 2009;Lee et al 2014), leading to an updated unified model (Shaw et al 2015) including the CVM-H velocity model (currently 15.1.0 version) and the CFM fault model. 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.…”

Application of Fullwaveform Tomography to VSP Walkaway Data

“…Due to the limiting computational power and the complexity of the forward solver, most of the applications in this domain are in 2D rather than 3D, and acoustic or visco-acoustic rather than visco-elastic; although recent applications with 3D elastic algorithms were reported in the literature (e.g. Lee et al, 2014). Several successful applications of fullwaveform tomography ranging from crustal studies using wide angle refraction data to reflection seismic can be found in the literature (e.g., Takam Takougang and Calvert, 2011, Mallinowski et al, 2011Kamei et al, 2014).…”