HR: 1340h
AN: S23B-0319    [Abstracts]
TI: 3D Seismogram Synthesis and Inversion for Finite Moment Tensors Using Receiver Green Tensors
AU: Jordan, T H
EM: tjordan@usc.edu
AF: Department of Earth Sciences, University of Southern California, 3651 Trousdale Pkwy, ZBH 117, Los Angeles, CA 90089 United States
AU: * Chen, P
EM: pochen@usc.edu
AF: Department of Earth Sciences, University of Southern California, 3651 Trousdale Pkwy, ZBH 117, Los Angeles, CA 90089 United States
AU: Zhao, L
EM: zhaol@usc.edu
AF: Department of Earth Sciences, University of Southern California, 3651 Trousdale Pkwy, ZBH 117, Los Angeles, CA 90089 United States
AU: Faerman, M
AF: Department of Computer Science and Engineering, University of California, San Diego, CA 92093-0114 United States
AB: The Southern California Earthquake Center (SCEC) is developing a Community Modeling Environment (CME) to facilitate the computational pathways of seismic hazard analysis (Maechling et al., this meeting). Major objectives of the CME project are to construct an efficient system for calculating synthetic seismograms from 3D regional models of elastic/anelastic structure (CME Pathway 2) and to use observed waveforms to invert for source structures and improve the 3D models (CME Pathway 4). In this presentation, we describe the implementation of an approach to these problems based on the use of receiver Green tensors $G_{ik}(\mathbf{r}, \mathbf{r}_{\mathrm{R}}; \emph{t})$ and seismic reciprocity. $G_{ik}(\mathbf{r}, \mathbf{r}_{\mathrm{R}}; \emph{t})$ is the \emph{i}th component wavefield at position $\mathbf{r}$ and time \emph{t} for a \emph{k}th component impulsive force at the receiver position $\mathbf{r}_{\mathrm{R}}$. Seismic reciprocity implies that the synthetic seismogram at $\mathbf{r}_{\mathrm{R}}$ excited by a point source with moment tensor $M_{ij}$ at position $\mathbf{r}_{\mathrm{S}}$ at time $t_{\mathrm{S}}$ is $s_k (t) = M_{ij} \partial^S_j G_{ki} (\mathbf{r}_{\mathrm{R}}, \mathbf{r}_{\mathrm{S}}; \emph{t}-\emph{t}_{\mathrm{S}})$. We calculated $G_{ik}$ for 33 broadband stations of the California Integrated Seismic Network in the Los Angeles region using the SCEC Community Velocity Model (CVM), version 3.0 (Magistrale et. al., 2000), and K. Olsen's (Olsen, 1994) finite-difference code. These receiver Green tensors were sampled on a regular mesh of 36 million grid points with a horizontal spacing of 200 m and archived on the Storage Resource Broke (SRB) system at the San Diego Supercomputer Center, where they occupy a total data volume of 24 TB. The SRB provides high-level digital library functionality, including a maintained association of data and metadata and tools for data queries and subset retrieval. We synthesize seismograms by retrieving $G_{ik}$ on small source-centered grid and calculating the source-coordinate gradient $\partial^S_j$ using a five-point-formula. At the same time, we calculate the higher-order gradients needed to invert waveform data for the centroid moment tensor (CMT) the finite moment tensor (FMT). The latter extends the CMT to include the characteristic space-time dimensions and orientation of the source (Chen, Jordan & Zhao, 2004). We discuss how the 3D synthetics can be used to recover frequency-dependent phase-delay and amplitude-reduction differentials from observed waveforms and demonstrate how these data can be inverted for CMTs and FMTs in Southern California. As discussed by Zhao et al. (this meeting), rapid access to receiver Green tensors is also required for the inversion of the same waveform data for improved 3D models of regional Earth structure.
DE: 7260 Theory and modeling
DE: 7200 SEISMOLOGY
DE: 7215 Earthquake parameters
DE: 3200 MATHEMATICAL GEOPHYSICS (New field)
DE: 3260 Inverse theory
SC: Seismology [S]
MN: 2004 AGU Fall Meeting