HR: 0830h
AN: S41B-11    [Abstracts]
TI: Application of Time Reversed Acoustics for Seismic Source Characterization
AU: * Lu, R
EM: lurr@mit.edu
AF: Earth Resources Laboratory, Massachusetts Institute of Technology, 42 Carleton St. Rm. E34-370, Cambridge, MA 02139 United States
AU: Toksöz, M
EM: toksoz@mit.edu
AF: Earth Resources Laboratory, Massachusetts Institute of Technology, 42 Carleton St. Rm. E34-370, Cambridge, MA 02139 United States
AB: Traditionally an earthquake is located and the source mechanism is determined by using P and S phases. This uses only a limited portion of the information contained in a seismogram. A large part of the information carried by the waveform is not used. In this study we investigate the applicability of the Time Reversed Acoustics (TRA) technique, and thus the whole waveform of the recorded signal, for earthquake locations and source characterization. The basic concept involved in TRA is the fundamental symmetry of time reversal invariance. Injecting the recorded signal, with time running backwards, can focus the wave field to the source. TRA has emerged as an important technique in acoustics with applications to medicine, underwater sound, and many other disciplines. Numerical simulations show that the TRA technique can successfully locate a seismic source inside a layered earth model and can also recover the source time function. Finite difference modeling results show that TRA can determine the fault dip, rupture direction, and rupture length. The method is especially advantageous when data are available only from a sparse station network. Full seismograms contain source information from both waves radiated along the source-station ray path and from waves that radiated in all other directions but scattered toward the receivers. Application of the TRA technique to seismic source characterization requires the Green's function, which can be obtained in two ways. If the earth structure is known then the Green's function can be calculated numerically. To improve the efficiency, the method of constructing a medium response library is developed. This improves computation time significantly. The second approach uses small events (e.g., aftershocks) as an empirical Green's function. The performance of the TRA technique is demonstrated with data from real earthquakes.
DE: 7203 Body wave propagation
DE: 7215 Earthquake parameters
DE: 7260 Theory and modeling
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2005 Joint Assembly