Time Reversed Acoustics and applications to earthquake location and salt dome flank imaging

The objective of this thesis is to investigate the applications of Time Reversed Acoustics (TRA) to locate seismic sources and image subsurface structures. The back-propagation process of the TRA experiment can be divided into the acausal and causal time domain. Studying the acausal process of TRA enables us to locate the source, such as an earthquake, inside a medium. The causal domain allows us to create a new datum through the TRA-based redatuming operators and then image the subsurface structures. The source location application directly uses the retro-focusing feature of the TRA technique. An earthquake is traditionally located using the arrival times of individual phases, such as P and S. As a supplementary tool, TRA provides an opportunity to locate earthquakes using whole waveforms. In this TRA technique, we first record the full seismograms due to an earthquake at an array of stations. The traces are then time-reversed and numerically sent back into the medium at those station locations using an a priori model of the medium. The wavefield of the back-propagation is tracked and in the end energy will concentrate at a focal spot which gives the original earthquake location. Both synthetic and field experiments show the capability of the TRA technique to locate the source. TRA, combined with the idea of empirical Green's function, also provides an alternative approach to quickly estimating the focal depth for shallow events. In several field studies, solutions from other independent methodologies confirm the validity of the results. The subsurface imaging application extends the TRA principle into a redatuming method, which allows us to image the target more effectively by bypassing the overburden - which could potentially be very complicated in certain situations - between the sources and receivers.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Lu, Rongrong

Advisor dc:contributor.advisor

• M. Nafi Toksöz.

• Earth, Atmospheric, and Planetary Sciences.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/43151

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/43151