HR: 1330h
AN: S42E-0211    [PDF]
TI: Detection And Location Of Long Period Surface Wave Energy Sources
AU: * Rhie, J
EM: rhie@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, 215 McCone Hall, UC Berkeley, Berkeley, CA 94720-4760 United States
AU: Barbara, R
EM: barbara@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, 215 McCone Hall, UC Berkeley, Berkeley, CA 94720-4760 United States
AB: Low-frequency surface waves are usually the dominant phases in waveforms generated from earthquakes. They have been widely used for determining global earth structure and for the retrieval of earthquake source parameters. In addition, they can be used for detecting the existence of special types of seismic sources, such as slow/silent earthquakes({\it Beroza and Jordan}, 1990), back ground free oscillations ({\it Ekstr\"om}, 2001) and other unknown sources. Usually, the low-frequency surface waves generated from these kinds of sources are too weak to be detected by a single station. We developed an array-based method which can detect Rayleigh type surface wave energy by using a regional array. For preliminary test of the method, we applied band pass filter between 50 and 200 sec but several different pass bands will be used to look at the frequency content of detected energies. Weak surface wave energy can be enhanced by stacking waveforms over an array. Waveforms are stacked by taking into account the dispersion of surface waves with respect to relative propagation distances between stations in one array and the center of the array. This method is designed to provide a rough estimate of arrival time and back azimuth of weak surface wave energy. Three different arrays in Northern California (BDSN), Germany (GRSN), and Japan (F-net) are then used to constrain the location ofthe sources. Our preliminary results over several years of data show that this method can locate reliably most seismic sources which have magnitude larger than 5.5. There are other detections that can be correlated across the three arrays and are not associated with known earthquakes as listed in the Harvard CMT catalog. We systematically analyze these detections in an effort to distinguish possible spurious errors from true surface wave energy, and discuss their temporal and geographical distribution, and in particular their possible relation to silent earthquakes as well as the source of the earth's continuous background free-oscillations.
DE: 1734 Seismology
SC: Seismology [S]
MN: 2003 Fall Meeting