ANOMALOUS SIGNALS RECORDED BY THE CERI NETWORK

LIN, T.-L,. and LANGSTON, C.A., Center for Earthquake Research and Information, University of Memphis, Memphis, TN 38152, tllin@memphis.edu.

A variety of atmospheric disturbances (e.g. sonic booms, meteoroid falls, and explosions) can be detected by a seismograph if the acoustic pressure wave energy is sufficiently strong. On 28^th January, 2004 at 01:58 UTC, the Center for Earthquake Research and Information (CERI) Cooperative Seismic Network recorded high signal-to-noise ratio seismic signals generated by an unknown source. A preliminary analysis of its waveforms suggested that an atmosphere disturbance was the most likely source. A grid search location technique by using arrival times at each station was used to fit the source location. Polarization of the waveform data was used to infer azimuth to verify the source location determined from the gird search. Also, a triangular array was used to estimate the horizontal phase velocity and azimuth across the array. Our conclusion is that the acoustic source initiated on the ground surface and not higher in the atmosphere because of the low apparent wave velocity across the network and across the triangular array. A near-surface source implies unusual atmospheric conditions that require a near-surface acoustic waveguide. The waveform data show large effects of near-surface site structure through large horizontal particle motions.