Previous studies have shown a variety of atmospheric disturbances (eg, sonic booms, meteoroid falls, thunder, and explosions) can be detected by a seismograph if the acoustic pressure wave energy is sufficiently strong. Kanamori et al.(1991) and Cates and Sturtevant (2002) used the seismic network in southern California to study sonic booms generated by the space shuttle and aircraft. Ishihara et al.(2003) used seismic data from a dense seismographic array in the northeastern region of Honshu Island, Japan, to determine the trajectory of a meteoroid. Kappus and Vernon (1991) analyzed the acoustic signature of thunder from a seismic instrument located at Kislovodsk, USSR.

Atmospheric shock waves generated by sonic booms, meteoroid falls, and explosions have been observed in the Center for Earthquake Research and Information (CERI) Cooperative Seismic Network (Johnston 1987; Langston 2004). On 28 January 2004 at 01: 58 UTC, 11 short-period and nine broadband CERI network stations (figure 1) recorded high signal-tonoise ratio signals generated by an unknown source (figure 2). A preliminary analysis of the waveforms and slow velocity across