GROUND MOTION INDUCED BY THUNDER

LANGSTON, C. A., LIN T.-L., and LIANG, C., Center for Earthquake Research and Information, University of Memphis, Memphis, TN 38152-3050, clangstn@memphis.edu.

Atmospheric shock waves from meteoroids and aircraft can be observed using seismic networks. A recent study of an atmospheric shock wave induced by a Taurid meteor over the CERI network demonstrated that such sources produce characteristic P and S wave reverberations that depend on near-surface site structure and that acoustic pressure sources may be a useful way to asses the nature of velocity structure in the near surface for earthquake hazards studies. However, shock waves from bolides are few and far between and supersonic aircraft are normally not allowed to fly over land. Thunder is a plentiful natural source of atmospheric shock waves created by lightning in thunderstorms. We attempted to recover thunder ground motion signals from the CERI network for major thunder storms over the network but found that radio telemetry problems and simplex modem data drop-outs were created by the electromagnetic lightning disturbance itself, i.e., no true ground motion signals could be observed. We performed a simple experiment by installing a CMG-6 seismometer at a rural location and continuously recording data for a period of two weeks. Clear ground motion signals were observed from thunder during a mild thunderstorm that passed over the instrument in May. Thunder from cloud-to-cloud and cloud-to-ground lightning was observed. A nearby ground strike produced impulsive signals displaying initial particle motion characteristic of the fluid/solid interface boundary condition and 5 Hz reverberations related to layered structure in the near surface. These data motivate a more thorough study of both the thunder source and its interaction with the ground using an acoustic/seismic array.