Inversion of acoustic thunder source spectral model from thunder-induced seismic waves in megacity

Thunder-induced seismic waves recorded at dense seismic stations in Seoul, South Korea are analysed for inversion of thunder source spectra. Thunder-induced seismic waves from four local thunder events are analysed. A theory is introduced for the inversion of acoustic source spectra from thunder-induced seismic waves. In the course of source-spectral inversion, the propagation and acoustic-to-seismic coupling effects are counted. The thunder-induced seismic signals were well identified at distances of 20 Hz). Vertical peak ground accelerations of thunder-induced seismic waves in local regions (0.024-0.110 m s(-)(2) at distances of 2.4-3.7 km) are equivalent to the ground motion levels induced by a moderate-size (similar to M5) earthquake at regional distances. The thunder-induced acoustic waves in the atmosphere are obtained by removing the acoustic-to-seismic coupling effect and site-response effect from the observed thunder-induced seismic waves. The quality factors for acoustic wave attenuation in the atmosphere are determined. Urban landscapes and atmospheric effects cause strong acoustic attenuation over atmospheric absorption. Acoustic thunder source spectra are determined by stacking the inverted acoustic spectra at all stations. The peak frequencies of acoustic thunder source spectra are around 34-36 Hz, suggesting the acoustic energy per unit length in lightning strikes to be similar to 4 x 10(6) J m(-1). Local seismic records are applicable for the investigation of thunder and lightning properties.

Automated summary

Thunder-induced seismic waves recorded at dense seismic stations in Seoul are analysed for inversion of thunder source spectra. A theory is introduced for the inversion of acoustic source spectra from thunder-induced seismic waves, considering the propagation and acoustic-to-seismic coupling effects. Thunder-induced seismic signals were identified and equivalent to the ground motion levels induced by a moderate-size earthquake. Acoustic thunder source spectra were determined by stacking the inverted acoustic spectra at all stations.