The Millikan shaking experiments and high-frequency seismic wave propagation in Southern California

Abstract

In order to study high-frequency seismic wave propagation, seismic wavefields generated by resonant-shaking experiments of the Millikan Library, on the campus of California Institute Technology (Pasadena, California, USA), were analysed. Because the resonant shaking frequencies are 1.12 Hz (the east-west direction) and 1.64 Hz (the north-south direction), this active-source experiment can provide opportunities for studying high-frequency seismic wave propagation in Southern California. Because they are very narrow frequency band data, the analyses must be quite different from ordinary time-domain analyses. We show, theoretically, that the signals must be dominated by surface waves. Adopting this surface wave assumption, we proceed to make two separate analyses, one on spectral amplitude and the other on phase. We present a new method to derive group velocity from phase based on the cross correlations between the station in the Millikan Library (MIK) and stations in the regional network. Our results support that an active-source experiment by resonant shaking of a building is a feasible approach for high-frequency seismic wave studies. © The Authors 2014. Published by Oxford University Press on behalf of The Royal Astronomical Society.