Temporal change of phase velocity beneath Mt. Asama, Japan, inferred from coda wave interferometry

Abstract

We estimated the temporal changes of phase velocity of Rayleigh waves extracted from cross correlations of S-coda waves recorded at 12 stations around Mt. Asama, Japan. First, we extracted a Rayleigh wave by taking cross correlations of S-coda waves for 315 regional earthquakes between October 2005 and February 2009. The dispersion curve of the Rayleigh wave was measured and compared with the one extracted from 18 days of ambient seismic noise. We found that both dispersion curves are consistent with each other, demonstrating the dominance of the fundamental Rayleigh waves. We then divided the entire time period into sub-periods, each of which consists of 80 earthquakes, to measure the temporal changes at frequencies between 0.3 and 0.6 Hz. The result shows the reduction of phase velocity by 1.5 % and the subsequent recovery before the eruption of Mt. Asama in 2008. Copyright 2010 by the American Geophysical Union.