HFER duration and displacement amplitudes from regional P waves as a possible tsunami earthquake discriminant

Abstract:

Hara (2007) showed that tsunami earthquakes could be characterized by long high frequency energy radiation (HFER) durations and small displacement amplitudes of P-waves in his analysis of tele-seismic data and suggested the possibility to discriminate tsunami earthquakes by measurements of HFER durations and displacement amplitudes. In this study, we investigated this possibility using waveform data recorded in a regional distance range (up to 30 degrees). We used a dataset compiled to develop a formula of M_hdd (Hara, 2013) for regional distance range (Hara, 2014, submitted). It consists of BHZ channel waveform data retrieved from the IRIS Data Management Center for 93 large shallow earthquakes that occurred between 1994 and July, 2013. Two tsunami earthquakes, the July 17, 2006 Java and October 25, 2010 Mentawai, were included. The distance correction for P wave displacements was done simply by a common logarithm of epicentral distance, although a slight different correction is adopted in the M_hdd formula. As was observed in the analysis of tele-seismic data, the tsunami earthquakes were characterized by long HFER durations and small displacement amplitudes measured from P waves. This suggests that it is possible to discriminate tsunami earthquakes by simple measurements of HFER durations and displacement amplitudes from regional P waves more rapidly than those from tele-seismic data. Since some strike slip events have the similar characteristics as tsunami earthquakes in terms of these measurements, rapid focal mechanism determination such as W phase source inversion would be helpful to distinguish tsunami earthquakes from these strike slip events.