Subsurface exploration with P-coda of local earthquakes using seismic interferometry

Abstract

 The purpose of our study is to evaluate the applicability of the seismic interferometry to P coda waves between first arrivals of P-wave and S-wave of local earthquakes in order to extract reflection signals and obtain reflection profiles. Our continuous observation with the dense seismometer array was carried out for about four months from December 2010 to April 2011 at Narita area in Chiba, Japan. At first of the data analysis, seismic event data of local earthquakes satisfying some conditions were extracted from the continuous record based on the unified earthquake catalog of Japan Meteorological Agency, then 437 seismic records were selected after the quality check with manual pick of P and S wave first arrivals. Second, the virtual reflection seismic data were generated from the P coda waves by applying the two types of interferometry, the correlation type and the deconvolution type. Finally, PP reflection profiles were obtained by following the conventional data processing for the pseudo reflection seismic data. In our results, the virtual source records with clear reflection from basin bottom could be generated. Then, the high-resolution PP reflection profiles were obtained along 1 km array with dense receiver deployment, and deep reflections were recognized on the section of the 5 km array with sparse receiver deployment. The deconvolution type interferometry was better than correlation type to apply to natural earthquakes because of ability to eliminate the effect of different source mechanism. We can conclude that the seismic interferometric is useful for subsurface imaging of sedimentary layers and basin structures from the P coda waves of local earthquakes.