Seismic imaging of deep crustal structures via reverse time migration using local earthquakes

Abstract

We developed a seismic imaging method based on reverse time migration (RTM) for exploring deep crustal structures using reflection waves of earthquakes without source information. Instead of wavefield extrapolation from both well-defined sources and receivers in a conventional RTM, only receiver-side wavefield extrapolation is required in the proposed method. Forward- and backward-extrapolated wavefields using the same observation records from all receivers are correlated to illuminate multiple reflections between surface and subsurface boundaries. In this study, we present a two-dimensional numerical simulation to validate the proposed method with a regional crustal structure model and quasi-actual source locations. We also show a case study of an application to actual records of a seismic network observation on land in the Kanto region, Japan. The seismic reflection image along a 190-km pseudo-survey line using hundreds of surrounding local earthquakes shows several continuous reflectors around 20 - 40 km in depth, which are likely part of the Philippine Sea slab. Our results suggest a potential for reflection imaging of deep structures by using the large energy of earthquakes. The proposed method may become a useful technique for imaging crustal structures from huge amounts of seismic data recorded by highdense seismic network observations.