The S to P convert wave from the bottom of sediment basin in the near-field seismic records

• Published in: Acta seismologica sinica Vol. 15; no. 5; pp. 493 - 502
• Main Authors: Wang, Pei-de, Stammler, Klaus
• Format: Journal Article
• Language: English
• Published: Beijing Springer Nature B.V 01.09.2002; Institute of Geophysics, China Seismological Bureau, Beijing 100081, China%Seismological Central Observatory, Federal Institute for Geosciences and Natural Resources, Erlangen 91054, Germany
• Subjects: basin; convert; Datong; Earthquakes; near-field; observation; River basins; Sedimentation & deposition; Seismic activity; Seismology; wave; Waveform analysis; S to P convert wave; near-field observation; Datong basin
• ISSN: 1000-9116; 1674-4519; 1993-1344; 1867-8777
• DOI: 10.1007/s11589-002-0017-y

From the near-field records of aftershocks of October 1989 and March 1991 Datong earthquakes, an extra phase between P and S arrivals is found. High-precision epicenter location shows that some of these records are obtained with the incidental angle less than the critical angle. This excludes the possibility that the extra wave phase is a refractive wave from ground surface. Particle motion analysis shows that the characteristic of the extra wave is similar to that of P wave, therefore it is very possible that the extra phase is an S to P convert wave from the bottom of sediment basin. Suppose a low velocity layer covers on a high velocity basement. Successful simulation by synthetic seismogram conforms that the extra phase is an S-P convert wave from the interface of basin bottom. Modifying the depth of interface at each ray path to match the waveform, we obtain an interface distribution in space. In this way a brief imagine of bottom could be shown, and Datong basin has a (V( shape basin bottom.