Earth Planets Space, Vol. 57 (No. 11), pp. 1039-1054, 2005
Mohamed F. Abdelwahed and Dapeng Zhao
Geodynamics Research Center, Ehime University, Matsuyama 790-8577, Japan
(Received January 6, 2005; Revised June 10, 2005; Accepted July 8, 2005)
The crustal structure beneath southwest Japan is investigated through waveform modellings of four local crustal earthquakes by using the generalized ray theory. High-quality seismograms recorded by the Hi-net seismic network are used. The focal mechanism solutions of the events used are estimated by using the first P-wave polarity data. Twenty-nine paths are used to characterize the crustal waveguide in SW Japan. Optimal 1-D velocity models for different paths are derived individually by waveform modelling. Synthetic tests are conducted to study the effects of different model parameters and to confirm the focal mechanism solutions. Modelling the waveforms individually is proven applicable for the heterogeneous regions. The resulted synthetics match the observed seismograms well. Considerable variations of the Conrad and Moho depths are found in the study area. The Conrad depth ranges from 14.8 to 19.7 km, and the Moho depth ranges from 28.4 to 33.4 km. Considerable variations in the crustal structure are found for the eastern portion of the study area where Biwa Lake lies. The effects of Biwa Lake on different paths are examined in detail.
Key words: Waveform modelling, generalized ray theory, synthetic seismogram, velocity structure, southwest