Toward systematic retrieval of earthquake source parameters from regional seismic waveforms

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Earthquakes are results of faulting in the Earth, and the characteristics of faulting are not simple in terms of fault geometry, size, and spatiotemporal distribution of displacement. In order to understand the physics controlling the complex source characteristics, it is important to accumulate a number of earthquake source parameters determined with the same technique. To attain such systematic analysis, software, which can be simple handling for anybody, is desired. In the present project, we have developed the software that can easily retrieve earthquake source parameters from regional seismic waveforms. Regional seismic networks are increasingly deployed over the world, and the waveforms include information on earthquake source characteristics that are hardly detected from teleseismic data. The software was tested for earthquakes in Turkey, Pakistan, and Chile, and provided successful results. A careful test of the software was finally done for the 2005 northern Chile, intermediate-depth earthquake. Waveform data were recorded by University of Chile using their five strong-motion accelerometers within 300 km of the epicenter, and it was a good chance for us to test our software for foreign earthquakes. The analysis generally came well. Although we met a problem from uncertainty of a velocity model in the region, we overcome the problem by relocating the earthquake with used data and adding the process to our software. Due to this improvement of the software, we believe that our software is applicable to earthquakes in many regions where velocity models are not well determined. In Turkey and Pakistan, we succeeded to estimate focal mechanisms of small earthquakes using the software, and the solutions were used to obtain the regional stress fields. The software is distributed along with its English manual. Further applications of the software to future earthquakes in the world will build up a significant database of earthquake source parameters.