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Generation of a great earthquake in the Tokai area, central Japan, is considered to be high possibility in near future. The reflection-refraction experiment across the central Japan showed the presence of high amplitude reflected phase from the subducting Philippine Sea plate in the southern part of the survey line. Almost the same place on the plate boundary is also showing slow slip since June, 2000. Both observations may suggest the presence of low-density material (e.g., water) along the plate boundary. The 1944 Tonankai Earthquake (M8.0) also showed the pre-slip in this area. If we deal with the possibility of the future Tokai-Tonankai Earthquake, it may be important to monitor the temporal change of interplate coupling strength in this region using the seismic reflections. The rapid change of the interplate coupling state may trigger large earthquakes in the Tokai and/or Tonankai region. In order to make trial of continuous monitoring as stated above, we started a seismic experiment in the Tokai region using the seismic ACROSS. We are continuously transmitting the 10-20Hz sweep sinusoidal seismic waves from Toki City, Gifu Prefecture since spring, 2004. In order to identify the travel paths for these seismic waves, we installed 22 seismic stations over 40-70km offset distance since November 2004. Preliminary analysis using 200 hours data obtained by a station at 57km distance showed good quality of P and S arrivals although we are working whether these are the interplate reflection phase or not. We believe that the use of longer data obtained by 22 stations may tell which are the interplate reflected phases and the magnitude of their temporal changes.
Note. Abstracts are published in author's edition
Last update: 06-Jul-2012 (11:44:54)