4:15 PM - 4:30 PM
[SSS33-10] A new model of P ans S wave attenuation structure for the Tokyo Metropolitan area using the MeSO-net station network
Keywords:Attenuation, Tomography, MeSO-net
We then use an ω2 model in order to estimate the source acceleration spectrum of several earthquakes occurring below the Kanto basin at depths ranging 30~80 km and to derive the PGA for P and S waves. We compared the observed PGA at the MeSO-net stations to the calculated PGA by our model. In order to estimate the observed PGA, we took a 4 sec window starting from the P or S wave arrival, and looked for the highest acceleration inside this window. The PGA values are moderately low west of the epicenter and highest in an area 20 km to the east of it for earthquakes occurring below the northern edge of Tokyo bay on the Pacific plate. These earthquakes are located exactly below the area were our model displayed significantly low Q values. Seismic waves passing through that area should be highly attenuated. This could be a possible explanation for the observed pattern of the intensity distribution. Although we are able to simulate the general trend in the PGA distribution, our model failed to exactly match the observed amplitudes. On the other hand the PGA distribution of shallow earthquakes does not exhibit a similar anomalous pattern. The distribution for both the observed and estimated PGA, for shallower earthquakes that probably occurred in the upper part of the Philippine sea plate, is characterized by amplitudes that drop almost concentric with increasing distance from the epicenter. Our attenuation tomography results suggest high Q values for the upper part of the crust. As a result, seismic waves passing through this area are very little attenuated. We also achieved better match of the observed and calculated PGA amplitudes in this case.