Katsuhiro Kamae

Source model composed of asperities for the 2003 Tokachi-oki, Japan, earthquake (MJMA = 8.0) estimated by the empirical Green’s function method

A preliminary source model composed of asperities for the 2003 Tokachi-oki, Japan, earthquake (MJMA = 8.0) was estimated by the empirical Green’s function method. The source parameters for three asperities located on the fault plane were determined from the comparisons of the synthesized broad-band ground motions with the observed ones. We found that the pulsive waveforms observed in north direction of the hypocenter were generated by the forward rupture directivity effect. Furthermore, the estimates of the stress parameter for asperities are higher than the averaged ones for past inland and subduction earthquakes.

Source model composed of asperities for the 2004 Mid Niigata Prefecture, Japan, earthquake (MJMA=6.8) by the forward modeling using the empirical Green’s function method

A preliminary source model composed of asperities for the 2004 Mid Niigata Prefecture, Japan, earthquake (MJMA=6.8) was estimated by the empirical Green’s function method. The source parameters for two asperities located on the fault plane were determined from the comparisons of the synthesized broad-band ground motions with the observed ones at several stations including near source. Furthermore, we performed the preliminary nonlinear analysis of the sedimentary soils to reproduce the observed ground motions at NIG019 of K-NET. Resultantly, we pointed out the need of more asperity in northern part on the fault plane and the importance of the quantitative analysis of the nonlinearity of the sedimentary soils at K-NET stations.

Source modeling of the 2005 off-shore Miyagi prefecture, Japan, earthquake (MJMA=7.2) using the empirical Green’s function method

A preliminary source model composed of asperities for the 2005 off-shore Miyagi prefecture, Japan, earthquake (MJMA=7.2) was estimated by the empirical Green’s function method. The source parameters for two asperities located on the fault plane were determined by comparing synthesized broad-band ground motions with observed ones at several stations. We concluded that the stress parameters of the asperities are very high (90 MPa for Asp-1,300 MPa for Asp-2) and that these values are nearly equal to those (73 MPa and 29 MPa) calculated by the Earthquake Research Committee (2005) in Japan for the off-shore Miyagi prefecture earthquake that is expected in the near future. However, the location of the asperities is not completely consistent with the expected event.

Prediction of strong ground motion at EURO-SEISTEST site using the empirical Green's function method

This paper presents some tests on the empirical Greens function method, performed in order to check its effectiveness to predict strong ground motion during future large earthquakes. These investigations basically consist of blind or pseudo-blind tests using part of the data set obtained at the Volvi (Greece) test-site within the framework of the EURO-SEISTEST project. In a first step, a moderate event (ML=4.1) is simulated by using a small event (ML=2.5), and taking into account the a priori knowledge of the relevant source parameters (magnitude and stress-drop) for both the base and target events. This check emphasizes the sensitivity of the prediction to the stress-drop values. In a second step, a pseudo-blind prediction is carried out in which the information on the target event is only the magnitude (ML=5.3) besides the geometrical parameters such as source location, strike and dip. The other important parameters (seismic moment, fault area, stress-drop) are determined on the basis of specific empirical scaling laws derived from several small and moderate events occurring in the area. The synthetic motions are computed for two nearby sites, which are located on the southern edge and in the center of the Mygdonian graben, respectively, and correspond to much different site conditions: weathered rock and thick sediments. They are found in good agreement with the observations, which were unveiled after the simulation. In particular, the amplitude and the phase of the late, local surface waves generated on the southern edge of the graben, are very well reproduced at valley center. Finally, the last step is an attempt to predict strong ground motion for a hypothetical large earthquake of magnitude ML=6.5. The results are shown to depend very significantly on the scaling laws.