Source Modeling of the 2007 Niigataken Chuetsu-oki Earthquake Using the Empirical Green's Function Method

The 2007 Niigataken Chuetsu-oki earthquake (MJMA6.8) occurred on July 16th, 2007. In this study, we estimate a source model of this earthquake through forward modeling of local strong motion records using the empirical Green's function method. The target frequency range of this modeling is broadband (0.3 Hz to 10 Hz). As the result, the first asperity was estimated that it was located on the NW-dipping fault plane including the hypocenter, and the rupture then transferred to the conjugated fault plane (SE-dipping plane). On the SE-dipping plane, two asperities are identified: one is located just near the first asperity (the second asperity); the other is off the coast of Kashiwazaki city (the third asperity). The estimated three asperities are located in the gaps of the aftershock distribution. Our source model can successfully reproduce strong motion in a wider area than the modeling area selected for source estimation. The estimated stress drop from our source model is almost 15 to 20 MPa, and it is similar to the stress drop empirically expected from the seismic moment and area of asperities.