Recently, structural damage caused by the middle-scale earthquake were reported. These damage were not so serious, but middle-scale earthquake is often generated. It is important that study of the source modeling the middle-scale earthquake. In this study, we attempted to make a source model of middle-scale earthquake by the empirical Green's function method. The target earthquake is inland crustal earthquake with Mj5.6 which occurred in southern Nagano prefecture in Japan on 25th June 2017. Resultantly, we proposed source model with single strong motion generation areas located in near hypocenter.
Characteristic strong ground motion which include semi-large pulse with a duration of 1 to 3 second was generated in the 1995 Kobe earthquake. It caused serious damage to many civil structures and many building structures. The characteristic ground motion was caused by forward rupture directivity effect from directional characteristics of source rupturing. After this earthquake, research on strong ground motion prediction including source modeling was conducted by many researchers energetically. As a result, "Recipe for strong ground motion prediction" was constructing based on several research findings. Effectiveness of the recipe was verifying by strong ground motion simulation against a large-size earth-quake. Recently, structure or lifeline system damages caused by the mid-scale earthquake were reported. Generally, damage scale by mid-scale earthquake was not so serious, but that earthquake is often generated. So it is important that study of the source modeling the mid-scale earthquake. In this study, we attempted to make a source model of mid-scale earthquake by the forward modeling (Kamae and Irikura, 1998) using empirical Green's function method (Irikura, 1986).
The earthquake of Mw5.2 (Mj5.6) which occurred in southern Nagano prefecture in Japan on 25th June 2017 was selected for target earthquake. The fault plane of this earthquake was estimated a reverse fault type with the strike of NNE-SSW direction from CMT solution (NIED) and after-shocks distribution. Table 1. shows parameter of the southern Nagano prefecture earthquake. Figure 1 shows location of the epicenter of the main-shock and after-shocks. These after-shocks were occurred within 24 hours from main-shock and its magnitude more than 2.