Earth Planets Space, Vol. 60 (No. 10), pp. 1017-1022, 2008LETTER
Active Fault Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8567, Japan
(Received July 2, 2007; Revised November 27, 2007; Accepted December 5, 2007; Online published November 7, 2008)
Characterization of the 2007 Noto Hanto, Japan, earthquake (MS 6.9), a moderate-size crustal event, was performed. The rupture process was firstly inferred from strong motion data. Inversion analysis revealed that the overall rupture finished within 6 s, and the seismic moment of this earthquake was estimated to be 1.1 × 1019 N m (Mw 6.6). Two areas of large slip and stress drop (asperities) were inferred on the fault plane. The maximum static stress drop calculated from the derived slip distribution exceeded 16 MPa for the major asperity, and the minor asperity has a similar maximum value. An area of negative stress drop corresponding to the distribution of small slip exists between the two asperities. This strongly suggests that the fault is segmented. A boundary between surface faults was located above the major asperity, but an area of negative stress drop appeared between the asperity and fault boundary. This suggests that the configuration of the surface faults reflects only a shallow part of the causative fault. The ratio of radiated energy to seismic moment was also estimated for the purpose of estimation of fault activity. Comparison of the derived value with those of other Japanese earthquakes suggests that the causative fault of the Noto Hanto earthquake is not very active.
Key words: 2007 Noto Hanto earthquake, rupture process, fault model, strong motion data, static stress change.