Characterization of the 2007 Noto Hanto, Japan, earthquake

Haruo Horikawa

doi:10.1186/bf03352862

Abstract

AbstractCharacterization of the 2007 Noto Hanto, Japan, earthquake (MS6.9), 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 1.1×1019N m (Mw6.6). 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.

Highlights

The 2007 Noto Hanto earthquake (MS 6.9), a moderatesize crustal event, occurred in the Noto region, located in the northernmost part of central Japan (Fig. 1)
I have shown that two asperities with comparative static stress drop are located on the fault plane and estimated the peak values to be 12–16 MPa
Miyatake (1992) analyzed four Japanese intraplate earthquakes—the 1969 Gifu earthquake (M 6.6), the 1974 Izu-Hanto-Oki earthquake (M 6.9), the 1980 Izu-Hanto-Toho-Oki earthquake (M 6.7) and the 1984 Western Nagano earthquake (M 6.8)—and shown that peak values of the stress drop range from 8 to 18 MPa

Summary

Introduction

The 2007 Noto Hanto earthquake (MS 6.9), a moderatesize crustal event, occurred in the Noto region, located in the northernmost part of central Japan (Fig. 1). Katagawa et al (2005) conducted a dense seismic survey in the west off-Noto area and have mapped three high-angle reverse fault systems associated with tiled blocks near the source region. No active fault in the peninsula has been found to the northeast of the surface fault (Ota et al, 1976) This detailed mapping provides a good opportunity to investigate the correspondence between surface faults and faults in depth. In this sense, characterization of the 2007 Noto Hanto earthquake is meaningful. An assumed fault plane was divided into small squares called subfaults, and both slip and rupture starting time of each subfault were inferred from observed ground motions with the recursive inversion procedure proposed by Matsu’ura and Hasegawa (1987). The equation system from different starting models has to be solved in order to reduce

HORIKAWA

Discussion