Abstract
Abstract The 2007 Noto Hanto Earthquake occurred on 25 March. We have constructed a detailed gravity anomaly map over the Noto peninsula. Four block boundaries which are identified by morphological/geological studies are also recognized on the gravity anomaly map. Various other observations indicate that the mainshock ruptured only one of the blocks, the Kuwatsuka block, although aftershocks are distributed over two blocks, the Kuwatsuka and the Saruyama blocks. The Bouguer anomalies over the Kuwatsuka block are relatively high compared to those of the Saruyama block, i.e. the basement depth of the Kuwatsuka block is shallower than that of the Saruyama block. This difference in the basement depth is consistent with the deformation pattern observed by SAR interferometry. At the block boundary, an offset is recognized in the aftershock distribution. Based on the relationships among the gravity anomalies, the geologic structures, the aftershock distribution and the source fault, we propose that the rupture size of the earthquake was constrained by the block structure in this region.
Highlights
The 2007 Noto Hanto (Noto Peninsula) Earthquake (MJMA 6.9) occurred on 9:41, 25 March 2007
The northern Noto peninsula is divided into four major bocks: Kuwatsuka (KT), Saruyama (SY), Hachibuse (HB), Houryu (HR)
In the gravity anomaly distribution, the KT and the SY blocks are clearly recognized by relatively high and low anomalies, respectively. This means that the basement depth of the KT block is shallower than that of the SY block
Summary
The 2007 Noto Hanto (Noto Peninsula) Earthquake (MJMA 6.9) occurred on 9:41, 25 March 2007. The Noto peninsula is not a very seismically active region. This is the first M 6 class earthquake since 1993, which occurred off the north coast of Suzu city (MJMA 6.6). We have compiled all of the gravity data available over the Noto peninsula (Kono et al, in preparation). Compiled gravity data obtained by Kanazawa University (Kono and Furuse, 1989), Hokuriku Electric Co. Ltd. The total number of compiled data points is over 13,000 in the research area (Fig. 1) They are spaced approximately one every 2 km on the land area. Compiling all these data, we constructed a detailed Bouguer anomaly map of the Noto peninsula (Fig. 3).
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