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Tokiwa, Tetsuya; Asamori, Koichi; Hiraga, Naoto*; Yamada, Osamu; Moriya, Hirokazu*; Hotta, Hikaru*; Kitamura, Itaru*; Yokota, Hideharu
Proceedings of 13th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM 2010) (CD-ROM), p.117 - 122, 2010/10
In this paper, we discuss the relationship between the accurate hypocentral distribution and 3-D geological structure in and around the Horonobe area, Japan. We carried out multiplet-clustering analysis by using data of the 421 micro-earthquakes which occurred from 1st September, 2003 to 30th September, 2007. The 3-D geological structure model was mainly constructed from previous seismic reflection profiles and drilling data. As a result of this analysis, although there are some differences in depth between them, the hypocenters are distributed in NNW-SSE direction and become deeper from the west toward the east. The distributed pattern of the hypocenters is similar to the one of the geological structure. These results indicate that the hypocentral distribution may represent existence of active zone related to the geological structure, and provide effective information which can contribute to establishing methods for estimating the future evolution of the geological environment.
Hotta, Hikaru*
JNC TJ5410 2005-004, 111 Pages, 2005/03
JNC-TJ5410-2005-004.pdf:19.25MB
We have compiled seismic data obtained by JNC seismographic station and JMA (Japan Meteorological Agency) Hi-net stations including Wakkanai-kita, Wakkanai-higashi, Wakkanai-nishi, Sarufutu-kita, Sarufutu-minami, Hamatonbetu, Horonobe, Toyotomi, Nakatonbetu, Teshio, Otoineppu and Nakagawa station from December 20th, 2002 to September 30th, 2004 in and around the Horonobe area. In that period, 1,618 earthquakes were recorded by JMA stations in the area. 103 events out of them were recorded at least two JNC seismographic stations and were able to detect the arrival time of P-and S-wave. In this study, the hypocenters were calculated by hypomh and cross-spectruma method on the basis of JMA and JNC data. Cross-spectruma method is higher precise than hypomh method. As a result of cross- spectruma analysis, we could identify the 7 groups of hypocenter areas in and around the Horonobe area. It is examined that the relationship between the hypocenter information and geological structures based on hypocenter areas, existing topographical and geological features.
Moriya, Hirokazu*; Niizato, Tadafumi; Kitamura, Itaru*; Hotta, Hikaru*; Ohara, Hidefumi
no journal, ,
The source locations of earthquakes at the Horonobe area, north of Hokkaido, Japan have been relocated by using the multiplet-clustering analysis (MCA) to identify the subsurface structures and to reveal the mechanism of earthquakes. The absolute source locations of 221 earthquakes were determined by the "hypomh" algorithm to find the overall structures in this area. After that, those earthquakes were classified into 10 groups of multiplets which are the groups of events with very similar waveforms and their source locations have been relocated based on the MCA in order to reveal the fine scale structures. The multiplet-clustering analysis has revealed that the earthquake locations show the structures trending from NS to NNE-SSW with reverse or strike-slip focal mechanism.
Moriya, Hirokazu*; Asamori, Koichi; Kitamura, Itaru*; Hotta, Hikaru*; Ohara, Hidefumi*; Niizato, Tadafumi
no journal, ,
Hypocenter locations of shallow earthquakes in Horonobe area were determined to reveal the mechanisms of earthquake occurrence. The absolute source locations of 211 earthquakes were determined; then, those earthquakes with similar waveforms were identified, and the source locations of 26 multiplet groups were relocated by using cross-spectrum and clustering analyses. The relocated hypocenters allowed two seismically active areas to be identified, at 10-20 km and around 25-30 km depth. The earthquake locations indicate structures trending nearly N-S, and the structures causing repeated stick-slips at asperities, thus generating similar earthquakes.
