Science Links Japan | The Relationship between Seismicity and Fluid Existing in the Crust Inferred from Vp/Vs Ratio -An Analysis of the Data from the Dense Microseismic Networks Installed in the Western Nagano Prefecture Region.

The Relationship between Seismicity and Fluid Existing in the Crust Inferred from Vp/Vs Ratio -An Analysis of the Data from the Dense Microseismic Networks Installed in the Western Nagano Prefecture Region.

Accession number;99A0456261

Title;The Relationship between Seismicity and Fluid Existing in the Crust Inferred from Vp/Vs Ratio -An Analysis of the Data from the Dense Microseismic Networks Installed in the Western Nagano Prefecture Region.

Author; TAKEDA JUNKO (Univ. of Tsukuba) IIO YOSHIHISA (National Res. Inst. Earth Sci. and Disaster Prevention) KOBAYASHI YOJI (Univ. of Tsukuba, Inst. of Geosci.) YAMAMOTO KIYOHIKO (Tohoku Univ., Grad. Sch.) SATO HARUO (Tohoku Univ., Grad. Sch.) OMI SHIRO (Disaster Prev. Res. Inst., Kyoto Univ.) ITO HISAO (Geol. Surv. of Japan, Agency of Ind. Sci. and Technol.) IKEDA RYUJI (National Res. Inst. Earth Sci. and Disaster Prevention) YAMAMOTO EIJI (National Res. Inst. Earth Sci. and Disaster Prevention)

Journal Title;Journal of the Seismological Society of Japan. Second Series

Journal Code:G0931A

ISSN:0037-1114

VOL.51;NO.4;PAGE.419-430(1999)

Figure&Table&Reference;FIG.9, TBL.2, REF.29

Pub. Country;Japan

Language;Japanese

Abstract;The relationship between seismicity and fluid existing in the crust has been discussed by several experiments since the middle of the 1960's. It is considered in these experiments that earthquakes occur at regions when and where pore pressure is high, since pore pressure has been thought to decrease the frictional strength. In this paper, the relationship between seismicity and fluid(degree of saturation) existing in the crust was investigated by analyzing the data sets of the seismicactivity and tomography obtained by the dense networks installed in the Western Nagano prefecture. The distributions of degree of saturation and crack density were inferred from the three-dimensional velocity tomography obtained from the 1986 Joint Seismological Research in Western Nagano Prefecture, by using the theory of new self-consistent scheme(NSC) or differential scheme(DS). Comparing distributions with the hypocentral distribution in thesame region, we found that earthquakes occur at the regions where the degree of saturation is low, namely, at little saturated rocks. Further, it appears that the blocks of low degree of saturation are surrounded by more saturated blocks. This result suggests that earthquakes possibly occur fluid begins to flow into cracks which are little saturated. (author abst.)

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