Strain and tilt changes measured during a water injection experiment at the Nojima Fault zone, Japan

Citation
K. Fujimori et al., Strain and tilt changes measured during a water injection experiment at the Nojima Fault zone, Japan, ISL ARC, 10(3-4), 2001, pp. 228-234
Citations number
7
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
ISLAND ARC
ISSN journal
1038-4871 → ACNP
Volume
10
Issue
3-4
Year of publication
2001
Pages
228 - 234
Database
ISI
SICI code
1038-4871(200109/12)10:3-4<228:SATCMD>2.0.ZU;2-2
Abstract
In order to make geophysical and geological investigations of the Nojima Fa ult on Awaji Island, Japan, three boreholes measuring 1800 m, 800 m and 500 m deep were drilled into the fault zone. The fault is one of the seismic s ource faults of the 1995 Hyogo-ken Nanbu earthquake of M7.2. A new multicom ponent borehole instrument was installed at the bottom of the 800 m borehol e and continuous observations of crustal strain and tilt have been made usi ng this instrument since May 1996. A high-pressure water injection experime nt within the 1800 m borehole was done in February and March 1997 to study the geophysical response, behavior, permeability, and other aspects of the fault zone. The injection site was located approximately 140 m horizontally and 800 m vertically from the instrument. Associated with the water inject ion, contraction of approximately 0.7 x 10(-7) str (almost parallel to the fault) and tilt of approximately 1 x 10(-7) rad in the sense of upheaval to ward the injection site were observed. In addition to these controlled expe riments, the strainmeter and tiltmeter also recorded daily variations. We i nterpret strain and tilt changes to be related to groundwater discharge and increased ultra-micro seismicity induced by the injected water.