Seismicity changes related to a water injection experiment in the Nojima Fault Zone

Citation
K. Tadokoro et al., Seismicity changes related to a water injection experiment in the Nojima Fault Zone, ISL ARC, 10(3-4), 2001, pp. 235-243
Citations number
30
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
235 - 243
Database
ISI
SICI code
1038-4871(200109/12)10:3-4<235:SCRTAW>2.0.ZU;2-D
Abstract
A water injection experiment was carried out by the scientific drilling pro gram named the 'Nojima Fault Zone Probe' during the two periods 9-13 Februa ry and 16-25 March 1997. The pumping pressure at the surface was approximat ely 4 MPa. The total amount of injected water was 258 m(3). The injection w as made between depths of 1480 m and 1670 m in the Disaster Prevention Rese arch Institute, Kyoto University (DPRI) 1800 m borehole drilled into the No jima Fault zone. A seismic observation network was deployed to monitor seis mic activity related to the water injections. Seismicity suddenly increased in the region not far from the injection hole 4 or 5 days after the beginn ing of each water injection. These earthquakes were likely to be induced by the water injections. Most of the earthquakes had magnitudes ranging from -2 to +1. Numerous earthquakes occurred during the first injection, but onl y one could be reliably located and it was approximately 2 km north of the injection site. Between the two injection periods, earthquakes concentrated in the region approximately 1 km northwest of the injection site. During a nd after the second injection experiment, earthquakes were located approxim ately 1.5 km west of the injection site. Those earthquakes were located app roximately 3 km or 4 km from the injection point and between 2 km and 4 km in depth. Values of intrinsic permeability of 10(-14)-10(-15) m(2) were est imated from the time lapse of the induced seismic activity. The coefficient of friction in the area where the induced earthquakes occurred was estimat ed to be less than 0.3.