In situ stress measurements in a borehole close to the Nojima Fault

Citation
H. Tsukahara et al., In situ stress measurements in a borehole close to the Nojima Fault, ISL ARC, 10(3-4), 2001, pp. 261-265
Citations number
10
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
261 - 265
Database
ISI
SICI code
1038-4871(200109/12)10:3-4<261:ISSMIA>2.0.ZU;2-B
Abstract
In situ stress was measured close to the fault associated with the 1995 Kob e Earthquake (Hyogo-ken Nanbu earthquake; January 1995; M7.2) using the hyd raulic fracturing method. The measurements were made approximately 2 years after the earthquake. The measured points were approximately 40 m from the fault plane at depths of about 1500 m. The maximum and the minimum horizont al compressive stresses were 45 MPa and 31 MPa, respectively. The maximum c ompressive stress and the maximum shear stress are very small in comparison with those of other seismically active areas. The azimuth of the maximum h orizontal compressive stress was estimated from the observed azimuths of we ll bore breakouts at depths between 1400 m and 1600 m and was found to be N 135 degrees (clockwise). The maximum stress axis is perpendicular to the fa ult strike, N45 degrees. These features are interpreted in terms of a small frictional coefficient of the fault. The shear stress on the fault was rel eased and dropped almost to zero during the earthquake and it has not yet r ecovered. Zero shear stress on the fault plane resulted from the perpendicu lar orientation of one of the principal stress to the fault plane.