Estimating the permeability of the Nojima Fault Zone by a hydrophone vertical seismic profiling experiment

Citation
T. Kiguchi et al., Estimating the permeability of the Nojima Fault Zone by a hydrophone vertical seismic profiling experiment, ISL ARC, 10(3-4), 2001, pp. 348-356
Citations number
14
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
348 - 356
Database
ISI
SICI code
1038-4871(200109/12)10:3-4<348:ETPOTN>2.0.ZU;2-V
Abstract
A multi-offset hydrophone vertical seismic profiling (VSP) experiment was d one in a 747 m deep borehole at Nojima Hirabayashi, Hyogo prefecture, Japan . The borehole was drilled to penetrate the Nojima Fault, which was active in the 1995 Hyogo-ken Nanbu earthquake. The purpose of the hydrophone VSP i s to detect subsurface permeable fractures and permeable zones and, in the present case, to estimate the permeability of the Nojima Fault. The analysi s was based on a model by which tube waves are generated when incident P-wa ves compress the permeable fractures (or permeable zones) intersecting the borehole and a fluid in the fracture is injected into the borehole. Permeab le fractures (or permeable zones) are detected at the depths of tube wave g eneration, and fracture permeability is calculated from the amplitude ratio of tube wave to incident P-wave. Several generations of tube waves were de tected from the VSP sections. Distinct tube waves were generated at depths of the fault zone that are characterized by altered and deformed granodiori te with a fault gouge, suggesting that permeable fractures and permeable zo nes exist in the fault zone. Tube wave analysis shows that the permeability of the fault gouge from 624 m to 625 m is estimated to be approximately 2 x 10(-12) m(2).