Electronic Resource
Oxford, UK
:
Blackwell Publishing Ltd
Geophysical journal international
107 (1991), S. 0
ISSN:
1365-246X
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
Notes:
The drilled geothermal reservoir of Milos island, Aegean sea (Greece) is densely sampled by seismic waves from local earthquakes occurring at depths of 4-6 km, recorded by numerous three-component seismographs. During the eight months of observation seismic activity on the island occurred in the form of a few swarms located in three different areas. The focal mechanisms of all earthquakes share an area of dilatational quadrants indicating a nearly vertical maximum compressive stress. This implies an extensional field consistent with the regional tectonics of the Aegean sea.Shear-wave splitting is widely observed. Most of the observed leading shear-wave polarizations are aligned around the N-S direction and they are parallel to the structural trends of faults observed at the surface. The other seismograms show a leading shear wave polarized along a N40d̀E direction. These polarizations are observed particularly at stations located between the geothermal drillholes, indicating probably the orientation of microfractures aligned in the geothermal reservoir by the present-day stress field.Variations of the anisotropy magnitude are deduced from the study of shear-wave delays in the vicinity of geothermal drillholes, and their distribution appears to correlate with the limits of a fractured medium detected by P and S velocity anomalies.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-246X.1991.tb01426.x
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