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Non‐double‐couple earthquake mechanisms at the Geysers Geothermal Area, California
Author(s) -
Ross Alwyn,
Foulger G. R.,
Julian Bruce R.
Publication year - 1996
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/96gl00590
Subject(s) - geothermal gradient , seismology , geology , explosive material , shear (geology) , amplitude , dipole , geophysics , petrology , physics , chemistry , organic chemistry , quantum mechanics
Inverting P ‐ and S ‐wave polarities and P:SH amplitude ratios using linear programming methods suggests that about 20% of earthquakes at The Geysers geothermal area have significantly non‐double‐couple focal mechanisms, with explosive volumetric components as large as 33% of the seismic moment. This conclusion contrasts with those of earlier studies, which interpreted data in terms of double couples. The non‐double‐couple mechanisms are consistent with combined shear and tensile faulting, possibly caused by industrial water injection. Implosive mechanisms, which might be expected because of rapid steam withdrawal, have not been found. Significant compensated‐linear‐vector‐dipole (CLVD) components in some mechanisms may indicate rapid fluid flow accompanying crack opening.