A. Ross et al., NON-DOUBLE-COUPLE EARTHQUAKE MECHANISMS AT THE GEYSERS GEOTHERMAL AREA, CALIFORNIA, Geophysical research letters, 23(8), 1996, pp. 877-880
Inverting P- and S-wave polarities and P:SH amplitude ratios using lin
ear programming methods suggests that about 20% of earthquakes at The
Geysers geothermal area have significantly non-double-couple focal mec
hanisms, with explosive volumetric components as large as 33% of the s
eismic moment. This conclusion contrasts with those of earlier studies
, which interpreted data in terms of double couples. The non-double-co
uple mechanisms are consistent with combined shear and tensile faultin
g, 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) compon
ents in some mechanisms may indicate rapid fluid flow accompanying cra
ck opening.