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Microearthquake spectra in the southeastern United States

SCHOOL OF GEOPHYSICAL SCIENCES GEORGIA INSTITUTE OF TECHNOLOGY, ATLANTA, GEORGIA 30332

Abstract

Displacement spectra from microearthquakes in the Clark Hill Reservoir Area and the Jocassee Reservoir Area, both in the Piedmont Crystalline Province, showed similar spectral properties typified by a sharp spectral corner, -cubic, high-frequency decay and ratios of P- and S-wave corner frequencies predominantly greater than unity. Displacement spectra from microearthquakes in the Maryville Tennessee Area in the Folded Appalachian Province showed transitional spectral corners, -square or less high-frequency decay and a ratio of P- to S-wave corner frequencies less than or equal to unity. These spectral characteristics are interpreted as evidence for a possible regional variation in the earthquake mechanism. The Clark Hill and Jocassee spectral characteristics are best explained by an earthquake mechanism typical of an equidimensional fault which nucleates rupture at a point of high resistance to slip and ruptures at a velocity greater than the S-wave velocity along an existing fracture. The Maryville spectral characteristics are best explained by rupture at velocities less than the S-wave velocity along faults which may show premature arrest of movement.

Footnotes

^* Now with Chevron U.S.A., Inc., Denver, Colorado.

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