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The Influence of Critical Moho Reflections on Strong Ground Motion Attenuation in California

by P. Somerville, N. Smith, R. Graves and D. Dreger

Somerville, P., N. Smith, R. Graves and D. Dreger (1991). The Influence of Critical Moho Reflections on Strong Ground Motion Attenuation in California. SMIP91 Seminar on Seismological and Engineering Implications of Recent Strong-Motion Data, p. 2-1 - 2-10.

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Abstract

Using strong motion recordings from the 1987 Whittier Narrows and 1989 Loma Prieta earthquakes, we show evidence that critical reflections from the lower crust control the attenuation of peak acceleration at distances beyond the critical distance, causing a flattening of the attenuation curve. Depending on the focal depth of the earthquake and the crustal thickness, this flattening can begin at distances from the source as close as 40 km.