Temporal change in coda associated with the Round Valley, California, Earthquake of November 23, 1984

Abstract

Seven thousand seismograms of small earthquakes in the Mammoth Lakes‐Bishop area were used to measure values of Q from the decay of the earthquake coda. These measurements were compared between events that occurred before and after the Round Valley earthquake (M=5.7). We found that in regions near the main shock epicenter, measurements of coda Q−1 for earthquakes that occurred after the main shock were higher than for those earthquakes that occurred prior to the main shock. The opposite behavior was found for regions farther away from the main shock, namely, lower coda Q−1 after the main shock than before. Measurements of coda Q−1 in the Long Valley caldera, outside of the immediate source region of the earthquake, were higher than in surrounding areas before the main shock, but the difference disappeared after the occurrence of the main shock. This indicates that the temporal variation in coda Q−1 is comparable to its spatial variation. The doughnut model (seismicity quiescence surrounded by a zone of activity) which was invoked for explaining the precursory seismicity pattern appears to be similar with the observed coda Q−1 variation associated with the Round Valley earthquake. The observed spatial variations in coda Q−1 also help to reconcile conflicting results published in previous studies of the coda Q−1 precursor.

Seismic observations at an overstep of the western North Anatolian Fault (Abant–Sapanca region, Turkey)

“…The low Q belt also follows the focal area of the 1967 Mudurnu Valley earthquake. The observation that after a strong earthquake the Q-value drops has been made by other seismologists too (Peng et al 1987).…”

Characteristics of Coda Waves and Inhomogeneity of the Earth.

“…Several studies reported decreases in Q-' value associated with earthquake occurrences (e.g., Jin and Aki, 1986;Sato, 1987;Peng et al, 1987). On the contrary, increases in Qc-1 value associated with earthquakes also have been obtained (e.g., Tsukuda, 1988;Peng et al, 1987). Precursory increases of Qc-1 value with earthquake occurrences have been reported by Gusev and Lemzikov (1985) and Jin and Aki (1986).…”

“…strongly depends on the location of hypocenter and the time window. Several studies reported decreases in Q-' value associated with earthquake occurrences (e.g., Jin and Aki, 1986;Sato, 1987;Peng et al, 1987). On the contrary, increases in Qc-1 value associated with earthquakes also have been obtained (e.g., Tsukuda, 1988;Peng et al, 1987).…”

Estimates of Coda-Q Using a Non-Linear Regression.

“…Since then, a great number of studies on the attenuation of coda waves have been carried out applying the single-scattering model, for numerous regions in the world (e.g., Roecker et al, 1982;Pulli, 1984;Pujades et al, 1990;Canas et al, 1991). Although there are more general models (e.g., Gao et al, 1983;Wu and Aki, 1988;Frankel and Wennerberg, 1987;Zeng et al, 1991), their use and application is less extended, due, in part, to the complexity of the mathematical expressions or to the instability of the numerical solutions (Peng et al, 1987).…”