Abstract

The earthquake in Vatnafjöll, 25 May 1987 (M = 5.8), was the largest earthquake in south Iceland since 1912 (M = 7), and it was one of the first earthquakes recorded on a local network of strong-motion acceleration recorders. In this study, the strong-motion records are used to obtain an estimate of the source parameters and the attenuation of high-frequency waves. The source parameters are obtained by fitting the data by a dislocation source model combined with an exponential model for the attenuation. The root-mean-squared acceleration is also estimated and compared to predicted values using the source parameters. The source parameters estimated here (M0 = 8.2 × 1024 dyn-cm, r = 4.6 km, Δσ = 38 bars, Δu = 36 cm, Td = 3 sec) and estimated moment magnitude (Mw = 5.9) agree well with values obtained previously from teleseismic waves and strain-meter data. Estimates of path-averaged crustal shear-wave quality factors give results in the range Q = 128 to 425, and k = 0.05 sec for the spectral decay parameter, confirming recent measurements of higher crustal Q for this region than in earlier studies.

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