Abstract

Field studies of surface faulting associated with the Guatemala earthquake of February 4, 1976, have documented the occurrence of afterslip at seven locations along the 230 km of surface rupture. The total displacement across the fault as measured in April 1976 averaged 110 cm. Displacement at one location increased from 60 cm on February 8, 1976, to 91 cm on October 6, 1977. Afterslip time histories determined at three sites show the afterslip to be proportional to the logarithm of time since the earthquake, and that the rate of afterslip is inversely related to the amount of displacement at a site. The regular variation in total slip and afterslip along about 50 km of the fault trace suggests that the afterslip is not controlled by local, near-surface geologic factors such as alluvial cover.

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