Abstract
Strain accumulation in the Shumagin seismic gap was estimated from repeated trilateration surveys made between 1980 and 1985. The measured rate of shear‐strain accumulation (0.01 ± 0.03 μrad/a) was an order of magnitude less than the rate (0.18 μrad/a) predicted for seismic subduction. The absence of measurable shear‐strain accumulation in the Shumagin Islands suggests that the main thrust zone there may not be locked but rather may slip stably. If this is indeed the case, the probability of a great, shallow thrust earthquake in the Shumagin gap is greatly diminished. A moderate earthquake (mb = 6.0) occurred at the seaward end of the trilateration network 4 months after the most recent survey. However, no significant anomalies that could be interpreted as precursors were detected in that survey.
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