Strain accumulation in the Shumagin and Yakataga seismic gaps, Alaska

Strain accumulation during the 1980-85 interval has been measured by means of trilateration surveys in the Shumagin and Yakataga seismic gaps, which are the two regions identified as the most likely sites for the next great thrust earthquakes along the Alaska-Aleutian arc. No significant strain accumulation was detected in the Shumagin gap, but experience at similar subduction zones and simple models of the subduction process suggest that a measurable amount of strain should have accumulated. The most likely explanation of the observation is that subduction mere is either aseismic or episodic. The strain accumulation measured in the Yakataga gap is consistent with that expected for the plate convergence rate, although the direction of maximum compression may suggest a somewhat more oblique convergence than expected.