Rupture process of the February 4, 1965, Rat Islands earthquake

The great Rat Islands underthrusting earthquake (M_w=8.7), of February 4, 1965, represents subduction of the Pacific plate beneath the North American plate along a 600-km segment of the western end of the Aleutian Islands. Body wave inversion techniques are used to determine the spatial and temporal heterogeneities associated with the Rat Islands earthquake. World-Wide Standard Seismograph Network long-period teleseismic P wave seismograms were deconvolved to obtain source time functions. Directivity associated with the three major pulses of moment release in the source time functions indicates a total source duration of 160 s, unilateral rupture in the direction 300°, fault length of 420 km, and average rupture velocity of 2.5 km/s. The three pulses of moment release are located along the fault, and these regions of high moment release are interpreted as asperities. The P wave seismic moment release of the Rat Islands earthquake is controlled by the lateral segmentation of the overriding plate. -from Authors