Of the May 7, 1986 Andreanof Islands Earthquake source parameters

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Abstract
Source characteristics of the May 7, 1986 Andreanof Islands earthquake (51.412°N, 174.830°W, NEIC) are investigated from WWSSN, GDSN and IDA records. First motions from over 60 stations determine one steeply dipping nodal plane. We constrained this nodal plane and inverted long‐period surface waves at a period of T=256 sec and determined the second nodal plane to be dip 18°, rake 116°, and strike 257°. This shallowly dipping thrust mechanism is consistent with plate motions in this region. Seismic moment from surface‐wave inversion is 1.3×1028 dyne‐cm corresponding to Mw=8.0. Amplitudes of body and surface waves from short‐period instruments yield magnitudes of and Ms=7.7. The teleseismic average P‐wave moment rate spectrum from 17 short‐ and intermediate‐period instruments is slightly lower than that of an average Mw=8.0 subduction‐zone event. We constrained the fault plane as determined above to deconvolve the first 90 secs of the long‐period body wave at 11 teleseismic stations to determine the source time function and the spatial distribution of moment release. The source time function consists of 4 moment‐releasing episodes which have a total moment release of 9.4×1027 dyne‐cm. The fault ruptured bilaterally with the largest moment releasing subevent occurring between 30‐45 sec. This subevent nucleates approximately 75‐90 km west of the determined epicenter. This region corresponds to the epicentral area of the 1957 Great Aleutian earthquake which is one of the largest earthquakes in recorded history.