Comprehensive study of the seismotectonics of the Aleutian Arc. Annual progress report, March 1, 1975--February 29, 1976 [report]

J.N. Davies, L. House, K.H. Jacob, R. Bilham, V.F. Cormier, J. Kienle
1976 unpublished
Seismological and geodetic research performed during the past contract- year has increased our understanding of the seismotectonics of the eastern Aleutian Island Arc. While generally aimed at producing a coherent theory for the evaluation of the entire arc, our research has focused on the Shumagin Islands seismic gap, a region within which a major earthquake is expected in the not too distant future. To collect basic seismological data and to investigate certain earthquake prediction
more » ... rediction techniques we maintain 19 short period and 3 long period seismograph stations, 2 strong motion accelerographs and a pair of strainmeters. To investigate possible regional tilting due to strain accumulation within the seismic gap we have made limited geodetic leveling measurements. We have expanded the baseline and increased the resolution of these tilt measurements with the installation of two remote tide gauges. In this report we present (1) historic seismicity maps of the Shumagin seismic gap vicinity which show the relatively low level of seismic activity in the gap, a possible offset in the Benioff zone, and a few events associated with the Bering shelf continental margin south of the Pribliof Islands; (2) a seismicity map and hypocenter cross-sections based on data from the local Shumagin Islands seismic network which show a very well developed Benioff zone beneath the Shumagin Islands; (3) studies of the focal mechanisms of April 6, 197.4 Shumagin Islands earthquake and the February 2., 1975 Near Islands earthquakes which respectively show thrust faulting perpendicular to the.arc and rightlateral strike-slip faulting oblique to the arc along the slip direction inferred from the relative motion of the plates; (4). the first strong motion accelerograph data from the eastern Aleutians, which show accelerations consistent with those observed for earthquakes in California; (5) this year's geodetic leveling results which when compared with those from 1972 indicate fHSTRlBUTlON OF THIS DOCUMENT IS UNLIMITED
doi:10.2172/7147836 fatcat:xaleqmyf6rfn3aiq7xgononb7e