Comprehensive study of the seismotectonics of the eastern Aleutian arc and associated volcanic systems. Annual progress report, March 1, 1983-February 29, 1984
Integration of seismic network data from the Shumagin Islands seismic gap with crustal deformation and volcanicity data indicate that the previously reported tilt anomaly in 1978 to 1980 was associated with an 80-cm amount of slip of the descending slab at depth between 20 and approx. = 80 km. The slip event was mostly aseismic although it caused increasing microearthquake activity. The shallow (< 30 km) main thrust zone remained locked but may have been further stressed so as to increase the likelihood for a future great earthquake. The basic conditional probability for the Shumagin Gap rupture in a great earthquake (M > approx. = 8) in the next decades has been determined to lie between 30 and 99%, probably the highest value for a potential great earthquake anywhere in the US. Composite focal mechanisms close to the location of the slip event are found to be highly variable since 1978 (both in space and time). An earthquake sequence in the Shumagins of February 14, 1983, included two moderately large shocks, M = 6.3 and 5.7, that provided significant strong-motion records. Three dimensional ray tracing has been applied to relocate hypocenters in the descending slab and thereby redefining the dipping slab geometry. We find the slab dips beneath 80 km at an almost constant dip of approx. = 45/sup 0/ to depths of approx. = 250 km without significant bend. 12 references.
- Research Organization:
- Columbia Univ., Palisades, NY (USA). Lamont-Doherty Geological Observatory
- DOE Contract Number:
- AC02-76ER03134
- OSTI ID:
- 5669233
- Report Number(s):
- DOE/ER/03134-46; COO-3134-46; ON: DE84002243
- Resource Relation:
- Other Information: Microfiche only, copy does not permit paper copy reproduction
- Country of Publication:
- United States
- Language:
- English
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