Comprehensive study of the seismotectonics of the easter Aleutian arc and associated volcanic systems. Annual progress report, March 1, 1978--February 28, 1979

Technical Report · Mon Jan 01 04:00:00 EST 1979

DOI:https://doi.org/10.2172/6389953· OSTI ID:6389953

Jacob, K. H.; Davies, J. N.; Beavan, J.; Johnson, D.; House, L.; Krause, J.; Hickman, S.; Winslow, M.; Hauptman, J.; Mori, J.; Sykes, L. R.

Based on the historic seismic record and accurate hypocenter data obtained from the eastern Aleutian seismic network, a relationship between the subduction-zone seismicity, volcano-trench separation, and the occurrence of great thrust earthquakes has been established for the Aleutian arc. On the basis of strong-motion accelerometer data it was found that high stress drops (540 t 650 bars) were associated with two moderate-size earthquakes (m/sub b/ = 6.0 and 5.8) within the Shumagin Islands seismic gap. This indicates that near the down-dip end of the major thrust zone, at depths of about 40 km, high tectonic stresses have accumulated within the gap segment of the arc. That such accumulation of stress is presently an ongoing process is corroborated by results from geodetic precision leveling on Unga Island. The leveling data indicate tilt rates of about 1 microradian/year. The tilting is directed down towards the trench and up towards the volcanic arc. Whether the recent activity of Pavlof, Shishaldin and Westdahl volcanoes indicates transmission of high tectonic stresses from the major thrust zone to the volcanic arc is unresolved. The search for a shallow magma chamber beneath the seismically monitored Pavlof volcano is still inconclusive although large amounts of recently acquired data remain to be analyzed. A geologic reconnaissance of the Shumagin Islands and the Adjacent Alaska Peninsula revealed Quaternary uplifted marine terraces and evidence for Holocene faulting. Both findings have severe implications for long-term tectonic activity and seismic hazards in the region of this seismic gap, portions of which are presently considered for off-shore hydrocarbon exploration and development. A critical analysis of th presently operating seimic data acquisition system reveals that a major change in remote sensing and central recording equipment is urgently needed for the Pavlof, Cold Bay, and Shumagin sections of the seismic array.

• Research Organization: Columbia Univ., Palisades, NY (USA). Lamont-Doherty Geological Observatory
• OSTI ID: 6389953
• Report Number(s): COO-3134-18
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580201* -- Geophysics-- Seismology & Tectonics-- (1980-1989)
ACCELERATION
ALEUTIAN ISLANDS
BERING SEA
EARTH CRUST
EARTHQUAKES
GEODETIC SURVEYS
GEOLOGIC FAULTS
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
GROUND MOTION
ISLANDS
MOTION
PACIFIC OCEAN
RISK ASSESSMENT
SEAS
SEISMIC EVENTS
SEISMIC P WAVES
SEISMIC WAVES
SEISMICITY
STRESS ANALYSIS
SURFACE WATERS
TECTONICS
VOLCANOES