Comprehensive study of the seismotectonics of the eastern Aleutian arc and associated volcanic systems. Annual progress report, March 1, 1980-February 28, 1981

• Main Authors: Jacob, K. H., Davies, J. N., House, L.
• Format: Report
• Language: English
• Published: Columbia Univ., Palisades, NY (USA). Lamont-Doherty Geological Observatory 1981
• Subjects: Islands; Geologic Structures; Plate Tectonics; Aleutian Islands; 58 Geosciences; Seismic Events; Volcanism; Seismicity; Earthquakes; Tectonics 580201* > Geophysics > Seismology & Tectonics > (1980-1989); Alaska
• Online Access: https://doi.org/10.2172/6746222; https://digital.library.unt.edu/ark:/67531/metadc1197597/

Refined hypocenter locations beneath the Shumagin Islands seismic network of the eastern Aleutian arc, Alaska, provide for the first time conclusive evidence for a double-sheeted dipping seismic (Benioff) zone in this arc. This refined seismicity structure was obtained in the arc section centered on the Shumagin seismic gap. A thorough review of three seismic gaps in the eastern Aleutian arc shows a high potential for great earthquakes within the next one to two decades in the Shumagin and Yakataga seismic gaps, and a less certain potential for a large or great earthquake in the possible Unalaska gap. A tilt reversal was geodetically observed to have occurred in 1978/79 in the forearc region of the Shumagin gap and could indicate the onset of a precursory strain relief episode prior to a great quake. A comparative study of the Pavlof volcano seismicity with that of other recently active volcanoes (i.e., Mt. St. Helens) indicates that island-arc (explosive-type) volcanoes respond to small ambient, periodic stress changes (i.e., tides). Stress drop measurements from earthquakes on the main thrust zone indicate high stress drops within the seismic gap regions of the Aleutian arc and low stress drops outside the gap region.