Comprehensive study of the seismotectonics of the eastern Aleutian arc and associated volcanic systems. Annual progress report, March 1, 1979-February 29, 1980

• Main Authors: Jacob, K. H., Davies, J. N., Sykes, L. R.
• Format: Report
• Language: English
• Published: Columbia Univ., Palisades, NY (USA). Lamont-Doherty Geological Observatory 1979
• Subjects: Research Programs; Probability; Volcanoes; Forecasting; Data; Stresses; Seismic Events 580201* > Geophysics > Seismology & Tectonics > (1980-1989); Earth Crust; Information; Aleutian Islands; 58 Geosciences; Graphs; Data Forms; Experimental Data; Islands; Numerical Data; Seismicity; Tectonics; Deformation; Earthquakes; Gulf of Alaska; Alaska
• Online Access: https://doi.org/10.2172/5731791; https://digital.library.unt.edu/ark:/67531/metadc1093810/

The modern and historic seismicity of the eastern Aleutian arc was thoroughly researched and shows clear evidence that the Shumagin Islands region of the arc has been ruptured at least partly by previous large or great earthquakes; has recurrence times for large earthquakes between 50 and 115 years; has presently the properties of a seismic gap, i.e., was not ruptured by a large or great earthquake for at least 76 years; shows a donut configuration of modest seismicity including high-stress-drop events around the rim of the expected rupture zone of a future large earthquake. From this combined evidence it is concluded that the likelihood for a large or great earthquake to occur within the Shumagin Island gap is high (about 50% probability) within the next decade and very high (about 80% to 90% probability) within the next three decades. This study includes detailed determinations of stress, stress-drop, and other source parameters of moderate earthquakes in the Shumagin islands gap, and similar results for the St. Elias earthquake near the Yakataga gap in the eastern Gulf of Alaska. Volcano seismicity, crustal deformantion, and P-residuals continue to be monitored and analyzed in the eastern Aleutian arc segment. 36 figures, 3 tables.