Space-time seismicity of the Alaska-Aleutian Seismic Zone

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This study examines space-time patterns in the distribution of major earthquakes of the Alaska-Aleutian seismic zone. The evidence suggests that major earthquakes of this zone tend to progress in time from east to west. Extrapolation of past trends indicates that a major Alaska-Aleutian earthquake may occur near 56°N, 158°W between about 1974 and 1980. Three kinds of evidence indicate that earthquakes of about magnitude 7.7 and larger should be used to identify space-time earthquake patterns in the Alaska-Aleutian seismic zones. (1) Space-time graphs of earthquakes of about magnitude 7.7 and larger show strong linear trends. (2) Aftershock zones of successive large earthquakes (M ≥ 7.7) are approximately adjacent. (3) The direction of fracture propagation is generally away from the focal zone of the previous adjacent large earthquake, which suggests that the concentration of stress before the event was greatest near the region of the adjacent earlier earthquake. Since this pattern is reasonably consistent, the linear trends of large earthquakes in this seismic zone are probably caused by some physical phenomena rather than some unusual chance distribution. The space-time distribution of the U.S. Coast and Geodetic Survey (CGS) epicenters for 1961–1967 suggest that past trends will continue. The epicenters show a distinct seismicity gap in the region predicted for the next major Alaska-Aleutian earthquake. In the past, such gaps have often occurred before major earthquakes. A suggestion of linear trends is also found in the space-time distribution of large earthquakes in some other circum-Pacific seismic zones. Although present information of these other areas is not sufficient for making predictions, there are at least two regions that should be monitored and studied further. The Commander Islands and the northern Kuriles both appear to be likely locations for future large earthquakes.