House, L.S., 1981, Studies of earthquakes and tectonics in the eastern Aleutians: New York City, New York, Columbia University, Ph.D. dissertation, 179 p., illust., maps.
This thesis contains several studies that, together, provide contributions to understanding several aspects of the geophysical and seismological manifestations of the subduction of lithospheric plates. The major seismologic manifestation, at least in terms of the release of energy, is that of the great earthquakes that result when portions of the subducting margins rupture. Typically, in the eastern Aleutians, 60 to 190 years elapse between repeated ruptures of a particular portion of the plate margin. This study finds high stress drops ((DELTA)(sigma) (DBLTURN) 650-900 bars) for both mainshocks of a distinctive sequence of earthquakes that occurred within the Shumagin Seismic Gap of the eastern Aleutians. The high stress drops of those earthquakes and the paucity of moderate size earthquakes within the gap are interpreted as long to intermediate term precursors to a great earthquake that is expected to occur there (although the probable time of occurrence of that earthquake can only be estimated as within the next several decades). The spatial and temporal distribution of moderate-size earthquakes, and their fault-plane solutions, as well as other geophysical data, provide more precise determination of the rupture process of a great earthquake that broke a 1000 to 1200 km long portion of the central and eastern Aleutians in 1957. Heterogenieties of both the subducting and overriding plates may have influenced the rupture and dimensions of that earthquake. Stresses within the descending slab of lithosphere probably result from many effects, one of which may be interaction between the plates at shallow depths that is punctuated by episodes of slip during great earthquakes. Stresses that arise from expansion of the downgoing plate as it is heated by the surrounding asthenosphere may have a large influence on the overall state of stress within some downgoing plates, such as the eastern Aleutians.
Theses and Dissertations