Seismicity of the Kodiak Island Region (1964-2001) and Its Relation to the 1964 Great Alaska Earthquake

Abstract

Earthquake relocation, first-motion, and waveform modeling studies of M >5.5 earthquakes are used to examine the seismicity associated with the Kodiak Island region since the 1964 great Alaska earthquake. Our results indicate that the most intense seismicity and moment release in this region occurred within the Pacific plate and along the plate interface of the southwestern edge of the Kodiak segment, where slip during the 1964 mainshock was less than 5 m. Few earthquakes have occurred within the North American plate. The intense seismicity correlates well with the northern edge of a zone of high plate interface coupling detected by Global Positioning System/geodesy studies. Our studies suggest that during 1964-1974, faulting within the Pacific plate was characterized by normal and normal-oblique faulting. However, since 1974 reverse-oblique faulting has become more common in the Pacific plate. Seismic moment release has been over 6 times greater in the Kodiak region than in the Prince William Sound-Cook Inlet region during the past 37 years. Unlike the Prince William Sound region, there is also a lack of down-dip migration of seismicity since 1964. Manuscript received 23 October 2001.