Jaume, S.C., 1994, Earthquakes in an evolving stress/strain field: New York City, New York, Columbia University, Ph.D. dissertation, 261 p.
In this thesis changes in the nature of seismicity are examined in the context of changes in the stress/strain field occurring as part of the earthquake process. The history of earthquake recording in Northern Pakistan, central California, and the Alaska-Aleutian subduction zone is examined to discriminate between artificial and natural seismicity changes. The earthquake process in central California and along the Alaska-Aleutian subduction zone is quantified by changes in the rate of seismic strain release with time. In central and southern California the earthquake process is examined in the context of a stress field changing in response to both earthquakes and long-term strain accumulation. A Coulomb failure function, which takes into account both shear and normal stress, is used to estimate the effect of the changing stress field on seismogenic faults. A decrease in seismicity coincident with the impounding of the Tarbela reservoir in northern Pakistan is most likely an artifact of a change in seismic network operation. In central California changes in the rate and location of moderate (5.5 ? M > 7.0) earthquakes are found to be consistent with a model of the evolution of the stress field due to the accumulation and release of strain in large and great earthquakes. This model explains both the timing and location of increases and decreases in seismicity. In southern California, the Joshua Tree-Landers-Big Bear earthquake sequence of April - June 1992 moved the San Bernadino and Coachella Valley segments of the San Andreas fault towards failure and the Mojave segment away from failure. If fluid flow occurs, the San Bernadino segment will move even closer to failure with time. The rate of seismic moment release in M ? 6.0 shallow earthquakes has accelerated in the last decade in the Shumagin Islands segment of the Alaska-Aleutian subduction zone. Similar changes in the rate of seismic moment release preceded previous great earthquakes in 1957 and 1964. In addition, an outer-rise earthquake showing arc-normal compression, a proposed intermediate-term seismic precursor, occurred in July 1990, the first such earthquake observed along the Alaska-Aleutian subduction zone.
Theses and Dissertations