Seismotectonics, and the mechanics of faulting inferred from seismic body wave inversions.
Committee ChairWallace, Terry C.
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PublisherThe University of Arizona.
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AbstractSeismotectonics plays a very important role in global and regional tectonic studies. The study of earthquakes as tectonic processes is known as seismotectonics. Seismotectonics integrates the earthquake process into the broader framework of tectonic geologic processes. Understanding the earthquake process can, in turn, provide valuable constraints on tectonic setting. In this dissertation, I have used three seismological examples to understand the regional tectonics. Although these examples are from very different tectonic settings, they all show that seismology provides us a quantitative view of the kinematic movement of a certain tectonic region. Also, seismology is a unique way to study nuclear explosions, very non-tectonic related events. One of the main interpretive tools in seismotectonics is focal mechanisms. I used broad band seismic body waves to retrieve the focal mechanisms and source time functions. The technique includes Joint inversion of body waves from a group of stations and single station moment tensor inversion. In Chapter II, the strike-slip earthquakes in Sudan sequence indicate shear movement of an intra-continental transform fault. The aftershocks of this event imply a more complicated interaction in the continent than typically observed on the ocean floor. Old structures in a continent can have significant influence in the faulting process. The 1990 Iranian earthquake sequence (Chapter III) demonstrates another significant phenomena when convergence is oblique to the geologic structure, slip partitioning could occur. In NW Iran, a region of compressional tectonics, most of the earthquakes display reverse or thrust faulting. However the strike-slip mechanism events in 1990 Iranian earthquake sequence (including the mainshock) occur because the slip vector of the convergence between the Eurasian and the Arab plates is very oblique to the general structure in NW Iran. In addition to the usual reverse faulting along NW fault plane, there is also left-lateral motion to accomplish this oblique movement. Chapter IV provides an example of seismotectonics providing understanding to a non-tectonic related phenomenon--nuclear explosions. Almost all the underground nuclear explosions show some sort of non-isotropic component and this non-isotropic component can be interpreted as tectonic release. The extensive studies around NTS (Nevada Test Site) show this tectonic release is related to the regional stress regime. Our studies on Lop Nor test site of Chinese nuclear explosions show strong evidence for tectonic release. The type of the tectonic release is based on the size or yield, of the explosions. Smaller explosions generate mainly thrust faulting, while larger explosions are associated with strike-slip faulting.