Historical accounts of earthquakes show a high degree of spatial variability and uncertainty associated with ground motion. For this reason, historical data are not often used as input for earthquake hazard assessment. Regionally, however, earthquake ground motion is related by the concept of attenuation. Seismic hazard assessment techniques usually rely on catalogues of earthquake epicenters together with empirical attenuation relationships to define the seismic hazard for a particular region. Such techniques, however, overlook local variations in ground motion associated with actual earthquakes. A technique for seismic hazard assessment that includes historical data using the theory of regionalized variables and linear estimation techniques best represents ground motion dichotomy. Modified Mercalli intensity observations for the period 1930 through 1971 were treated as regionalized variables to define the seismic hazard for a region of Southern California centered around San Fernando. Despite variations in construction quality and individual sensitivity to ground motion, intensity values associated with seventy percent of the earthquakes that occurred during this period, for which at least five intensity observations were recorded, were accurately treated as regionalized variables. A Gumbel analysis computed using spatially regular data sets developed from these intensity values precisely associated high hazard regions with active faults near San Fernando. Other earthquake ground motion data can also be treated, accurately, as regionalized variables. These data include peak instrument recordings of spectral acceleration, velocity, and displacement. Moreover, response to earthquake ground motion at discrete frequencies, as recorded by response spectra, is also regionalized. These data, therefore, are accurately estimated using kriging. Fundamentally, because earthquake ground motion is shown to be a regionalized variable, all aspects of regionalized variables theory are applicable for these data, including disjunctive kriging, conditional simulation, and co-kriging.

Numerous observations suggest that the elastic description of the subduction earthquake cycles is incomplete. Micro-seismicity is recorded in active margins that are believed to be locked, while peculiar extensional earthquakes occur in convergent plate boundaries following tsunami earthquakes. The morphology of active margins, which evolves on time scales of 100s of kyr, shows similarities to ongoing deformation documented over 10–100 yrs and the coastal domains of Cascadia, Chile, and other subduction zones record long-term uplift. Lastly, the very threshold where faults break and earthquake nucleate has been vigorously debated for years. In this thesis, I combine various geophysical tools to study short- and long-term processes and learn how their interplay can shape the deformation field imparted by earthquake cycles, mainly in the upper plate of subduction zones. In the first chapter, I analyze surface heat flow measurements taken in the proximity of the southern Dead Sea fault to demonstrate its friction is 0.27±0.17. In the second chapter, I compute an updated horizontal and vertical GNSS velocity field for Bangladesh, Myanmar, and adjacent regions. I show that the Kabaw fault, which lies east of the primary thrust system, is accommodating shortening that was initially attributed to the main thrust and demonstrate that the Indo-Burma subduction is locked, converging, and capable of hosting great megathrust events. In the third chapter, I use thermomechanical models to show that reducing the dip angle of a subducting slab, on a timescale of millions of years, can result in extensional fault failure above a megathrust earthquake on timescales of seconds to months. In the fourth chapter, I demonstrate how the buildup of interseismic elastic stresses brings sections of the forearc into compressional failure, which yields irreversible uplift of the coastal domain per evidence from Chile. Finally, I argue that combining short- and long-term processes into subduction zone models can better mitigate tsunami and earthquake hazards. I show how long-term reduction of slab dip angle could culminate in devastating tsunamis. I argue that the collection of long-term uplift records of upper plates or volcanic arc migration can constrain slab dip changes and so may identify areas with increased tsunami potential. In addition, upper plate irreversible deformation should be introduced to earthquake rupture models as these may hold significant implications for understanding and mitigating earthquake hazards.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1981. / Microfiche copy available in Archives and Science. / Bibliography: leaves 273-291. / by Mai Yang. / Ph.D.