Earthquake rupture processes and recurrence, seismicity and thermal modeling: Several studies of how, where and when earthquakes occur

This dissertation contains several studies of different aspects of earthquake occurrence. The first two papers explore details of the rupture process of three large earthquakes. Using broadband teleseismic body waves we inverted for the mechanism(s), seismic moment, fault plane orientation and spatial distribution of slip of these earthquakes. The study of the 1991 M{dollar}rmsb{lcub}w{rcub}=7.7{dollar} Valle de la Estrella earthquake gives insight in the tectonic setting of Costa Rica. This back-arc thrusting event appears to have ruptured the northern end of the North Panama Deformed Belt. A strike slip zone that cuts across Costa Rica may be an incipient plate boundary, isolating an independent Panama Block. The 570 km deep M{dollar}rmsb{lcub}w{rcub}=7.6{dollar} Fiji Island and 660 km deep M{dollar}rmsb{lcub}w{rcub}=8.2{dollar} Bolivia earthquakes of 1994 are the first large deep earthquakes permitting a study with high quality broadband data. In spite of the detailed pictures obtained for their ruptures and some observable differences with shallow (brittle failure) earthquakes, the physical mechanism causing deep earthquakes remains elusive.; The third and fourth chapters look at the larger scale picture of patterns in seismicity. Using a model based on the physics of static dislocations and the principle of fault segmentation we generate a synthetic earthquake catalog for the San Andreas and San Jacinto Faults in California, that is long enough to calculate recurrence statistics. The model reproduces observed seismicity over four orders of magnitude and is consistent with geologic and paleoseismic data. Segment interaction leads to much more irregular recurrence than generally assumed in seismic hazard analyses, and irregularity decreases with increasing earthquake magnitude. Motivated by this, the longest and most complete historical and paleoseismic catalogs were reanalyzed. Large irregularity was found even for M {dollar}ge{dollar} 8 earthquakes.; The final chapter describes a present day three-dimensional thermal model of the Mendocino Triple Junction, based on its well-documented kinematic history. The thermal model agrees with large scale features imaged using seismic tomography, but needs further adjustments to fit observed surface heatflow. Thermal modeling of this complex area can yield insight in the distribution of seismicity and crustal deformation.