Exotic seismic sources: Nearly identically repeating events and non-double-couple earthquakes

This dissertation investigates two exotic seismic sources: non-double-couple earthquakes and nearly identically repeating events. Using non-double-couple earthquakes, I aim to better understand the connection between earthquake production and geothermal/magmatic systems. I focus on a 100-km-wide circular area centered at the Long Valley caldera and comprehensively search for events greater than M3.5 since 1993 with significant coseismic volume changes. Using three-component broadband digital waveforms at regional distances, I solve for four different source models: DC, deviatoric (DC+CLVD), DC+isotropic, and full moment tensor (DC+CLVD+isotropic). Using the F test as a statistical aid, the best model is determined for each event. I then conduct stability tests to determine the robustness of the focal mechanism solutions and isotropic components. The results show that fluid-influenced earthquakes in the magnitude range studied are quite rare in the Long Valley volcanic region. Of 33 high quality events, 28 are best characterized by a simple DC source model, four by a DC+isotropic source model, and one by a full moment tensor model.; Nearly identically repeating events, or repeating earthquakes (REs), are sequences of events that have nearly identical waveforms and are interpreted to represent fault asperities driven to failure by loading from aseismic creep on the surrounding fault surface at depth. REs are identified using a combination of cross-correlation and spectral coherence techniques. I investigate the location of these REs along faults in central California to determine which faults exhibit creep and to examine the spatio-temporal distribution of this creep.; Between March 1984 and May 2005, I investigate the occurrence of REs at both the juncture of the San Andreas and southern Calaveras-Paicines faults and west of the creeping section of the San Andreas fault within the Coast Range. REs in these areas reflect a heterogeneous creep distribution along the fault plane with significant variations in time. Creep at depth appears to mimic the behaviors seen of creep on the surface in that evidence of steady slip, triggered slip, and episodic slip phenomena are also observed in the RE sequences. Additionally, REs are sometimes observed to occur in bursts, suggesting that these REs are not produced by steady aseismic creep of the surrounding fault surface.; I also investigate RE sequences on the central Calaveras fault to investigate postseismic deformation after the 1984 M6.2 Morgan Hill earthquake. Both the accelerated slip transients due to the earthquake as well as the return to interseismic background creep rates can be imaged from our dataset. A comparison between the regions of the fault that ruptured coseismically and the locations of the REs show that the REs preferentially occur in areas adjacent to the coseismic rupture. A mechanical forward model of the subsurface slip distribution 6 months after the mainshock is compared with the observed surface electronic distance meter (EDM) line length changes between stations near the Morgan Hill rupture area. Our modeling shows that RE data consistently underpredict the observed line-length changes, possibly due to the lack of REs, and thus RE-derived slip information, below the seismogenic zone and within the velocity strengthening portions of the fault.