| Spatial and temporal patterns in seismicity contain valuable information about the processes that trigger earthquakes. Large errors in earthquake locations can obscure these patterns, making inference of triggering mechanisms difficult. The goal of this work is to use double difference relative relocation techniques and cross-correlated waveform data to discern accurately the faults and structures that experience seismic activity, and to understand the complex interactions between earthquakes and stress changes, fault properties, and other earthquakes. I investigate various triggering phenomena in one of the most extensive earthquake sequences in California, the 1992 Joshua Tree-Landers-Big Bear and 1999 Hector Mine earthquake sequences.; I examine 42 foreshocks of the 1999 Hector Mine earthquake and obtain precise relocations even for small events with low signal-to-noise ratios, and for the mainshock too. I find that the foreshocks and mainshock occur on different planes, but I cannot clarify the triggering effect of the foreshocks using Coulomb stress calculations.; I relocate ∼50,000 earthquakes in the 1992 Joshua Tree-Landers-Big Bear aftershock sequence. Aftershocks near the Landers and Joshua Tree mainshock planes show that complexity at the surface continues at depth. Temporary deepening of the maximum depth of aftershocks suggests velocity-weakening behavior initiated by mainshock slip. Aftershocks near the Big Bear mainshock define numerous conjugate planes. High values of friction, 0.35–0.75, inferred on these planes suggest that the active faults are immature.; The aftershock locations provide compelling evidence of earthquakes triggered by pore fluid changes. I find the signature of the pore fluid effect, an anomalously protracted aftershock sequence, within the Johnson Valley-Homestead Valley fault jog following the Landers earthquake. Coulomb stress calculations suggest that the poroelastic effect generates ∼0.3MPa of Coulomb stress. Investigating patterns in the aftershocks, I find that poroelastic stress transmission is a less likely triggering mechanism than fluid infiltration or pore space compaction.; Finally, I use precise earthquake locations to understand temporal changes in stress using the formulation of Dieterich (2000). Following Landers earthquake stress decreased on certain Joshua Tree faults but not others. Also, a sequence of earthquakes in 1996 likely increased stress on the future Hector Mine hypocenter. |
