This research measures precise differential arrival times between similar earthquakes earthquakes using waveform cross-correlation. These precise measurements are used to estimate accurate relative event locations. Rather than estimate absolute hypocentral location, the method solves for the vector position difference between earthquake hypocenters. In doing so one is able to reduce dramatically errors in earthquake locations. The technique is currently being extended to work with much larger data sets, up to ~100,000 earthquakes, using both a hierarchical inversion scheme. This capability to address a number of research issues, including: what is the origin of recently discovered seismicity streaks in fault zones? What is the state of stress in close proximity to major faults? What constraints can be placed on strain localization as a fault zone matures? What can we learn about the time-dependent nature of friction on faults at depth? How is seismicity related to regions of aseismic versus seismic slip?
