Understanding Slip on Triggered Faults in the Presence of a Large Regional Deformation

The Mw 7.2 El Mayor-Cucapah (EMC) earthquake occurred on April 4th 2010 with an epicenter 48 km SSE of Calexico, CA. Slip associated with the EMC event is on the order of 3 meters, whereas slip on the faults north of the rupture is measurable in centimeters. Unmanned Air Vehicle Synthetic Aperture Radar (UAVSAR) data has been collected in the Salton Trough, north of the US border since 2009, and has been flown six times since the EMC event in order to monitor change in the area. The resulting interferograms encompass the northern most extent of the main rupture, as well as the surrounding area north of the border. The interferograms show slip after the EMC event where there had previously been no evidence of faulting. The displayed slip corresponds to the Yuha fault, a recently discovered NE trending sinistral fault with 4.5 cm of displacement and a subtly expressed fault scarp. The large signal from the EMC event,-superimposed over the much smaller signals from faults to the north-east, make it difficult to infer details of behavior on the responding faults. Using QuakeSim tools it is possible to test the level to which we can invert for slip on the corresponding faults north of the rupture. We used QuakeSim's forward dislocation modeling program called Disloc to create a UAVSAR equivalent interferogram of the published four fault mainshock slip parameters and slip from the Yuha Fault. We then used the Simplex component of QuakeSim to model elastic inversions of crustal deformation from the simulated interferograms. The series of models tested how well one can invert the synthetic data for small slips when there is a large regional deformation gradient from the main fault. One variation consisted of modeling fixed parameters for the main fault while varying different parameters for the Yuha fault such as strike, location, and strike slip and dip slip motions. The next step is to invert the observed UAVSAR interferogram for characteristics of slip along the Yuha fault. The QuakeSim tools make data accessible for scientists at every level to garner a better understanding of active tectonics earthquake processes.