Modeling Events in the Lower Imperial Valley Basin

The Imperial Valley below the US-Mexican border has few seismic stations but many significant earthquakes. Many of these events, such as the recent El Mayor-Cucapah event, have complex mechanisms involving a mixture of strike-slip and normal slip patterns with now over 30 aftershocks with magnitude over 4.5. Unfortunately, many earthquake records from the Southern Imperial Valley display a great deal of complexity, ie., strong Rayleigh wave multipathing and extended codas. In short, regional recordings in the US are too complex to easily separate source properties from complex propagation. Fortunately, the Dec 30 foreshock (Mw=5.9) has excellent recordings teleseismically and regionally, and moreover is observed with InSAR. We use this simple strike-slip event to calibrate paths. In particular, we are finding record segments involving Pnl (including depth phases) and some surface waves (mostly Love waves) that appear well behaved, ie., can be approximated by synthetics from 1D local models and events modeled with the Cut-and-Paste (CAP) routine. Simple events can then be identified along with path calibration. Modeling the more complicated paths can be started with known mechanisms. We will report on both the aftershocks and historic events.