InSAR ANALYSIS OF THE 2008 MOGUL EARTHQUAKE: A STRIKE-SLIP EVENT SUGGESTING INCIPIENT WALKER LANE STYLE DEXTRAL FAULTING THROUGH RENO, NEVADA

A swarm of small magnitude (M 1-M 3), shallow (< 2 km) earthquakes began on February 28, 2008 near Mogul, 10 km west of Reno, Nevada. The swarm continued for two months, producing several thousand events and culminating in an M 4.7 (M_w 5.0) main event on April 25, 2008. An InSAR analysis detected measureable ground deformation associated with the main event, the smallest event detected with InSAR in the Basin and Range.

We analyzed 19 descending InSAR pairs and 13 ascending pairs using data obtained from the WInSAR and GeoEarthscope archives. Six descending and six ascending interferograms were selected for stacking and synthetic forward-modeling using the University of Miami program Geodmod. Interferograms delineate a well-defined northwest-striking fault trace at least 8 km in length. As much as 2-2.5 cm of radar LOS change was found within a 5-7 km radius of the main M 4.7 epicenter, with prominent LOS-up lobes positioned to the east and west of the epicenter on the respective descending and ascending pairs, an InSAR deformation pattern consistent with dextral strike-slip deformation. Forward modeling of the InSAR-detected ground deformation indicates that the best-fit fault parameters define a 20-40 cm displacement on a N45W dextral fault surface that is 4-5 km in length, 1-5 km in width, and at a depth of 1-1.5 km. As much as 4 cm of right-lateral displacement occurred across the surface fault trace, consistent with GPS data (Blewitt et al., 2008).

The results provide new insights into the contemporary tectonics of the greater northern Walker Lane region. The earthquake occurred on a previously unknown, northwest-striking, concealed fault within the Reno basin at the northern end of the Sierra Nevada block, an area of east-west extensional faulting lying to the west of the Walker Lane. InSAR modeling clearly defines a dextral fault that exhibited as much as 4 cm of right-lateral surface displacement during the event. This faulting mechanism is unique for the Reno basin but it is consistent with the orientation and kinematics of major Walker Lane structures to the north and east of Reno. We believe the Mogul event was consistent with regional Walker Lane dextral shear motion, suggesting the initial encroachment of Walker Lane style faulting into the previous extensional domain of the Reno basin.