Seismic investigation of recent events in the Mendocino Triple Junction region: Stress release and orientation within the Gorda plate and along the Mendocino fault
The Mendocino Triple Junction (MTJ) is defined by the intersection of the San Andreas fault zone, Mendocino fault, and Cascadia subduction zone as well as the North American plate, Gorda plate, and Pacific plate. This region has a history of strong earthquakes of magnitude 6.5 or greater, with much of the seismicity within the Gorda plate. I investigate recent earthquakes in the MTJ region. Data for this study has been collected as digital data downloaded from the North California Earthquake Data Center (NCEDC) from the Berkeley Digital Seismic Network (BDSN) for years 1992 to 2002. I modeled each event for focal mechanism and total moment. The results have been combined with larger events with known focal mechanisms and moment from the Harvard Centroid Moment Tensor (CMT) and NCEDC catalogs to reveal the overall state of stress for the region. I divide the events by magnitude and class of focal mechanism (thrust, strike slip, transpressive and normal) and plot the direction of moment as a function of the P-axis (maximum compressional stress). I find that the larger strike-slip events in the Gorda plate align with a P-axis that might be expected for motion along the San Andreas fault; smaller events align with an expected Mendocino fault orientation, and very few events have an orientation related to the Cascadia subduction zone. These results suggest that Gorda plate deformation is not presently relieving stresses associated with the Cascadia subduction zone, and that the state of stress release for the entire region is dominated by the Mendocino fault.
Theiner, Todd R, "Seismic investigation of recent events in the Mendocino Triple Junction region: Stress release and orientation within the Gorda plate and along the Mendocino fault" (2004). ETD Collection for University of Texas, El Paso. AAI1423700.