Receiver Functions and Tomography Study along the Monterey Micro-Plate and Isabella Anomaly

Paul A. Cox, Igor Stubailo, & Paul M. Davis

In Preparation 2014, SCEC Contribution #2060

Two hypotheses were tested on the origin of the ‘Isabella tomographic anomaly,’ which has been interpreted as either a lithospheric delamination (Ducea and Saleeby, 1998) or a remnant of the Farallon plate possibly attached to the Monterey micro-plate (Wang et al., 2013). P-wave receiver functions and tomography based on teleseismic events recorded by 41 stations were used to construct a simple geometry tomographic model of the Isabella anomaly, and to test whether the Monterey micro-plate can be connected with the location of the anomaly. A rectangular plate model was used to fit the arrival-time residual pattern, and the best-fit model has its top surface located at 50km below the Great Valley. The model dips 65º toward the Sierra Nevada with 100 km thickness. Top and bottom surfaces of the Monterey micro-plate oceanic crust were modeled as a negative-positive dipole receiver function signals. Such dipoles are observed around 10 km below the Moho at the Coast Ranges. These P-to-S converted phases from the top of the oceanic crust could also be traced from the Coast Ranges to the Great Valley where the top surface of the tomographic model is located. The combined results of the receiver functions and tomography suggest that the partially subducted Monterey micro-plate or an unrelated Farallon slab segment extends east beyond the San Andreas fault and that the initially low angle of subduction in the west increases its dip east below the Great Valley.

Cox, P. A., Stubailo, I., & Davis, P. M. (2014). Receiver Functions and Tomography Study along the Monterey Micro-Plate and Isabella Anomaly. Bulletin of the Seismological Society of America, (in preparation).