geodynamics | research group

*Using Receiver Functions to Analyze Rapid Transitions in Crustal Structure and Deformation in Northern California*		Back
		Gavin P. Hayes

Receiver functions at FREY, plotted with back azimuth. Main features are identified, indicative of a low velocity zone and moho dip.	The crust of the Northern California Coast Ranges has undergone significant deformation over the past 20Ma in response to the northward migration of the Mendocino Triple Junction. A pattern of crustal thickening and thinning consistent with the Mendocino Crustal Conveyor model (Furlong and Govers, 1998) has been identified in previous studies, which suggest rapid thinning of the crust occurs in the region of the FREY seismic station. Here we perform a detailed receiver function analysis at broadband seismometers acrosss the Coast Ranges in an attempt to constrain where major thinning occurs and its affect on the crustal structure local to these stations. Detailed receiver function analysis suggest the presence of dip on the moho beneath FREY, and a flat Moho at CVLO and HOPS. Moving from CVLO in the north to HOPS in the south, the crust thins from ~35km to ~18km thickness over a distance of less than 100km, apparently localized around FREY. These results are matched by local tomography studies (left), which identify the thickest crust immediately to the north and east of FREY. Cross-sections through the tomography cooborate a dipping Moho. Receiver functions also suggest the presence of melt in the lower crust at FREY and HOPS, where particularly high values of Poisson's Ratio are seen. These observations likely correspond to large nagative amplitude features in the raw receiver functions, probably due to the low S-wave velocity of melts, and agree with results from high-density seismic reflection surveys shot in the area by the MTJSE group (Levander et al., 1998). Related topics: *Integrating Seismological Studies of Crustal Structure in the northern California Coast Ranges to Construct a Regional 3D Strain Model*
Grid search over layer thickness, poisson's ratio, strike and dip to find the best fitting combination of parameters for receiver functions at FREY.
Tomography at 25km depth in the area of FREY, annotated with inferred dip on the moho. Cross-sections show approximate location of receiver function conversions on a dipping moho.

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