Mantle control of plate boundary deformation
The seismic wavefield propagating along the recently instrumented Pacific-North American plate boundary (California) displays remarkable variation, with regional shear waves arriving at coastal stations up to 20 seconds earlier than equidistant stations in eastern California. Broadband modeling of this data reveals that coastal paths sample fast upper mantle typical of Miocene-aged ocean plate (>50 Km thickness). Inland paths sample slower uppermost mantle, with the seismic lithosphere, or lid, measuring less than 5 Km thick, characteristic of the Basin and Range extensional province. The boundary in the uppermost mantle between these provinces is sharp, expressing the juxtaposition of the stronger Pacific plate with weaker continental North America. The lid step coincides with regionally maximum dextral strain rates measured with GPS, suggesting the uppermost mantle modulates long term, regional-scale continental margin deformation and evolution.
Additional Information© 2001 American Geophysical Union. Manuscript Accepted: 11 July 2001; Manuscript Received: 9 March 2001. This work was supported under National Science Foundation grants EAR-9973191 to Melbourne and EAR-97-2508 to Helmberger. Caltech Seismological Laboratory Contribution #8762
Published - 2001GL013167.pdf