| Integrating
Seismological Studies of Crustal Structure in the northern California
Coast Ranges to Construct a Regional 3D Strain Model |
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| Gavin P. Hayes | ||
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 Base map showing shear zones indetified through correlation of receiver functions and tomography model. |
The Coast
Ranges of California has been the target of a number of recent
seismological studies aimed at constraining various aspects of crustal
architecture. The combination of techniques used provides a suite of
complimentary constraints; the active source Mendocino seismic
experiment gave 2D velocity data and delineated interfaces from
reflectivity, while tomography provided a smoothed 3D velocity picture.
Receiver function studies have characterized crustal interfaces and
provide information on the nature of the velocity contrasts across
these interfaces. This latter information is key in determining the way
in which processes driven by the passage of the Mendocino Triple
Junction have driven crustal evolution of the Coast Ranges. Combining
the results of these various studies, we test models of thickening and
subsequent thinning of the crust in response to the Mendocino Crustal
Conveyor. Specifically we use crustal structure models from receiver functions generated at a number of stations in the region, combined with the 3D tomography of the area, to develop a model of crustal architecture over the entire Coast Ranges. Analyzing these results within the framework of the Mendocino crustal conveyor model allows us to move beyond simply describing the structure; rather it allows us to develop a 3-D model of present-day crustal strain that provides constraints on mechanical properties of the Coast Ranges crust, where shear zones develop within that crust, and the role they may play in the evolution of the San Andreas Fault system. Our results show that the location of vertical shears indentified by producing strain and velocity maps for layers within the crust correlate well with the northern extensions of the Hayward Fault System. The western horizontal shear may indicate a link between these faults and the San Andreas Fault further west, while the eastern horizontal detachment is an indication of a decoupling of the shallow and deep crust. This latter effect may mask the geodetic signiture of the thickening and thinning at depth. Related topics: Using Receiver Functions to Analyze Rapid Transitions in Crustal Structure and Deformation in Northern California  Cross sections through velocity grids computed over the Coast Range area for distinct layers in the crust. Cross-sections in plate motion direction, separated by 30km starting from the coast of California and moving east. |
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 Interpretation of shear zones shown above, and their relationship with fault systems in Northern California. |
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© 2003 Pennsylvania State University
