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www.solid-earth-discuss.net/3/839/2011/
doi:10.5194/sed-3-839-2011
© Author(s) 2011. This work is distributed
under the Creative Commons Attribution 3.0 License.
Constraining fault interpretation through tomographic velocity gradients: application to Northern Cascadia
Department of Geosciences, The University of Tulsa, Tulsa, Oklahoma, USA
Abstract. Spatial gradients of tomographic velocities are seldom used in interpretation of subsurface fault structures. This study shows that spatial velocity gradients can be used effectively in identifying subsurface discontinuities in the horizontal and vertical directions. Three-dimensional velocity models constructed through tomographic inversion of active source and/or earthquake traveltime data are generally built from an initial 1-D velocity model that varies only with depth. Regularized tomographic inversion algorithms impose constraints on the roughness of the model that help to stabilize the inversion process. Final velocity models obtained from regularized tomographic inversions have smooth three-dimensional structures that are required by the data. Final velocity models are usually analyzed and interpreted either as a perturbation velocity model or as an absolute velocity model. Compared to perturbation velocity model, absolute velocity model has an advantage of providing constraints on lithology. Both velocity models lack the ability to provide sharp constraints on subsurface faults. An interpretational approach utilizing spatial velocity gradients applied to northern Cascadia shows that subsurface faults that are not clearly interpretable from velocity model plots can be identified by sharp contrasts in velocity gradient plots. This interpretation resulted in inferring the locations of Tacoma Fault, Seattle Fault, Southern Whidbey Island Fault, and Darrington Devils Mountain fault much clearly. The Coast Range Boundary Fault, previously hypothesized on the basis of sedimentological and tectonic observations, is inferred clearly from the gradient plots. Many of the fault locations imaged from gradient data correlate with earthquake hypocenters indicating their seismogenic nature.
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Notice on Discussion StatusCitation: Ramachandran, K.: Constraining fault interpretation through tomographic velocity gradients: application to Northern Cascadia, Solid Earth Discuss., 3, 839-856, doi:10.5194/sed-3-839-2011, 2011. Bibtex EndNote Reference Manager XML
