Graduate Thesis Or Dissertation
 

Crustal structure and faulting of the Gulf of California from geophysical modeling and deconvolution of magnetic profiles

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  • Using gravity, magnetic, bathymetric and seismic refraction data, I have constructed a geophysical cross-section of the central part of the northern Gulf of California. The section exhibits a crustal thickness of 18 km and features an anomalous block of high density lower basement (3.15 g/cm³) which probably resulted from rifting processes during the opening of the Gulf. The magnetization of the upper basement ranges from 0.0005 to 0.0030 emu/cm³. Three different layers of sediments are modeled, ranging from unconsolidated (1.85 g/cm³) to compacted (2.50 g/cm³). I present a deconvolution method for automated interpretation of magnetic profiles based on Werner's (1953) simplified thin-dike assumption, leading to the linearization of complex nonlinear magnetic problems. The method is expanded by the fact that the horizontal gradient of the total field caused by the edge of a thick interface body is equivalent to the total field of a thin dike. Statistical decision making and a seven point operator are used to insure good approximations of susceptibility, dip, depth, and horizontal location of the source. After using synthetic models to test the inversion method, I applied it to the Northern Gulf of California using data collected in 1984 by the Continental Margins Study Group at Oregon State University. Fault traces, computed by the deconvolution, are plotted on a map. The faulting pattern obtained is in good agreement with that proposed by other workers using other methods. The depths to the top of the faults range from 4 to 5 km in the eastern part of the Gulf, where they may be interpreted as the top of the structural basement. Deeper estimates are obtained for the western part of the Gulf.
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