Graduation date: 1979

Geophysical surveys in the Gulf of California provided the data to construct contour maps of bathymetry, free-air anomalies and total field magnetic anomalies for the area north of 27° N. Major faults such as the Ballenas- Salsipuedes, Tiburón, Guaymas, and the South Cerro Prieto are clearly observable on these maps. Spectral analysis, using 2-D Fast Fourier Transform methods, of the magnetic anomalies north of 29° N, allowed the identification of at least three distinct magnetic source horizons. The shallowest depth magnetic horizon, with an average depth to the top of 3.1 km below sea level, is interpreted as the top of the magnetic basement. The intermediate depth magnetic horizon, with an average depth to the top of 5.3 km below sea level, may represent either a lithological discontinuity in continental crust, or a transition zone characterized by the intrusion of igneous rocks, faulting, and fracturing associated with rifling processes. Some lineaments observed in the contour map on this horizon are oriented about 15° counterclockwise from the expected orientation of faults. Other lineaments are almost perpendicular to those faults. The deepest magnetic horizon is not apparent at all locations. Computed depths to the bottom of the magnetized crust average 11.5 km below sea level. The depth to the bottom of the magnetic crust is interpreted as the depth of the Curie-point isotherm. Assuming a Curie-point temperature of 580°C and a thermal conductivity of 2.2 W/m °C, the calculated heat flow averages 114 mW/m². Using a two-dimensional Maximum Entropy Method (2DMEM) to obtain the power spectrum of the magnetic anomalies increased the horizontal spatial resolution of the depth determinations by a factor of 4. This method when used to compute the depth to the top of the intermediate horizon, shows an improvement in the delineation of structures. However, the other magnetic horizons and the depth to the bottom of the magnetic crust were not clearly observable using this technique. / Graduation date: 1988

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. / Graduation date: 1990

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