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Open-File Report 00-219

Preliminary Potential-Field Constraints on the Geometry of the San Fernando Basin, Southern California

By V.E. Langenheim, A. Griscom, R.C. Jachens, and T.G. Hildenbrand

Thumbnail of and link to report PDF (128 kB)Abstract

Gravity and magnetic data provide new insights on the structural underpinnings of the San Fernando Basin region, which may be important to ground motion models. Gravity data indicate that a deep basin (>5 km) underlies the northern part of the San Fernando Valley; this deep basin is required to explain the lowest gravity values over the Mission Hills thrust fault. Gravity modeling, constrained by well data and density information, shows that the basin may reach a thickness of 8 km, coinciding with the upper termination of the 1994 Northridge earthquake mainshock rupture. The basin is deeper than previous estimates by 2 to 4 km; this estimate is the result of high densities for the gravels of the Pliocene-Pleisocene Saugus Formation. The geometry of the southern margin of the deep basin is not well-constrained by the gravity data, but may dip to the south. Recently acquired seismic data along the LARSE (Los Angeles Regional Seismic Experiment) II profile may provide constraints to determine the location and attitude of the basin edge. Gravity and aeromagnetic models across the eastern margin of the San Fernando Valley indicate that the Verdugo fault may dip to the southwest along its southern extent and therefore have a normal fault geometry whereas it clearly has a thrust fault geometry along its northern strand.

First posted June 21, 2000

For additional information, contact:
Geology, Minerals, Energy, and Geophysics Science Center
U.S. Geological Survey
345 Middlefield Road, MS 901
Menlo Park, CA 94025-3591

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Suggested citation:

Langenheim, V.E., Griscom, A., Jachens, R.C., and Hildenbrand, T.G., 2000, Preliminary Potential-Field Constraints on the Geometry of the San Fernando Basin, Southern California: U.S. Geological Survey Open-File Report 00-219, 22 pp.,




Geologic Setting

Gravity, Aeromagnetic, and Physical Property Data

Discussion of Potential-Field Anomalies and Modeling Results

Discussion and Conclusions


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