Slip Partitioning in the Western U.S.

In the future I hope to put a few images in here from the various papers, but for now there's just a bunch of text.

Papers:

MIT 1985 Field Geophysics Course (C. H. Jones, M. R. Nelson, G. Abers, C. Decker, J. Hegley, R. Herrmann, M. Kohn, T. Madden, R. Manikkalingam, J. Matarese, D. Meinholz, P. Molnar, and C. Ruppel) and S. Biehler, A geophysical investigation of the northern Panamint Valley, Inyo County, California: Evidence for possible low-angle normal faulting at shallow depth in the crust, J. Geophys. Res., 92, 10427-10441, 1987.

Abstract. Gravity, magnetic, seismic refraction, electrical resistivity, and magnetotelluric measurements in northern Panamint Valley indicate that the alluvial and pluvial fill in the basin is thin and that basement under the valley floor lies at a shallow depth. Contours of the Bouguer gravity anomaly field do not define a low over the valley and do not mimic the mapped boundaries of alluvial fill. Electrical resistivity and seismic refraction measurements indicate that the playa in northern Panamint Valley is underlain by no more than about 200 m of sediment. This is consistent with the absence of any local lows in the Bouguer gravity anomaly field over the valley exceeding about 15 mGal in amplitude. There are no anomalies more than 50 nT in amplitude along an east-west magnetic profile across the valley floor. In contrast, upward continuations of magnetic profiles measured across basalt outcrops present at the valley margins still contain anomalies exceeding 75 nT in amplitude at heights of 300 m. Because the inferred thickness of sediment under a width between 5 and 9 km of the valley is less than 300 m, it is insufficient to conceal the signal expected from such magnetized basalt buried under the sediment. We interpret this finding as indicating that the valley is not underlain by basalt except at its margins, which implies that the west side of the valley has moved between 6 and 10 km away from the Panamint Range, in a direction parallel to the Hunter Mountain fault (~N55°ree;W). A balanced cross section across the valley constrains the required low-angle normal fault to be between 0.5 and 3 km beneath the valley floor.

Jones, C. H., and S. G. Wesnousky, Variations in strength and slip rate along the San Andreas Fault system, Science, 256, 83-86, 1992.

Abstract. Convergence across the San Andreas fault (SAF) system is partitioned between strike-slip motion on the vertical SAF and oblique-slip motion on parallel dip-slip faults, as illustrated by the recent Ms = 6.0 Palm Springs, Ms = 6.7 Coalinga, and Ms = 7.1 Loma Prieta earthquakes. If the partitioning of slip minimizes the work done against friction, the direction of slip during these recent earthquakes depends primarily on fault dip and indicates that variations in the normal stress and frictional coefficient (µ (mu)) exist among the faults. Additionally, including the location and geometry of active dip-slip faults adjacent to the SAF reduces fault slip rate estimates along the vertical trace of the SAF by about 50% in the Loma Prieta and by about 100% in the North Palm Springs segments.

Wesnousky, S. G., and C. H. Jones, Slip partitioning, spatial and temporal changes in the regional stress field, and the relative strength of active faults in the Basin and Range, Geology, 22, 1031-1034, 1994.

Abstract. When viewed with stress transformation laws and an idealized physical model, observations of oblique slip and slip partitioning in the Basin and Range (western United States) are interpreted to show that (1) separate regions with the same net extension direction are not necessarily characterized by the same regional stress field, (2) fault systems exhibiting partitioning where one of the faults is near vertical generally do not require temporal changes in the stress field to explain the disparate slip vectors on the adjacent faults, and (3) the relative strengths of active fault zones may vary by more than an order of magnitude.
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Last modified on Aug 3, 1995

Last modified at 00:04 MST on Dec 16, 1997