GEOPHYSICAL MONOGRAPH SERIES, VOL. 170, PP. 301-311, 2006
The strength of the San Andreas Fault: A critical analysis
The longstanding debate over the strength of the San Andreas fault arose because heat flow measurements failed to show a narrow
heat flow anomaly centered on the fault. The conclusion was that the shear stress on the fault cannot be larger than the stress-drops
of earthquakes, ∼10 MPa, as compared with the ∼100 MPa expected from laboratory values of rock friction. There are two issues:
1, Can the fault be shown to be weak independently from the heat flow interpretation? and 2, If it is weak, what is the mechanism
The bulk of stress measurements in California conflicts with the weak SAF hypothesis. They indicate that the SAF has a strength consistent with a friction coefficient of 0.6 comparable with that of the surrounding crust. Because a minor fault adjacent to the SAF has been found to be strong in an absolute sense, so must be the SAF. The exception is the creeping section of the fault, which appears to be weak. All schemes proposed to explain how the fault can be weak are either geologically implausible or are contradicted by observations. Thus the hypothesis fails on both counts. The problem seems to lie in the heat flow model, which assumes steady-state slip with conductive heat transfer, whereas heat is generated only at the time of large earthquakes, at a rate some 109 times larger. I propose that, as a result, heat transfer at depth is by advection of water, which spreads the heat laterally, producing the broad heat flow anomaly that is associated with the SAF.
Citation: Scholz, C. H. (2006), The strength of the San Andreas Fault: A critical analysis, in Earthquakes: Radiated Energy and the Physics of Faulting, Geophys. Monogr. Ser., vol. 170, edited by