Heat flow near major strike-slip faults in California

Abstract

An experiment to measure heat flow in the vicinity of major strike-slip faults was begun in 1965, since near seismically active faults a significant amount of strain energy might be converted to heat by means of dissipative processes operating during fault slippage. Calculations based on the Gutenberg-Richter seismic energyearthquake magnitude relation and the probable occurrence of two 8-magnitude earthquakes per century along the length of the San Andreas fault suggested that if the amount of energy converted to heat was at least as great as that appearing as seismic waves [Bullard, 1954], and depending on fault geometry, a measurable heatflow anomaly could exist near the trace of a major fault. The existence or nonexistence of a measurable heat-flow anomaly associated with large faults permits limits to be set on the average frictional stresses acting across fault planes 7924

An Analysis of thermal data from the vicinity of Cajon Pass, California

“…The overall quality of the latter data is comparable to that of our own, except that Henyey and Wasserburg (1971) typically measured many more thermal conductivities for a given well than we did. Our choice of fewer samples per well was dictated by a number of practical considerations.…”

“…For completeness sake, heat flows previously published by Henyey and Wasserburg (1971) are also presented in Table 1. The overall quality of the latter data is comparable to that of our own, except that Henyey and Wasserburg (1971) typically measured many more thermal conductivities for a given well than we did.…”

“…The primary scientific goal of this well is to provide data bearing on the fact that there is no observational evidence for a heat-flow anomaly over the San Andreas fault in spite of experimental evidence for high friction, a paradox (Henyey, 1968;Brune and others, 1969;Henyey and Wasserburg, 1971;Sass, 1973, 1980). Interpretation of the heat flow from the existing 1.8 km well at this site is complicated by the structure and Pleistocene -Holocene tectonic history of the Transverse Ranges (Lachenbruch and others, 1986a, b).…”

Scientific drilling into the San Andreas fault and site characterization research: Planning and coordination efforts. Final technical report

“…A "weak" fault is one whose strength is on the order of the stress relieved by an earthquake (c 20 m a ) while a "strong" San Andreas would have a substantially greater strength, on the order of 50-100 MPa (e.g., Lachenbruch and McGarr, 1990). Support for a weak San Andreas fault came originally from the absence of frictionally generated heat in shallow boreholes along the San Andreas fault (e.g., Brune et al, 1969;Henyey and Wasserburg, 1971;Sass, 1973, 1980). Arguments for high shear stresses on the San Andreas and other active faults come primarily from models for the frictional strength of faulted rock, using laboratorydetermined coefficients of friction, p, ranging from 0.6 to 0.9 (Byerlee, 1978) and assuming hydrostatic pore pressures (e.g., Sibson, 1974Sibson, , 1983Brace and Kohlstedt, 1980).…”

The Cajon Pass Scientific Drilling Experiment: Overview of phase 1

“…Approximately 100 measurements of conductive heat flow near the San Andreas fault have detected no frictionally generated heat (Henyey, 1968, Brune et al, 1969Henyey and Wasserburg, 1971;Lachenbruch and Sass, 1973;, implying that the average shear stress acting on the San Andreas fault is less than about 20 MPa. This result conflicts with the average shear stresses that would be inferred from application of MohrCoulomb theory using laboratory-derived coefficients of friction (Sibson, 1974) and with in situ stress measurements (McGarr and Gay, 1978;Brace and Kohlstedt, 1980;McGarr et al, 1982;Pine et al, 1983;Zoback and Healy, 1984).…”