Heat Flow near Major Strike-Slip Faults in Central and Southern California

Geophysics

Henyey, Thomas Louis ; Wasserburg, Gerald J.

University:California Institute of Technology

Department:Geological and Planetary Sciences

关键词: Geophysics;   

Others  :  https://thesis.library.caltech.edu/10795/1/Henyey_TL_1968.pdf

美国|英语

来源: Caltech THESIS

【 摘 要 】

Seventeen heat flow measurements have been made near theSan Andreas, San Jacinto, and Garlock faults of California in regions representative of several levels of seismic activity. Data from these measurements in conjunction with results of other heat flow investigations in central and southern California show no maxima directly attributable to the fault zones. This negative result along with stress-dropresults from earthquakes suggests an upper bound of the order of 200 bars for the absolute stress in the vicinity of the San Andreas fault. In addition, the average heat flow in the four regions investigated (San Bernardino Mountains - Lake Hughes, Anza, Hollister, and TehachapiMountains) is the same; the mean value of 23 determinations is 1.7 μcal/cm²/sec ± 0.1 s.d.

In the region between Lake Hughes and San Bernardino, presently seismically inactive but in the zone of rupture from the ~8 magnitude Fort Tejon earthquake, six measurements show no correlation with distance from the San Andreas fault. Near the San Jacinto fault in an area characterized by frequent medium magnitude earthquakes, determinations at 1 and 4 km from the fault are equalbut 20 per cent higher than a measurement 13 km to the west, but not appreciably different from a probable regional average 25 km to the east. Near Hollister where the San Andreas is actively creeping at a rate of several centimeters per year, a measurement 8 km east of the fault yields a flux twice as great as one 30 km to the west, butvalues at intermediate points suggest that this anomaly may reflect more the regional geology than the San Andreas fault alone. Finally, measurements across the historically inactive Garlock fault exhibit high fluxes near the fault in comparison with a determination 8 km to the north, but do not differ significantly from determinations in theMojave Block to the south.

In California, the major fault systems appear to lie in transition zones between blocks of crust characterized by Basin and Range heat flows -- Mojave Block and Salton Trough -- and blocks representative of normal continental heat flows -- Central Valley and the crustal strip between the San Jacinto-San Andreas fault system and the Pacific continental margin.