A major problem in structural geology and tectonics today is the so called “heat-flow paradox” on the San Andreas (SAF) fault where little agreement exists on whether this plate boundary is weak or strong . Simply stated, a conspicuous local heat flow anomaly should be observed on the SAF due to repeated earthquakes if standard laboratory-based frictional strengths are used to generate frictional heat; however, no such localized anomaly has been observed. A possible solution to this problem is that the SAF is in fact a weak fault and laboratory-based friction studies do not apply. The study of frictional melting on faults (producing so called pseudotachylytes ) has the potential to resolve this weak versus strong fault debate. Moreover, the study of the chemistry of pseudotachylytes can also shed light on the chemical and physical conditions during earthquakes, since substantial frictional heating only occurs during earthquakes. The study of frictional heating on faults is therefore ultimately motivated by a desire to understand earthquakes.
References
O’Hara, K., 2004. Paleo-stress estimates on ancient seismogenic faults based on frictional heating of coal. Geophysical Research Letters, 31, L03601.
Allen, J., O’Hara, K. and Moecher, D. P., 2003. Structural geometry and thermal history of pseudotachylytes from the Homestake shear zone, Sawatch Range, Colorado. in Erslev, E. and Magloughlin, J. (Eds.) Geological Society of America annual field trip guide, p. 1-19, Denver meeting, Colorado.
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and Sharp, ZD, 2001. Oxygen isotopic composition of natural and artificial pseudotachylytes, Earth Planet. Science Letters. 84, 393-406
O’Hara, K. D., 2001. A pseudotachylyte geothermometer.
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O’Hara, K. D
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and Sharp, ZD, 2001. Oxygen isotopic composition of natural and artificial pseudotachylytes, Earth Planet. Science Letters. 84, 393-406

O’Hara, K, D.1992, Major and trace element constraints on the petrogenesis of a faultrelated pseudotachylyte, western Blue Ridge province, North Carolina.
Tectonophysics , 204, 279-288.