Editor's Summary
16 August 2007
Talc about friction
High rates of creep along parts of the San Andreas fault have been attributed to low fault strength associated with serpentinized rocks. This is problematic because the frictional strength of serpentine minerals is considered too high to account for any weakness. Diane Moore and Michael Rymer now report that talc — the soft magnesium silicate mineral familiar in its pure form as talcum powder — may be behind the high creep rate. They discovered talc in serpentinite samples collected during drilling of the SAFOD (San Andreas Fault Observatory at Depth) main hole in 2005. The frictional strength of talc at elevated temperatures is sufficiently low to meet the constraints on shear strength of the fault, and its inherently stable sliding behaviour is consistent with fault creep.
News and Views: Seismology: Talc at fault
The behaviour of the San Andreas fault varies along its length — it slips in some places and creeps in others. The discovery of the ultrasoft mineral talc in rocks from deep inside the fault could help to explain why.
Christopher Wibberley
doi:10.1038/448756a
Letter: Talc-bearing serpentinite and the creeping section of the San Andreas fault
Diane E. Moore & Michael J. Rymer
doi:10.1038/nature06064
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