Journal
GEOLOGY
Volume 41, Issue 9, Pages 1015-1018Publisher
GEOLOGICAL SOC AMER, INC
DOI: 10.1130/G34483.1
Keywords
-
Categories
Funding
- NASA-Ames through NASA grant [NNX09AQ44A]
- National Science Foundation grant [EAR0948740]
- Natural Sciences and Engineering Research Council of Canada Discovery grants
- NASA [103935, NNX09AQ44A] Funding Source: Federal RePORTER
Ask authors/readers for more resources
Dynamic reduction of fault strength is a key process during earthquake rupture. Many mechanisms for causing coseismic weakening have been proposed based on theory and laboratory experiments, including silica gel lubrication. However, few have been observed in nature. Here we report on the first documented occurrence of a natural silica gel coating a fault surface. The Corona Heights fault slickenside in San Francisco, California, is covered by a shiny layer of translucent silica. Microstructures in this layer show flow banding, armored clasts, and extreme comminution compared to adjacent cataclasites. The layer is composed of similar to 100 nm to 1 mu m grains of quartz, hydrous crystalline silica, and amorphous silica, with 10-100 nm inclusions of Fe oxides and ellipsoidal silica colloids. Kinematic indicators and mixing with adjacent cataclasites suggest the shiny layer was fluid during fault slip. The layer therefore represents a relict silica gel that formed during fault motion, and which could have resulted in frictional instability. These observations confirm that the silica gels formed in rock friction experiments do occur in natural faults and therefore that silica gel formation can act as a dynamic weakening mechanism in faults at shallow crustal conditions.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available