Chemical and Physical Characteristics of Pulverized Tejon Lookout Granite Adjacent to the San Andreas and Garlock Faults: Implications for Earthquake Physics
We present new detailed analyses of samples of pulverized Tejon Lookout granite collected from sections adjacent to the San Andreas and Garlock faults in southern California. The Tejon Lookout granite is pulverized in all exposures within about 100 m from both faults. Chemical analyses indicate no or little weathering in the collected samples, although XRD analysis shows the presence of smectite, illite, and minor kaolinite in the clay-size fraction. Weathering products may dominate in the less than 1 micron fraction. The average grain size in all samples of pulverized Tejon Lookout granite ranges between 26 and 208 microns (silt to fine sand), with the particle size distribution in part a function of proximity to the primary slip zone. The San Andreas fault samples that we studied are generally finer grained than those collected from adjacent to the Garlock fault. The particle size distribution for each studied sample from both faults follows a pseudo-power law with a continuously changing exponent, which suggests that pulverization is not simply a consequence of direct shear. The average particle size that we determined for our samples is considerably coarser than reported in previous investigations, which we attribute to possible measurement errors in the prior work. Our data and observations suggest that dynamic fracturing in the wall rock of the San Andreas and Garlock faults only accounts for about 1% or less of the earthquake energy budget.
Key wordsPulverized rocks particle size distribution rock weathering fault-zone structure earthquake physics
Unable to display preview. Download preview PDF.
- Abercrombie, R., McGarr, A., Kanamori, H., and Di Toro, G. (eds.) Earthquakes: Radiated Energy and the Physics of Faulting, Geophysical Monograph Series, Vol. 170, (2006) 327 pages, hardbound.Google Scholar
- Ben-Zion Y. and Huang, Y. (2002). Dynamic rupture on an interface between a compliant fault zone layer and a stiffer surrounding solid, J. Geophys. Res. 107(B2): Art. No. 2042, doi 10.1029/2001JB000254.Google Scholar
- Brune, J.N. (2001), Fault normal dynamic loading and unloading: an explanation for “non-gouge” rock powder and lack of fault-parallel shear bands along the San Andreas fault, EOS Trans. Am. Geophys. Union, 82.Google Scholar
- Dor, O., Rockwell, T. K., and Ben-Zion, Y. (2006b), Geological observations of damage asymmetry in the structure of the San Jacinto, San Andreas and Punchbowl Faults in southern California: A possible indicator for preferred rupture propagation direction, Pure Appl. Geophys. 163 (2–3), 301–349.CrossRefGoogle Scholar
- Dor, O., Yildirim, C., Rockwell, T. K., Ben-Zion, Y., Emre, O., Sisk, M., Duman, T. Y. (2008), Geologic and geomorphologic asymmetry across the rupture zones of the 1943 and 1944 earthquakes on the North Anatolian Fault: Possible signals for preferred earthquake propagation direction. Geophys. J. Int. 173, 483–504, doi: 10.1111/j.1365-246X.2008.03709.x.CrossRefGoogle Scholar
- Dor, O., Chester J. Ben-Zion Y., Rockwell T., Brune J. (2009), Characterization of damage in sandstones along the Mojave section of the San Andreas Fault: Implications for the shallow extent of damage generation, Pure Appl. Geophys. 166, (10).Google Scholar
- Folk, R. L., Petrology of Sedimentary Rocks, (hemphill Publishing Company 1974).Google Scholar
- Mitchell, T.M., Shimamoto, T, Ando, J. Ben-Zion, Y. (2008). The seismic velocity and permeability properties of pulverized rocks, Geophys. Res. Abstract 10, EGU2008-A-00000, EGU General Assembly.Google Scholar
- Rockwell, T.K. (2000), Use of soil geomorphology in fault studies: In Quaternary Geochronology: Methods and Applications. J.S. Noller, J.M. Sowers, and W.R. Lettis, eds. AGU Reference Shelf 4 Am. Geophys. Union, Washington D.C., 2000, pp 273–292.Google Scholar
- Sisk, M., Rockwell, T., Girty, G., Dor, O., and Ben-Zion, Y. (2005), Potentially pulverized granites along the Garlock fault: An analysis into their physical and chemical properties, EOS Trans, Amer. Geophys. Union 86(52), Fall Meet. Suppl., Abstract S41B-0994.Google Scholar
- Stillings, M. (2007), Structural, textural and geochemical analyses of fault damage zones: Clark strand, San Jacinto fault zone, southern California, M.S. Thesis, San Diego State University, San Diego, California.Google Scholar
- Wilson, B. T. (2004). Meso-and micro-structural Analysis of the San Andreas Fault at Tejon Pass, California, USA, M.S. Thesis, University of Oklahoma, Norman, Oklahoma.Google Scholar