Fault zone damage and chemical reactions at depth in the San Andreas Fault Zone: A study of SAFOD drill core samples
Final Report Abstract
Our research project was structured around a series of questions addressing some basic issues in fault dynamics. The central scientific question was “Why are the San Andreas and some other major faults absolutely or relatively weak?" In response to this question several deformation mechanisms (e.g. amorphous material, nano-scale pore spaces, dissolutionprecipitation processes, intracrystalline plasticity), operating in the fault gouge of SAFOD core samples, were successfully analyzed using TEM, SEM and microprobe analyses. Amorphous material and nano-scale pore spaces were proofed as possible weakening mechanisms. Furthermore and in agreement with previous studies we also suggest that the high amount of weak clay minerals in general and the growth of Mg-rich phyllosilicates in particular may play a key role in the mechanical behavior of the San Andreas fault and can be directly related to fault weakening. The presence of abundant clay minerals is often related to the occurrence of nano-scale porosity that may indicates high fluid pressure. However, the SAFOD borehole was drilled into a creeping (aseismic) portion of the San Andreas Fault. The mechanisms relating earthquakes and aseismic creep remain still elusive due to the absence of microstructures that enable the evaluation of coseismic slip in SAFOD core samples. So, the inclusion of TCDP and Nojima fault drilling samples enabled us to identify key similarities and differences between characteristic microstructures of slip zones recently formed by co-seismic processes in earthquake faults (TCDP; Nojima fault) and active but aseismic creep that is evident in the SAFOD borehole by pronounced and ongoing casing deformation.
Publications
- (2009): Micro- and Nanostructures of SAFOD Core Samples - First Results, (EOS, Transactions, American Geophysical Union, Fall Meeting Suppl.; 90, 52), AGU 2009 Fall Meeting (San Francisco, 2009)
Janssen, C., Wirth, R., Rybacki, E., Naumann, R., Kemnitz, H.
- (2010). Amorphous material in SAFOD core samples (San Andreas Fault): Evidence for crush-origin pseudotachylytes? Geophys. Res. Lett., 37, L01303
Janssen, C., Wirth, R., Rybacki, E., Naumann, R., Kemnitz, H., Wenk, H.-R., Dresen, G.
(See online at https://doi.org/10.1029/2009GL040993) - (2010): The effects of fluid-rock interactions on faulting within active fault zones – new results from the San Andreas Fault at Depth (SAFOD) compared with insights from the Nojima and Chelungpu fault zone drilling projects. AGU 2010 Fall Meeting (Teipei, Taiwan 2010)
Janssen, C ., Wirth, R., Rybacki, E., Wenk, H.-R. Dresen, G.
- (2011). Low-temperature deformation in calcite veins of SAFOD core samples (San Andreas Fault) – microstructural analysis and implications for fault rheology. Tectonophysics
Rybacki, E., Janssen, C., Wirth, R., Chen, K., Wenk, H.-R., D. Stromeyer, Dresen, G.
(See online at https://doi.org/10.1016/j.tecto.2011.05.014) - (2011). Mechanical twinning in quartz: Shock experiments, impact, pseudotachylytes and fault breccias, Tectonophysics
Wenk, H-R., Janssen, C ., Kenkmann, T., Dresen, G .
(See online at https://doi.org/10.1016/j.tecto.2011.06.016) - (2011). Nanoscale porosity in SAFOD core samples (San Andreas Fault). Earth and Planetary Science Letters 301, p. 179-189
Janssen, C ., Wirth, R., Reinicke, A., Rybacki, E., Wenk, H.-R., Dresen, G.
- (2011): Effects of fluids on faulting within active zones - evidence from drill core samples recovered during the San Andreas Fault Observatory at Depth (SAFOD) drilling project, AGU 2011 Fall Meeting (San Francisco, USA 2011)
Janssen, C., Wirth, R., Kienast, M., Morales, L. F., Rybacki, E., Wenk, H., Dresen, G.
- (2011): Fault zone damage and chemical reactions at depth in the San Andreas Fault Zone: A study of SAFOD drill core samples, IODP/ICDP-Kolloquium 2011 (Münster, 2011)
Janssen, C., Wirth, R., Rybacki, E., Wenk, H.-R. Dresen, G.
- (2011): Fault zone deformation microstructures, SAFOD Workshop (Austin, USA 2011)
Janssen, C., Wirth, R., Kienast, M., Rybacki, E., Morales, L., Wenk, H.-R. Dresen, G.
- (2011): Microstructural analysis of deformed calcite veins of SAFOD samples with implications for the San Andreas Fault rheology. Vol. 13, EGU2011-PREVIEW, 2011 (Wien, Austria 2011)
Rybacki, E., Janssen, C ., Wirth, R., Chen, K., Wenk, H.-R., Dresen, G.
- (2011): Microstructure and mineral fabric analysis of San Andreas Fault zone gouge from drill cores of the SAFOD borehole, Parkfield, CA, DRT Meeting 2011 (Oviedo, Spain)
Kienast, M., Morales, L., Janssen, C., Wenk, H.-R., Rybacki, E., Dresen, G.
- (2012). Clay fabrics in SAFOD core samples, Journal of Structural Geology
Janssen, C ., Kanitpanyacharoen, W., Wenk, H-R., Wirth, R., Morales, L., Rybacki, E., Kienast, M., Dresen, G.
(See online at https://doi.org/10.1016/j.jsg.2012.07.004) - (2012). Faulting processes in active faults- Microstructural, mineralogical and geochemical characterization of drill core samples, Graduate School of Science, TOHOKU UNIVERSITY, Workshop (Sendai, Japan)
Janssen, C., Wirth, R., Morales, L., Naumann, R.
- (2012): Fault zone deformation microstructures, Universität Bremen, Einladungsvortrag (Bremen, 2012)
Janssen, C., Wirth, R., Kienast, M., Rybacki, E., Morales, L., Wenk, H.-R. Dresen, G.
- (2012): Fault zone microstructures – evidence from drill core samples recovered during the San Andreas Fault Observatory at Depth (SAFOD) Drilling project; Institute of Geology, Chinese Academy of Geological Sciences, Einladungsvortrag (Peking, 2012)
Janssen, C., Wirth, R., Kienast, M., Rybacki, E., Morales, L., Wenk, H.-R. Dresen, G.
- (2012): Micro- and nanostructures of J-FASR 343 core samples - first results, AGU 2012 Fall Meeting (San Francisco, USA 2012)
Dresen, G., Janssen, C., Wirth, R., Naumann, R., Morales, L. F
- (2012): Microstructural and geochemical observations on gouge samples from the San Andreas Fault Observatory at Depth (SAFOD), AGU 2012 Fall Meeting (San Francisco, USA 2012)
Kienast, M., Janssen, C., Wirth, R., Rybacki, E., Morales, L. F., Dresen, G.
- (2013). TEM microstructural analysis in a fault gouge sample of the Nojima Fault Zone, Japan. Tectonophysics, 583, 101-104
Janssen, C., Wirth, R., Aiming, L.; Dresen, G.
- (2013): Fault Zone microstructures formed by coseismic and aseismic faulting –evidences from SAFOD and TCDP drill core samples, Universität Freiburg, Einaldungsvortrag im Rahmen des Universitäts-Kolloquiums (Freiburg, 2013)
Janssen, C., Wirth, R., Kienast, M., Naumann, R., Morales, L., Wenk, H.-R.
- (2014). Faulting processes in active faults – evidences from TCDP and SAFOD drill core samples. Journal of Structural Geology 65, 100-116
Janssen, C., Wirth, R., Wenk, H.-R., Morales, L., Naumann, R., Kienast, M., Song, S.- R., Dresen, G.
(See online at https://doi.org/10.1016/j.jsg.2014.04.004)
