[Erzinger] Geochemistry of gases in seismogenic depths of the San Andreas Fault Zone
German Title: Geochemistry of gases in seismogenic depths of the San Andreas Fault Zone
Current Status: completed
Main Applicant:Prof. Dr. Joerg Erzinger
The origin of gases and fluids in seismogenic depths of the San Andreas Fault (SAP), their composition, spatial distribution, temporal variations, migration mechanisms, as well as the link to seismic processes are only in part understood. We propose to perform gas and fluid studies on drill core, drill cutting, and drill mud gas from the SAFOD core drilling campaign in 2007, in order to gain quantitative information on the geochemistry of fluids and gases in seismogenic depths. Own drill-mud gas analysis from the SAFOD main hole (MH) revealed important information on the contribution of mantle-derived fluids to the total fluid inventory of the SAF and the migration of such fluids, and on the origin and distribution of the main non-atmospheric gaseous components on relatively large spatial scale. However, some questions addressed to gases at the SAF remained open: 1) the origin of the huge amounts of H2 in drill-mud gas found during drilling the SAFOD MH and 2) absolute gas concentrations and small-scale distribution of gases and fluids in fault zone rock which would help to understand fluid migration mechanisms at seismogenic depths. Drill-mud gas samples and drilled rock samples have been collected for investigations on isotopes (noble gases, (13C on CO2 and hydrocarbons, H/D on H2 and CH4) as well as mechanochemical gas synthesis. In combination with results from on-site experiments, this information provides better understanding of the behaviour of fluids and gases at seismogenic depths of the SAF.
Wiersberg, Thomas, Erzinger, Jörg (2011). "Chemical and isotope compositions of drilling mud gas from the San Andreas Fault Observatory at Depth (SAFOD) boreholes: Implications on gas migration and the permeability structure of the San Andreas Fault" Chemical Geology 284 p148-159