Geochemistry of gases in seismogenic depths of the San Andreas Fault Zone

在圣安德烈亚斯断层（SAP）的孕震深度的气体和流体的起源，其组成，空间分布，时间变化，迁移机制，以及地震过程的联系，只有部分了解。我们建议对2007年SAFOD岩心钻探活动的岩心、钻屑和钻井泥浆气体进行气体和流体研究，以获得孕震深度流体和气体地球化学的定量信息。SAFOD主孔（MH）的钻井泥浆气体分析揭示了有关幔源流体对SAF总流体存量的贡献和此类流体的迁移以及主要非大气气体组分在相对较大空间尺度上的起源和分布的重要信息。然而，SAF的一些气体问题仍然悬而未决：1）在SAFOD MH钻井过程中发现的钻井泥浆气体中大量H2的来源; 2）断裂带岩石中气体和流体的绝对浓度和小规模分布，这将有助于了解孕震深度的流体迁移机制。已收集钻井泥浆气体样品和钻取的岩石样品，用于研究同位素（稀有气体，CO2和碳氢化合物的13 C，H2和CH 4的H/D）以及机械化学气体合成。结合现场实验的结果，这些信息提供了更好地了解流体和气体的行为在SAF的孕震深度。

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.