The electrical conductivity structure between the transitional (near SAFOD) and locked (SE of Cholame) segments of the San Andreas Fault, including the source region of the non-volcanic tremors

圣安德烈亚斯断层(SAF)深部观测站(SAFOD)附近的DeepRoot大地电磁(MT)实验显示，在地震定义的SAF两侧向东北方向有一个陡峭的上地壳高电导率带，向下地壳加宽，在那里它似乎与上地幔中的一个广泛异常有关。Becken等人。(2007a)认为，高电导率是地壳和/或地幔流体上升的深层次通道。深部(约20-40公里)、非火山地震(NVT)仅在SAFOD东南约40公里的区域观测到，在那里它们被认为是由流体振荡引起的。NVT的存在或不存在似乎与SAF从锁定(Cholame)到中间蠕变(SAFOD)的转变相一致，并可能反映出影响SAF这一部分深部液压系统的重大结构变化，而这反过来又可以通过MT检测到。在这里，我们提出了一项实验，用MT站网络对活动板块边界的整个段进行成像，从太平洋进入大谷，穿过乔拉姆附近SAF下的NVT地区。这些结果对于SAFOD的位置特征是重要的，因为沿走向的导电性结构的变化可能反映了控制SAF仍然有争议的力学状态的深层结构变化。

The DeepRoot magnetotelluric (MT) experiment near the San Andreas Fault (SAF) Observatory at Depth (SAFOD) revealed a steeply dipping upper crustal high electrical conductivity zone flanking the seismically defined SAF to the NE, widening into the lower crust where it appears to be connected to a broad anomaly in the upper mantle. Becken et al. (2007a) suggested that the high conductivity represents a deep-rooted channel for crustal and/or mantle fluid ascent. Deep (~20-40 km), non-volcanic seismic tremors (NVT) have only been observed in an area ~40 km SE of the SAFOD where they are thought to originate from oscillation of fluids. The presence or absence of NVT appears to coincide with the transition of the SAF from being locked (Cholame) to intermediate creep (SAFOD) and could reflect significant structural changes affecting the deep hydraulic system along this portion of the SAF which in turn could be detectable with MT. Here, we propose an experiment to image an entire segment of an active plate boundary with a network of MT stations, from the Pacific into the Great Valley, crossing the NVT region beneath the SAF near Cholame. These results are important for the site characterization of the SAFOD as along-strike variations of the conductivity structure may reflect deep structural changes controlling the still debated mechanical state of the SAF.