A Geomagnetic Induction Study of the California Coast Range Near the Mendocino Triple Junction

PI发现了一个主要的电导率异常，与俯冲的戈达板块南缘的埋藏半扩张中心有关。该异常的几何形状表明，至少在几个世纪里，戈达板块的运动是由布兰科断裂带的方向而不是门多西诺断裂带的方向控制的。对该异常进行更多的测绘将对板块运动提供进一步的限制。了解异常的详细结构将有助于了解埋藏扩张中心如何产生该地区极其重要的地热资源，以及机械系统必须如何工作。然而，这种异常现象似乎基本上是三维的。它可能涉及到电流的传导，通过其他电阻海岸范围，这是在附近的高导电性表面结构，如海洋感应。将进行三维建模工作，以了解异常的各种特征，例如其缺乏频率依赖性，以及有限的现场工作，以真正扩展我们的阵列并为建模工作提供MT约束。这些都是为了利用EMAP（电磁阵列剖面）等创新技术对结构进行详细成像而进行的主要现场工作的必要前奏。

The PI has discovered a major electric conductivity anomaly related to a buried half spreading center at the south edge of the subducted Gorda Plate. The geometry of this anomaly shows that the motion of the Gorda Plate has been controlled by the orientation of the Blanco Fracture Zone and not the Mendocino Fracture Zone for at least several My. More mapping of the anomaly will provide further constraints on the plate motions. Understanding the detailed structure of the anomaly will provide insight into how the buried spreading center has produced the enormously important geothermal resources of the area and how the mechanical system must work. The anomaly, however, appears to be fundamentally 3-D. It probably involves conduction of currents through the otherwise resistive Coast Range, which are induced in nearby highly conductive surface structures such as the ocean. A 3-dimensional modeling effort to understand various features of the anomaly such as its lack of frequency- dependence will be carried out, as will a limited field effort to a really extend our array and to provide MT constraints for the modeling effort. These are both a necessary prelude to a major field effort designed to image the sturcture in detail using an innovative technique such as EMAP (Electro Magnetic Array Profiling).