Collaborative Research: Targeting the Phase lll SAFOD Drilling

圣安德烈亚斯断层深度观测站（SAFOD）项目的一个关键目标是钻穿一次小型重复地震的破裂带。破裂斑块的大小在几十米左右；因此，以相当的精度了解其位置对SAFOD的成功至关重要。我们正在进行的工作对SAFOD钻井的最后阶段至关重要，需要达到10米左右的目标地震定位精度。为了完成这项任务，我们利用了在第二阶段钻井结束时安装的井管柱，这将使地震传感器非常接近目标区域（约100米）。然后我们会拍6张50-100磅的照片。在9到12个月的时间里，在临时地震记录地点附近，通过我们的临时阵列、SAFOD先导井的井管柱和SAFOD二期井管柱进行同步记录。由此产生的主动式和被动式数据集将为校准和改进地震波速模型提供有力手段，使我们能够达到第三阶段钻井所需的10米精度。最后，我们将在第三阶段钻井完成后继续分析收集到的数据，以完善和扩展我们的San Andreas断裂带结构模型。

0454463RoeckerA key objective of the San Andreas Fault Observatory at Depth (SAFOD) project is to drill through the rupture patch of a small repeating earthquake. The size of the rupture patch is on the order of tens of meters; hence knowing its location to a comparable degree of accuracy is vital to SAFOD's success. The work we are carrying out is critical to this final phase of SAFOD drilling, and requires reaching a level of location accuracy for the target earthquakes of about 10 meters. We are approaching this task by taking advantage of a borehole string, to be installed at the end of Phase II drilling, that will bring earthquake sensors very close (~100 m) to the target zone. We will then set off 6 shots of about 50-100 lbs. near temporary earthquake recording sites during a ~9 to 12 month period of concurrent recording by our temporary array, a borehole string in the SAFOD Pilot Hole, and the Phase II SAFOD borehole string. The resulting combined active and passive data set will provide a potent means for calibrating and improving the seismic wavespeed models that will enable us to achieve the 10 m accuracy required for the Phase III drilling. Finally, we will continue to analyze data collected after Phase III drilling is completed in order to refine and extend our models of San Andreas fault zone structure.