Using Temperature to Measure Fault Stress: Analysis of Data from the Fault Zone of the Mw 7.9 Wenchuan Earthquake

用温度测量断层应力：汶川7.9级地震断层带数据分析

• 批准号: 1220642
• 负责人: Emily Brodsky
• 金额: $ 25.38万
• 依托单位: University of California-Santa Cruz
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-07-15 至 2016-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1220642&HistoricalAwards=false
• 关键词: Using; Temperature; Measure; Fault; Stress

The devastating 1999 Mw 7.9 Wenchuan thrust earthquake generated a 300 kilometers-long surface rupture with an average offset of about 5 meters. If the resisting stress of faults is controlled by Byerlee?s friction law, this slip should have resulted in significant energy dissipated as heat. The Wenchuan Fault Zone Scientific Drilling Project has successfully measured multiple temperature profiles within 2 years after the earthquake. In a pilot hole intersecting the major fault zone at 589 m depth, 13 high-quality repeated temperature logs were taken over a 1.5 year period. In addition, temperature logs were performed before casing completion and continuous measurements were made at a few points between profile runs. Preliminary inspection and modeling of the data indicates that any transient temperature anomaly over the fault is less than 0.05 degrees C, which suggests that the equivalent coefficient of friction during the earthquake is less than 0.05 and, by implication, that the earthquake completely relieved the stress stored up from plate motion. However, the preliminary modeling did not account for several important effects such as advection and fault structure. The goal of this project is to determine the actual value of the stress on the fault during the earthquake by: (1) employing a more sophisticated numerical model that includes the cooling effect of water flow along the fault in order to better interpret the borehole data; and (2) by collection and analysis of new temperature and pressure data in a second borehole that intersects the most prominent fault zone at 1247-1250 meters and extends to 1400 meters total depth and in a third borehole planned for completion in 2013.Earthquakes are the result of motions of the tectonic plates and the driving forces are well understood. However, the resisting force impeding the motion on the faults is much more poorly constrained. This frictional stress during an earthquake is one of the major unknown parameters in earthquake mechanics. The processes controlling friction at high slip velocities are vigorously debated with many theoretical possibilities. Field measurements are needed to constrain the dominant processes on actual faults. This project would take advantage of new and planned temperature measurements in boreholes that penetrate the fault that generated the Wenchuan earthquake that would allow determination of the coefficient of friction during the earthquake.

毁灭性的1999 MW 7.9 Wenchuan推力地震产生了300公里长的表面破裂，平均偏移约为5米。如果断层的抵抗应力由Byerlee的摩擦定律控制，则该滑移应导致大量的能量消散为热量。 Wenchuan断层区科学钻井项目在地震后2年内成功地测量了多个温度曲线。在589 m深度的主要断层区域的试点孔中，在1。5年的时间内采用了13个高质量的重复登录。此外，在套管完成之前进行了温度对数，并在轮廓运行之间的几个点进行连续测量。对数据的初步检查和建模表明，断层上的任何瞬时温度异常小于0.05度C，这表明地震期间摩擦的等效系数均小于0.05，并且暗示地震使地震完全缓解了储存的应力从平板运动中释放出来。但是，初步建模并未考虑到几种重要效果，例如对流和断层结构。该项目的目的是确定地震期间断层压力的实际值：（1）采用更复杂的数值模型，其中包括沿断层的水流的冷却效果，以便更好地解释井眼数据； （2）通过收集和分析第二个钻孔中的新温度和压力数据，该井眼与1247-1250米处最突出的断层区域相交，并扩展到1400米的总深度，并计划在2013年完成的第三个钻孔中进行。地球是构造层和驱动力运动的结果。但是，阻碍运动对断层的抵抗力的约束要差得多。地震期间的这种摩擦应力是地震力学中的主要未知参数之一。在高速速度下控制摩擦的过程以许多理论上的可能性进行了激烈的争论。需要进行现场测量来限制实际故障的主要过程。该项目将利用钻孔中的新的和计划的温度测量值，这些温度测量渗透到产生Wenchuan地震的断层，该断层可以确定地震期间摩擦系数。