Estimates of Fault Strength, Frictional Heat, and Energy for the Chi-Chi, Taiwan Earthquake

该项目的主要目的是寻找1999年台湾集集地震(Mw7.6)在车龙铺断裂上与断层有关的温度异常。断层上的任何温度变化都会给出地震时产生的摩擦热的估计。确定摩擦热水平为地震学中一个长期存在的关于大地震期间断层的绝对应力水平和强度的问题提供了有价值的信息。为了测量温度，我们使用了台湾车龙埔断层钻探计划(TCDP)的钻孔，该钻孔深度约为1100米，位于大滑动区域。利用该项目开发的高分辨率钻孔仪器，于2005年9月连续测量了该钻孔的温度分布。地震后6年获得的结果显示，断层上的温度略有上升。这一微小的温度信号被解释为地震时的残余摩擦热。模拟的温度数据表明，断裂过程中断层上的剪应力水平在0.8~1.7 Mpa之间。该值对应于0.08至0.1的表观摩擦系数，这是一个非常低的值。如果这是大断层区域的代表值，则需要显著的低摩擦机制来解释断层。材料特性，如导热系数的变化，可能会影响温度信号的解释。研究这些影响是后续项目的目的。该项目中的其他研究调查了来自井芯的断裂带的物理性质，并进行了抽水试验以确定流体的流动性质。

The main purpose of this project was to look for a temperature anomaly associated with faulting from the 1999 Chi-Chi, Taiwan earthquake (Mw7.6) on the Chelungpu fault. Any temperature change across the fault would give an estimate of the frictional heat produced at the time of the earthquake. Determining the level of frictional heat adds valuable information to a long-standing problem in seismology about the absolute stress levels and strengths of faults during large earthquakes. For the temperature measurements we able to use the Taiwan Chelungpu fault Drilling Project (TCDP) borehole which penetrated the fault at a depth of about 1100 meters in a region of large slip.Using a high-resolution borehole instrument developed in this project, we measured continuous temperature profiles in the borehole in September 2005. The results, which were obtained 6 years after the earthquake, showed a small increase of temperature across the fault. This small temperature signal is interpreted as the residual frictional heat from the time of the earthquake. The modeled temperature data showed that a shear stress level of 0.8 to 1.7 MPa on the fault during the rupture. This value corresponds to an apparent coefficient of friction of 0.08 to 0.1, which is a very low value. If this is a representative value for the area of large faulting, significant low friction mechanisms are needed to explain the faulting.Material properties, such as variations in heat conductivity, may affect the interpretation of the temperature signal. Investigating these effects is the purpose of a follow-up project. Other studies in the project investigated physical properties of the fault zone from the borehole cores and a water pumping test was done to determine the fluid flow properties.