Fault zone Temperature Measurements to Search for a Thermal Anomaly in the Chelungpu Fault, Taiwan

1.Objective The energy released when earthquakes occurs can be divided into three types, fracture energy, radiated energy, and frictional heat. It is important to know the amount of frictional energy, when we try to understand how earthquakes occur. So, we are measuring the temperature near the fault zone of a recent large earthquake, to try to find a heat anomaly. A heat anomaly will enable us to estimate the frictional energy produced by the earthquake. This is one of the first efforts to directly measure the heat produced by a large earthquake. 2.Observations We are investigating the 1999 Chichi earthquake in Taiwan. The moment magnitude of this event is 7.6 and there was about 8 m slip on the fault near the measurement site. We installed thermometers in a borehole that penetrates the Chelungpu fault at a depth of about 1110m, and are currently measuring the temperature near the fault zone starting from early March 2005. In the observation, we use 5 platinum resistance thermometers and 2 quartz crystal oscillator thermometers. The temperature sensors are spread over a distance of about 30 m in the vicinity of the fault. 3.Measurement Results The data from the platinum resistance thermometers are connected to a computer on the surface so that we can monitor the temperature measurements. When the system works well, the accuracy of the data is about 0.02_E#381;. We are continuously monitoring the temperature over time to estimate the stability of the temperature and look for any temporal effects that remain from the drilling. We should be able to observe a frictional heat residual from the earthquake, if it is larger than about 0.1 _E#381;. Theoretical calculations indicate that 5 years after the earthquake, a temperature anomaly of about 0.2_`0.6_E#381; should remain, assuming a range of values for the apparent coefficient of friction. Therefore, the resolution of our measurements should be accurate enough to detect a temperature anomaly.