Double Difference Relocation, Determination of Local and Duration Magnitude of Microearthquakes in the “XYZ” Geothermal Field

Abstract

During the fluid injection in the “XYZ” geothermal field from February 1998 until March 1998, 37 microearthquakes were recorded around this field. We have determined the locations of those microearthquakes using highly precision hypocenter double difference (HypoDD) earthquake location algorithm. We found that microearthquake hypocenters distribution, which were sparsely distributed around the injection wells, became tightly elongated distribution. We also calculated the local magnitude scale using those microearthquakes data and then calculated the relationship between local magnitude and signal duration to determined the duration magnitude scale. As the result, we calculated the value of geometric spreading parameter, n, 3.4064, and attenuation parameter, k, -0.3477, so the local magnitude scale for “XYZ” geothermal field is ML = log A – 3.4064 log(r/17) + 0.3477(r-17) + 2. From the relationship between local magnitude and signal duration, we found : MD = 2.2 log(duration) – 1.1. Finally, we have found the local magnitude duration of microearthquakes are - 0.18 less than ML less than 1.55 and -0.23 less than MD less than 0.94.