Microearthquake Monitoring in “AFA” Geothermal Fied: Microearthquake Analysis, Determination Hypocenter, Station Correction, and 1-D Seismic Velocity

Abstract

Microearthquake monitoring is one of geophysical method that can be used to determine fluids injection movement and subsurface physical properties (seismic velocity and attenuation). One of microearthquake characteristic is high frequency content, based on this study frequency content of microearthquake (2-66 Hz) is higher than regional earthquake (0.6-10 Hz). Hypocenter determination of microearthquakes of Mount “AFA” has been conducted by GAD method (Geiger’s method with adaptive damping). After that, we then determine 1-D seismic velocity model using coupled velocity-hypocenter method. Coupled hypocenter-velocity method is a method of relocating earthquake, 1-D seismic wave velocity model determination and correction stations simultaneously using the principle method of Geiger. Result from 1D velocity model show low Vp/Vs ratio at depths of -0,2 to 0,8 km. Our interpretation is this anomaly may be related to a rock layer which is saturated by vapor (gas or steam). With station correction we can interpret material condition around station. If the values of station correction are low it is indicated that material condition around station is more massif than another area.