Determining the hydrothermal flow media using seismicity properties in Kaliulo geothermal field, Semarang, Central Java, Indonesia

Geothermal system requires specific geological condition that allow deep circulation of ground water to extract heat from the heat source. Faults and fractures play a major role in the localization and evolution of hydrothermal flow on several scales. The research aim was to obtain the permeability pattern of hydrothermal fluid base on response of micro seismic waves to subsurface structures. In one dimensional structure, average Horizontal to Vertical (H/V) spectral ratios can be assumed to measure the ellipticity of fundamental mode Rayleigh wave. Hence the shape of H/V ratios can be used to estimate the shear-wave velocity profile. The poisson's ratio value of the hot spring corresponds to the physical properties of rock containing fluids. The thickness of the sand deposit and the soft layer indicated in the hot spring zone. We interpreted that we have warm springs in the research area comes up by the fracture or fault zone and permeable zone of sand soil. The mixing waters flow to the earth's surface through the structure. (paper)