Strong reflectors observed in geothermal fields

Since geothermal fields are highly fractured and form complex structures, the results of seismic reflection surveys are often poor because of attenuation, scattering, and absorption of seismic waves. In this situation, it is important to improve the S/N ratio. By applying diffraction stacking to the seismic reflection data obtained in the geothermal field, we obtained strong and continuous reflectors with a higher S/N ratio than conventional CMP method. The cause of strong reflectors in geothermal fields is controversial. Strong reflectors acts as a decoupling plane in the upper continental crust; it developed as a consequence of the extensional tectonics and high heat flow. Such strong reflectors correspond to a level of fractured rocks, saturated with hydrothermal fluids and minerals. Such a condition could cause a strong contrast in acoustic impedance. The strong reflectors may be related to thermal structure such as a rheological boundary (brittle-ductile boundary) that separates a brittle upper part from a ductile lower part. We compare the seismic section with both the hypocenter distribution of microearthquakes and isotherm lines obtained from deep boreholes. A high seismicity zone lies over the strong reflector, indicating that a brittle zone lies above the strong reflector. And also, the strong reflector coincides with the 350 C.