Magnetotelluric Experiments in the Aliaga Geothermal Field, Western Turkey

Abstract

Western Turkey has a number of hot-water springs and attracts attention for new prospects. For example, the geological investigations carried out around Aliaga shows that the region may have valuable resources for the geothermal energy production. Consequently, the magnetotelluric (MT) and transient electromagnetic (TEM) methods have been applied to delineate the source rock, faults and other subsurface features over a profile that consists of 21 measurement stations in this probable geothermal field. The length of the profile was 5 km.
Since the measurement profile is close to petrochemical and metallurgy manufacturing sites, the MT data have been severely distorted by directional industrial noise. The noise is typically “V” type around 10 Hz. After the rotation of the data to the principal axis of the impedance tensor, the level of noise contamination becomes relatively high in the mode perpendicular to the profile direction. A new smoothing algorithm is developed to overcome the directional noise problem. The method is based on the combination of a fitting function that simulates the behaviour of the frequency-normalised impedance. The random and systematic noises were represented by weight coefficients derived from the differences between the measured and smoothed frequency-normalised impedance data. The smoothed apparent resistivity datasets are then computed from the impedance data in order to employ as the input of the interpretation algorithms.
The static-shift correction has been employed by the help of theoretical MT datasets obtained from the one-dimensional earth models that are computed from the inversion of the transient electromagnetic method (TEM) data measured in the same location. The MT data have been interpreted by the application of two-dimensional inversion techniques. The computed resistivity-depth section has been interpreted in view of geology of the area. An overall picture of the subsurface including major faults has delineated and the promising parts of the geoelectrical section for geothermal energy are identified.