| Title | Geophysical Characterization of the Eburru Geothermal Field, Kenya from the Analysis and Interpretation of Magnetotelluric and Gravity Techniques |
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| Authors | Justus MAITHYA, Yasuhiro FUJIMITSU |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Magnetotelluric, Gravity, 3-D Inversion, Eburru Geothermal Field |
| Abstract | Magnetotelluric (MT) and gravity surveys were carried out in the area to delineate the heat source, estimate the geothermal reservoir, and assess the extent of geothermal system. Three-dimensional magnetotelluric interpretation of geothermal systems is a powerful tool for characterization of the deep electrical resistivity structure of geothermal reservoirs with high resolution and accuracy. Three- dimensional magnetotelluric (MT) inversion of Eburru datasets using ModEM program was performed to obtain the resistivity structure of the field. The preferred electrical resistivity model shows a conductive zone ( less than 10 Ωm) interpreted as the cap rock within 1 km from the surface overlaying an intermediate resistive layer (~ 35 Ωm) and a deep conductor ( less than 10 Ωm) extending from sea level to a depth of 2.5 km below sea level. Additionally, the 3-D resistivity model shows pronounced low resistivity regions which trend in the north-south direction, consistent with the local fault strike. A total of 375 gravity data points were used in creating the Bouguer anomaly, using a Bouguer density of 2.27 g/cm3. Gravity survey results indicate Bouguer anomaly having both high and low amplitude anomalies. Three-dimensional MT inversion based on full impedance tensor and three- dimensional gravity model obtained by inverting Bouguer anomaly imaged similar features. The gravity model shows that the high-density anomaly bodies occur along the fault zones. A relatively low resistivity and a high density body located approximately 1.5 km below sea level may be related to the geothermal reservoir which is likely heated by magmatic fluid emanating from deeper melt sources. |