Fault Characterization in Tondano Depression Using Focal Mechanism Analysis
Astha Dandari Kusuma WARDHANI, R.M Tofan SASTRANEGARA, Tommy HENDRIANSYAH, Lendriadi AGUNG, Fadhilaz Didgaya HAQ, Sigit SURYANTO, and Imam B. RAHARJO
[Pertamina Geothermal Energy, Indonesia]
Faults play an important role for hydrothermal fluid conduits in geothermal systems. Thus, studies of such objects are useful for geothermal exploration. One of them is seismicity. A series of faults in Tondano depression are partially covered by younger volcanic deposits, and the topographic expressions are relatively weak. This condition has become a substantial challenge when investigating the geological structures for geothermal well targetting. A focal mechanism study was conducted to identify faults geometry and to understand the faulting mechanism as well as the stress regime in Tondano depression. The study was started from the determination of major compressive and tensional stresses orientation of the region on the basis of the global earthquake database and the regional tectonic settings to the analysis of local microearthquakes focal mechanisms. Focal mechanism solutions of deep local microearthquakes events occured in Tondano depression reveal faults with two dominant strike orientations, which are SW-NE and NE-SW. The type of displacement are mostly normal right-lateral oblique and normal left-lateral oblique. This observation is in agreement with the interpretation on the fracture orientation derived from borehole fractures imaging of nearby geothermal wells which also reveals the same orientation. Relation between the major stresses orientation of the region from global earthquake dataset and local microearthquakes as well as its tectonic settings suggests that Tondano depression is extensional regime which is mainly affected by major compressional stresses from North Sulawesi Sea plate in the northwest which trends NW-SE and Molucca Sea plate collision in the east which trends E-W.
|        Topic: Geophysics||Paper Number: 13057|