1:45 PM - 3:15 PM
[SCG46-P02] Stress Field Orientation Obtained from Earthquake Focal Mechanisms in Indonesia Region
Keywords:Stress mapping, Indonesia, SHmax, Stress inversions
Examination of the stress field is essential to understanding occurrence mechanisms of earthquakes, but most of them in Indonesia only focus on several part of Indonesia region. In the present study, we constructed the stress map in the entire Indonesia and its surrounding area using focal mechanism data derived from the GCMT and the Source parameter determination based on Waveform Inversion of Fourier Transformed seismograms (SWIFT) by NIED with stations of BMKG from the period 1990 until 2021, which is the first detailed stress map for Indonesia. In total, we used 3,756 focal mechanism data of earthquakes with depths of < 30 km in the Indonesia region.
We applied two methodologies in this study. First, we created the 75 km x 75 km mesh of spatial mean of maximum horizontal compression stress (SHmax) and fault type. Then, we also performed the stress tensor inversion method to confirm the spatial mean of SHmax orientations because more accurate stress orientation can be obtained by the method. We got the steeper plunge angles in West and Central Java, the East Java, the Sumba subduction segments than other regions, while very declivous plunges of sigma 1 happened in the northern North Maluku, southern North Maluku, and Batu-Mentawai-Pagai subduction segments. We confirmed that the two methodologies showed the same SHmax orientation in general. In our stress map, the orientations of SHmax are commonly perpendicular to the trench in the subduction zone and subparallel to the plate motion. We confirmed that the normal faulting associated with SHmax parallel to the trench is intense near the trench of Java and Sumba subduction segments, indicating this area as the uncouple subduction zone. This stress map also showed the fault type distribution, which is generally consistent with the tectonic setting and focal mechanisms of large earthquakes in Indonesia. Stress map in this study has possibility to assess the potential slip of faults in Indonesia for future prospects.
We applied two methodologies in this study. First, we created the 75 km x 75 km mesh of spatial mean of maximum horizontal compression stress (SHmax) and fault type. Then, we also performed the stress tensor inversion method to confirm the spatial mean of SHmax orientations because more accurate stress orientation can be obtained by the method. We got the steeper plunge angles in West and Central Java, the East Java, the Sumba subduction segments than other regions, while very declivous plunges of sigma 1 happened in the northern North Maluku, southern North Maluku, and Batu-Mentawai-Pagai subduction segments. We confirmed that the two methodologies showed the same SHmax orientation in general. In our stress map, the orientations of SHmax are commonly perpendicular to the trench in the subduction zone and subparallel to the plate motion. We confirmed that the normal faulting associated with SHmax parallel to the trench is intense near the trench of Java and Sumba subduction segments, indicating this area as the uncouple subduction zone. This stress map also showed the fault type distribution, which is generally consistent with the tectonic setting and focal mechanisms of large earthquakes in Indonesia. Stress map in this study has possibility to assess the potential slip of faults in Indonesia for future prospects.