Interpreting Fault Dynamics in Terms of Hypocenter Relocation and Fault Characterization

Abstract

Southeast and Central Sulawesi are the areas characterized by high tectonic activity due to the presence of the active Matano fault. The seismicity along this fault is high. However, the initial hypocenter often deviates from the fault’s trend line, thus causing the need for earthquake relocation with an improved local structure description. The double difference method stands out as a precise technique for hypocenter relocation, utilizing the data on relative travel time between hypocenter pairs. After relocation, the selected hypocenter facilitates the derivation of a focal mechanism, crucial in determining fault types. In this research, we relocated the hypocenters of 485 events of January 2009 to December 2016, ranging in magnitude from M2 to M6.1, 427 of which showed a pattern close to the general trend of major and minor faults. Seismic offsets along the Matano fault are predominantly oriented in the southeast or northwest direction. Moreover, most of the earthquake activity recorded at a depth of 10 km before relocation is no longer visible. Based on the statistics, the time residuals from –2.5 to +2.5 ms resulting from the relocation procedure are better close to 0 than those of –4.5 to +4.5 ms for the events before relocation. The focal mechanism solutions of 16 events of final relocation are dominated by strike-slip faulting. The Matano fault is predominantly sinistral-type. The seismicity along this fault zone results from an activity of this fault, which is the main source of earthquakes, and from its interaction with the neighboring Palu-Koro and Sorong faults.