Determination of Earthquake Hypocenter Distribution using the Modified Joint Hypocenter Determination (MJHD) Method throughout the Palu-Koro Fault (Case Study: August-October, 2018)

The area of Sulawesi, especially along the Palu Koro Fault, is an area that is largely influenced by the confluence and movement of plates as well as regional fault activity pathways with high levels of seismicity. Determining the location of the hypocenter accurately through relocation is required in identifying the detailed tectonic structures in the area. Relocation of the hypocenter using the Modified Joint Hypocenter Determination (MJHD) method using the IASP91 velocity model in the period August to October 2018 with the arrival time data from BMKG catalog. The results of hypocenter relocation using the MJHD method show that from 132 earthquake distribution points to 63 earthquake hypocenter points after the relocation. The change in the location of the hypocenter was much denser along the Palu Koro Fault route than before the relocation as evidenced by the mean value of rms (root mean square) before relocation was 1.31 and after relocation it became smaller (0.61). Changes in parameter values after relocation using the MJHD method caused the distribution of the earthquake hypocenter to be tighter towards the Palu Koro fault than before the relocation, where the distribution had a random and scattered pattern.

RELOKASI HIPOSENTER GEMPABUMI MENGGUNAKAN METODE MODIFIED JOINT HYPOCENTER DETERMINATION (MJHD) UNTUK ANALISIS ZONA SUBDUKSI SUMATERA BAGIAN SELATAN

The part of south Sumatera is very vulnerable region in case of earthquake disaster caused by convergent boundary of two tectonic plates Indo-Australian Plates and Eurasian Plates. Precise hypocenter analysis is needed to understand about the accurate tectonic setting such as subduction zone in the area. Hypocenter relocation is used to recalculate earthquake hypocenter to become more accurate. To produce a more accurate hyposenter this hyposenter relocation is done by using the method of Modified Joint Hypocenter Determination (MJHD). Relocation using the Modified Joint Hypocenter Determination (MJHD) method uses IASP91 wave velocity which assumes that the inner structures are heterogeneous. In this study, used data P-wave and S-wave arrival time in the period January 2010 s.d December 2016 with coordinates -3.5º s.d -9º LS - 99º s.d 106.5º BT. The results of the relocation using MJHD showed a change of earthquake hypocenter shown by RMS (Root Mean Square) value ranging from 0.2 s.d 0.5. There are three subduction of the part in south sumatra. The subduction zone formed in Bengkulu is about 26.78º, the subduction zone of Lampung is around 30.225º and the subduction of the Sunda Strait is about 52.53º. Subduction zone of Bengkulu at depth of 250 km, Lampung and Sunda Strait at depth 400 km.