In eastern Indonesia, Sulawesi Island lies at the triple junction of the
Australian, Sunda, and Phillippine Sea plates. The distinctive K-shape
of Sulawesi, consisting of four arms (North, South, East, and
Southeast), resulted from continuous geological evolution at different
stages. Consequently, each arm has a different deformation style and
tectonic setting. We studied the seismotectonics of Sulawesi using the
updated dataset for earthquake seismicity and focal mechanisms,
including additional supporting data. We grouped Sulawesi shallow part
(< 60 kilometers) into six regions, while the deep part
(60-400 kilometers) related to the Celebes Sea and Sula slabs. Regarding
the shallow part, we found a lack of seismicity in the northern
Palu-Koro fault and near the center of the North Sulawesi Trench,
although these zones have high slip rates. On the deep part, the Celebes
Sea slab showed an increasing dip as depth increased, whereas the Sula
slab showed a steeply dipping slab. Moreover, the western Sula slab
indicated an absence of shallow depth earthquakes (60–230 kilometers).
Based on our investigations, we derived the following well-founded
conclusions: (1) The northern Palu-Koro fault was beyond the high
relative motion of the Makassar and North Sula blocks, resulting
inactive seismicity. (2) A seismic gap or aseismic slip from the Celebes
Sea subduction probably produced the low seismicity level near the
center of the North Sulawesi Trench. (3) The shallow inactive seismicity
in the western Sula slab might be due to the upper slab detaching during
the first stage collision in the Early Miocene.
Salah satu gempabumi merusak yang terjadi di Indonesia pada tahun 2012 yaitu gempabumi Ransiki, Papua Barat 21 April 2012, Mw 6,7. Yang menarik dari gempabumi ini yaitu lokasi gempabumi yang berdekatan dengan dua sesar, yaitu sesar Ransiki dan sesar Yapen sehingga tujuan penelitian ini yaitu membuat pemodelan dan menganalisis mekanisme sumber gempabumi untuk mengetahui sesar penyebab gempabumi Ransiki. Mekanisme sumber gempabumi dimodelkan dari proses inversi tensor momen menggunakan program Isola. Untuk menentukan bidang sesar sebenarnya digunakan program HC-plot. Hasil inversi tensor momen menunjukan bahwa gempabumi Ransiki merupakan gempabumi mekanisme sesar geser dengan bidang nodal 1; strike 3550, dip 680, rake -1650 dan bidang nodal 2; strike 2590, dip 760, rake -230. Pengolahan dengan program HC-plot menghasilkan bidang sesar sebenarnya yaitu bidang nodal 2 dengan strike 2590, dip 760, rake -230. Hasil ini menunjukan bahwa gempabumi Ransiki 21 April 2012 Mw 6,7, disebabkan oleh sesar Yapen dengan mekanisme sesar geser mengiri berarah barat-timur.
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