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Source analysis and seismotectonic context of the 2021 MW 5.8 and MW 6.2 Tojo Una-Una earthquake in Sulawesi (Indonesia)

Authors

Daniarsyad,  Gatut
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Sianipar,  Dimas
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Serhalawan,  Yopi
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Arimuko,  Abraham
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Ulfiana,  Emi
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Daryono,  Daryono
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Pranata,  Bayu
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Adi,  Suko Prayitno
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Karnawati,  Dwikorita
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

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Citation

Daniarsyad, G., Sianipar, D., Serhalawan, Y., Arimuko, A., Ulfiana, E., Daryono, D., Pranata, B., Adi, S. P., Karnawati, D. (2023): Source analysis and seismotectonic context of the 2021 MW 5.8 and MW 6.2 Tojo Una-Una earthquake in Sulawesi (Indonesia), XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG) (Berlin 2023).
https://doi.org/10.57757/IUGG23-3845


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5020700
Abstract
On 26 July 2021, two significant earthquakes took place beneath the Gulf of Tomini, Sulawesi, Indonesia. The first earthquake, an MW 5.8, was followed by an MW 6.3 earthquake and caused light damages in the nearby town. The origin of these earthquakes was unclear, and their relations to regional seismotectonic were not well understood. In this study, we analyze the source characteristics of these earthquakes by using seismograms came from regional and global seismic stations. We obtain the double-couple focal mechanisms for four selected events using regional waveform inversion and indicate normal-faulting mechanisms for all earthquakes with centroid depths in the middle crust (depth of about ~10-13 km). We contribute the possible finite-fault rupture of the MW 6.3 event by using a teleseismic inversion. This event has only one single asperity with a peak slip of about 146 cm and a high stress drop of about 80 bars. The average slip in this asperity is approximately 87 cm, and the rupture duration is about 7–s. Our hypocenter relocation procedure favors the northeast-dipping plane (strike 290°, dip 48°) as a possible active fault ruptured during the earthquakes. We propose that the 2021 Tojo Una-Una earthquakes correspond to a possible active normal fault that has not been identified previously in the earthquake hazard map. This normal fault could be related to extensional tectonics beneath the Gulf of Tomini.