SEISMOTECTONIC ANALYSIS OF MW 7.6 2023 SOUTH MOLUCCA INTERMEDIATE-DEPTH EARTHQUAKE

Abstract

On January 10, 2023, a significant earthquake with M_w 7.6 occurred in the southern part of Molucca, Indonesia, and generated widespread ground shaking around IV-VI MMI, followed by building damages and early tsunami warning. The hypocenter was located deeper than the common slab contour, which may indicate another blind tectonic system called intraslab. Joint analysis was applied by correlating the waveform inversion with hypocenter relocation to identify the current seismic activities. The main objective of the finding results is to configure the seismotectonic system that has generated several intermediate-depth earthquakes in the southern part of Molucca. Therefore, a total of 1711 earthquakes were obtained from the 2019 - 2022 catalog which were recorded by 72 stations associated with 9125 P-phase and 4217 S-phase. As many as 90% (1530) of the total earthquakes were successfully relocated, while 10% (170) were not relocated because they did not meet the predetermined criteria. Furthermore, the mainshock was resolved with thrusting fault with NW – SE orientation, steeply dipping to the SW direction and a moment magnitude estimation M_w of 7.6 ± 0.03 at depth 35.50 ± 2 km. The focal parameters include two nodal planes, i.e., first nodal plane with strike 319°, dip 15.5° and rake 101°, and second nodal plane with strike 127°, dip 74.8° and rake 86.8°. The results show successfully the existence of the hidden intraslab beneath the collision between the Australian plate and the Eurasian plate, which can provide new insight and also contribute to the recent tectonic system in East Indonesia