*Article* **Seismic Structure Beneath the Molucca Sea Collision Zone from Travel Time Tomography Based on Local and Regional BMKG Networks**

**Gazali Rachman 1,2,\*, Bagus Jaya Santosa 1, Andri Dian Nugraha 3,4, Supriyanto Rohadi 5, Shindy Rosalia 3,4, Zulfakriza Zulfakriza 3,4, Sungkono Sungkono 1, David P. Sahara 3,4, Faiz Muttaqy 6, Pepen Supendi 5, Mohamad Ramdhan 6, Ardianto Ardianto <sup>7</sup> and Haunan Afif <sup>8</sup>**


**Abstract:** The Molucca Sea Plate, and Sangihe and Halmahera plates have a complex tectonic setting and interact to create the Molucca Sea Collision Zone. We re-picked 1647 events recorded from 2010 to 2017 from 32 of The Agency for Meteorology, Climatology, and Geophysics (BMKG) stations and obtained P- and S-arrivals of ~17,628 phases. Hypocenter locations were determined using the software NonLinLoc. Then, we performed a travel time tomography in order to image the subsurface and approximate the Molucca Sea Plate subduction angle beneath Sulawesi's north arm, the relationship subduction zone and volcanic activity in Halmahera, and depth comparison of the Molucca Sea Plate. Our results show that (i) high Vp, high Vs, and low Vp/Vs are associated with the Molucca Sea Plate beneath Sulawesi's north arm, and the approximate subduction angle is ~40◦. (ii) Low Vp, low Vs, and high Vp/Vs beneath the northern and southern Halmahera Volcanic Arc are associated with a possible magma source. Volcanoes in the north have experienced eruptions and are dormant in the south. This group of volcanoes is connected by partial melting above the Molucca Sea Plate subducts to the east. (iii) High Vp, high Vs, and low Vp/Vs are interpreted as double subduction of the Molucca Sea Plate. It is submerged deeper in the north compared with the south, which is nearer to the surface.

**Keywords:** travel time tomography; Molucca Sea Plate; magma source; partial melting

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).
