Local seismotectonic analysis of the July 2019 Molucca Sea earthquake sequence based on moment tensor solutions

Aditya Dwi Prasetio,Mohammad Hasib,Cinantya Nirmala Dewi,Andi Amran,Febty Febriani,Syuhada Syuhada,Titi Anggono

doi:10.1186/s40562-021-00200-z

Aditya Dwi Prasetio, Mohammad Hasib + Show 5 more

Open Access

https://doi.org/10.1186/s40562-021-00200-z

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Abstract

We investigate the local seismotectonic of the Molucca Sea area using moment tensor calculations for the earthquakes that occurred in July 2019 at a depth of 10–55 km. The mainshock of Mw 6.8 occurred on July 7, followed by aftershocks until July 18, with magnitudes ranging from Mw 4.6 to Mw 5.8. Moment tensor solutions are calculated by applying Isolated Asperities (ISOLA) software using the full waveform data recorded at regional seismic stations. The analyzed frequency bands used in this study are 0.01–0.03 Hz and 0.04–0.05 Hz for the event with Mw ≥ 5 and Mw < 5, respectively. We provide validations of new moment tensor solutions for Mw < 5 events in the Molucca Sea region for the period during the earthquake sequence. The results show that thrust and oblique faults are dominant during this event, which indicate a compressional stress of divergent double subduction (DDS) of the Sangihe and Halmahera arcs. Only one full moment tensor solution reveals the normal fault mechanism, which may indicate the manifestation of strain release of compressional stress in the surrounding area. Furthermore, these results also support the previous studies suggesting that the Talaud-Mayu Ridge located in the middle of the Molucca Sea has developed as a consequence of the transpressional tectonic activity.

Highlights

The Molucca Sea, an area well known for its tectonic complexity, is a region with high seismicity, located between the eastern arm of Sulawesi Island and Halmahera Island in the eastern part of Indonesia
We only examine moment tensor solutions with high variance reduction (VR) and DC values and low condition number (CN) values
All tectonic activities occur in the upper lithosphere and the Molucca Sea Plate, according to the cross-section of tectonic settings used by Silver and Moore (1978) and Zhang et al (2017)

Summary

Introduction

The Molucca Sea, an area well known for its tectonic complexity, is a region with high seismicity, located between the eastern arm of Sulawesi Island and Halmahera Island in the eastern part of Indonesia (see Fig. 1a). The Molucca Sea Plate is subducted under the arc-arc collision between Sangihe in the west and Halmahera in the east This region is the only unique example of an active arc– arc collision on earth that consumes an oceanic basin via subduction in a different direction. It is formed by the convergence of the Sangihe and Halmahera arcs into the Molucca Sea Plate in eastward and westward directions, respectively (see Fig. 1b).

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