[S-EM15] Electric, magnetic and electromagnetic survey technologies and scientific achievements

[SEM15-05] Depiction of the Lombok Island’s geological and tectonic features inferred by the gravity and magnetic data

*Febty Febriani¹、Cinantya Nirmala Dewi²、Teti Zubaidah³、Karit Lumban Gaol¹、King Adhen El Fadhila⁴、Raa Ina Sidrotul Munthaha⁴、Bagas Triarahmadhana⁴、Ryokei Yoshimura⁵ (1.Research Center for Geological Disaster National Research and Innovation Agency、2.Graduate School of Science, Kyoto University, Kyoto, Japan、3.Magister of Disaster Mitigation, University of Mataram、4.Directorate of Geospatial Reference System, Geospatial Information Agency、5.Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan)

キーワード：Lombok, earthquake, gravity, geomagnetic

Lombok Island, located in eastern Indonesia, is part of the West Nusa Tenggara province. It is home to Mount Rinjani, the second-highest volcano in Indonesia, standing 3,726 meters above sea level. The island is also characterized by several active faults. These geological features make the island a site of intense tectonic activity, as evidenced by the devastating series of earthquakes that struck in July and August 2018. These events were the largest and strongest earthquakes recorded in Lombok’s history, with magnitudes exceeding 6, causing severe fatalities and widespread destruction. The island’s active tectonic setting and history of destructive earthquakes highlight the need for a thorough understanding of its subsurface characteristics to support disaster preparedness and risk mitigation. A previous study using InSAR and Sentinel-1 data was conducted after the 2018 Lombok earthquake to obtain a more detailed subsurface image of the island. However, there is a lack of comprehensive geophysical data on Lombok’s subsurface, which limits the accuracy of hazard assessments and mitigation efforts. Therefore, a detailed subsurface investigation of the study area is crucial for improving hazard assessments. To gain a more detailed understanding of Lombok Island’s subsurface, we applied gravity and geomagnetic methods in this study. Gravity data acquisition was conducted across the island from 2019 to 2023, with a total of 203 observation points. Gravity data were acquired using the Scintrex CG-5 gravimeter (2019) and the LaCoste & Romberg G-804 gravimeter (2022–2023). Meanwhile, geomagnetic data were acquired from 2022 to 2023, focusing on northeastern Lombok Island, near the epicenter of the 2018 earthquakes. A total of 107 geomagnetic observation points were acquired using a proton precession magnetometer (PPM). This research analyzes the magnetic properties of geological formations using geomagnetic data, while gravity data help to understand density variations in the crust, providing a more detailed and accurate depiction of the island’s geological and tectonic features. This approach will also allow for a more precise evaluation of the earthquake and volcanic hazard potential on Lombok Island, contributing to enhanced risk assessments and disaster preparedness.