New insights into regional tectonics of the Sunda–Banda Arcs region from integrated magnetic and gravity modelling

• New geomagnetic survey on Lombok shows strongest anomalies of the Sunda–Banda Arcs.
• It reveals new insights to the tectonic and hazard assessments of this region.
• Two potentially reactivated large normal faults are identified in southern parts.
• The Flores Thrust is considered mature. It extended to the northwest of the island.
• Progressive subduction is identified from fast decreasing of field intensities.

The Lombok Island (Indonesia), situated along the Sunda–Banda Arcs transition region, lies between zones characterized by very large intensity magnetic anomalies. These anomalies have been noted as being part of the eight most important ones seen on the 1st edition of the World Digital Magnetic Anomaly Map. Unfortunately, only marine magnetic data of surroundings are available, and no regional high-resolution magnetic surveys of this island had been done. Since 2004, we have carried out several geomagnetic ground surveys in this region. Here, we present modelling results for a new geological and tectonic interpretation of the magnetic anomalies. The new results confirm the general pattern of contiguous negative–positive anomalies, revealing two active Quaternary normal faults and a magmatic arc related to a subduction region. This outcome agrees with earlier results in surrounding areas obtained by satellite, aeromagnetic, and marine platforms, and provides a more detailed picture of strong anomalies on this island. Considering both magnetic anomalies and gravity models, it is possible to suggest an extension of the Flores Thrust zone (reaching the northwest off the Lombok Island). The Flores Thrust zone may be considered as a mature subduction in the back arc region, showing a tendency of progressive subduction during last decades.