Intraplate crustal deformation in Sabah: Preliminary results of Global Positioning System/Global Navigation Satellite System measurements in the Ranau area

Abstract

The Ranau area is one of the most earthquake-prone areas in Sabah due to the ongoing intraplate deformation in the region. Numerous active faults have been mapped here, but to date these faults are yet to be fully documented in terms of their exact locations and movements. Since 2018, the Department of Mineral and Geoscience (JMG) has installed and monitored 31 GPS/GNSS (Global Positioning System/Global Navigation Satellite System) monuments in the Ranau area to determine crustal movements in this region. Preliminary results show minor horizontal and vertical movements (ranging from 0.1 cm to 4.3 cm) indicating that the Ranau area is undergoing intraplate crustal deformation due to both NW-SE compressional and extensional tectonics. A clear demarcation of upward and downward vertical movements recorded in areas to the NW and SE of Kundasang could be related to uplift and subsidence associated with a large open anticline and syncline. A consistent northwestward horizontal movement from Kundasang to Kota Belud indicates the presence of a single crustal block moving away from the NE-SW trending Lobou-Lobou Fault Zone. Southwestward horizontal movement in the Nalapak-Nabutan area indicates the presence of a NW-SE trending fault possibly associated with the Matupang Fault Zone. These preliminary results show that the GPS/GNSS campaign has proven to be quite successful in locating the major earthquake-generating faults in the Ranau area. However, the locations and nature of the movements of other active faults are still uncertain. It is hoped that the activity of these faults will become clearer after a few more years of monitoring.