The Lombok region of Indonesia lies within the tectonically active Sunda Arc, where the Indo-Australian Plate subducts beneath the Eurasian Plate at rates of approximately 6–7 cm per year. This convergence generates frequent seismic activity, including both megathrust events and shallower crustal earthquakes. Lombok itself is situated on the western portion of the Lesser Sunda Islands, adjacent to the volcanic arc that includes the active Mount Rinjani stratovolcano. The island’s geology reflects ongoing subduction-related processes, with a mix of sedimentary basins, volcanic deposits, and fault systems capable of producing moderate to large earthquakes.
Between 11:46 on 5 August 2018 and 18:21 on 6 August 2018, a seismic swarm comprising eight earthquakes was recorded in the Lombok region. The sequence began with a magnitude 6.9 event at 34 km depth, followed within hours by additional events ranging from magnitude 3.7 to 5.5. Subsequent shocks on 6 August included magnitudes 5.3, 5.1, and a final 5.3 event. Depths throughout the swarm varied between 10 km and 34 km, indicating activity across both upper-crustal and intermediate-depth structures. The entire sequence lasted 30 hours and 34 minutes.
This swarm represents the sole seismic swarm recorded in the Lombok region since 1 January 2000 according to SeismoSight internal classification. Its occurrence underscores the persistent seismic hazard in the area, where clustered earthquake activity can precede or accompany larger tectonic readjustments along the subduction interface and associated back-arc faults.
The 2018 Lombok sequence occurred in a region with a well-documented history of destructive earthquakes driven by the same plate-boundary forces. Volcanic processes linked to Rinjani also contribute to local stress fields, though the primary driver remains tectonic. Updated monitoring by regional and global networks continues to track aftershock patterns and strain accumulation along the arc, informing hazard assessments for nearby populations and infrastructure.