Preliminary Report of September 14, 2025 Udalguri, Assam Earthquake by National Centre for Seismology

way2barak September 14: A moderate earthquake of magnitude 5.8 occurred in Udalguri District Assam on 14th September 2025 at 16:41:50 IST at a depth of 05 km with epicentre at 26.78 N, 92.33 E. The event was recorded by National Centre for Seismology and located 89 km NE of Guwahati city of Assam State and 48 SE of Tezpur, Major Town in Assam. The preliminary analysis shows that the events are located near the Kopili Fault and closer to the 28th April 2021 M 6.4 Sonitpur earthquake. The preliminary fault plane solution derived from moment tensor inversion suggests a strike-slip fault. Figure-1 also depicts the region’s seismicity (M ≥ 2.0) during the period April 28, 2020 – April 27, 2024. Felt report of maximum Intensity VI (MMI scale) and minimum intensity of II have been reported from a distance around 5km and 500 km from the epicentre respectively. Two aftershocks (M 3.1, M 2.9) have reported till the preparation of report and we may expect more aftershock od Magnitude in the similar range.

However the seismic shaking gets attenuated at the fastest pace because of the source zones of mainshock and its aftershocks (M5.8; M 3.1 and M2.9) are already associated with fracture and cracks since April 2021 Sonitpur EQ (M 6.4) and its then aftershock sequence.

The event was well recorded by more than 20 broadband seismic stations installed by National Centre for Seismology. The historical and instrumentally recorded earthquake data (NCS catalogue) reveals that the region is affected by moderate to large earthquakes. The most prominent events among these are M 6.4 28th April 2021, M 6.4 21th Sept 2009 Bhutan earthquake and 29thJuly1960 Assam earthquake of M 6.0.

In addition to above, noteworthy earthquakes, the events originating in the Assam and neighbouring region are often felt in the region with slight to strong intensity. The occurrence of earthquakes in the region is attributed mainly to the tectonic sources in the Himalaya such as Himalayan Frontal Thrust (HFT), Main Boundary Thrust (MBT) and main Central Thrust (MCT), Kopili Fault and Dhubari Fault. Seismologically as well as geologically, it is evidenced that the region has been quite active and falling in the highest seismic hazard zone V. The Assam region falls in the high seismic zones V of the seismic zoning map of Bureau of Indian Standards (BIS).

The earthquake was widely felt across Assam and neighboring states, with calculated intensities ranging from II to VI on the Modified Mercalli Intensity (MMI) scale within a distance of approximately 0 to 300 km from the epicentre. A total of 03 felt reports were received through the NCS website and mobile app, indicating intensities between III and VI on the MMI scale.