| Abstract Submission No. | ABS-1.2-0067 |
| Title of Abstract | Active Fault Mapping in the Off-Nicobar Islands, Andaman Sea using Local Earthquake data |
| Authors | Mahesh Perugu*, Pawan Dewangan, Aswini KK, Raj Kumar |
| Organisation | CSIR-National Institute of Oceanography |
| Address | CSIR NATIONAL INSTITUTE OF OCEANOGRAPHY, Dona Paula North Goa, GOA, India Pincode: 403004 E-mail: pmahesh.nio@csir.res.in |
| Country | India |
| Presentation | Oral |
| Abstract | Following the devastating megathrust earthquake on December 26th, 2004, the Off-Nicobar region experienced a series of earthquake swarms in 2005, 2014, 2015, and 2019, indicating persistent tectonic unrest and possible reactivation of fault systems. To investigate the origin of these seismic events and to map active fault systems and magma dynamics, the CSIR National Institute of Oceanography carried out a passive Ocean Bottom Seismometer (OBS) experiment in the eastern offshore area of the Nicobar Islands, in the Andaman Sea. Between October 10th, 2023, and January 20th, 2024, We deployed eight high-quality broadband OBS units equipped with four components (X, Y, Z, and pressure) and five ocean-bottom geophones. We report seismicity and mapped active faults in the Off-Nicobar region for the first time using local earthquake data recorded by OBS. A total of 610 small-to-moderate sized (1.0< ML<4.5) earthquakes were located during our OBS deployment period in the study region. The spatial distribution of relocated epicenters clearly delineates the ~N-S oriented Andaman Nicobar Fault (ANF) and the NW-SE oriented Seulimeum Fault (SLF), a northern strand of the Great Sumatra Fault and a N-S oriented trend T1. The seismicity pattern indicates that ANF is seismically active from east of Nicobar Islands to Andaman Islands and the SLF extends northward to approximately 8 degree north, where it closely parallels the volcanic arc. The observed spatial correlation SLF and the volcanic arc indicates a pronounced tectono-magmatic coupling, likely driven by the interplay between strike-slip faulting and subduction-related magmatic activity. The depth distribution of earthquake hypoceters reveals that both the ANF and SLF are seismically active down to 30 km depth. The ANF, and SLF collectively accommodate tectonic strain and control regional deformation regime. |
| Keywords | Ocean-Bottom Seismometers, Off-Nicobar Islands, Seismicity, Active faults, Volcanic arc |