A statistical analysis of volcano-tectonic earthquake swarms in the off Nicobar region of the Andaman Sea.

The present research work is primarily carried out to select the suitable and better variants or functions of ETAS models to describe the energetic offshore earthquake swarms following 26 December 2004 (MW 9.1) and 21 March 2014 (MW 6.5) along the Andaman–Sumatra subduction zone. An attempt has also been made to inspect the variability of the selected model parameters from this robust estimation to discuss the physical mechanism differences between the SSE-related and fluid- or magma-related swarm sequences. For this purpose, different variants of ETAS models, such as single ETAS model, combined ETAS model, Boxcar swarm model, and exponential swarm model, are utilized for investigating the seismic anomalies by estimating the model parameters from the earthquake occurrence times using maximum likelihood method. The estimated AIC (Akaike information criterion) values for all these models suggest that the exponential swarm model outperforms the other models in successfully explaining the transient changes of background seismicity for the five energetic earthquake swarms triggered by the volcano-tectonic activities in the Andaman Sea. The reason is undoubtedly related to the localized nature of magmatic intrusion or fluid migration that caused the swarms and the exponential decay patterns of earthquakes after the initiation of the swarms. Although the swarms exhibit the shape of exponential function, the background seismicity shown by the parameter μ increases by one order during the swarm as compared to the pre-swarm period in the sub-catalogue. Therefore, the procedure of identifying improved variants or functions of ETAS models and estimating model parameters using earthquake occurrence times enhances our understanding of earthquake-triggering mechanisms, potential swarm activity patterns, and the intricate interplay between seismicity and volcanic processes in submarine volcanic arcs. While this approach might not facilitate real-time forecasting, it remains instrumental in characterizing seismic patterns and providing essential information for effective hazard assessment and the formulation of mitigation strategies within the coastal areas of the Andaman–Nicobar Islands region. [ABSTRACT FROM AUTHOR]