The Role of the Fluid in the Genesis of the 2022 Champhai Swarms at the Eastern End of the Indo-Burmese Arc.

Between July 26 and August 25, 2022, during the peak monsoon season, a significant seismic swarm occurred in the Champhai region of Mizoram. The swarm comprised 270 earthquakes, with magnitudes ranging from ML 0.4 to 4.4, concentrated at shallow depths of 5–10 km. To investigate the swarm's characteristics and potential causative mechanisms, we conducted a comprehensive analysis incorporating seismic waveform data and Interferometric Synthetic Aperture Radar (InSAR) observations. Moment tensor inversion for four selected earthquakes indicated a dominant negative compensated linear vector dipole (CLVD) component, suggesting a non-tectonic or complex tectonic origin of the events. A notable feature of this swarm was the low average stress drop, estimated at approximately 2.5 MPa, indicative of low-energy release and likely aseismic slip or fluid-assisted faulting. The seismicity exhibited a diffusivity of 67 m²/s, pointing to rapid subsurface fluid migration through fractured rock under high pressure. This high diffusivity supports the hypothesis that fluid activity played a critical role in triggering and sustaining the seismic swarm. The findings imply that both elastic and poroelastic mechanisms were active during the swarm. As fluid pressure fluctuated in response to stress changes, it facilitated the outward migration of seismicity, a hallmark of fluid-induced swarm behavior. This study underscores the complex relationship between tectonic stress and fluid dynamics in triggering seismic swarms in structurally intricate regions like the outer Indo-Burmese Wedge. The results highlight the importance of integrating seismic and geodetic data to unravel the physical processes underlying swarm-type seismicity in fluid-rich, faulted crustal environments.