Seafloor Spreading Event Revealed by In Situ Seismogeodesy

A groundbreaking investigation into seafloor spreading events has been achieved through the deployment of cutting-edge in situ seismogeodetic instruments along the Southeast Indian Ridge. Autonomous hydrophone arrays moored within the SOFAR channel captured high-fidelity acoustic signals from seismic events and volcanic activity, enabling precise localization of nearly 500 T-wave seismic events with kilometer-scale accuracy. This marks a transformational step beyond traditional land-based seismic catalogs hampered by location uncertainties exceeding 20 kilometers in these remote oceanic regions.

Complementing the hydroacoustic data, a network of acoustic transponders, mounted on tripods equipped with pressure, temperature, and conductivity sensors, employed direct-path acoustic ranging to monitor horizontal seafloor displacements down to millimeter precision. Despite technical challenges such as tripod tilt of up to 12 degrees and rugged seabed topography, repeat measurements over months resolved baseline changes that reveal complex fault slip and magmatic intrusion processes beneath the spreading ridge.

A self-calibrating bottom-pressure recorder (BPR) precisely tracked vertical deformation of the axial valley floor over an 11-month period. The BPR’s dual quartz pressure sensors, corrected for instrumental drift and tidal influences, recorded millimeter-scale seafloor subsidence coincident with large-magnitude earthquakes. Elastic dislocation modeling constrained these seismic sources to shallow depths less than 5 kilometers, corroborating geophysical hypotheses of near-surface fault slip controlling crustal extension and magma pathway evolution.

Advanced two-dimensional elastic half-space models were leveraged to simulate fault slip, dyke opening, and sill intrusion simultaneously, allowing more detailed interpretations of the observed deformation field. Employing Monte Carlo sampling, researchers inverted for source parameters consistent with seafloor motions, notably inferring a vertically opening dyke and adjacent normal fault slip controlling transient deformation patterns. These models highlight the intricate mechanical interplay driving the episodic uncoupling and rupture of oceanic crustal segments.

Static Coulomb stress change computations further elucidated how a segment-scale dyke intrusion influences stress on neighboring faults, including the nearby transform systems. This mechanistic insight underscores the potential for volcanic processes to trigger seismicity along transform boundaries, modulating seismic hazard in complex ridge-transform ecosystems. The methodology exemplifies a novel integration of high-resolution seismology and geodesy to capture the anatomy of submarine rifting in near real-time.

This pioneering in situ seismogeodetic approach not only advances fundamental understanding of mid-ocean ridge dynamics but also establishes a template for detecting and characterizing undersea tectonomagmatic activity with unprecedented spatial and temporal granularity. As oceanic crust formation governs global plate tectonics and volcanic hazards, such real-time monitoring platforms promise to revolutionize our ability to anticipate and respond to submarine geohazards.

The study’s integration of acoustic hydrophones, precise acoustic ranging, bottom-pressure sensing, and sophisticated modeling represents a landmark achievement in oceanographic instrumentation and earthquake science. These findings open new frontiers for interdisciplinary research into the mechanisms governing Earth’s dynamic seafloor and highlight the vital role of technological innovation in unraveling elusive submarine processes.