Microearthquake reveals the lithospheric structure at mid-ocean ridges and oceanic transform faults

Mid-ocean ridge and oceanic transforms are among the most prominent features on the seafloor surface and are crucial for understanding seafloor spreading and plate tectonic dynamics, but the deep structure of the oceanic lithosphere remains poorly understood. The large number of microearthquakes occurring along ridges and transforms provide valuable information for gaining an in-depth view of the underlying detailed seismic structures, contributing to understanding geodynamic processes within the oceanic lithosphere. Previous studies have indicated that the maximum depth of microseismicity is controlled by the 600-°C isotherm. However, this perspective is being challenged due to increasing observations of deep earthquakes that far exceed this suggested isotherm along mid-ocean ridges and oceanic transform faults. Several mechanisms have been proposed to explain these deep events, and we suggest that local geodynamic processes (e.g., magma supply, mylonite shear zone, long-lived faults, hydrothermal vents, etc.) likely play a more important role than previously thought.