This phenomenon provides deep insight into the chemical and physical changes occurring inside a subducting plate. The upper layer of quakes is usually at the top of the slab, while the lower layer is inside the slab’s “cold core.” The quakes are triggered by “dehydration embrittlement”—as minerals like serpentine release water under high pressure, the water reduces friction, allowing the rock to break. Studying these zones helps scientists understand the complex water cycle of the Earth’s mantle and how fluids influence deep-seated seismic activity.