Silica's melting point is lowered when mixed with water, so oceanic faults can have actual molten magma lubricating and weakening the fault line. Otherwise, you

Silica's melting point is lowered when mixed with water, so oceanic faults can have actual molten magma lubricating and weakening the fault line. Otherwise, you'd have the stronger malleable solid mantle at the joint, and lose much more energy whenever the fault tried to move. Having at least some faults that slippery is necessary to keep the system from locking up.