HYDROTHERMAL STRESS DROPS AND CONVECTIVE PATTERNS AT 3 MID-OCEAN SPREADING CENTERS

Near-bottom deep-tow surveys of the East Pacific Rise 21°N, the Galapagos Spreading Center 86°W and the East Pacific Rise 8°24′N reveal discrete hydrothermal phenomena localized at or near the axial central highs and adjacent to the marginal zones of the inner rifts. At the center, primary discharge is localized at discrete vents. Here the recharge zone may totally surround the discharge. Away from the center, where the crust cools and contracts, secondary permeability rapidly increases. Tension cracks serve both as entrances and exits to secondary water circulation. Water may circulate along the strike of the fissures. When fluid pressures build up above hydrostatic, the increase of stress might initiate seismic responses with stress drops within the range of microseismic activity. © 1979.