Earthquake-induced changes in a hydrothermal system on the Juan de Fuca mid-ocean ridge

Hydrothermal vents on mid-ocean ridges of the northeast Pacific Ocean are k nown to respond to seismic disturbances, with observed changes in vent temp erature(1-4). But these disturbances resulted from submarine volcanic activ ity; until now, there have been no observations of the response of a vent s ystem to nonmagmatic, tectonic events. Here we report measurements of hydro thermal vent temperature from several vents on the Juan de Fuca ridge in Ju ne 1999, before, during and after an earthquake swarm of apparent tectonic origin. Vent fluid temperatures began to rise 4-11 days after the first ear thquake. Following this initial increase, the vent temperatures oscillated for about a month before settling down to higher values. We also observed a tenfold increase in fluid output from the hydrothermal system over a perio d of at least 80 days, extending along the entire ridge segment. Such a lar ge, segment-wide thermal response to relatively modest tectonic activity is surprising, and raises questions about the sources of excess heat and flui d, and the possible effect on vent biological communities.