Physical response of mid-ocean ridge hydrothermal systems to local earthquakes

Abstract

Observations from the East Pacific Rise (EPR) and the Endeavour segment of the Juan de Fuca Ridge show that local earthquake swarms can lead to increased hydrothermal venting temperatures after a delay of several days. I develop two models for this process. In the temperature perturbation model, a new pathway opens to a heat source, and the temperatures of fluids leaving the reaction zone increase. By considering the exchange of heat between the fluid flowing up a conduit and the wall rock, I solve for the resulting perturbation to venting temperatures. For flow in a crack the response is delayed, and the delay increases as the crack narrows or the reaction zone deepens, but for a pipe the venting temperature increases either quickly or barely at all. In the pressure perturbation model, there is a transient increase in pressures at depth due to a decrease in porosity, the release of overpressured fluids, or a readjustment of pressures in response to a change in the relative permeabilities of the upflow and downflow zones. One-dimensional solutions for pressure diffusion show that this model can lead to a delayed increase in outflow fluxes which may be accompanied by increased venting temperatures. The temperature perturbation model fits the data from the EPR event well. The Endeavour event is less well constrained, and both models can fit the observations adequately. Local seismic networks and time series of fluid flux, chemistry, and temperature will be required to fully exploit hydrothermal perturbation events to infer subseafloor hydrology. Copyright 2004 by the American Geophysical Union.