The relation between earthquakes, faulting, and submarine hydrothermal mineralization

Abstract

Although the relationship between submarine hydrothermal activity and earthquakes was recognized over 20 years ago, it has still not been precisely defined. Faulting and permeability control fluid flow in the oceanic crust and therefore submarine hydrothermal activity at mid‐ocean ridges. Microearthquakes associated with submarine hydrothermal activity tend to be small in magnitude and occur in swarms. Swarms of microearthquakes associated with hydrothermal vents are thought to be related to cracking of the oceanic crust. The depths of the microearthquakes may mark the brittle‐ductile transition which denotes the downward limit of seawater circulation into the oceanic crust. The maximum depth of microearthquakes on the Mid‐Atlantic Ridge is 10 km, compared with 3 km on the East Pacific Rise. The brittle layer tends to be thinnest where mid‐ocean spreading rates are fastest. Seismic pumping is a mechanism for the transport of hydrothermal fluids within fractures and may account for stockwork mineralization within the ocean crust. Submarine hydrothermal mineralization is episodic on time scales ranging from 1 to 105 years and is controlled by volcanic and tectonic processes in a manner not yet completely understood. Emphasis in the study of submarine hydrothermal activity is changing from observation to long‐term monitoring. The U.S. Navy's Sound Surveillance System (SOSUS) has been very successful in detecting megaplume events caused by dike injection on the Juan de Fuca and Gorda Ridges. The long‐term deployment of large arrays of ocean bottom seismometers on the ocean floor will become routine in the future. Such a program will contribute to an understanding of the factors controlling the episodicity of submarine hydrothermal activity and mineralization on the sea floor. On the Izu‐Bonin Arc, hydrothermal mineralization has been observed in a number of volcanic Calderas. This region appears to have many advantages for the future monitoring and evaluation of microseismicity in hydrothermally active areas.