Hess Deep

Hess Deep

Hess Deep is a seismically active rift valley at the westward propagating tip of the Galapagos Spreading Center in the Pacific Ocean. Several characteristics of Hess Deep make it an excellent region to study the brittle breakdown process during rifting, including negligible sediment cover that leaves rift structures well exposed, young prerift crust that has undergone little deformation prior to rifting, and a relatively simple tectonic setting that can be modeled as a propagating crack in an elastic plate.

From May 1996 to October 2000, an array of six autonomous moored hydrophones recorded more than 200 low-magnitude (Mw ~ 1.8 to 4.4) earthquakes in Hess Deep. These data are particularly advantageous for studying seismic characteristics of the rifting process, because ridge earthquake magnitudes typically lie below the ~4.5 moment magnitude (Mw) detection threshold of teleseismic networks.

Hess Deep Stress and Strain Models

The hydroacoustic earthquake data reveal distinct phases of tectonic loading, rift nucleation, and ridge propagation into oceanic crust formed at the East Pacific Rise.  The patterns of seismicity and faulting, as explained in Floyd et al. (2002), are similar to those observed in the process zone of laboratory-scale propagating tensile cracks.

By studying rift propagation in a relatively simple tectonic environment like Hess Deep, we can begin to determine the fundamental mechanisms by which rifts propagate and thereby begin to better understand structurally more complex rifting environments, such as the Woodlark Basin. Future studies in this region will focus on better understanding the role of process zone-like deformation in the rift nucleation process.

Publication: Floyd, J.S., Tolstoy, M., Mutter, J.C., and Scholz, C., 2002, Seismotectonics of mid-ocean ridge propagation in Hess Deep, Science, 298, 1765-1768.