M.J. Hornbach | Geology Reports

USGS2010

High tsunami frequency as a result of combined strike-slip faulting and coastal landslides

Earthquakes on strike-slip faults can produce devastating natural hazards. However, because they consist predominantly of lateral motion, these faults are rarely associated with significant uplift or tsunami generation. And although submarine slides can generate tsunami, only a few per cent of all tsunami are believed to be triggered in this way. The 12 January Mw 7.0 Haiti earthquake exhibited primarily strike-slip motion but nevertheless generated a tsunami. Here we present data from a comprehensive field survey that covered the onshore and offshore area around the epicentre to document that modest uplift together with slope failure caused tsunamigenesis. Submarine landslides caused the most severe tsunami locally. Our analysis suggests that slide-generated tsunami occur an order-of-magnitude more frequently along the Gonave microplate than global estimates predict. Uplift was generated because of the earthquake?s location, where the Caribbean and Gonave microplates collide obliquely. The earthquake also caused liquefaction at several river deltas that prograde rapidly and are prone to failure. We conclude that coastal strike-slip fault systems such as the Enriquillog-Plantain Garden fault produce relief conducive to rapid sedimentation, erosion and slope failure, so that even modest predominantly strike-slip earthquakes can cause potentially catastrophic slide-generated tsunamig-a risk that is underestimated at present. ?? 2010 Macmillan Publishers Limited. All rights reserved.

Nature Geoscience↗

USGS2007

Three-dimensional structure of fluid conduits sustaining an active deep marine cold seep

Cold seeps in deep marine settings emit fluids to the overlying ocean and are often associated with such seafloor flux indicators as chemosynthetic biota, pockmarks, and authigenic carbonate rocks. Despite evidence for spatiotemporal variability in the rate, locus, and composition of cold seep fluid emissions, the shallow subseafloor plumbing systems have never been clearly imaged in three dimensions. Using a novel, high-resolution approach, we produce the first three-dimensional image of possible fluid conduits beneath a cold seep at a study site within the Blake Ridge gas hydrate province. Complex, dendritic features diverge upward toward the seafloor from feeder conduits at depth and could potentially draw flow laterally by up to 10 3 m from the known seafloor seep, a pattern similar to that suggested for some hydrothermal vents. The biodiversity, community structure, and succession dynamics of chemosynthetic communities at cold seeps may largely reflect these complexities of subseafloor fluid flow.

Blake Ridge↗