We have been working with colleagues at the USGS to better understand earthquake deformation and the turbidity flows they generate along the Cascadia subduction zone. The Cascadia subduction zone extends from northern California to Canada and is where the Juan de Fuca and Gorda tectonic plates move towards and descend under the North American plate. 

The Cascadia subduction zone is capable of producing mega earthquakes (i.e., larger than a magnitude 9). Paleo-seismic investigations unequivocally show that very large earthquakes periodically generate huge tsunamis that inundate the coast along the entire Cascadia margin. The most recent of these events occurred in 1700. During these large events the entire margin is shaken enough to initiate simultaneous turbidity currents along the many parallel canyons that are cutting into the continental shelf. These sediment flows leave turbidites on the seafloor that become buried over time. The turbidite record found on the abyssal plain below these submarine canyons has been utilized to estimate the recurring frequency of large earthquakes on the Cascadia subduction zone. 

These data shows events occur on time scales of hundreds of years, frequent enough to pose a significant societal concern. However, an accurate recurrence interval of earthquake-stimulated turbidity currents from the deposits they leave has been hard to obtain. The faults where the seafloor ruptures during larger earthquakes and the resulting turbidite deposition occurs are in deep water (>3 km) making access limited. MBARI’s mapping AUVs and ROV Doc Ricketts are designed to work in these depths. With these tools the geologic deposits and fault ruptures can be mapped out and sampled in detail. This work is enabling us to distinguish earthquake related deposits from other landslide events and to establish how and when they happened.

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