Analysis of Past and Future Debris Flows and Turbidity Currents Generated by Slope Failures Along the Sigsbee Escarpment in the Deep Gulf of Mexico

摘要

There are many seafloor features on and near the base of thernSigsbee Escarpment that were formed as the result of massrngravity flows. Accordingly, a multidisciplinary team conductedrnan evaluation of these features as part of an overallrnstudy of geohazards. The goals of these evaluations were to:rn1) catalog the varieties of mass gravity flows that have occurredrnin the past, 2) understand the causes of these events, 3)rncharacterize the kinematics (e.g., speeds, dimensions) of thesernflows, and 4) portray the relative magnitudes of the spatiallyrndependent exposures to possible future events.rnTo accomplish these goals, there was extensive use ofrnpreviously collected seismic exploration data that includedrnseafloor bathymetric images and shallow reflection amplitudes.rnMaps of mass gravity flow features, sources, and flowrnpaths were developed. These were used to plan a comprehensivernprogram of bottom surveying with an autonomous underwaterrnvehicle (AUV). The fieldwork also included a programrnof navigated deep piston-cores and box cores, along withrnvideo observations from an ROV. One goal of the field programrnwas to acquire adequate data to characterize seafloorrnmass gravity flow features and deposits. These were used asrninputs and “targets” for numerical modeling to simulate thernfeatures. The approach is that properly detailed mathematicalrnrepresentations of the physics of mass gravity flows are usedrnto “backcast” the behaviors and flow kinematics of the eventsrnthat caused the observed features. This provides model calibration,rnwhich allows the model to be applied in arnprognostic mode.rnSediments were described and analyzed for grainrnsize, erodibility and age. Geophysical data were reduced andrnarchived in a GIS system. Numerical models of debris flow,rnmudflows and turbidity currents were applied.rnThe results show that several types and scales ofrnmass gravity flows (debris flows and turbidity currents) havernbeen active all along the portion of the Sigsbee Escarpmentrncovered by the surveys. The scale and form of these featuresrnare localized and predictable. Representative flow kinematicsrnwere determined for each of the flow types using the results ofrnthe fieldwork and modeling. Activity of these features diminishedrnmarkedly over the past 10,000 years as sea level rosernfollowing the last ice age.