Slope instability may be a consideration when siting offshore facilities. Understanding the frequency and triggers of past slope failures may be useful in estimating the likelihood of future slope failures. In addition, knowledge of the volume of material from past slope failures may be useful for assessing potential debris-flow run-out or debris-structure impact of future slope failures. Geophysical and geotechnical data have been used to identify mass transport deposits (MTDs) from previously failed slopes. Differences in interpretation of MTDs in geophysical data and cores are presented. Limitations on the vertical resolution of geophysical data and line spacing of the two-dimensional survey creates uncertainty in the size and number of MTDs in a given survey area. This is illustrated by comparing MTDs in cores and in geophysical data at a deepwater site. What is interpreted as large MTDs in the geophysical data can be several thinner, stacked MTDs observed in core samples. Reconciling differences in MTDs observed in the different datasets may be useful to more fully characterize past slope failures. The trigger for past slope failures at the site is likely tied to sea level. During periods of lower sea level, the sedimentation rates at the site are high, and the frequency of slope failures increases. Conversely, in periods of higher sea level, the sedimentation rate decreases, and the frequency of slope failure decreases.
Eric Liedtke and Daniel R. Spikula
Keywords: slope stability, mass transport deposits, geochronology
Publisher: DFI