Morphology of late Quaternary submarine landslides along the U.S. Atlantic continental margin

This paper is not subject to U.S. copyright. The definitive version was published in Marine Geology 264 (2009): 4-15, doi:10.1016/j.margeo.2009.01.009.The nearly complete coverage of the U.S. Atlantic continental slope and rise by multibeam bathymetry and backscatter imagery provides an opportunity to reevaluate the distribution of submarine landslides along the margin and reassess the controls on their formation. Landslides can be divided into two categories based on their source areas: those sourced in submarine canyons and those sourced on the open continental slope and rise. Landslide distribution is in part controlled by the Quaternary history of the margin. They cover 33% of the continental slope and rise of the glacially influenced New England margin, 16% of the sea floor offshore of the fluvially dominated Middle Atlantic margin, and 13% of the sea floor south of Cape Hatteras. The headwall scarps of open-slope sourced landslides occur mostly on the lower slope and upper rise while they occur mostly on the upper slope in the canyon-sourced ones. The deposits from both landslide categories are generally thin (mostly 20–40 m thick) and comprised primarily of Quaternary material, but the volumes of the open-slope sourced landslide deposits can be larger (1–392 km3) than the canyon-sourced ones (1–10 km3). The largest failures are located seaward of shelf-edge deltas along the southern New England margin and near salt domes that breach the sea floor south of Cape Hatteras. The spatial distribution of landslides indicates that earthquakes associated with rebound of the glaciated part of the margin or earthquakes associated with salt domes were probably the primary triggering mechanism although other processes may have pre-conditioned sediments for failure. The largest failures and those that have the potential to generate the largest tsunamis are the open-slope sourced landslides.The U.S. Nuclear Regulatory Commission and the U.S. Geological Survey are acknowledged for their support of this research.Work was funded by US Nuclear Regulatory Commission grant N6480 Physical study of tsunami sources

三田史學會規約 奥付

Coastal and submarine landslides are frequent at the western tip of the Gulf of Corinth, where small to medium failure events (106–107 m3/ occur on average every 30–50 years. These landslides trigger tsunamis and consequently represent a significant hazard. We use here a dense grid of high-resolution seismic profiles to realize an inventory of the large mass transport deposits (MTDs) that result from these submarine landslides. Six large mass wasting events are identified, and their associated deposits locally represent 30% of the sedimentation since 130 ka in the main western basin. In the case of a large MTD of 1 km3 volume, the simultaneous occurrence of different slope failures is inferred and suggests an earthquake triggering. However, the overall temporal distribution of MTDs would result from the time-dependent evolution of pre-conditioning factors rather than from the recurrence of external triggers. Two likely main pre-conditioning factors are (1) the reloading time of slopes, which varied with the sedimentation rate, and (2) dramatic changes in water depth and water circulation that occurred 10–12 ka ago during the last post-glacial transgression. Such sliding events likely generated large tsunami waves in the whole Gulf of Corinth, possibly larger than those reported in historical sources considering the observed volume of the MTDs

Sedimentary impacts of recent moderate earthquakes in different settings in the Western Gulf of Corinth, Greece

International audience11 short gravity cores retrieved in the Western Gulf of Corinth, Greece, allowed identifying event deposits whose age ranges were compared to an updated earthquakes catalogue for the area. 210Pb-derived age-depth curves show that the majority of the event deposits may have been triggered by earthquakes. These results show that moderate earthquakes (Mw ~6.0-6.5) may significantly impact different marine settings, from shallow shelves (70-100 m deep) to the basin floor (330 m deep). The deepest coring sites show the best possible record, but one major earthquake is missing and the age of one event deposit does not fit with any known earthquake. More cores are needed to check the spatial extent of each deposit and to validate the absence of record of some earthquakes, like the 1995 Aigion earthquake

Sedimentary impacts of recent moderate earthquakes from the shelves to the basin floor in the western Gulf of Corinth

International audienceIn seismically active areas, long term records of large earthquakes are indispensable to constrain reccurence patterns of large earthquakes. In the western Corinth Rift, one of the most active areas in Europe in terms of seismicity, data about ancient earthquakes are still insufficient, despite historical records covering the last two millenia and several studies in onshore paleoseimology. In this paper, we test the use of offshore sediments from the Gulf of Corinth to identify sediment failures and tsunamis that have been triggered by historical earthquakes Two shelves (40-100 m deep), one sub-basin (180 m) and the basin floor (330 m) have been sampled by short gravity cores. The cores were analysed in order to identify and characterize event deposits. The age control has been provided by 137Cs and 210Pb activity measurements showing that the cores represent 2 to 4 centuries of sedimentation. In each site, sandy event deposits are interbeded in the muddy, hemipelagic sedimentation. The age of event deposits has been compared to the record of historical earthquakes using new and published macroseismic data. This comparison shows temporal coincidence of some event deposits and documented earthquakes with a macroseismic intensity ≥ VII in the area, e.g. in A.D. 1861, 1888 and 1909. In nearshore shallow-water settings, the record of event deposits does not exactly fit with the historical record of large earthquakes because too few event deposits are present. This may be due to the absence of sediment failures or to a lower preservation of the deposits in such settings. In the deepest site, in the basin floor, the correspondenceis better: a sandy turbidite probably corresponds to each large earthquake since A.D. 1850, except one aseismic sediment density flow that occurred at the end of the 20th century. Surprisingly, the Ms=6.2, June 15, 1995 Aigion earthquake is only possibly recorded in one nearshore site on the Aigion Shelf, in the form of a tsunami back-wash flow deposit. This study showed that moderate earthquakes (M 5.8-6.5) can significantly impact marine sediments. Regarding the evaluation of seismic hazard in the area, the basin floor is proposed as a promising site for long term paleoseismology in the Gulf of Corinth, while shallower settings need to be considered more carefully

Sedimentary impacts of recent moderate earthquakes in different settings in the Western Gulf of Corinth, Greece

International audience11 short gravity cores retrieved in the Western Gulf of Corinth, Greece, allowed identifying event deposits whose age ranges were compared to an updated earthquakes catalogue for the area. 210Pb-derived age-depth curves show that the majority of the event deposits may have been triggered by earthquakes. These results show that moderate earthquakes (Mw ~6.0-6.5) may significantly impact different marine settings, from shallow shelves (70-100 m deep) to the basin floor (330 m deep). The deepest coring sites show the best possible record, but one major earthquake is missing and the age of one event deposit does not fit with any known earthquake. More cores are needed to check the spatial extent of each deposit and to validate the absence of record of some earthquakes, like the 1995 Aigion earthquake

Sedimentary impacts of recent moderate earthquakes in different settings in the Western Gulf of Corinth, Greece

International audience11 short gravity cores retrieved in the Western Gulf of Corinth, Greece, allowed identifying event deposits whose age ranges were compared to an updated earthquakes catalogue for the area. 210Pb-derived age-depth curves show that the majority of the event deposits may have been triggered by earthquakes. These results show that moderate earthquakes (Mw ~6.0-6.5) may significantly impact different marine settings, from shallow shelves (70-100 m deep) to the basin floor (330 m deep). The deepest coring sites show the best possible record, but one major earthquake is missing and the age of one event deposit does not fit with any known earthquake. More cores are needed to check the spatial extent of each deposit and to validate the absence of record of some earthquakes, like the 1995 Aigion earthquake