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H.J. Lee

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Following the 1964 M9.2 megathrust earthquake in southern Alaska, Seward was the only town hit by tsunamis generated from both submarine landslides and tectonic sources. Within 45 seconds of the start of the earthquake, a 1.2-km-long section of waterfront began sliding seaward, and soon after, ~6-8-m high waves inundated the town. Studies soon after the earthquake concluded that submarine landslides along the Seward waterfront generated the tsunamis that occurred immediately after the earthquake. We analyze pre- and post-earthquake bathymetry data to assess the location and extent of submarine mass failures and sediment transport. New NOAA multibeam bathymetry shows the morphology of the entire fjord at 15 m resolution....
Categories: Publication; Types: Citation
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In 1996 a major flood occurred in the Saguenay region, Quebec, Canada, delivering several km3 of sediment to the Saguenay Fjord. Such sediments covered large areas of the, until then, largely contaminated fjord bottom, thus providing a natural capping layer. Recent swath bathymetry data have also shown that sediment landslides are widely present in the upper section of the Saguenay Fjord, and therefore, should a new event occur, it would probably expose the old contaminated sediments. Landslides in the Upper Saguenay Fjord are most probably due to earthquakes given its proximity to the Charlevoix seismic region and to that of the 1988 Saguenay earthquake. In consequence, this study tries to characterize the permanent...
Categories: Publication; Types: Citation; Tags: Marine Geology
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The M9.2 Alaska earthquake of 1964 caused major damage to the port facilities and town of Valdez, most of it the result of submarine landslide and the consequent tsunamis. Recent bathymetric multibeam surveys, high-resolution subbottom profiles, and dated sediment cores in Port Valdez supply new information about the morphology and character of the landslide deposits. A comparison of pre- and post-earthquake bathymetry provides an estimate of the net volume of landslide debris deposited in the basin and the volume of sediment removed from the source region. Landslide features include (1) large blocks (up to 40-m high) near the location of the greatest tsunamiwave runup (~50 m), (2) two debris lobes associated with...
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Sedimentary strata on the Southern California shelf and slope (Point Conception to Dana Point) display patterns and rates of sediment accumulation that convey information on sea-level inundation, sediment supply, and oceanic transport processes following the Last Glacial Maximum. In Santa Monica Bay and San Pedro Bay, postglacial transgression is recorded in shelf deposits by wave-ravinement surfaces dated at 13-11 ka and an upsection transition from coastal to shallow-marine sediment facies. Depositional conditions analogous to the modern environment were established in the bays by 8-9 ka. On the continental slope, transgression is evidenced in places by an increase in sediment grain size and accumulation rate...
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In oceanic areas underlain by sediment with gas hydrate, reduction of sea level initiates disassociation along the base of the gas hydrate, which, in turn, causes the release of large volumes of gas into the sediment and creates excess pore-fluid pressures and reduced slope stability. Fluid diffusion properties dominate the disassociation process in fine-grained marine sediment. Slope failure appears likely for this sediment type on moderate slopes unless pressures can be adequately vented away from the gas hydrate base. Pleistocene eustatic-sea level regressions, likely triggered seafloor landslides on the continental slope of the Beaufort Sea and other margins where gas hydrate is present in seafloor sediment....
Categories: Publication; Types: Citation; Tags: Marine Geotechnology
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