| Title | Seismic hazard in passive margin frontier basins: geological estimates of the frequency of large earthquake-triggered submarine landslides in Orphan Basin, offshore Canada |
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| Author | Piper, D J ;
Tripsanas, E; Mosher, D; MacKillop, K |
| Source | Abstracts, AAPG Annual Convention 2010; 2010 p. 1 |
| Links | Online - En ligne (pdf)
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| Year | 2010 |
| Alt Series | Earth Sciences Sector, Contribution Series 20090221 |
| Publisher | AAPG |
| Meeting | AAPG Annual convention; New Orleans; US; April 2010 |
| Document | Web site |
| Lang. | English |
| Media | on-line; digital |
| File format | pdf |
| Province | Newfoundland and Labrador; Eastern offshore region |
| Area | Atlantic Ocean; Orphan Basin; Grand Banks |
| Lat/Long WENS | -51.0000 -45.0000 51.0000 48.0000 |
| Subjects | marine geology; geophysics; surficial geology/geomorphology; engineering geology; fossil fuels; stratigraphy; continental margins; continental slope; sedimentary basins; seismic risk; seismicity;
earthquakes; earthquake risk; earthquake magnitudes; landslides; slope failures; petroleum industry; petroleum engineering; building codes; geophysical surveys; seismic surveys, marine; seismic reflection surveys; seismic profiles; marine sediment
cores; piston cores; marine sediments; volcanic ash; turbidites; shear strength; 2005 Building Code of Canada; 1929 Grand Banks Earthquake; Heinrich Layers; Methodology; Infrastructures; Phanerozoic; Cenozoic; Quaternary |
| Program | Offshore Geoscience |
| Released | 2010 05 05 |
| Abstract | Seismic hazard assessment for engineering design is important but challenging in frontier basins with low seismicity, such as the Canadian east coast offshore. Here the instrumental record of past
earthquakes is short and seismological estimates of recurrence suggest a Mw > 7 earthquake every 3 ka per 100 km length of continental slope, an estimate incorporated in the 2005 Building Code of Canada. Such estimates appear much higher than the
frequency of slope failure in the same area. For example, near the 1929 Mw=7.2 Grand Banks earthquake and landslide, submarine landslides of similar size have occurred every 150?200 ka. Order of magnitude differences in estimates of seismic hazard
are a cause for concern.
Ultra-high resolution seismic reflection profiles from the continental slope in the highly prospective Orphan Basin, off Newfoundland, reveal a stratigraphic record of large submarine slope failures back to 0.1 Ma. C-14
dating of Heinrich and ash layers in many piston cores provided chronology of seismic markers at ~3 ka resolution after 40 ka and ~5 ka resolution prior to 40 ka. Slump-generated turbidites on the basin floor have a distinctive petrology,
sedimentology and distribution, with ~1 ka chronologic resolution. Large slope failures occurred synchronously over margin lengths of 50-330 km. In the past 0.1 Ma, 5 failures affected a >120-km-long sector of the slope and 15 failures were large
enough to be recognised in seismic and/or cores. We present arguments that the widespread failures were earthquake triggered: other mechanisms for triggering laterally extensive synchronous failure do not apply.
Triaxial shear measurements on
cores from the continental slope show a c/p ratio of typical sediment of 0.48, implying considerable stability. The c/p ratio falls to as low as 0.25 at some weak layers based on shear vane measurements. Relationships between seismic acceleration and
c/p are examined for the 1929 Grand Banks earthquake and compared with recent data from the US Atlantic margin. This indicates that the larger Orphan Basin slope failures represent earthquakes ranging from Mw ~6.5 to ~7.5 with a mean recurrence
interval for 'large' earthquakes of 20 ka. This compares with the seismological estimate of a 1.5 ka recurrence interval for a Mw = 7 earthquake somewhere in this sector of the continental margin. This study demonstrates a methodology for seismic
hazard assessment in other passive margin petroleum basins. |
| GEOSCAN ID | 248026 |
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