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Seismic triggering of landslides and turbidity currents offshore Portugal

Seismic triggering of landslides and turbidity currents offshore Portugal
Seismic triggering of landslides and turbidity currents offshore Portugal
Sediments in deep water basins often include turbidites that record sediment input from adjacent continental margins. In seismically active areas, where turbidity currents are triggered by earthquakes, the basinal turbidite sequence may thus contain a record of palaeoseismicity, which can be used to infer the frequency of earthquakes affecting the margins of the basin. This is particularly useful where large earthquakes have a recurrence interval than is greater than the historical record. However, turbidity currents can be triggered by several processes, and it is often difficult to trace individual turbidites to their precise source areas and to assign a definite trigger to a particular turbidite. Here, we demonstrate that turbidites emplaced at ?6600 and ?8300 Cal yr BP in the Tagus Abyssal Plain, off Portugal, correlate with erosional hiatuses in two submarine canyons on the continental margin. The turbidites are sourced from simultaneous landsliding in both canyons, requiring regional triggers interpreted as earthquakes. An earthquake recurrence interval for the continental margin of ?4000 years is estimated by extrapolation to deeper turbidites in the basin sequence. However, the example of the 1755 earthquake, which caused widespread devastation in southwest Iberia, shows that palaeoseismic interpretations must be made with caution. The 1755 earthquake had a magnitude >8.5 and yet the associated turbidite in the abyssal plain is typically ?5 cm thick, while older turbidites can be >1 m thick. Given the large 1755 earthquake magnitude, the difference in turbidite thickness is unlikely to be related to the relative size of triggering earthquakes. Instead, we suggest that the offshore location of the 1755 earthquake, coupled with low sedimentation rates during the Holocene, may have limited the size of the associated turbidite
1525-2027
Q12011
Masson, D.G.
edd44c8b-38ca-45fb-8d0d-ac8365748a45
Arzola, R.G.
403ebca0-9574-4cfa-bbe5-03ba68731df0
Wynn, R.B.
72ccd765-9240-45f8-9951-4552b497475a
Hunt, J.E.
43fd3144-04cd-43d9-b341-b70f2a03bf91
Weaver, P.P.E.
1ab10035-6132-46aa-8a5c-6fb23a1b8ab4
Masson, D.G.
edd44c8b-38ca-45fb-8d0d-ac8365748a45
Arzola, R.G.
403ebca0-9574-4cfa-bbe5-03ba68731df0
Wynn, R.B.
72ccd765-9240-45f8-9951-4552b497475a
Hunt, J.E.
43fd3144-04cd-43d9-b341-b70f2a03bf91
Weaver, P.P.E.
1ab10035-6132-46aa-8a5c-6fb23a1b8ab4

Masson, D.G., Arzola, R.G., Wynn, R.B., Hunt, J.E. and Weaver, P.P.E. (2011) Seismic triggering of landslides and turbidity currents offshore Portugal. Geochemistry, Geophysics, Geosystems, 12, Q12011. (doi:10.1029/2011GC003839).

Record type: Article

Abstract

Sediments in deep water basins often include turbidites that record sediment input from adjacent continental margins. In seismically active areas, where turbidity currents are triggered by earthquakes, the basinal turbidite sequence may thus contain a record of palaeoseismicity, which can be used to infer the frequency of earthquakes affecting the margins of the basin. This is particularly useful where large earthquakes have a recurrence interval than is greater than the historical record. However, turbidity currents can be triggered by several processes, and it is often difficult to trace individual turbidites to their precise source areas and to assign a definite trigger to a particular turbidite. Here, we demonstrate that turbidites emplaced at ?6600 and ?8300 Cal yr BP in the Tagus Abyssal Plain, off Portugal, correlate with erosional hiatuses in two submarine canyons on the continental margin. The turbidites are sourced from simultaneous landsliding in both canyons, requiring regional triggers interpreted as earthquakes. An earthquake recurrence interval for the continental margin of ?4000 years is estimated by extrapolation to deeper turbidites in the basin sequence. However, the example of the 1755 earthquake, which caused widespread devastation in southwest Iberia, shows that palaeoseismic interpretations must be made with caution. The 1755 earthquake had a magnitude >8.5 and yet the associated turbidite in the abyssal plain is typically ?5 cm thick, while older turbidites can be >1 m thick. Given the large 1755 earthquake magnitude, the difference in turbidite thickness is unlikely to be related to the relative size of triggering earthquakes. Instead, we suggest that the offshore location of the 1755 earthquake, coupled with low sedimentation rates during the Holocene, may have limited the size of the associated turbidite

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Published date: 2011
Organisations: Geology & Geophysics, Geochemistry, Marine Geoscience

Identifiers

Local EPrints ID: 208515
URI: http://eprints.soton.ac.uk/id/eprint/208515
ISSN: 1525-2027
PURE UUID: f860dfbd-2fd4-4e75-b133-2e52d62e6a85

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Date deposited: 19 Jan 2012 15:10
Last modified: 14 Mar 2024 04:43

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Contributors

Author: D.G. Masson
Author: R.G. Arzola
Author: R.B. Wynn
Author: J.E. Hunt
Author: P.P.E. Weaver

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