Transcript FOOT OF THE SLOPE DETERMINED AS THE THE POINT OF …

FOOT OF THE SLOPE
DETERMINED AS THE THE POINT
OF MAXIMUM CHANGE OF
GRADIENT
(CHAPTER 5)
Harald Brekke
Foot of the continental slope
• ”In the absence of evidence to the contrary,
the foot of the continental slope shall be
determined as the point of maximum
change of gradient at its base”
(Paragraph 4 (b))
• The CLCS regards the determination of the foot of
the continental slope by means of the point of
maximum change in the gradient at its base, as the
general rule
(See 5.1.3)
Fundamental requirements
• The identification of the region defined as
the base of the continental slope
• The determination of the location of the
point of maximum change in gradient at the
base of the continental slope
(See 5.1.3)
Continental slope definition
• The CLCS defines the continental slope as the
outer portion of the continental margin that
extends from the shelf edge to the upper part of
the rise or to the deep ocean floor where a rise is
not developed.
• The rise is the wedge-shaped sedimentary body
having a smaller gradient than the continental
slope
(See 5.4.4)
Determination of foot of slope
Sketch of geological principles
Continental margin
OUTER
PLATEAU
Foot of slope
Mid - oceanic
ridge
EROSJONSDAL
Continental
rise
Deep ocean floor
6-15 Km
30 - 50 Km
Oceanic crust
Crystalline continental crust
Earth's mantle
MHe
13.10.99
Melted
mantle
RL9909003/5
The base of the continental slope
• The CLCS defines the base of the continental
slope as a region where the lower part of the
slope merges into the top of the continental
rise, or into the top of the deep ocean floor
where a continental rise does not exist
(See 5.4.5)
Relevant data types
• To identify the base of the slope:
–
–
–
–
Bathymetric data
Geomorphological data
Geological data
Geophysical data
• To determine the point of maximum change
in the gradient:
– Bathymetric data
(See 5.2.1)
Relevant bathymetric data
• Single-beam echo soundings
• Multi-beam echo soundings
• Hybrid side-scan sonar measurements
• Interferometric side-scan sonar measurements
• Seismic reflection-derived bathymetric
measurements
(See 5.2.2)
Relevant geological and
geophysical data
• In situ samples and measurements
• Geochemical and radiometric data
• Reflection and refraction seismic data
• Grav/mag potential field data
• Side-scan imagery
(See 5.2.6-9)
Mathematical determination of
the foot of the slope
• The point of maximum change in gradient to be
determined by means of mathematical analysis of:
– Two-dimensional profiles
– Three-dimensional bathymetric models
• Second derivative-based analyses may be most
relevant, but the CLCS will not prescribe any
particular method
• Methods based on a purely visual perception of
bathymetric data will not be accepted by the
CLCS
(See 5.4.7-11)
Filtering and smoothing
• Mathematical analyses for determining the
point of maximum change in the gradient
may require filtering and smoothing of the
bathymetric data in order not to enhance
noise and/or irrelevant features
• The CLCS may request full disclosure of all
original data and the details of the filtering
and smoothing algorithms
(See 5.3)
Selection of foot of slope point
• Among several points of change in gradient
at the base of the slope, the point of
maximum change is to be selected
• The selection of any other point (other than
the maximum) will be regarded as an
exception and must be supported by
evidence to the contrary to the general rule
(See 5.4.12)