Bathymetry, Gravity and Magnetic Images of the Mediterranean water

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Bathymetry, Gravity and Magnetic Images of the
Mediterranean water of the Nile Delta, Egypt,
using GIS Technique, Part IV
Interpretation of Gravity Data of the Northern
Mediterranean Sea Coast of Egypt
Morad B. Awad Professor of Marine
Geophysics, National Institute of Oceanography
and Fisheries, NIOF
Presentation submitted to the Conference
Egyptian Coasts,Problems and Solutions, As
National Awareness Meeting held in Ismaeillia,
University of Suez Canal on 10th -11th ,
December 2003,
Organized by
Suez Canal University, in corporation with
Egyptian Society for Coastal Protection.
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STUDY AREA
Fig. 1 Location Map of the Study Area
The study area lies at northern Mediterranean Sea
coast of Egypt opposite to the Nile Delta,
Egypt. It includes four small water bodies
represented by the Lakes (Maryut, Idku, Burullus
and Manzalah) that distributed along the
northern shoreline of the Egypt, northern Nile
Delta,
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Qualitative Interpretation of Bouguer Gravity
Anomaly Maps
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Qualitative Interpretation of Bouguer Gravity
Anomaly Maps

• Two negative anomalies occupying the southern
  part of the study area and two major positive
  gravity closures occupying the northern part of
  the study area, to the sea side between latitude
  31.5o and 32o N. These negative and positive
  gravitational field anomalies may reflect the
  variation in depth and composition of the
  causative masses

• Bouguer anomalies are ranging from -20 m.gal, at
  the south to 48 m.gal at its north and
  characterized by a sharp gradient near the shore
• line, that trending east-west direction parallel
  to a normal fault system, i.e. parallel to the
  shoreline.

• Contour lines have an abrupt change near Lake
  Manzala which indicates
• a strike slip fault crossing the expected normal
  fault and younger than it

• The general model of the fault system of the
  study describes that in the first stage, the
  stratigraphical unit is affected by a fault
  system, that striking along the east-west
  direction, and in a second stage, it is affected
  by the strike slip fault striking along the north
  east direction .

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• Delineable interpretation of the Bouguer
• anomaly mapa and the assumed fault
• System.

• The positive closures may be due to
• either the existence of submerged
• island of high density material, or to
• a sort of uplifting in basement rocks.

• The negative closures are expected to be due to
  sediments of low
• density that had been loaded by Nile River
  through
• Pliocene/Pleistocene and recent times.

• Regional and residual gravity anomaly
  distribution is described by 4th
• order best fitting polynomial mathematical
  model that representing the
• anomaly trend in the study area.

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• The regional anomaly is ranging between 7 to 31
  m.gal and increase
• toward north, which may indicate that the
  basement is uplifted
• toward the north with a gentle slope, i.e. this
  is one of the Mediterranean
• plate characterizing the north Africa tectonics.

• The residual gravity anomaly map indicates
  gravity anomalies that
• ranging between -8 m.gal, in the south, to 20
  m.gal in the north.
• Its gradient shows an abrupt change near the
  shoreline and also at Lake
• Manzala, as mentioned on Bouguer gravity anomaly
  map. These
• anomalies are probably due to surface and near
  surface causative
• bodies in addition to geomorphologic features.

Geomorphological Implications

• The distribution of positive and negative gravity
  closures, their shapes,
• features and structures, may have their
  implications on the shore line
• and its associated geomorphology (i.e. gulfs,
  heads, and lakes).

• The distribution of northern lakes, Idku, Maryut
  and Manzalah is
• associated with negative closures since the lakes
  have a low density
• material loaded by the Nile River and its
  branches.

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Fig. (7) Regional Bouguer anomaly map of
southern Mediterranean Sea
coast of Egypt. C.I. 2
m.gal
Fig. (8) Residual Bouguer anomaly map of
southern Mediterranean Sea
coast of Egypt. C.I. 2
m.gal
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Geomorphological Implications (Cont.)

• There is a normal fault associating the shoreline
  and crossing the area
• from east to west which considered as older
  one.
• There is a strike slip fault affecting the area,
  crossing the normal fault
• and is covered by sediments.
• Lake Burullus is affected with a high level
  gradient anomalies which is
• observed in both of Bouguer- and residual-
  maps.
• The positive closure appears in the residual map
  has a larger area
• when compared with that one in the Bouguer
  map. This means that in
• this area the effects of the basement and the
  sediment sections are
• clear which reaches approximately to the
  residual effect.
• The negative closures associated with lakes,
  appear in the residual map,
• are due to the low density of sediments.
• The basement takes a gentle slope and is
  uplifting towards the north
• direction.

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Qualitative Interpretation of Gravity Anomaly
Profiles
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Qualitative Interpretation of Gravity Anomaly
Profiles (Cont.)
Interpretation of profile AA1, illustrates the
sub-surface structures,\It shows the main normal
fault affecting the study area. The sloping of
the basement surface is indicated in relation
with the North African plate slope, which is
uplifted north-ward.
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Qualitative Interpretation of Gravity Anomaly
Profiles (Cont.)
Interpretation of profile BB1, illustrates the
sub-surface structures,\It shows the main normal
fault affecting the study area. The sloping of
the basement surface is indicated in relation
with the North African plate slope, which is
uplifted north-ward.
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Qualitative Interpretation of Gravity Anomaly
Profiles (Cont.)
Interpretation of profile CC1, illustrates the
sub-surface structures,\It shows the main normal
fault affecting the study area. The sloping of
the basement surface is indicated in relation
with the North African plate slope, which is
uplifted north-ward.
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Quantitative Interpretation of Gravity Anomaly
Profiles (Cont.)
Spectral analysis along gravity profile AA
Depth of the 3rd segment (shallow seated), KM Depth of the 2nd segment (intermediate seated) ,KM Depth of the 1st segment (deep seated), KM Length of profile, KM profile
- .431 2.873 102 AA1
- .169 2.123 88 BB1
- .262 2.258 93 CC1
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Quantitative Interpretation of Gravity Anomaly
Profiles (Cont.)
Spectral analysis along gravity profile BB
Depth of the 3rd segment (shallow seated), KM Depth of the 2nd segment (intermediate seated) ,KM Depth of the 1st segment (deep seated), KM Length of profile, KM profile
- 2.912 102 AA1
- 2.315 88 BB1
- 2.683 93 CC1
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Quantitative Interpretation of Gravity Anomaly
Profiles (Cont.)
Spectral analysis along gravity profile CC
Depth of the 3rd segment (shallow seated), KM Depth of the 2nd segment (intermediate seated) ,KM Depth of the 1st segment (deep seated), KM Length of profile, KM profile
- 0.471 1.486 102 AA1
- 0.172 1.052 88 BB1
- 0.249 1.397 93 CC1
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Quantitative Interpretation of Gravity Anomaly
Profiles (Cont.)
Two Dimensional Model study Along profile AA

• The computed structural model
• along the profile AA1 shows that
• the study area is affected by a set
• of normal faults namely F1/, F2
• /, and F3/ from north to south.
• The normal fault zones are
• separating alternating horsts and
• grabens which are defined by
• high and low gravity belts. The
• thickness of the sedimentary
• section varies along the profile
• from 1 Km to 3 Km, from north to
• south, where the basement is
• uplifted from south to north.
• This is one of the Africa basement
• configurations.

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Quantitative Interpretation of Gravity Anomaly
Profiles (Cont.)
Two Dimensional Model study Along profile BB

• The computed structural models along the profiles
  BB1, CC1 show that the study area is effected by
  a series of normal faults namely F4/, and F5/ in
  the first profile and F6/, F7/, and F8/ in the
  second one from north to south. The thickness of
  the sedimentary section is varying from 1 Km to 3
  Km from north to south along these profiles.

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Quantitative Interpretation of Gravity Anomaly
Profiles (Cont.)
Two Dimensional Model study Along profile CC

• Accordingly it is concluded that
• the area is suffering from a set of
• normal faults, one of them is found to be
  delineated from east to west parallel to the
  shoreline, while the basement is dipping up
  towards the north direction. The eastern and
  western sides of the shoreline are underlain by a
  thick sedimentary section.

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