Remote sensing has become an essential tool to improve data collection and spatial
analysis in the geosciences. Identification of passive margin structures that are exposed along
the Egyptian coast of the Red Sea, and their control on landforms has been hampered by
limited data resolution and restricted access to this arid and inaccessible region. A major
challenge lies in distinguishing features in the landscape that formed due to long-term tectonic
activity and erosion from those features that modified the landscape recently. The goals of this
thesis were to determine to what degree the study area is currently tectonically active, and
what major hazards might affect the touristically developing coastal region.
This study deals with the structural and geomorphological evolution of the rift-related
structures and their impact on the sediment distribution and landforms variation in the
northern Quseir area. In such a remote desert area, field and remote morphostructural analysis
are needed to understand the structural and geomorphological evolution. The current study is
mainly based on high-resolution QuickBird image analysis and field investigation. Field
mapping was limited to one season, owing to acute safety concerns in the Eastern Desert.
In the study area, the pre-rift stratigraphy includes Pan-African basement rocks overlain by
pre-rift clastic and carbonate successions that range in age from Cambrian to Eocene. Syn-rift
clastic and carbonate rocks range in age from Late Oligocene to recent and show depositional
patterns controlled by fault systems. The field area exposes a section of a tectonically uplifted,
amagmatic sedimentary sequence, which formed due to passive-margin-related rifting of the
Red Sea: the Mesozoic and Tertiary sedimentary units that fill the 7-km wide coastal strip are
perfectly exposed as tilted fault blocks.
The results of my field mapping and structural analysis show that the fault architecture of
the area is dominated by a large NW-SE-striking fault system. A series of SE-dipping normal
faults are consistent in cross-section with listric fault geometry, rooting into an E-dipping
detachment at depth. Our mapping also revealed that left-steps in at least one of the major NS-
striking faults are accommodated by a flower structure, but not by SW-NE-oriented cross
faults as previously proposed in a neighboring area. Thus seismic activity is more likely to
occur on the large NW-striking normal faults, leading to potentially larger Magnitude
earthquakes than previously recognized in the area. The left-step may act as a barrier to
rupture propagation and should be examined in more detail.
The northwestern Red Sea coast is part of the straight coastal segment that is generally
characterized as seismically inactive. However, during the geological field mapping, I found
evidence for Plio-/Pleistocene vertical coastal uplift, likely due to earthquake-related coastal
and offshore faulting. Pliocene marine deposits emerged recently due to sea level-drop and
earthquake-related uplift. Even the presence of up to five distinct Pleistocene coral terraces
implies that at least some of the coastal uplift was seismogenic, because terraces of the same
age can be found at different elevations along strike. Presumably, some of the seawarddipping,
N-S-striking normal faults are active today, despite the lack of recent instrumental
seismicity. These findings imply long recurrence intervals for active faults in the northern
Quseir area. These results differ from previously published results for the adjacent Quseir-Um
Gheig sub-basin area, were E-W-striking strike-slip faults were mapped to offset the N-Sstriking
faults, and had been inferred as earthquake-generating faults by Abd El-Wahed et al.
(2010). Based on our mapping, we postulate that the large rift-parallel normal faults are
seismogenic.
Drainage network evolution within the study area is often structurally controlled and the
nature of these controls was examined in this study. The Wadi Siatin stream channel network
is classified in a relatively simple way, based on the high-resolution satellite data, with
dendritic, and rectangular considered the most fundamental channel geometries.
It was possible to distinguish the different morphological elements of the network, as well as
the anomalies that affect the patterns. This analysis revealed, in the northern Red Sea area
basins, the existence of old structures whose successive reactivations have left their mark on
the drainage network. Comparison of joint systems direction with the directions of the main
trunk stream channel of Wadi Siatin shows that the channel is highly affected by tectonic
jointing. First-order channels follow easily erodable faults.
Investigations concerning the relationship of stream-flow orientation with geological
structure in the Wadi Siatin Basin shows that, generally, the least influenced flows are those
of first-order which are governed simply by the valley side slopes on which they developed.
However, in certain geological and geomorphological situations, there are clear exceptions to
this generalization. Certainly, locally, geological control of these small streams may be even
higher than in many streams of higher order. In the peripheral parts of the Basin, expansion of
drainage into the available space has obviously been easiest along lines of weakness and, as a
consequence of this, streams of the first order come to exhibit a high degree of adjustment to
the underlying structure. The maximum structural control is reached by the streams of the
third order. Towards the higher orders, the influence of local structure becomes weaker.
| Identifer | oai:union.ndltd.org:MUENCHEN/oai:edoc.ub.uni-muenchen.de:17071 |
| Date | 11 June 2014 |
| Creators | Elkhashab, Mohamed |
| Publisher | Ludwig-Maximilians-Universität München |
| Source Sets | Digitale Hochschulschriften der LMU |
| Detected Language | English |
| Type | Dissertation, NonPeerReviewed |
| Format | application/pdf |
| Relation | http://edoc.ub.uni-muenchen.de/17071/ |
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