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Geodynamics Research International Bulletin (GRIB), Vol. (2), No. 05, SN:08, Winter 2015
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Vol. (2), No. 05, SN:08, Winter 2015
1st Article- P. I to VIII
ISSN 2345 - 4997
Geodynamics Research
International Bulletin
A DEM Based Appraisal of Neotectonics in Potwar Plateau,
N. Pakistan
Seyed Amer Mahmood 1*, Jahanzeb Qureshi2, Amer Masood3
1
2
Associate Professor, Department of Space Science, University of the Punjab, Lahore, Pakistan
Assistant Professor, Department of Space Science, University of the Punjab, Lahore, Pakistan
3
Department of Space Science, University of the Punjab, Lahore, Pakistan
* Corresponding Author ([email protected])
Article History:
Revised: Feb. 25, 2014
Received: Feb. 15, 2014
Accepted: Mar. 08, 2014
Reviewed: Feb. 21, 2014
Published: Mar. 16, 2014
ABSTRACT
The Potwar Plateau is a lower part of North West Himalayan thrust and fold belt and is a result of ongoing subduction of Indian
plate beneath Eurasia. The objective of this investigation is to identify active tectonics and associated severe topographic
deformation through geomorphic indices from DEM. The SRTM DEM with 90 m resolution is used for such analysis. The
stream-length gradient index, concavity, steepness, relative uplift rates and isobase map were extracted using standard
algorithms. Comprehensive analyses were carried out based on geomorphic indices. These analyses indicated the direct control of
neotectonics over the local topography drainage network. The steepness index shows that the northern Potwar is more elevated
than the southern Potwar. The spatial distributions of variable uplift rates are indicative of unique surface deformation within the
Potwar plateau. The isobase map revealed different local base-level inconsistencies that correspond to the prominent active
structures and lithological demarcations as presented in the printed geological maps. The orientation, deflection and interruptions
of the local base levels correspond well with the local active tectonics, regional uplifts. The visual interpretation of Landsat
imagery shows major tectonic control over drainage network and offset streams which are consistent with river longitudinal
profile analysis.
Keywords: DEM, River Profile Analysis, Isobase, Neotectonics, Potwar Plateau.
1. INTRODUCTION
Fold and thrust belts are created as a result of
collisional zones, e.g., the northwest-Himalayan
Folded and Thrusted Belt (NWHFTB) is a
consequence of downward movement of the IndoPak continent below the continent of Eurasia. The
NWHFTB is comprised of skinny tectonics. The
Potwar Plateau (PP) is situated at the west edge of
Indian Eurasian crash zone. The topography of
Potwar Plateau (PP) is an aftermath of composite
interaction between regional tectonics and erosion.
The rugged region is an utmost protruding
topographic feature on the planet earth. In the
absence of erosion, the apparent surface geometry of
a hilly terrain may reflect dominance of tectonic
processes (Mahmood and Gloaguen, 2011). Potwar
plateau (PP) extends down from MBT in the north to
the salt range in the south and shows low activity in
the context of earthquakes and is structurally very
composite. Jhelum and Kalabagh faults make a
conjugate set in the eastern and western sides of the
Potwar Plateau, respectively.
Mangla and Maira faults are located in the eastern
part of PP and are about 10 km long. They are
tectonically active features and are oriented with a
dip slip movement that has been documented along
their traces (Nakata et al., 1991). Another prominent
active tectonic feature in the PP region is the Kheri
Murat fault in the tectonic map of PP with different
local faults.
The Indo-Pakistan Plate belongs to the east
Gondwanaland (Valdiya, 1997). Gondwana was
named after of a district in India where the fossil
plant named Glossopteris was found (Wadia, 1957;
Ganser, 1964). Potwar plateau emerged as a result of
collision between Eurasian and the Indian plate that
created large scale regional structures. This plateau is
roughly defined by the rivers Indus and Jhelum to the
west and east, the Kalachitta-Margalla Hill Ranges to
the north and the Salt Range to the south. It is mostly
covered by the Siwalik sequence. At some places,
upper Eocene shales and lime-stones crop out locally
in folded inliers. Its northern region, termed as the
North Potwar and complex folds, reversed to the
south and clipped by steep-angle faults.
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Geodynamics Research International Bulletin (GRIB), Vol. (2), No. 05, SN:08, Winter 2015
NPDZ is followed to the south by asymmetrical,
wide and broad Soan syncline with a gently
northward dipping southern flank along the Salt
Range and a steeply dipping northern limb along
NPDZ . In the western part, this basin consists of
many east-west, broad and gentle folds (wavelength
26-40 km). In its eastern part, the strike sharply
changes to the northeast and the structures comprise
tightly folded anticlines and broad synclines (fold
wavelength 10-12 km). Axial zones of most
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anticlines dip steeply or are overturned. Faulting of
the anticlines is rare (Pennock, et al. 1989). This east
to west difference in the structural style has been
attributed to the reduced thickness of evaporates and
lesser basement slope in the eastern part of the
Potwar and Salt Range. Increased drag at the base of
the section has formed relatively complicated
structures due to greater internal deformation (Lillie,
et al. 1987) (Figs.1, 2).
Fig 1. Tectonic of Hindu Kush-Himalaya –Karakoram- Pamirs shows reported new confirmed faults with inset in Pakistan and surrounding
areas (Mahmood and Gloaguen, 2011).
Fig 2. Location of the study area of Potwar Plateau and Kalabagh fault zone (northern Pakistan)
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Northern Potwar Plateau Deformed Zone (NPDZ) is
more deeply deformed. Is it characterized by eastwest, tight and complex folds reversed to the south
and clipped by steep-angle faults.
The spatial distribution of the neotectonics in SubHimalayan Thrust Belt (SHTB) is of great
importance for scientists because of its implication to
better understand the Himalayan development
(Ahmad et al, 2005). On the other hand, a very
modest consideration has been given to the SHTB,
particularly towards the connection between
neotectonics, erosion and topographic processes. The
purpose of this research is to inspect the connection
among neotectonics and surface processes and
consequential neotectonic deformation in the SHTB
by analyzing DEM-based geomorphic indices and
visually interpreted structures from Landsat data.
Stream profile analysis is the main focus of this
research due to its ability to provide vital information
about the neotectonic deformation and erosional
processes in the study area (Mahmood and Gloaguen,
2011). An isobase map for the Potowar plateau was
generated in order to constrain neotectonics; related
surface deformation, erosional scarps and their
relationship with the local faults/lineaments or
lithologic variations. This investigation is elevation
based automatically extracted stream system which is
then employed through stream power law. The
isobase map would be another tool to cross validate
the steepness and relative uplift maps as it yields
information regarding different erosional and
neotectonic stages of landscape development with
variations in different local base levels. Both these
techniques are quite handy tools to constrain
neotectonics surface deformation in the Potwar
Plateau.
2. MATERIALS AND METHODS
The SRTM DEM 90 m is used to extract the
geomorphic features including hack index, relative
uplift rate and Isobase level. The drainage network
was extracted automatically using Matlab-based
algorithm from the SRTM DEM 90 m.
The SRTM DEM is unable to collect data at some
places with rugged relief, due to which pits/holes are
accumulated as part of the dataset and can pose
problems for the smooth extractions of stream
network, which is used for the stream profile
analysis. These holes are fixed using Inverse
Distance Weighted (IDW) interpolation that
produced location dependent values for such pits in
DEM. The stream length gradient index is calculated
by using the method employed by Hack (1957, 1973)
and is illustrated as:
(1)
S = k s A −θ
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The concavity θ is computed via the θ values of the
upper segments of all individual streams.
Consequently, normalized steepness index “ksnn” is
computed by means of θ . The knick points are
important as their upstream migration helps to know
the response of landscape to a local based level drop
and the consequent sediments fluxes from revived
catchments (Bishop et al, 2005). We identified many
knick-points on various river longitudinal elevationdistance profiles to see the tectonic/ lithological
contrast.
We used SRTM DEM (http://srtm.csi.cgiar.org)
(Jarvis et al, 2008) with spatial resolution of 90 m to
extract drainage network of different Strahler orders
(Strahler, 1952) automatically, e.g., 1, 2, 3 and so on.
The local base level map is prepared on the basis of
intersection of Strahler stream order, for example a
third order tributary is s fragment along the
downstream, the meeting of any two second order
tributary and a third order segment is formed by the
confluence of any two third order tributaries and so
on. To generate a second order isobase level map, we
use all Strahler order tributaries instead of those of
the first order tributaries. Isobase map represents a
simplified shape of actual3D Landscape where we
actually neglect the relief above the Isobase surface.
Previously, physical generation of isobase maps was
a time-consuming procedure.
Drainage network classification based on different
Strahler orders and the explanation of isobase lines
needs highly qualitative toposheets at an appropriate
scale. For the DEM based automatic extraction and
classification of drainage network permits the
required data for a larger area in a quick and efficient
manner with no cost (Grohmann et al, 2011). It is
observed that the Strahler stream order highly relies
on spatial resolution of the DEM, which means that
high resolution DEM will generate denser stream
network and vice versa. It simply means that the
main rivers will represent a higher Strahler order.
The DEM based stream network classification along
with the elevation points used to interpolate the
isobase surfaces can be derived by draping the
required Strahler stream order with the DEM based
contours (Stewart and Hannock, 1990).
The exclusion of the first order Strahler streams
decreases the noise in the digital elevation model that
can help improve the detection of a fault
scarp/erosional scarp or any other morphotectonic
feature that can be significant in topographic
development. For instance, the geomorphic
development of a thrust fault scarp, the preliminary
boundary condition is perturbed by the thrust fault
and the knick zones along the river longitudinal
profile explain the convex up/ concave down profiles
due to the thrust evolution different boundaries of
erosional surface and accordingly the profile
geometry development in a way that the erosional
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processes start appearing significant in different
stages. According to (Zuchiewicz and Oaks., 1993)
105-106 years is enough to fade out a recently
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developed tectonic scarp to a stage somewhere, all
the off cuts have been removed (Fig. 3).
Fig 3 Mechanism of isobase line preparation, junction of 2nd and 3rd order streams with the local contour map such that the junction of 2nd and 3 rd
order stream intersect the contour line and generate one point whose interpolation gives rise to local base levels (isobase levels)
3. RESULTS AND DISCUSSION
The stream distribution is not uniform because of the
different tectonic activities in the PP and KBFZ. The
change in the channel space in SHTB is presented by
the extracted drainage densities. Extracted drainage
densities and patterns present the variations of
channel space and configurations in the SHTB. The
sharpness of knick points represents neotectonic
events, river captures or lithologic contrasts (Fig. 4).
A very sharp knick point means it has developed
more recently (Wobus et al, 2006).
Fig. 4. Geological map of Potwar Plateau draped over SRTM DEM.
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Geodynamics Research International Bulletin (GRIB), Vol. (2), No. 05, SN:08, Winter 2015
The sudden changes in the geomorphic indices
indicate changes due to neotectonic activity and a
gradual change in lithology. Higher values of
steepness index or relative uplift rates are observed in
eastern section of the plateau because the steepness
index is directly proportional to the relative uplift as
compared to the center and west of the of the PP,
which means more active deformation . Previous
studies (Moghal et al, 2003) also suggest a similar
scenario. The hack map shows predominantly more
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gradient values in the NPDZas compared to SPPZ.
This map shows hack indices interpolated (from topo
to raster) from values of each segment of the
automated extracted drainage network (segment
interval = 100m). The known major fault traces are
shown by thick black lines. The highest hack index
values which underline actually anomalously steep
slopes are mainly encountered along plateau margins
and near the fault traces. (Fig. 5)
Fig 5. Hack gradient index map PP showing the spatial distribution of variations indicative of both tectonic (anticlines and synclines) and
lithological control on the local drainage network.
We prepared the relative uplift map for the Potwar
Plateau and outskirts for the first time using the
above mentioned geomorphic indices.
We have tried to correlate the relative uplift map to
the recent ongoing deformation process. The relative
uplift map shows differential uplift conditions in
different parts of the study area. In the north-northeast (NNE) of the study area, the uplift rate ranges
from 0.61 to 1.07 mm/year.
In the western section, it ranges from 0.23 to 0.60
mm/year. In the southern section, these rates range
from 0.07 to 0.35 mm/year. This clearly suggests that
the NNE section is being uplifted more compared to
the rest of the Potwar Plateau.
The obtained results also showed that the spatial flow
pattern of the streams and their orientations are also
controlled by the local faults e.g. in the study area
most of the local faults in the Potwar Plateau are
NNE-SSW oriented, East-West oriented and so is the
drainage network.
The localized lineaments play a crucial role in the
development of the shape of the local spatial
drainage patterns, which are based on Strahler stream
orders with the DEM based contours (see Figure 6).
Stream profile analysis used the assumption of
dynamic equilibrium under the steady state condition.
The spatial distribution of relative uplift rate in
Potwar Plateau and its vicinity is quite variable. This
is a clear indication that the present existence of
different sections of the Potwar Plateau with different
relative uplift rates was developed at different stages.
(Fig. 6).
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Fig. 6. Map showing relative differential uplift rates interpolated from uplift rate index (steepness index) values for selected streams.
Keeping in view the past studies regarding the
understanding of regional scale morphotectonics, the
isobase map for the Potwar Plateau and Kalabagh
fault zone was prepared using the second and third
stream Strahler orders. This map revealed excellent
results. We generated isobase contours with spatial
intervals (100 m) using ArcGIS 10 and prepared
isobase maps as shown. Both small and large
structures can be identified from the generated
isobase maps in the visual context. Some of these
structures are associated with neotectonic activity
(Fig. 7).
Fig. 7. Isobase map with 100 m interval isobase contour lines
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The ellipse #1 shows the Attock-Cherat-Range
(ACR). We can clearly observe the deflection of
isobase contour lines which are NE-SW oriented
along the NE-SW propagation of the ACR indicating
various differential stages of erosion. This deflection
indicates that ACR is a tectonically active range and
isobase maps reveal a possible of five to six episodes
of quick relative neotectonic/erosional /uplift stages.
The existing deep narrow canyons/gorges and valleys
in ACR could have been developed due to the
episodic neotectonic uplift resulting from the
subsequent erosion and shaping. The eroded
sediments were dumped in the foothills of the ACR
as alluvial fans at the piedmont-mountain junction
and plains in the southern Peshawar basin. The
neotectonic activity along ACR is shown by the
capture of Indus River in a NE-SW direction as
initially it was flowing in N-S direction just after the
confluence of Kabul and Indus rivers. The river
capture is under the neotectonic influence of ACR
rather than lithologic one. The ellipse#2 illustrates
the region of Main boundary thrust (MBT) and the
closely packed isobase lines in this region again
reflect the severe nature of E-W oriented thrust
faulting. A strong E-W orientation of the isobase
lines evidences the orientation of the MBT. This zone
tips-off a major drainage capture as the Jhelum River
flows in a SSE, SSW and then SSE direction again
while making sudden inflexions in a very short
distance. The quick inflexion of the rivers dictates the
strong neotectonic influence over the Jhelum River.
The ellipse#3 in the isobase map represents the
region of Salt Range in Potowar Plateau, which
shows relatively more erosion compared to MBT and
ACR. It means that the Salt range may be less active
seismically in comparison with MBT and ACR
which are more active tectonically, for they show
higher local base level values.
Higher isobase values are indicators of more uplifted
conditions/less eroded areas. The ellipse#4 in the
isobase map represents the region 60 km north of
Mianwali, at Kalabagh site, the Indus River is
captured by the dextral Kalabagh fault. A prominent
NE-SW inflextion of the river can be observed
clearly while Indus River makes an exit from
Potowar Plateau.
The higher isobase values in the north-eastern section
of the Salt Range Thrust (SRT) are higher compared
to the south-western and central parts of the SRT,
Which means that all these three different parts of the
SRT show differential erosion rates which is another
indication of the non-steady state environment or
zones of differential relative uplift rates. The
alignment of automated lineaments reveals that they
are very much in accordance with the already
published local and regional structures (e.g., in MBT
in the NE, ACR in the NW and in entire salt range in
southern Potwar Plateau.
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4. CONCLUSION
The automated drainage network based on DEM is
an important tool for computer based analysis of
stream profiles as it gives information about the
landscape and surface deformation in the study area.
As the tectonics of the region continues to develop,
in the same way the drainage network continues to be
influenced accordingly. The relative uplift rate map
of the study area indicates that NPDZ is more
deformed tectonically (higher uplift) compared to the
SPPZ. The stream length gradient map also shows
higher gradients on the NNE side than on the SSW
side. The spatial drainage network seems to be
controlled by the local and regional faults. This
suggests that lineaments and streams have a local
correlation which is clear from the orientation style
of drainage network and local faults. The
Geomorphometric features are important and
effective indicators for neotectonic studies in a young
tectonic regime with low elevation.
SRTM DEM based isobase technique has been quite
useful, quick and efficient for morphotectonic
investigation. In this research, an example from the
Potwar Plateau and its outskirts was examined for the
differential erosional/neotectonic events. Isobase map
prepared from the automated DEM based drainage
network using second and third Strahler stream order
has generated excellent results which are consistent
with the neotectonics of the Potwar Plateau. The eastwest orientation of the MBT, NE-SW orientation of
the ACR and NE-SW orientation of the SRT and the
resulting major drainage capture of Indus River at
ACR and at dextral Kalabagh Fault Zone (KBFZ)
correspond to recent tectonic activity. The
morphostructures drawn from the isobase map also
provides a close visual relationship with the in situ
scenario. Isobase maps permit the quick, delineation,
recognition and orientation of neotectonics that
present either poor or very less exposed expressions
on the thematic maps. Free usage of remote sensing
data (SRTM DEM) and MATLAB software
facilitates state of the art research in the field of
tectonic geomorphology
ACKNOWLEDGMENT
The authors are thankful to department of space
science, university of the Punjab, Lahore, Pakistan,
for providing necessary remote sensing and GIS
laboratories facilities and field work support.
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