tectonics zagros dehbozorgi
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Quantitative analysis of relative tectonic activity in the Sarvestan area,central Zagros, Iran
M. Dehbozorgi a,, M. Pourkermani a, M. Arian b, A.A. Matkan c, H. Motamedi d, A. Hosseiniasl c
a Faculty of Earth Science, Beheshti University, Velenjak Street, Tehran, Iranb Faculty of Earth Science, Science and Research Branch, Azad University, Hesarak, Punak Sq. Tehran, Iranc Department of Remote Sensing and GIS, Faculty of Earth Science, Beheshti University, Velenjak Street, Tehran, Irand NIOC Exploration Directorate, Seoul Ave., 1st Dd end, Tehran, Iran
a b s t r a c ta r t i c l e i n f o
Article history:
Received 15 May 2009
Received in revised form 27 April 2010
Accepted 7 May 2010
Available online xxxx
Keywords:
Tectonic geomorphology
Morphometry
Geomorphic indices
Active tectonics
Zagros Mountains
Iran
Neotectonicsis a major factor controllinglandform development in tectonicallyactive regions,and it hassignificantly
affected fluvial systems and mountain-front landscapes in the Sarvestan area of the central Zagros, Iran. The area is
located along thesimply foldedbeltof the Zagros, andis anoutcome ofthe SWNE oriented tectonicconversion that
initiated in the Late Cretaceous and strengthened during the Early Miocene due to the collision of the Arabian and
Eurasianplates. To assess tectonic activities in the area, we analyzedgeomorphic indices: the stream-gradient index
(SL), drainage basin asymmetry (Af), hypsometric integral (Hi), valley floor widthvalley heightratio(Vf), drainage
basinshape(Bs), and mountain-front sinuosity (J). These indices werecombinedto yield the relativeactive tectonics
index (Iat) using geographic information systems (GIS). Based on Iatvalues, the study area was divided into four
parts: Class 1 (very high relative tectonic activity, 1.0% in area);Class 2 (high,20.0%); Class 3 (moderate, 67.0%), and
Class 4 (low, 12.0%). The results are consistent with field observations on landforms and geology.
2010 Published by Elsevier B.V.
1. Introduction
Thelandforms and geologyof the Zagros Mountains in southwest Iran
such as fault scarps, triangular facets, truncated folds, and Quaternary
deposits alongfolded/faultedmountainfronts reflectrecenttectonics.The
seismic record in the Zagros is characterized by the high frequency of
relatively small magnitude (b4) earthquakes and infrequent large
earthquakes, making a seismological evaluation of active tectonics
difficult. Geomorphological studies of active tectonics in the late
Pleistocene and Holocene are important to evaluate earthquake hazards
in tectonically active areas such as the Zagros (Keller and Pinter, 2002).
Spatial tools including geographic information systems (GIS) and
morphometric analyses may provide useful information on this subject.
This articleapplies a quantitativegeomorphological method to an area
in the Zagros to evaluaterelativerates of active tectonics. Considering thediversity of the morphotectonic features (Keller and Pinter, 1996;
Burbank and Anderson, 2001), we analyzed six geomorphic indices: the
stream-gradient index (SL), drainage basin asymmetry (Af), hypsometric
integral (Hi), valley floor widthvalley height ratio (Vf), drainage basin
shape (Bs), and mountain-front sinuosity (J). We then computed a single
index (Iat) from the six indices to characterize relative active tectonics.
This kind of methodology has been found to be useful in various
tectonically active areas such as the SW USA (Rockwell et al., 1985),
the Pacific coast of Costa Rica (Wells et al., 1988), the Mediterraneancoast of Spain (Silva, 1994), and the southwestern Sierra Nevada of Spain
(El Hamdouni et al., 2007). We also evaluated the results from the
morphometric analyses based on field-based geomorphological
observations.
2. Regional geology
The Zagros is a fold-thrust belt within the Arabian plate, extending
from northeastern Iraq to thenorthernStrait of Hormuzin the Persian
Gulf (Fig. 1). It hasdeveloped under stronginfluence of tectonics since
the Late Cretaceous.
The study area (5350 km2) is located along a simply folded belt of
southeastern Zagros (Alavi, 2004). It is underlain by Phanerozoic
sedimentary sequences in elongated, doubly-plunging, box-shaped
anticlines, and the synclines are partly buried by younger Quaternary
alluvium (Fig. 2). The SWNE oriented contraction has led to the
development of NWSE trending, SW-verging folds, and NE-dipping
thrusts in the Phanerozoicsedimentary stratacovering the Afro-Arabian
basement, above a detachment zone of the InfracambrianCambrian
Hormuz evaporite (Kadinsky-Cade and Barzangi, 1982; Alavi, 1994).
Theother fault systems in the study area (Kazerun-Borazjan / Karebass /
Sabz Pushan / Sarvestan; Fig. 2) can be viewed as orogen-scale, horse-
tail, strike-slip faults which transfers dextral slips along the main recent
fault into the thrust-fold of the Zagros belt (Fig. 1; Authemayou et al.,
2005). The Sarvestan fault system is often marked by the salt diapirs
Geomorphology xxx (2010) xxxxxx
Corresponding author. Fax: +98 2129902628.
E-mail address: [email protected] (M. Dehbozorgi).
GEOMOR-03284; No of Pages 13
0169-555X/$ see front matter 2010 Published by Elsevier B.V.
doi:10.1016/j.geomorph.2010.05.002
Contents lists available at ScienceDirect
Geomorphology
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that emerged to the surface. In contrast, the Kharman Kuh in the
northeastern study area is situated on a salt diapir, which has not
emerged yet.
We categorized the level of rock resistance based on rock types
shown in Fig. 2 and field observations: very low (alluvial deposits),
low (older alluvial fan deposits, weakly consolidated conglomerate,
Fig. 1. Location of the study area in (A) a map of the Middle East and (B) a schematic structural map of the Fars.
Modified after Lacombe, 2006.
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and marl), moderate (gypseous marl, chalky fine dolomitic lime-
stone, and gypsum), and high (limestone, sandstone, dolomite, shale,
and hard conglomerate) (El Hamdouni et al., 2007). A map showing
the distribution of the rock resistant levels was created using GIS
(Fig. 3).
3. Morphometric analysis and results
3.1. Morphometric indices
Geomorphic indices useful for studying active tectonics include the
stream-gradient index (SL), drainage basin asymmetry (Af), hypsomet-
ric integral (Hi), valley floor widthvalley height ratio (Vf), drainage
basin shape (Bs), and mountain-front sinuosity (J) (Keller and Pinter,
1996). Because most of these indices are obtained for river basins, the
present research has considered the basin of the Ghare Aghaj River
flowing southwestward. This basin is subdivided into 72 subbasins
(Fig. 4).
3.1.1. Stream-gradient index (SL)
Rivers flowing over rocks and soils of various strengths tend to
reach an equilibrium with specific longitudinal profiles and hydraulic
geometries (Hack, 1973; Bull, 2007). Hack (1957, 1973, 1982) defined
the stream-gradient index (SL) to discuss influences of environmental
Fig. 2. Geological map of the study area.
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Fig. 3. Distribution of rock strength levels and SL index anomalies.
Fig. 4. Seventy-two subbasins of the Ghare Aghaj River basin.
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variables on longitudinal stream profiles, and to test whether streams
has reached an equilibrium. SL is defined as
SL = H=Lr Lsc 1
where H is change in altitude, Lr is length of a reach, and Lsc is the
horizontal length from the watershed divide to midpoint of the reach.
The SL index can be used to evaluate relative tectonic activity (Keller and
Pinter,2002). Althoughan area on soft rocks with high SL values indicatesrecent tectonic activity, anomalously low values ofSL may also represent
such activity when rivers and streams flow through strike-slip faults.
We calculated SL along rivers using a digital elevation model
(extracted from a digitized 1:25000 topographic map) and GIS
(Figs. 5 and 6) and computed its average value for each subbasin. The
value ranges from 55 (Subbasin 55) to 3046 (Subbasin 29). The values
wereclassified into three categories: 1 (SL500), 2 (300SLb500) and
3 (SLb300) (El Hamdouni et al., 2007). The result of the classification is
shown in Table 1.
3.1.2. Asymmetric factor (Af)
The asymmetric factor (Af) can be used to evaluate tectonic tilting
at the scale of a drainage basin (Hare and Gardner, 1985; Keller and
Pinter, 2002). Afis defined as:
Af = 100 Ar =At 2
whereAr is the area of a part of a watershed on the right of the master
stream (looking downstream) and At is the total area of the
watershed. Both Ar and At were measured in ArcGIS. Afis close to 50
if there is no or little tilting perpendicular to the direction of the
master stream. Afis significantly greater or smaller than 50 under the
effects of activetectonics or stronglithologic control. In thestudyarea,
Afvaries from 1.1 (Subbasin 51) to 91.5 (Subbasin 33). Afvalues were
grouped into three classes: 1 (Af65 or Afb35); 2: (35Afb43 or
57Afb65), and 3 (43Afb57) (El Hamdouni et al., 2007) (Fig. 7;
Table 1).
3.1.3. Hypsometric integral (Hi)
The hypsometric integral (Hi) describes the relative distribution
of elevation in a given area of a landscape particularly a drainage
basin (Strahler, 1952). The index is defined as the relative area below
the hypsometric curve and thus expresses the volume of a basin
that has not been eroded. A simple equation to approximately
calculate the index (Pike and Wilson, 1971; Mayer, 1990; Keller and
Pinter, 2002) is:
Hi = average elevationmin:elev: = max:elev:min:elev: : 3
Using Eq. (3), we computed Hi for each subbasin. It ranges from
0.11 (Subbasin 60) to 0.54 (Subbasin 7). Then Hi values were
grouped into three classes with respect to the convexity or concavity
of the hypsometric curve: Class 1 with convex hypsometric curves
(Hi0.5); Class 3 with concave hypsometric curves (Hib0.4); and
Class 2 with concaveconvex hypsometric curves (0.4Hib0.5)
(Fig. 8 and Table 1).
Fig. 5. SL index along the drainage network.
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3.1.4. Ratio of valley floor width to valley height (Vf)
Another index sensitive to tectonic uplift is the valley floor width
to valley height ratio (Vf):
Vf = 2Vfw = Ald + Ard2Asc 4
where Vfw is the width of the valley floor, and Ald, Ard and Asc are the
altitudes of the left and right divides (looking downstream) and the
Fig. 6. Longitudinal river profiles and measured SL values for three subbasins in the
study area.
Table 1
ValuesofAt (totalsubbasin area),the classes ofSL (stream-gradient index),Af(drainage
basin asymmetry), Hi (hypsometric integral), Vf (valley floor widthvalley height
ratio), Bs (drainage basin shape) and J (mountain front sinuosity) and values and
classes ofIat(relative tectonic activity).
Basin
no.
At(km2)
Class
of SL
Class
of Af
Class
of Hi
Class
of Vf
Class
of Bs
Class
of J
Value
of Iat
Class
of Iat
1 16.07 3 1 3 2 1 2.00 2
2 53.32 3 1 3 2 1 2.00 2
3 17.15 3 1 3 2 3 1 2.17 34 54.88 3 1 3 2 2 1 2.00 2
5 62.89 3 3 2 1 3 1 2.17 3
6 58.26 3 1 3 1 3 1 2.00 2
7 19.94 1 1 1 3 1 1.40 1
8 52.69 1 1 3 3 1 1.80 2
9 92.65 3 3 3 1 1 2.20 3
10 30.16 1 1 1 3 1 1.40 1
11 18.32 1 3 3 1 2.00 2
12 29.21 3 3 3 3 1 2.60 4
13 60.72 3 1 3 1 3 1 2.00 2
14 28.90 3 2 3 3 2.75 4
15 104.33 2 2 2 3 2 1 2.00 2
16 38.05 2 2 3 3 1 2.20 3
17 31.05 3 1 2 3 2.25 3
18 28.40 3 1 3 3 2 2.40 3
19 128.08 1 1 3 3 1 1.80 2
20 42.66 3 3 3
3
3.00 421 58.50 3 1 3 3 3 2 2.50 3
22 23.84 3 1 3 3 2 2.40 3
23 411.42 3 2 3 2 1 2.20 3
24 23.07 3 1 3 3 2 2.40 3
25 101.43 3 1 3 3 1 2.20 3
26 46.58 3 1 3 1 3 2 2.17 3
27 59.63 3 2 3 3 1 2.40 3
28 65.71 3 1 3 2 3 2 2.33 3
29 83.99 1 3 3 1 3 1 2.00 2
30 77.93 1 1 3 1 3 2 1.83 2
31 90.94 3 1 2 2 1 1.80 2
32 142.25 3 1 3 2 3 1 2.17 3
33 39.64 3 1 3 3 2 2.40 3
34 17.69 3 1 3 1 2.00 2
35 56.18 3 2 3 1 2 2.20 3
36 57.02 3 2 3 1 3 1 2.17 3
37 74.11 3 1 3 3 1 2.20 3
38 88.17 3 1 3 3 3 1 2.33 339 82.38 3 1 3 2 1 2.00 2
40 31.70 3 3 3 1 2.50 3
41 32.03 3 1 3 2 2.25 3
42 48.94 3 2 3 3 3 1 2.50 3
43 19.79 3 2 3 1 2.25 3
44 385.30 3 2 3 1 3 1 2.17 3
45 30.04 3 1 3 3 2.50 3
46 19.88 3 1 3 2 2.25 3
47 30.39 1 2 3 3 2.25 3
48 45.29 3 3 2 2 1 2.20 3
49 45.44 3 1 3 3 3 2 2.50 3
50 91.64 3 1 3 1 1 1.80 2
51 313.99 3 3 3 3 3 1 2.67 4
52 36.47 3 2 3 3 1 2.40 3
53 21.11 3 2 3 1 1 2.00 2
54 487.67 3 3 3 1 2.50 3
55 27.69 3 3 3
3 1 2.60 456 29.74 3 1 3 3 1 2.20 3
57 132.46 3 3 3 2 3 1 2.50 3
58 57.47 3 3 3 2 3 1 2.50 3
59 29.11 3 3 3 3 1 1 2.33 3
60 167.64 3 1 3 3 1 2.20 3
61 39.36 3 1 2 2 1 1.80 2
62 67.73 3 1 3 3 2 1 2.17 3
63 30.72 3 1 2 3 3 1 2.17 3
64 80.82 3 1 3 3 1 2.20 3
65 44.87 3 1 3 3 1 2.20 3
66 51.84 3 1 3 3 1 2.20 3
67 12.74 3 1 3 3 2.50 3
68 44.39 3 1 3 3 1 2.20 3
69 93.01 3 3 3 3 1 2.60 4
70 90.71 3 2 3 3 2.75 4
71 111.27 2 2 3 3 1 2.20 3
72 30.20 3 1 3 3 2.50 3
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stream channel, respectively (Bull, 2007). Bull and Mcfadden (1977)
found significant differences in Vf between tectonically active and
inactive mountain fronts, because a valley floor is narrowed due to
rapid stream downcutting.
Valleys upstream from the mountain front tend to be narrow
(Ramrez-Herrera, 1998), and Vf is usually computed at a given
distance upstream from the mountain front (Silva et al., 2003).We set
a distance between 0.5 and 1 km, and within this range, the distance
increased with an increasing subbasin size. Vfwas calculated for the
main valleys that cross mountain fronts of the study area using cross-
sections drawn from the DEM and the digitized 1:25,000 topographic
map (Fig. 9). Then Vfwas classified into three classes: 1 (Vf0.5); 2
(0.5Vfb1.0) and 3 (Vf1) (El Hamdouni et al., 2007) (Table 1). Therange of Vf is from 0.11 (Subbasin 6) to 4.07 (Subbasin 51). Vf is
relatively low for V-shape valleys but high for U-shape valleys.
According to the obtained Vfvalues, most valleys in the study area are
V-shaped.
3.1.5. Basin shape index (Bs)
The horizontal projection of a basin may be described by the basin
shape index or the elongation ratio, Bs (Cannon, 1976; Ramrez-
Herrera, 1998):
Bs = Bl = Bw 5
where Bl is the length of a basin measured from the highest point, and
Bw is the width of a basin measured at its widest point. Relatively
young drainage basinsin tectonically activeareastend to be elongated
in shape, normal to the topographic slope of a mountain ( Bull and
McFadden, 1977; Ramrez-Herrera, 1998). Therefore, Bs may reflect
the rate of active tectonics.Bs wascomputed using the DEMand classified into three classes: 1
(Bs4); 2 (3Bsb4) and 3 (Bs3) (El Hamdouni et al., 2007). Bs
ranges from 1.0 (Subbasin 70) to 6.8 (Subbasin 35). About two-thirds
of the studied subbasins belong to Class 3 with nearly circular shapes
(Table 1).
3.1.6. Mountain-front sinuosity index (J)
The mountain-front sinuosity index (J) is defined by Bull and
McFadden (1977) and Bull (2007) as:
J = Lj = Ls 6
where Lj is the planimetric length of a mountain front along the
mountainpiedmont junction, and Ls is the straight-line length of the
front. J is commonly less than 3, and approaches 1.0 where steep
mountains rise rapidly along a fault or fold (Bull, 2007). It represents
a balance between stream erosion processes tending to cut some
parts of a mountain front and active vertical tectonics that tend to
produce straight mountain fronts (Bull and McFadden, 1977; Keller,
1986).
The values of J was calculated for 27 mountain fronts (Fig. 10)
using Lj and Ls values measured from SRTM images, and divided into
three classes: 1 (Jb
1.1), 2(1.1Jb
1.5), and 3 (J1.5) (El Hamdouni
Fig. 7. Distribution ofAfclasses.
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et al., 2007). All the observed values, however, are between 1.0 and
1.17 and belong to Classes 1 and 2 (Table 2).
3.2. Spatial distribution of index values
Some rivers on the northern flank of the Sefidar anticline
demonstrate anomalously high values of SL, corresponding to the
Sabz Pushan fault zone (Figs. 3 and 5). The fault zone is seismically
active, with right-lateral strike-slip faults. Some anomalously high SL
values arealso recorded along Subbasins11, 15,and 20 along theEW
Kahdan fault in the northern part of the Kolah Ghazi anticline ( Figs. 3
and 5). The SL values of Subbasins 29 and 30, along the Tudej anticline
and the Sarvestan fault zone respectively are also high (Figs. 5 and 6).
SL of Subbasin 47 on the Kharman Kuhdiapiric dome with an exposed
fault segment is also high (Figs. 5 and 6).
According to the acquired data and the geological maps, almost
all moderately anomalous values of SL are located either along
active faults such as the southernfl
ank of the Ahmadi anticline(Maharlu fault zone) and the Gharabagh, Kheirabad and Runiz
faults or fault zones, or where the underlying rock is resistant
(Figs. 3 and 5).
Although structural control plays a significant role in the
development of basin asymmetry (El Hamdouni et al., 2007), the
highest values ofAfthat demonstrate the most prominent asymmetry
occur in the Sarvestan and Sabz Pushan fault zones (Fig. 7); examples
are Subbasins 2, 4, and 39. The subbasins with the highest values ofHi
also occur along these fault zones. Note that they are not the cases of
high Hi due to incision into a young depositional surface (El
Hamdouni et al., 2007). The distribution of Vf indicates that rivers
are deeply incised into the ground where they flow over an active fold
or fault (Fig. 9).
The most elongated subbasins with the highest values ofBs occur
along the Sarvestan fault zone.Jvalues reflect the existence of straight
mountain fronts in the study area and thus active tectonics. Three of
them (Fronts 18, 19, and 24) have been truncated by the Sarvestan
fault (Fig. 10).
3.3. Evaluation of relative tectonic activity
Previous studies on relative tectonic activity based on geomorphic
indices tend to focus on a particular mountain front or area (Bull and
McFadden, 1977; Rockwell et al., 1985; Azor et al., 2002; Molin et al.,
2004). This study tried to evaluate tectonics in a wider area, using a
number of geomorphological parameters. The average of the six
measured geomorphic indices (Iat) was used to evaluate the distribu-
tion of relative tectonic activity in the study area (El Hamdouni et al.,
2007). The values of the index were divided into four classes to definethe degree of active tectonics: 1very high (1.0 Iatb1.5); 2high
(1.5 Iatb2.0); 3moderate (2.0 Iatb2.5); and 4low (2.5 Iat) (El
Hamdouni et al., 2007).
The distribution of the four classes is shown in Fig. 11, and Table 1
shows the result of the classification for each subbasin. About 1% of
the study area (about 50 km2) belongs to Class 1; 20% (1050 km2) to
Class 2; 67% (3580 km2) to Class 3; and 12% (660 km2) to Class 4. Iat
tends to be high along the Sarvestan fault zone (Fig. 11).
4. Discussion
The values of the six geomorphic indices as well as Iat often
change corresponding to the distribution of fault zones. The 78 km-
long Sarvestan fault zone is the most typical case according to thedistribution ofIat. The fault zone, cutting across the fold-thrust belt
of Zagros, is dominated by strike-slip (Berberian, 1995), and has
deformed some of the previously formed folds including the Kuhe
Siah anticline, the Kolah Ghazi anticline, and the eastern part of the
Ahmadi anticline (Fig. 12). It has also uplifted the eastern block by
several hundred meters, causing prominent fault scarps, and has
raised some active diapirs such as the Sarvestan diapir. The rises of
the diapirs are associated with normal faulting, which is affected by
the degree of the coupling between the brittle overburden and
viscose substratum materials (Jackson, 1994; Bahroudi 2003). The
Sarvestan diapir is characterized by high altitudes and a relatively
high effective precipitation, and the exposed salt may be eroded
rapidly (Bruthans et al., 2009). This erosive condition may have
started around 6ka BP, when a wetter climate since ca. 10ka BP was
Fig. 8. Hypsometry curves of three subbasins. A: total surface of the subbasin. a: surfacearea withinthe subbasin above a given elevation h, H: highestelevation of thesubbasin.
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Fig. 9. Location of sections for Vfcalculation.
Fig. 10. Twenty-seven mountain front segments for assessing the J index.
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replaced by a recent drier climate (Burns et al., 1998; Staubwasser
and Weiss, 2006). Therefore, thick vegetation cover at the Sarvestan
diapir probably disappeared around 6 ka, leading to rapid erosion
and more anomalous values of the geomorphic indices. Faulting of
the cretaceous limestone near the Sarvestan diapir indicates an
uneven strikefracture pattern, suggesting intermittent vertical
uplift which has been coupled with the movement of the diapir.
Here, Iat is particularly high, suggesting the impact of the complex
tectonics.Thepattern of tectonic deformation in the study area remained the
same over the last 5 million years (Allen et al., 2004; Talebian and
Jackson, 2004). An N2030 compression prevailed (Molinaro et al.,
2005; Lacombe et al., 2006), and the oblique ArabiaEurasia
convergence has been accommodated by both shortening and
strike-slip (Lacombe et al., 2006). This type of long-term deformation
along the Sarvestan fault zone explains the high values of Iat. The
N2030 compression is also consistent with dextral motions along
the other NWSE trending faults such as the Sarvestan and Sabz
Pushan faults (Bachmanov et al., 2004). Iatfor areas along these faults
is high to very high, although the Sarvestan fault is partly buried due
to recent sedimentation (Fig. 12), confirming the effectiveness of the
Iat index.
Local tilting of the upper-Pliocene Bakhtyari conglomerates
throughout the Zagros (Hessami et al., 2001) suggests a recent
folding. This is consistent with well-developed triangular facets
associated with anticlines, a series of deep, narrow, parallel gorges
incised into mountain fronts (Fig. 13), and the accumulation of
Table 2
Valuesand classesofJ(mountain front sinuosity) forthe defined mountain fronts. Class
1: Jb1.1, Class 2: 1.1Jb1.5.
Mountain fron t no. Basin no. J Class
1 64, 68, 71 1.04 1
2 50 1.10 2
3 5759, 62 1.04 1
4 57 1.01 1
5 48, 50, 52, 56, 65 1.04 1
6 65 1.07 17 66 1.04 1
8 51 1.06 1
9 51 1.06 1
10 29, 51 1.08 1
11 32, 36, 42, 49, 60 1.05 1
12 25 1.05 1
13 2124, 28, 44 1.17 2
14 13 1.06 1
15 44 1.02 1
16 19 1.15 2
17 710, 19, 23 1.03 1
18 30 1.10 2
19 31 1.08 1
20 39 1.00 1
21 37, 27 1.03 1
22 31 1.11 2
3 25 1.02 124 15, 3, 5 1.05 1
25 2 1.02 1
26 1, 4, 6, 12 1.08 1
27 2 1.09 1
Fig. 11. Distribution of Iatclasses.
10 M. Dehbozorgi et al. / Geomorphology xxx (2010) xxxxxx
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Please cite this article as: Dehbozorgi, M., et al., Quantitative analysis of relative tectonic activity in the Sarvestan area, central Zagros, Iran,Geomorphology (2010), doi:10.1016/j.geomorph.2010.05.002
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about 250 m of alluvial deposits. These observations as well as the
values of the geomorphic indices suggest moderately to highly
active tectonics.
Iatis high throughout thesouthwest part of thestudyarea(Fig. 11),
which corresponds to a straight mountain front and triangular facets
along theSabz Pushan fault (Fig. 14). On the other hand, the lowest Iat
values(class 4) mainlyoccurin thenorthernand northeasternpartsofthe study area (Fig. 11), where all geomorphic indices suggest low
tectonic activity. This could be related to the inactive syncline axes
associated with vast plains.
5. Conclusions
Geomorphic indices computed using GIS are considered to be
suitable for evaluating the effects of active tectonics over a large
area. The method was applied to the Sarvestan area of the central
Zagros to identify geomorphic anomalies and evaluate tectonic
activity, because the central Zagros lacks proper works on active
tectonics, and the low-frequency seismic record for the study area
limits the possibility of seismological evaluation of tectonics. We
used seven geomorphic indices: the stream-gradient index (SL),
Fig. 12. The Sarvestan Fault and adjacent landforms. EMja:E oceneMiocene limestone of Jahrom formation, Esa: Eocene marl of Sachun formation, Ktb: Upper Cretaceous limestone
of Tarbur formation, MPLa: MiocenePliocene sandstone of Aghajari formation, Mrz: OligoceneMiocene marl of Razak formation, Q: Quaternary deposits.
Fig. 13. A deep gorge cutting the Tudej Anticline.
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Please cite this article as: Dehbozorgi, M., et al., Quantitative analysis of relative tectonic activity in the Sarvestan area, central Zagros, Iran,Geomorphology (2010), doi:10.1016/j.geomorph.2010.05.002
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