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

j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / g e o m o r p h

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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
mailto:[email protected]://dx.doi.org/10.1016/j.geomorph.2010.05.002http://www.sciencedirect.com/science/journal/0169555Xhttp://dx.doi.org/10.1016/j.geomorph.2010.05.002http://dx.doi.org/10.1016/j.geomorph.2010.05.002http://www.sciencedirect.com/science/journal/0169555Xhttp://dx.doi.org/10.1016/j.geomorph.2010.05.002mailto:[email protected]


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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.

3M. Dehbozorgi et al. / Geomorphology xxx (2010) xxxxxx

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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.


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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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