Appraisal of Active Tectonics in Hindu Kush: Insights from DEM Derived Geomorphic Indices and Drainage Analysis

GEOSCIENCE FRONTIERS 3(4) (2012) 407e428

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RESEARCH PAPER Appraisal of active tectonics in Hindu Kush: Insights from DEM derived geomorphic indices and drainage analysis

Syed Amer Mahmood a,b,*, Richard Gloaguen a a Remote Sensing Group, Institute of Geology, Freiberg University of Mining and Technology, Bernhard V. Cotta Str. 2, 09599 Freiberg (Saxony), Germany b Department of Space Science, University of the Punjab, Quaid-e-Azam Campus, 54590, Lahore (Punjab), Pakistan

Received 13 May 2011; accepted 3 December 2011 Available online 11 December 2011

KEYWORDS Abstract Landscapes in tectonically active Hindu Kush (NW Pakistan and NE Afghanistan) result Active tectonics; from a complex integration of the effects of vertical and horizontal crustal block motions as well as Geomorphic indices; erosion and deposition processes. Active tectonics in this region have greatly inﬂuenced the drainage IRAT (index of relative system and geomorphic expressions. The study area is a junction of three important mountain ranges active tectonics); (Hindu Kush-Karakorum-Himalayas) and is thus an ideal natural laboratory to investigate the relative Hindu Kush; tectonic activity resulting from the India-Eurasia collision. We evaluate active tectonics using DEM PakistaneAfghanistan derived drainage network and geomorphic indices hypsometric integral (HI), stream-length gradient

(SL), fractal dimension (FD), basin asymmetry factor (AF), basin shape index (Bs), valley floor width to valley height ratio (Vf ) and mountain front sinuosity (Smf). The results obtained from these indices were combined to yield an index of relative active tectonics (IRAT) using GIS. The average of the seven measured geomorphic indices was used to evaluate the distribution of relative tectonic activity in the study area. We defined four classes to define the degree of relative tectonic activity: class 1__very high (1.0 IRAT < 1.3); class 2__high (1.3 IRAT < 1.5); class

* Corresponding author. Remote Sensing Group, Institute of Geology, Freiberg University of Mining and Technology, Bernhard V. Cotta Str. 2, 09599 Freiberg (Saxony), Germany. Tel.: þ49 3731444035. E-mail address: [email protected] (S.A. Mahmood). 1674-9871 ª 2011, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.

Peer-review under responsibility of China University of Geosciences (Beijing). doi:10.1016/j.gsf.2011.12.002

Production and hosting by Elsevier 408 S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428

3dmoderate (1.5 IRAT < 1.8); and class 4dlow (1.8 IRAT). In view of the results, we conclude that this combined approach allows the identification of the highly deformed areas related to active tectonics. Landsat imagery and field observations also evidence the presence of active tectonics based on the deflected streams, deformed landforms, active mountain fronts and triangular facets. The indicative values of IRAT are consistent with the areas of known relative uplift rates, landforms and geology. ª 2011, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.

1. Introduction In mountain ranges, recent and active tectonics can be viewed as the main factor contributing to rock uplift, their present-day Tectonic geomorphology is one of the emergent disciplines in topography being the result of the competition between tectonic geosciences due to the advent of novel geomorphological, geodetic and erosional processes (Andermann and Gloaguen, 2009; Perez- and geochronological tools which aid the acquisition of rates (uplift Pena et al., 2009). The drainage pattern in tectonically active rates, incision rates, erosion rates, slip rates on faults, etc.) at vari- regions is very sensitive to active processes such as folding and able time-scales (103e106 years; Burbank and Anderson, 2001; faulting which are responsible for accelerated river incision, basin Azor et al., 2002; Keller and Pinter, 2002; Bull, 2007). This disci- asymmetries, drainage geometry and complexity and river pline is important because the results of regional studies on neo- deﬂections (Cox, 1994). The geomorphic indices are important tectonics are signiﬁcant for evaluating natural hazards, land use indicators capable of decoding landform responses to active development and management in populated areas (Pedrera et al., deformation processes and have been widely used as a reconnais- 2009). Besides its socio-economic importance, study of neo- sance tool to differentiate zones deformed by active tectonics tectonics is based on a multi-disciplinary approach, integrating data (Keller and Pinter, 2002; Chen et al., 2003). from remote sensing imagery, geomorphology, structural geology, This investigation applies a quantitative analysis of geomor- stratigraphy, geochronology, seismology, and geodesy. phic indices extracted from the digital elevation model (DEM) in

Figure 1 Regional tectonic framework (Hindu Kush-Himalaya-Pamir-Karakorum) with inset showing the study area (Fig. 2). GPS velocity vectors (Red) with respect to Eurasia ﬁxed reference frame from Mohadjer et al. (2010), the purple vector is transformed with respect to Pak- istaneIndia ﬁxed. Abbreviations of fault names: DkF, Darvaz Karakul fault; AM, Alburz Marmul; CbF, Central Badakhshan fault; HvF, Henjvan fault; HF, Herat fault; CF, Chaman fault; MoF, Mokar fault; GzF, Gardez fault; KoF, Konar fault; SBF, Sulaiman Base front; MBT, Main Boundary Thrust; MFT, Main frontal thrust; MMT, Main Mantle Thrust; and MKT, Main Karakorum Thrust, Reshun fault; TMF, Tirch Mir fault; SF, Sarobi fault; ST, Spinghar Thrust; AF, Andarab fault; TbF, Tarbella fault; BgF, Bazgir fault; Sources: Lawrence et al., 1981; Wheeler et al., 2005; Doebrich and Wahl, 2006; Mahmood and Gloaguen, 2011. S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428 409

Figure 2 Tectonic setting of the study area (A), sub-basins with reference numbers (B). 410 S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428

Hindu Kush and its neighbourhood to evaluate relative active analyzed 33 sub-basins (Fig. 2B) using seven geomorphic indices: tectonics. The Hindu Kush is one of the most tectonically active hypsometric integral (HI), stream-length gradient (SL), fractal regions in the world as a result of the India-Eurasia collision dimension (FD), basin asymmetry factor (AF), basin shape index (Fig. 1). For the detailed study of the morphotectonic features as (Bs), valley ﬂoor width to valley height ratio (Vf ) and mountain described by Keller et al. (1996) and Keller and Pinter (2002),we front sinuosity (Smf). We then combined these seven indices to

Figure 3 SL mechanism (modified after Hack, 1973) (A), and geological strength level map and SL anomalies (B). S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428 411 provide a global estimator to characterize active tectonics (El rugged (Burtman and Molnar, 1993), (Figs. 1 and 2). Northern Hamdouni et al., 2008). Similar approaches were found to be Hindu Kush consists of folded Mesozoic and predominantly useful in various tectonically active areas such as the SW USA Tertiary sediments, while the southern part consists of highly (Rockwell et al., 1985), the Pacific coast of Costa Rica (Wells complicated metamorphic rocks, marbles and intrusions of et al., 1988), the Mediterranean coast of Spain (Silva et al., granodiorites (Gansser, 1964; Molnar and Tapponnier, 1975). 2003), the southwestern Sierra Nevada of Spain (El Hamdouni Evidences of active tectonics exist in the Western Karakoram, et al., 2008) and in Beotia. The previous studies (Dehbozorgi the Tirich Boundary Zone (Hildebrand et al., 2001) connected et al., 2010) were mainly conducted on relatively small areas with the Chaman-Gardez-Konar fault system (Mohadjer et al., (5350 km2) while we performed our analyses on a relatively large 2010). As a result, this activity is inferring a sinistral transpres- areas (132,259 km2) and introduced an additional fractal dimen- sional tectonic regime, which is ascribed to the progressive sion index (FD), which was found to improve the analysis of indentation and a possible anticlockwise regional rotation of India tectonic geomorphology. We also combined results from these into Eurasia (Tapponnier et al., 1981; Hildebrand et al., 2001). The analyses with the geomorphic expressions mapped on enhanced Hindu Kush region is tectonically active with deep Landsat 7, þETM (Enhanced Thematic Mapper) imagery. (w70e300 km) and intense seismicity (Pavlis and Das, 2000). The sinistral Chaman transform fault south of the Hindu Kush infers the highest slip rate of 26 mm/y (Apel et al., 2006). The 2. Tectonic, geologic and geomorphic setting sinistral movement of Chaman transform fault appears to be influencing continental deep-subduction in the Pamir region as its The Hindu Kush is a very complex mountain range system in slip is distributed into several fault systems in the north (Mohadjer terms of tectonics, geology and geomorphology. This region et al., 2010), e.g., chaman-Mokar-Gardez.Konar-Main Karakorum located at the western syntaxis of Himalayas, in a broad defor- thrust-Tirch Mir-Reshun fault system and presumably, Chaman- mation belt created by the India-Eurasia collision zones is highly Gardez-Laghman-Bazgir fault system (Mahmood et al., 2009).

Figure 4 Some examples of longitudinal river proﬁles and the measured SL index. Figure 5 Interpolated SL index map for the drainage network of Hindu Kush and its neighbourhood (A), Standardized SL-index values for all individual sub-basins (B). S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428 413

3. Geomorphic indices and results systems display slightly concave longitudinal profiles (Schumm et al., 2000). Deviation from this stable river profile may be 3.1. Geomorphic indices induced by tectonic, lithological and/or climatic factors (Hack, 1973). The SL index was defined by Hack (1973) to discuss influences of environmental variables on longitudinal stream The geomorphic indices are either based on analysis of the profiles, and to test whether streams have reached equilibrium or drainage network or mountain fronts. These indices may detect not, mathematically SL is given by, anomalies in the drainage system or along mountain fronts (El Hamdouni et al., 2008). These anomalies are possibly due to SLZðDH=DLrÞ Lt ð1Þ local changes from tectonic activity resulting from uplift or where DH is change in altitude, DL is length of a reach, and L is subsidence. We analyze different indices in the Hindu Kush (33 r t the horizontal length from the watershed divide to midpoint of the sub-basins) and neighbouring mountain ranges (Fig. 2B) and reach (Fig. 3A). The SL index can be used to evaluate relative assign them different tectonic classes based upon the range of tectonic activity (Keller and Pinter, 2002). Although an area on values of individual geomorphic indices. These classes are then soft rocks with high SL values indicates recent tectonic activity, summed and averaged and arbitrarily divided into an index of anomalously low values of SL may also represent such activity relative active tectonics (IRAT) over the entire study area. when rivers and streams flow through strike-slip faults (Keller and Pinter, 2002). 3.1.1. Stream-length gradient index (SL) We computed SL along streams and rivers (some examples are The topographic evolution results from an adjustment between the shown in Fig. 4) using ASTER GDEM with spatial resolution of erosional processes as streams and rivers flow over rocks and soils 30 m and GIS (Fig. 5A) and calculated its standardized average of variable strength (Hack, 1973). This adjustment eventually value for each sub-basin (5B). The value ranges from 55 (sub- reaches a dynamic equilibrium (erosion Z uplift) and river basin 55) to 3046 (sub-basin 29). The values were classified into

Table 1 Values and classes of geomorphic indices and IRAT (index of relative active tectonics). Basin Nos. Class of geomorphic indices IRAT value IRAT class

SL FD Bs AF HI Vf Smf 1 1 2 1 3 1 1 1 1.43 2 2 2 1 2 1 1 1 1 1.29 1 3 1 1 1 3 1 1 2 1.43 2 4 2 2 2 2 1 1 1 1.57 3 5 1 1 1 1 1 1 1 1.00 1 6 11112e 2 1.33 2 7 1 1 1 1 1 1 2 1.14 1 8 12321e 1 1.67 3 9 21131e 1 1.50 2 10 1 1 1 3 1 1 1 1.29 1 11 1 1 2 3 1 1 1 1.43 2 12 1 1 1 1 1 1 1 1.00 1 13 1 1 2 1 1 1 1 1.14 1 14 2 2 1 1 1 e 1 1.33 2 15 2 1 1 1 2 2 1 1.43 2 16 3 3 2 1 2 1 2 2.00 4 17 3 2 1 2 1 3 2 2.00 4 18 2 3 3 1 1 e 1 1.83 3 19 3 2 2 3 2 2 2 2.29 4 20 2 1 1 1 2 1 2 1.43 2 21 2 2 2 2 2 2 1 1.86 3 22 3 2 3 1 3 e 2 2.33 4 23 3 1 2 1 3 2 2 2.00 4 24 2 1 3 2 2 e 1 1.83 3 25 2 2 2 3 1 1 1 1.71 3 26 2 2 2 1 2 e 1 1.67 3 27 2 1 2 1 2 e 1 1.50 2 28 2 2 3 1 1 e 1 1.67 3 29 3 1 3 3 1 e 1 2.00 4 30 2 2 1 1 1 e 1 1.33 2 31 2 1 1 1 1 3 2 1.57 3 32 2 2 1 2 2 2 1 1.71 3 33 3 1 2 1 1 3 1 1.71 3 414 S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428

In order to assess the effect of lithology we simply classiﬁed the level of rock resistance based on rock types (Fig. 3B) and a GIS map showing the distribution of the rock resistant levels was prepared.

3.1.2. Asymmetry factor (AF) The asymmetry factor (AF) is a way to evaluate the existence of tectonic tilting at the scale of a drainage basin (Fig. 6). The method may be applied over a relatively large area (Hare and Gardner, 1985). AF is deﬁned by,

AFZðAr=AtÞ100 ð2Þ

where Ar is the area of the basin to the right (looking downstream) of the trunk stream, At is the total area of the drainage basin and both were measured in ArcGIS. AF is sensitive to change in inclination perpendicular to the stream direction. AF significantly greater or smaller than 50 shows influence of active tectonics/ lithologic control or differential erosion, as for example the stream slipping down bedding plains over time (El Hamdouni et al., 2008). AF close to 50, if there is no or a little tilting perpendic- Figure 6 Drainage response to uplift along a fault by migrating ular to the direction of the trunk channel. In tectonically active topography, the landforms are characterized by relatively steep, laterally in a down-tilt direction, Ar is the area of the basin to the right mountainous sides and flat floors. The steep sides are created by (looking downstream) of the trunk stream and At is the total area of the drainage basin (modified after Keller and Pinter, 2002). displacement on faults such that the valley floor moves down relative to the surrounding margins, or, conversely, the margins move up relative to the floor. This movement results in basin three classes: class 1 (1076e750), class 2 (366e749) and class 3 tilting and causes the river to migrate latterly and deviate from the (SL 365) according to El Hamdouni et al. (2008). The result of basin midline. Also, structural control of the orientation of the classification is shown in Fig. 5 and Table 1. bedding may play a vital role in the growth of basin asymmetry

Figure 7 Map showing widespread basin asymmetry factor and tilting direction related to relative active tectonics. S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428 415 and tilting of bedding allows for preferred migration of the valley expresses the volume of a basin that has not been eroded in the down-dip direction, producing an asymmetric valley (Cox, (Fig. 9A). The simple equation that may be used to calculate the 1994). index (Mayer, 1990; Keller and Pinter, 2002)is In order to express the tilting direction of the catchments, in the northern and southern slopes of the Hindu Kush and neighbouring ZElevmean Elevmin ð Þ ranges, we articulated AF as the absolute value minus 50, with an HI 4 Elevmax Elevmin arrow indicating the asymmetry direction in (Fig. 7). This index is similar to the SL index in that rock strength as

AFZjðAr=AtÞ100 50j ð3Þ well as other factors affects the value. High values of HI generally mean that not as much of the uplands have been eroded, and may The AFe50 value is the amount of difference between the propose a younger landscape (Fig. 9B), possibly produced by neutral value of 50 and the calculated AF value. For the purpose of active tectonics. High HI could also result from recent incision evaluating the relative active tectonics, the absolute difference is into a young geomorphic surface formed by deposition. In our what is important, and values of AFe50 range from 0.22 (almost analysis of HI, we suppose that if part of the HI is convex in the symmetric sub-basin 1) to 35.39 (highly asymmetric sub-basin lower portion, it may relate to uplift along a fault. High HI values 33). AF values were divided into three classes: class 1 are possibly related to young active tectonic and low values are (AF > 5.91); class 2: (2.95 > AF 5.91), and class 3 (AF 2.95) related to older landscapes that have been more eroded and less as shown in Fig. 8 and Table 1. impacted by recent active tectonics (Fig. 9B). Using Eq. (4),we computed HI for each sub-basin. It ranges from 0.36 (sub-basins 3.1.3. Hypsometric integral (HI) 23) to 0.78 (sub-basin 9). Then HI values were grouped into three The HI is generally derived for a particular drainage basin and is classes with respect to the convexity or concavity of the hypso- an index that is independent of basin area. The HI is an index that metric curve: class 1 with convex hypsometric curves explains the distribution of elevation of a given area of a land- (0.51e0.78); class 2 with concaveeconvex hypsometric curves scape, particularly a drainage basin (Strahler, 1952). The index is (0.37e0.50) and class 3 with concave hypsometric curves (<0.37) deﬁned as the area below the hypsometric curve and thus as shown in Fig. 10 and Table 1.

Figure 8 Asymmetry factor map for the sub-basins. 416 S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428

Figure 9 Typical hypsometric curves (HC) after (Strahler, 1952) and geomorphic cycle development (Perez-Pena et al., 2009) showing changes in hypsometric curves (A), convex HC and high HI (sub-basin 12) describes youthful stages, S-shaped curves and concave curves together with medium (sub-basin 32) and low HI values are typical for mature and old stages (basin 23) (B).

3.1.4. Ratio of valley floor width to valley height (Vf ) sections upstream for Vf estimation in case of large basins and Valley floor width-to-height ratio (Vf )(Bull and McFadden, 1977) then took the average of these values as a representative of that is a geomorphic index conceived to discriminate between V-sha- particular basin. The Vf was calculated for the main valleys that ped and U-shaped flat-floored valleys. This index is defined as: cross mountain fronts of the study area using cross section drawn from the DEM (Fig. 6). Then Vf was classified into three classes: e e e 2Vfw class 1 (0.02 0.44); class 2 (0.45 1.0) and class 3 (1.01 3.25) as Vf Z ð5Þ shown in Fig. 12 and Table 1. The range of Vf is from 0.02 (sub- Eld þ Erd 2Esc basin 2) to 3.25 (sub-basin 33). Vf is relatively low for V-shape where Vfw is the width of the valley floor, Eld and Erd are eleva- valleys but high for U-shape valleys. According to the Vf values, tions of the left and right valley divides (facing downstream) most valleys in the study area are V-shaped. respectively, and Esc is the elevation of the valley floor (Fig. 11). Because uplift is associated with incision, the index is thought to 3.1.5. Basin shape index (Bs) be a proxy for active tectonics where low values of Vf are asso- Relatively young drainage basins in active tectonic areas tend to ciated with higher rates of uplift and incision. Deep V-shaped be elongated in shape parallel to the topographic slope of valleys (Vf < 1) are connected with linear, active downcutting a mountain. The elongated shapes are transformed into circular streams distinctive of areas subjected to active uplift, while flat- basins, as tectonic activity reduces with time and continued floored (U-shaped) valleys (Vf > 1) show an attainment of the topographic evolution (Bull and McFadden, 1977). The reason of base level of erosion mainly in response to relative tectonic this transformation is because the drainage basin widths are much quiescence (e.g., Keller and Pinter, 2002; Keller, 1986). narrower near the mountain front in tectonically active areas Valleys upstream from the mountain front tend to be narrow where the energy of the stream has been directed primarily to (Ramırez-Herrera, 1998), and Vf is usually calculated at a given downcutting; by contrast, a lack of continuing rapid uplift permits distance upstream from the mountain front (Silva et al., 2003). We widening of the basins upstream from the mountain front. The set a distance between 2 and 4 km because of the large size of the horizontal projection of a basin may be described by the basin study area, and within this range, the distance increased with an shape index or the elongation ratio, Bs (Ramırez-Herrera, 1998)or increasing size of the sub-basin. We took more than one cross elongation ratio is expressed as: S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428 417

Figure 10 HI classes for the studied sub-basins.

Bl slope, and Ls is the length of the mountain front measured along BsZ ð6Þ Bw a straight line (Fig. 14A). This index has been used to evaluate the relative tectonic activity along mountain fronts (Keller and Pinter, where Bl is the length of a basin measured from the headwaters 2002; Silva et al., 2003). In active mountain fronts, uplift will point to the mouth, and Bw is the width of a basin measured at its prevail over erosional processes, yielding straight fronts with low B widest point (Fig. 13A). High values of s are associated with values of Smf. Along less active fronts, erosional processes will elongated basins, generally associated with relatively higher generate irregular or sinuous fronts with high values of Smf. Some B tectonic activity. Low values of s indicate a more circular-shaped studies have proposed that the lower values of the Smf index basin, generally associated with low tectonic activity. Therefore, (<1.4) are indicative of tectonically active fronts (Keller, 1986), B B s may reflect the rate of active tectonics. s was computed using while higher Smf values (>3) are normally associated with inactive the DEM and classified into three classes: class 1 (1.77e3.22); fronts in which the initial rangeefront fault may be more than e e class 2 (1.21 1.76) and class 3 (1.11 1.20). Bs ranges from 1.11 1 km away from the present erosional front (Bull, 2007). (sub-basin 18) to 3.22 (sub-basin 7). More than two-thirds of the The values of Smf were calculated for the 49 mountain fronts studied sub-basins belong to classes 1 and 2 and are elongated using Lmf and Ls values measured from ASTER GDEM elevation with higher Bs values as compared to class 3 with less Bs values model with a spatial resolution of 30 m and divided into three and are nearly circular shapes (Fig. 13B, Table 1). classes: class 1 (1.00e1.09), class 2 (1.1e1.16) and class 3 (>1.16) as shown in Fig. 14B and Tables 1 and 2. 3.1.6. Mountain front sinuosity index (Smf) Mountain front sinuosity index Smf (Bull, 2007) is defined as, 3.1.7. Fractal dimension of drainage patterns (FD) L The drainage patterns present irregularities with self-similar S Z mf ð Þ mf 7 (fractal) characteristics (Guillermo et al., 2004; Gloaguen et al., Ls 2007; Dombradi et al., 2007). The space filling nature of the where Lmf is the planimetric length of a mountain front along the drainage network is a strong marker of the area vulnerable to mountainepiedmont junction, i.e., the topographic break in the tectonic deformation. The highly steepened regions cause the 418 S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428

Figure 11 Mechanism for measuring Vf ratio (A), locations of sections for Vf calculation (B).

drainage network to reorganize and linearize which is an evidence counting method (BCM), the BCM uses a moving box of variable of uplifted conditions (Mahmood and Gloaguen, 2011). In size on a binary image of DEM derived drainage network showing tectonically active Hindu Kush, drainage systems are influenced black drainage pattern as 1 and empty white space as 0, and counts by the type, geometry and the recent activity of the regional and the number of drainage pixels (Fig. 15A) within the box local faults. The FD quantifies the degree of irregularity or (Guillermo et al., 2004; Dombradi et al., 2007). In each grid, the segmentation of an object or spatial pattern (Gloaguen et al., 2007; box sizes s and relevant number of boxes N(s) are counted. The Mahmood and Gloaguen, 2011). FD value is calculated by using the following equation: Fractal dimension allows us to measure the degree of log NðsÞ complexity of self-similar dimension by evaluating how fast our FDZ lim ð8Þ s/0 logð1=sÞ measurements increase or decrease as our scale becomes larger or smaller. The aim is to quantify the influence of neotectonic where N(s) is the number of boxes and s is the length of the box activity on the drainage network by measuring the reduction of size applied. The slope of the best fit line for the log-log plot of complexity as the deformation intensity increases. This means that N(s) and 1/s is equal to FD. The relative analysis of the spatial for a site highly vulnerable to neotectonic deformation, lower FD distribution of FD can be categorized into three classes: class 1 values should be obtained (Mahmood and Gloaguen, 2011). We (1.03e1.06) stands for high vulnerability to active surface defor- expect that the drainage network looses its dendricity to become mation, class 2 (1.07e1.10) corresponds to moderate surface linearized as topographical changes triggered by faults modify the uplift and the class 3 (1.11e1.40) corresponds to the regions with flow network geometry. For this purpose we implemented the box- low tectonic uplift (Fig. 15B and Table 1). S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428 419

Figure 12 Classes of Vf and its distribution for the studied basins.

3.2. Spatial distribution of geomorphic indices in channel slope due to glacial erosion is good example. Because the rocks in the valley were crushed by glacial body, low indices We analyzed seven geomorphic indices stream-length gradient are expected. However, we interpret the existence of these high (SL), asymmetry factor (AF), hypsometric integral (HI), valley and anomalous values of the SL index in the higher reaches floor width to valley height ratio (Vf ), basin shape index (Bs), highlights the domination of the tectonic processes over the glacial mountain front sinuosity (Smf) and fractal dimension (FD), erosion. Moreover this area is also affected by recently activated together with topographic river profiles in areas affected by the NEeSW trending Konar fault, (KoF), Main Karakorum thrust active faults previously described. The spatial distribution of the (MKT), Chitral Gol fault (CGF), Reshun fault (RF) and Tirch Mir anomalously high values of SL is widespread in the study area. In fault zones (KoF-MKT-CGF-RF-TMF) in the sub-basin 7 (Fig. 5) order to differentiate values as the index related to rock resistance, which is another indication of recent tectonic activity. Regarding different levels of average rock strength were defined (by rock the other geomorphic analyzed parameters for the sub-basin 7 type) from low strength (Quaternary alluvium, conglomerate, along this fault zone displays high AF, HI, Bs values (Figs. 7, 8, sandstone, siltstone and loess) to very high strength (granodiorite 10 and 13, Table 1) and low Vf, Smf, and FD values (Figs. 12, 14 plutons, amphibolites, green schists, quartzite, gneiss, etc). The SL and 15, Table 1). These values show that, this sub-basin 7 is index anomalies were then plotted on the relative rock resistance highly asymmetric, less dissected, highly elongated, v-shaped, map (Fig. 3B), and their relation to rock strength were analyzed having linearized drainage and almost straight active mountain utilizing GIS applications (Figs. 3, 4, 5A, 5B). The high values of fronts. The relation between lithological resistance and hypso- the SL index show a variable distribution throughout the entire metric curve is not notable as the Chitral River is almost flowing Hindu Kush. The high and anomalous values of the SL index in over hard rock lithology (granodiorites Fig. 3B), but tectonic has the study area are found in the valley of Chitral (NE-Hindu Kush, been a factor. The HI value for the Chitral valley is high (0.53), Fig. 5A). These values are >1075 gradient metres or found convex in shape and the only possible explanation for this is between 750 and 1075 m where they may be influenced by Late neotectonic control over this sub-basin. As the Chitral valley was Pleistocene glaciations. The sensitivity of the SL values to change the biggest in the study area, so we choosed five well distributed cross channel profiles (7a, 7b, 7c, 7d, 7e, Fig. 11B) for the Vf 420 S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428

Figure 13 Basin shape index (Bs) calculation (A), and map showing Bs classes (B). calculation and then took the mean of all the resultant values. The primarily to downcutting. This also indicates the active nature of resulting mean Vf (0.31) for the Chitral valley belongs to class 1 the mountain fronts with low Smf values in case of Chitral valley. which means that it is completely a V-shaped valley and is under The linearized drainage pattern of the Chitral River with low FD the influence of neotectonic activity of the above mentioned fault value (Mahmood and Gloaguen, 2011) also confirms the recent zone (Keller and Pinter, 2002; Mahmood and Gloaguen, 2011). tectonic activity and active deformation in the sub-basin 7). The basin shape index value is the highest for the Chitral valley Anomalous and higher SL, values can also be seen in the sub- (3.22) which means that this sub-basin is highly elongated in basins 1, 2, 3, 5, 6, 8, 10, 11 and 12 along the NW flank of the shape and is parallel to the topographic slope along the KoF- Hindu Kush near the Alburz Marmul (AM) fault, Henjvan fault MKT-CGF-RF-TMF fault zone. The reason of this high elonga- (HvF), lower Darvaz Karakul fault (DkF), Andrab fault (AF), tion is because the drainage basin widths are much narrower near Panjsher fault (PSF) and Central Badakhshan fault (CbF) zones the mountain fronts where the stream energy has been directed (Figs. 2B, 3B and 5A). Again, other geomorphic parameters S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428 421

Figure 14 Mechanism of calculation of mountain front sinuosity, Smf (A) and 49 mountain front segments for evaluating the Smf index (B). analyzed for these sub-basins are also consistent and indicate low appears to be inﬂuencing the continental deep-subduction in the Vf, Smf, FD values (Figs. 12, 14, and 15, Table 1) and high AF, HI, Pamir region (Mahmood et al., 2008, 2009; Zhang et al., 2011). Bs values (Figs. 7, 8, 10 and 13, Table 1) with the exception of Along the Dir and Swat River valley, SL indices increase wher- low AF values for the sub-basins 1, 3 and 10. This is due to the ever they come across the DT and MMT or when they cross the presence of a large wind gap at the junction of sub-basins 3, 10, mountain fronts related to these faults (sub-basins 15 and Along 12 and 13 and complex nature of compressional and strike slip Alinger River, the highest values of the indices are related to tectonics at this junction. The CbF is assumed to be an active fault unpublished fault (Laghman fault) in the harder granites, (possible continuation of the CF-HF-PSF fault system) and amphibolites, quartz and marbles (Figs. 3B, 4 and 5). Some 422 S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428

Boundary Thrust (MBT) along sub-basins (23, 25 and 31), though Table 2 Values and classes of S (mountain front sinuosity for mf the underlying rocks are resistant (Fig. 3B), but the reason for the 49 identified mountain fronts). these moderate to low SL values is because of the strike slip nature Mountain Basin Nos. Smf Class of the segments of the above mentioned faults as suggested by front Nos. Keller and Pinter (2002). These findings are consistent with the 1 29, 25 1.02 1 high to moderate values of AF, HI and Bs and moderate to low Vf, 2 1, 3, 5, 6, 8 1.02 1 Smf, FD values for the afore-mentioned sub-basins. The relatively 3 16 1.06 1 low SL values are also observed in Peshawar basin (sub-basins 19, 4 7, 20 1.01 1 22, 26 and 30) where streams flow over relatively soft Quaternary 5 7, 13 1.05 1 alluvium and in the upper part of the sub-basin 10 (a plateau type 6 25 1.04 1 region in the central Hindu Kush linking) and hence showing low 7 20 1.03 1 SL gradients. 8 32 1.04 1 Because of the numerous sub-basins in the study are, we select 9 20, 22, 23 1.15 2 sub-basins 12 and 32 from the western and eastern Hindu Kush 10 19, 22 1.12 2 respectively just to a give a critical evaluation of all the combined 11 33 1.05 1 indices used. The hypsometric curve of the Panjsher valley 12 16 1.04 1 (Fig. 9B, sub-basin 12) is characterized by a strong convex shape 13 17 1.15 2 which indicates its youthful stage. This basin is characterized by 14 17 1.14 2 a less eroded (HI, class 1) highly asymmetric (AF, class 1) elon- 15 17 1.14 2 gated basin (Bs, class 1) with a perfect V-shaped valley (Vf, class 16 16 1.11 2 1) along the active mountain front (Smf, class 1), linearized Pan- 17 13 1.03 1 jsher River (FD, class 1) and moderate to low SL values. The 18 2, 10 1.00 1 landscape in the Panjsher River valley is clearly conditioned by 19 12 1.01 1 the presence of recent and active dextral PSF that produced 20 10 1.06 1 a higher differential uplift and less erosion. The moderate to low 21 11, 12 1.03 1 SL values in this sub-basin are because of the river flow along an 22 11 1.01 1 active strike-slip fault (PSF) in a linear fashion according to Keller 23 3 1.00 1 and Pinter (2002). The sub-basin of Swat valley (32) is a good 24 3, 6 1.16 2 example of convex-concave-convex case; the Swat valley (Gabral 25 5, 6 1.01 1 and Ushu River valleys) is moderately eroded and intermediate in 26 24 1.07 1 age. The Swat River flows in a bit narrow valley in the upper parts 27 27, 30, 31 1.06 1 before making its first contact with the MMT. After the first 28 26 1.00 1 contact, it becomes wider for some distance with high erosion 29 24, 27 1.04 1 before it makes the second contact with the MMT. The lower 30 26, 27, 28, 30 1.05 1 convex portion of the Swat sub-basin represents its third contact 31 4 1.02 1 with the most active part of the MMT and here it passes through 32 4 1.09 1 Malakand granite before entering the Peshawar basin to join 33 7 1.05 1 Kabul River. We assume that if part of the hypsometric integral is 34 7 1.02 1 convex in the lower portion, it may relate to uplift along a fault or 35 2, 4, 10 1.04 1 perhaps uplift associated with recent thrusting. The moderate 36 7 1.00 1 range values for most of the geomorphic indices correspond well 37 21 1.01 1 (mostly, class 2) for this sub-basin except the basin shape index 38 19, 21 1.08 1 value, which is higher because of the shape of the sub-basin. The 39 21 1.01 1 FD values are lower and moderate in the upper and middle part 40 10 1.04 1 because of linearized drainage flow along MMT and are more in 41 7 1.01 1 the lower part due to meandering characteristics of the Swat River 42 32 1.12 2 in the Peshawar basin. 43 7 1.13 2 44 7 1.08 1 45 13, 16 1.03 1 4. Evaluation and discussion of IRAT 46 15 1.05 1 47 15, 33 1.04 1 Previous studies for the evaluation of relative active tectonics 48 15, 7 1.03 1 based on geomorphic indices mostly focused on a particular 49 7, 9, 15 1.06 1 mountain front or small area (Bull and McFadden, 1977; Rockwell et al., 1985; Azor et al., 2002; Silva et al., 2003; El Hamdouni et al., 2008). This investigation is an attempt to eval- anomalously high SL values are also recorded in sub-basins uate relative active tectonics in a large area (132,259 km2) based (2, 13) along the NEeSW Bazgir fault (BgF). on several sub-basins and using a number of geomorphic indices. In some instances, moderate to low SL values are observed The average of the values of seven computed indices was along lower part of dextral PSF (sub-basin 12), lower part of the combined to yield (IRAT) and was used to assess the spatial KoF (lower part of sub-basin 7), lower part of Swat-Dir valleys distribution of relative tectonic activity in the study area. The (sub-basins 15, 32 and 33) along MMT, and parts of Main values of the IRAT were grouped into four classes to define the S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428 423

Figure 15 Estimation of FD using box-counting method (A) and fractal dimension map (B). 424 S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428 degree of relative tectonic activity (El Hamdouni et al., 2008): fronts, high stream-length gradients and hypsometric integrals. class 1; very high (1.0e1.29); class 2; high (1.33e1.50); class 3; The geomorphic indices for most of sub-basins show IRAT class 1 moderate (1.57e1.86); and class 4; low (2.0e2.33) relative and 2 within most of the Hindu Kush and IRAT class 3 and 4 in tectonic activity respectively. The distribution of the four IRAT the adjacent regions where the relative tectonic activity is assumed classes is shown in (Fig. 16, Table 1), and Table 1 shows the to moderate or less. For example, the HvF-DkF, NE extension of results of all the seven geomorphic indices and their classiﬁcation the HF (PSF-CbF), BgF, CF-GzF, KoF-TMF-RF fault systems are for all 33 sub-basins. About 38% of the study area (about the most typical cases according to the distribution of IRAT 50,044 km2) belongs to class 1; 25% (32,773 km2) to class 2; 19% (Fig. 16). The CF and HF meet 80 km north of Kabul approxi- (25,098 km2) to class 3; and 18% (24,342 km2) to class 4. The mately at 353400000 N and 692204500. From the south, the CF IRAT tends to be high along the Henjvan-Darvaz Karakul (HvF- starts at the triple junction where the Arabian Plate, the Eurasian DkF), Chaman-Gardez (CF-GzF), Bazgir (BgF), Konar-Tirch Mir- Plate and the Indo-Australian Plate meet, just off the Makran Reshun (KoF-TMF-RF) and Dir Thrust (DT) fault zones. Coast of Pakistan (Fig. 1). The fault tracks NE across Baluchistan Numerous approaches used a combination of two or more than and then NNE into Afghanistan, runs just to the west of Kabul, two indices to give semi-quantitative information regarding the and then NE across the dextral HF, up to where it merges with the relative tectonic activity in active mountain ranges (Bull and Pamir fault system (HvF-DkF-MPT) north of the 38 parallel McFadden, 1977; Silva et al., 2003, El Hamdouni et al., 2008). (Ruleman, 2005; Zhang et al., 2011). Along the KoF, We recog- The utilization of the seven geomorphic indices as well as IRAT nized sinistral offsets in deposits of active alluvial fans, which is exhibit change mostly corresponding to the distribution of the evidence of recent surface faulting (Fig. 18B). Farther to the NE, prominent fault zones in the study area. Neotectonic movements the KoF merges into a NNE-trending TMF-RF fault zone. in the Hindu Kush and the dynamic characters of the resulting In contrast, the common pattern of Quaternary faults trends NW structures indicate north-south compression, east-west extension and cuts across these older NE-trending faults. The young, and NEeSW trending faults. In addition, neotectonic movements NW-trending features appear to be strike-slip fault zones that are show strong vertical uplifting, total rising, differential tilting that expressed as lineaments across the Hindu Kush. The prominent have created steepest slopes, highly asymmetric valleys, elongated difference between the older NE-trending structural grain and the basins, V-shaped valleys, linearized drainages, active mountain younger N- to NW-trending features suggests that a change in

Figure 16 Distribution of index of relative active tectonics (IRAT) in the Hindu Kush and the adjacent regions. S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428 425 deformational style and mechanics has occurred; from an initial 4.1. Remote sensing and ﬁeld evidence of neotectonics phase of contraction, to a more recent phase of shearing and NW- directed crustal extrusion along strike-slip faults. This deformation In steep terrains such as the Hindu Kush, erosion rates are very style supports the observation of Verma et al. (1980) and (Ruleman, high and ﬂuvial incision has produced a landscape with variable 2005; Wheeler et al., 2005) that NW-trending seismicity lineaments degree of dissection. Straight mountain fronts with triangular extend from the MBT of the NW-Himalayas to the Panj River in facets along the active faults are widespread (Figs. 14B and 17A). north-central Afghanistan. They also found that thrust and strike-slip Their development appears to be controlled by active tectonics, faults are equally prevalent in this tectonic domain. A very high and therefore they record information about the Quaternary (class 1) to high (class 2) IRAT values within the above mentioned landscape evolution and several stages of uplift. No uplift rates for tectonic domain reveal the complex tectonics framework, high the active tectonics are available yet for most of the Hindu Kush. erosion due to less vegetation cover, enhanced incision and highly Along the eastern Hindu Kush, IRAT show class 1 (very high), steepened regions for most of the Hindu Kush and its vicinity. and this is one of the areas with altitudes between (5500 and The IRAT is high throughout from the eastern towards the 7700 m asl) and north of Chitral Town (in NW Pakistan) stands western Hindu Kush margins in the study area (Fig. 16), which Tirich Mir, at 7702 m, the highest peak in the Hindu Kush. In this corresponds to almost straight mountain fronts and triangular region along the Chitral River, the mountain front (Fig. 17A) facets along the prominent faults (Figs. 16, 17A and 18B). On the shows well-developed triangular facets produced by streams other hand, the low IRAT values (class 4) mainly occur in some dissection along the NE border of the Hindu Kush. These facets parts of the Kabul block (Afghanistan) and Peshawar basin suggest active faulting during the Quaternary (Hildebrand et al., (Pakistan) of the study area (Fig. 16), where majority of the 2001). Also triangular facets at different elevations are indica- geomorphic indices suggest low tectonic activity, and this may be tive of several stages of uplift and neotectonic process at different related to the less erosive conditions and alluvial fan deposits in times (Fig. 17A). We can clearly see 3e4 generations of triangular the relatively plain areas. facets along this Konar-Tirch Mir fault zone, the lower two or

Figure 17 Chitral River valley, NW Pakistan, showing steep, terraces due to high incision, with active mountain fronts, triangular facets and alluvial deposits (A), and Dir thrust, with fault scarps and triangular facets (B). 426 S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428

Figure 18 Landsat imagery showing the evidence of active tectonics, near Saroubi fault (A), along Konar fault (B) in NE Afghanistan and near Attock range and MBT (C) in NW Pakistan. three sets of facets are clearly shown on the current mountain front expression of active tectonics (Fig. 18B). Straight mountain fronts, (shown by red line in the Fig. 17A) and others are at higher active drainage streams and active alluvial deposits are charac- elevations closer to the crest of the mountain range. The Konar teristics of fault scarps. Displacement on the Sorubi fault, north- fault, forming a prominent set of mountain fronts has geomorphic east of Kabul, appears to be primarily dip-slip (vertical), but it S.A. Mahmood, R. Gloaguen / Geoscience Frontiers 3(4) (2012) 407e428 427 may also have a small dextral (right-lateral) component of slip gradient (SL), fractal dimension (FD), basin asymmetry factor (Fig. 18A). Micro earthquake studies support some right-lateral (AF), basin shape index (Bs), valley floor width to valley height motion on the Sorubi fault (Prevot et al., 1980). In the neigh- ratio (Vf ), mountain front sinuosity (Smf) and a combination of all bouring region of NW Himalayan fold and thrust belt, we observe these indices called (IRAT) that categorize the landscape into four the neotectonic activity along the Punjab-Khairabad thrust fault classes with respect to their degree of relative tectonic activity. and Main Boundary Thrust (MBT) fault system. This area is the The values of AF show widespread basin asymmetry related to junction of deeply incising Kabul River flowing from Afghanistan tilt block tectonics. The values of Bs, HI, SL were found to be high and confluencing the braided Indus River near Attock range in along major faults and the values of Smf propose that majority of Pakistan (Fig. 18C). The braided pattern of the Indus River is due the mountain fronts are tectonically active. The low values of Vf to the rising of the base level of Indus near the active Attock range demonstrate that many valleys are narrow, steep, deep and along Punjab-Khairabad thrust which is also confirmed by the hanging, signifying a high rate of incision coupled with active presence of big water gap on the right side of the junction point tectonic uplift. The low FD values for drainage network are (Fig. 18C). After passing through the Attock gorge, the Indus indicative of loosing dendricity to become linearized under the River takes a very sharp turn near Brotha and flows towards west influence of active tectonics. Very high class 1 of IRAT is mainly for 16e18 km due to the neotectonic uplift along the Main in the Hindu Kush and in some parts along AM, HvF and MKT Boundary Thrust (MBT) before entering into northern Kohat and (Fig. 16), while the rest of the study areas have moderate class 3 Potwar plateau (Fig. 18C). (Swat valley, Kurram agency, Mohmand agency and parts of SF The discussion of above tectonic landforms corresponds well and MBT) to high class 2 (active tectonics AF, HvF-DkF, ST in with the classification of IRATof moderate (3) to high (2) and very Jalalabad basin, Shishi valley, Dir valley and some segments of high (1) relative tectonic activity. This becomes almost a direct MBT). The low class 1 of IRAT is found in Kabul basin, Peshawar evidence for neotectonics that reflect the values of the geomorphic basin and Orakzai agency. indices. As a secondary evidence related to drainage network and Evaluation of the active tectonics by Landsat imagery and field erosion, we observe that, geomorphic analysis of drainage networks observations also match well with the geomorphic indices and IRAT. and stream profiles are reflected as anomalies in the Hack SL index Indeed, IRAT classes 1 and 2 are consistent with the areas having described earlier. We observed SL anomalies in most of the river most fault scarps, active mountain fronts, triangular facets, steep profiles in Swat valley along MMTand mostly along the Eastern and hanging valleys, deformed alluvial deposits, and deep narrow river Western Margin of Hindu Kush. The deep fluvial incision is another gorges. There is still a need of detailed evaluation of Quaternary evidence of the neotectonic activity that includes steep V-shaped geochronology, characteristics of the major tectonic features and hanging valleys and highly asymmetric basins throughout the Hindu geological investigation in future along with major displacements. Kush and in the neighbouring mountain ranges. The deep narrow gorges are observed near the mountain fronts that cut apart the alluvial fans emerging from those fronts is an indication of recent Acknowledgements tectonic activity. The Fig. 18C shows deeply incising Kabul River passing through the Attock gorge before its confluence with the Financial support to Syed Amer Mahmood from University of the Indus River which shows braided pattern due to active uplift due to Punjab, LahoreGovernment of PakistanRemote Sensing GroupTU Attock range and rising local base level. Freiberg, Germany and partial support from German Academic Again, the presence of steep terraces in the eastern Hindu Kush Exchange Association (DAAD)International Association of along most of the Chitral River (NEeSW elongated, highly Mathematical Geosciences (IAMG) is gratefully acknowledged. asymmetric, V-shaped sub-basin) up to 250e350 m high is an The authors would also like to thank Miss Saima Siddiqui (Ph. D indication of high fluvial incision. For this region, no uplift rates student, Department of earth sciences, Unimore, Italy) who gave are available yet, but for the near by Karakorum the actual rates of an important support regarding GIS related issues. uplift come to 2 mm/y, for the Kashmir basin 4e10 mm/y, and for the centre of Nanga Parbat 5e10 mm/y, So, assuming an average uplift of 5 mm/y, the Hindu Kush would have risen by some 500 m References over the last 100 ka, or at a rate of 2.5 mm/y it would have been 250 m accordingly (U. Kamp Jr. et al., 2004). 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