Geospatial assessment of active tectonics using SRTM DEM-based morphometric approach for Meghalaya, India

ABSTRACT Meghalaya, situated over the Shillong Plateau in the northeastern region of India, is considered a seismo-tectonically active region because of the Indian-Eurasian convergence and rising since the Cenozoic era. The present study aims to identify active deformation zones due to tectonic activity following a morphometric approach. Based on DEM data and GIS techniques, morphometry parameters along with geomorphic indices are obtained which allows the analysis of geomorphic processes responsible for the region’s landscape evolution, and indices of relative active tectonics (IRAT) are calculated by combining them. High drainage density, larger ruggedness number, intermediate to high hypsometric integral values with S/convex-type hypsometric curve, lower valley floor width-to-height ratio and stream sinuosity index values suggesting the region is tectonically active and according to IRAT, the Khasi and Jaintia Hills region (the central and eastern part) of the Meghalaya possesses relatively higher tectonic levels. The variation of tectonic activity is not uniform in the same structural feature and is found to be lower in the western portion and higher towards the east along the same Dauki Fault.


Introduction
The tectonic and surficial processes govern landscape evolution in the active deformation region. The endogenic geomorphic processes deform the lithosphere as a deeply incised valley, whereas exogenic processes shape the topography by erosional and depositional mechanisms (Keller & Printer, 2002). Tectonic geomorphology quantifies landscape geomorphic responses resulting from the interaction of active tectonics and geomorphological processes. The emergence of highquality remotely sensed data, and geomorphological and geodetic tools with GIS have facilitated the tectonic geomorphological studies (Pérez-Peña et al., 2010), which helps in identifying active tectonic deformations, natural-hazard-prone regions and land use planning (Mahmood & Gloaguen, 2012).
The quantitative measurements of landscape shape facilitate the comparison of different landforms and the calculation of elementary parameters using topographic maps (Chen et al., 2003). The morphometric parameters are significant in understanding the structural control of the basin by assessing its areal or relief characteristics (Thomas et al., 2010). In contrast, geomorphic indices detect basin anomalies due to tectonic activities, corresponding to endogenic geomorphic processes (El Hamdouni et al., 2008). These parameters are sensitive to active faulting and tectonic uplift, resulting in river deflection, basin asymmetry and drainage geometry (Keller & Printer, 2002).
Morphometric analysis observes the silent changes in a river in the form of channel incision, river length profile, gradient change and accelerated erosion in response to faulting, folding and differential uplift at the variable timescale of thousands to millions of years (since Neogene and Quaternary times; Sharma & Sarma, 2017). Several geomorphic indices and morphometric parameters are successfully used to analyse the tectonically active areas (Amine et al., 2020a;Argyriou et al., 2017;Baruah et al., 2022;Bull & Mcfadden, 1977;Cox, 1994;El Hamdouni et al., 2008;Hare & Gardner, 1985;Mishra, 2019;Ramírez-Herrera, 1998). Chen et al. (2003) evaluated the relative activities of tectonic features in Taiwan's western foothills and identified five morphotectonic provinces based on stream-gradient and hypsometric analysis. El Hamdouni et al. (2008) assessed the relative tectonic activity of southern Spain by quantifying the IRAT using different geomorphic indices. A similar set of geomorphic indices are also adopted in other studies (e.g. Ayaz & Dhali, 2020;Mahmood & Gloaguen, 2012;Sarma et al., 2015;Softa et al., 2018;Taesiri et al., 2020;Zhang et al., 2019). Font et al. (2010) emphasised the application of stream length index using DEM and GIS to study the fluvial system with active tectonics. Dar et al. (2014) used morphometric and morphotectonic parameters to identify the tectono-geomorphic evolution of the Karewa basin of Kashmir valley, India, and observed the significant role of late Quaternary climate changes and tectonic upliftment in the valley landscape evolution. Similarly, Shukla et al. (2014), Sharma and Sarma (2017), Argyriou et al. (2017), Anand and Pradhan (2019) and Bhat et al. (2020) also adopted both morphometric parameters and geomorphic indices. Nevertheless, all these studies have shown no standard set of parameters/indices that can alone be employed to evaluate regional relative active tectonics in orogenic areas.
Meghalaya possesses a complex seismotectonic setting (Figure 1a,b) and falls under seismic zone V (zone factor of 0.36 g; high-risk zone) as per the Indian building design code (IS1893, 2016. The NER of India in the Eastern Himalayas is one of the most critical orogenic belts and seismically active regions due to collision tectonics of Indian-Eurasian Plates in the north and active subduction beneath the Indo-Burman ranges along the eastern part of the region (Catherine, 2004). The Shillong-Mikir plateau results from such interaction and is actively deforming (Duarah & Phukan, 2011). The present structural alignment of Meghalaya was attained during the Cenozoic Era (Baruah et al., 2022), and continuous tectonic movement has influenced the region's geomorphology (Devi, 2008). The study aims to analyse the drainage basins and stream networks of Meghalaya to identify the ongoing tectonic activity and consequent geomorphic response using morphometric parameters and geomorphic indices ( Figure 1c; Table 1; Anand & Pradhan, 2019;Argyriou et al., 2017). IRAT is obtained to understand the degree of relative active tectonics of the region.
The lower values are suggestive of lower active tectonics and softer underlying rock >500 300-500 <300 (Hack, 1973;Keller & Printer, 2002;Dar et al., 2014;Zhang et al., 2019) Stream Sinuosity Index (SSI) SSI ¼ C=V, the ratio of channel length (C) to the valley length (V) Low values indicate the region is tectonically active and vice versa <1.5 1.5-2.5 >2.5 (Bull & Mcfadden, 1977;Gomez & Marron, 1991) to 7467 mm per year (Indian Meteorological Department; Prokop, 2014). Physiographically, the Shillong plateau is a northeastern extension of the Indian Peninsular shield (Figure 1a; Raghukanth et al., 2011). The area has a rich network of streams, mostly rain-fed, and forms tributaries of the Brahmaputra and Meghna rivers. The important rivers in the Garo Hills region are Daring, Digaru and Someshwari, and in the Khasi and Jaintia Hills regions are Kopilli, Myntdu, Umina and Umkhri. Several studies such as Biswas et al. (2007) estimated the Indian-Eurasian crustal movement accommodated across the Shillong Plateau varies from 0.7 to 7 mm/year. Vernant et al. (2014) recorded an increase in velocity from ~3 mm/year to ~6 mm/year at the west of the Dauki Fault to the east, suggesting the rotation of the Shillong Plateau. The Dauki Fault, responsible for plateau upliftment, acts as a northdipping seismogenic thrust forming the southern escarpment along the southern plateau margin (Bilham & England, 2001). In the west (Garo Hills), N-S trending Dhubri Fault and Dapsi Thrust (Chen & Molnar, 1990;Kayal & De, 1991), and in the central and the northeast portion, Barapani shear zone, Umrangso and NW-SE trending Kopili Faults are the major tectonic features (Biswas et al., 2007). The region has also experienced significant earthquakes, including the 1897 Great Assam Earthquake (Mw = ~8.3).
Meghalaya is lithologically diverse and covered by late Cenozoic era alluvial fills to the unclassified gneissic complex of Archaean to Paleoproterozoic aeons (Strong et al., 2019). Approximately 44% of the areas belong to the unclassified gneissic complex (Figure 2a), overlain by sediments and greenstones of the Shillong group (Mishra, 2019). The portion along the southern escarpment is of the late Mesozoic to the Cenozoic era. The inner upland region of the plateau and highly dissected plateau margins in the northeast consists of Granitoid of Neoproterozoic to an early Palaeozoic era (Figure 2a), and the plateau basement experienced erosion to a peneplain till Jurassic. Due to lithological diversification, different erosional rock strengths are produced. Following Selby (1980), the erosional resistance of geological units of Meghalaya is grouped into gneiss, quartzite and granite are  classified as very strong to strong; sandstone, schist, conglomerate are of typically medium to low strength and classified as strong to moderately weak, whereas the alluvial deposits and debris flow have weak erosional strength. A significant portion of the study area is occupied by moderately dissected (~41%) and highly dissected (~30%) structural upper plateau ( Figure 2b). The plateau margins, mainly in the study area's northern, eastern and southern portions, consist of denuded dissected hills and valleys along the steep to moderate side slopes.

Dataset
Drainage basins are extracted from 1-arcsec (~30 m) Shuttle Radar Topography Mission digital elevation model (SRTM DEM) version 3 (https://earthexplorer. usgs.gov/). The SRTM data offers better accuracy of about ±16 m (RMSE of 9.73 m) worldwide and is based on C-band radar interferometry data. It showed an absolute horizontal accuracy of ±8.8 m and vertical accuracy of ±6.2 m (90% confidence; Elkhrachy, 2018). The geological setting and lineament data are obtained from the Bhukosh-Geological Survey of India (GSI) (https://bhukosh.gsi.gov.in/Bhukosh/ Public). Using the spatial analyst tool in ArcGIS 10.8, the lineament density is calculated from the lineament dataset as high lineament density regions are more susceptible to erosion than other areas (Taesiri et al., 2020). The earthquake data representing the seismicity of the region are compiled from several sources such as the Bhukosh-GSI, USGS and International Seismological Centre-GEM catalogue (Gupta et al., 2021).
The DEM data is further processed in GIS, and using the Hydrology tools, 43 drainage basins (Table 2) are demarcated. The extraction process involves DEM preprocessing, filling voids, accessing flow direction, quantifying flow accumulation, and stream network and drainage basin extraction. The Strahler stream order of the basins ranges from 5 to 7 (Figure 1c; A.N. Strahler, 1952).

Areal parameters
The areal parameters identify the degree of erosional activity due to exogenic geomorphic processes and lateral propagation of folds (Keller & Printer, 2002). It mainly includes drainage density (D d ), form factor (Ff), basin elongation ratio (Re) and circularity ratio (Rc ;  Table 1; Horton, 1945). D d is influenced by the rainfall intensity, basin's lithological setup and soil texture, geological setting and vegetation cover (Horton, 1945). Ff, Re and Rc can describe the basin shape. The basins having lower Ff (<0.3) values represent the elongated basins indicating structural and tectonic control over the drainage basin area (Anand & Pradhan, 2019). The Re is the ratio of the diameter of a circle of the equivalent area as the basin to the basin length (Schumm, 1956). The lower values of Re (<0.5) represent a more elongated basin controlled by active tectonics (Sarma et al., 2015). Another significant parameter, Rc, shows the degree of basin circularity (Table 1). It indicates the dendritic stages by reflecting the role of deformation by erosion versus tectonics and is influenced by the topography and geological setting of a basin (Dar et al., 2014).

Relief parameters
The relief parameters are basin relief (R), relief ratio (Rr) and ruggedness number (Rn; Table 1; Thomas et al., 2010). R represents the elevation range of the considered basin and is defined as the topography's ruggedness (Keller & Printer, 2002). Rr is the ratio of drainage basin relief (R) to the basin length (L b ). Rr is used to analyse the steepness of the basin to interpret the effectiveness of the geomorphic processes occurring in the area. The dimensionless Rn represents the river system's geometric characteristics and is expressed as a product of D d and maximum basin relief. The low value of Rn (<0.75) indicates less susceptibility to the basin degradation processes, and a high value (>1.5) indicates high relief with a highly dissected nature and structural complexity (Anand & Pradhan, 2019).

Geomorphic indices
The geomorphic indices characterise the landscape processes and active tectonics based on the basins' shape, tilting, relative incision and erosional status (Argyriou et al., 2017). In the present study, the hypsometric curve -hypsometric integral (HI), valley floor width to valley height ratio (Vf), basin shape index (BSI), transverse topographic symmetry index (TTSI), asymmetry factor (Af), stream length gradient index (SLGI) and stream sinuosity index (SSI) are considered (Table 1; Dehbozorgi et al., 2010;Rimando & Schoenbohm, 2020). The HI refers to the relative area distribution at different elevations in a drainage basin and represents the area under the hypsometric curve (HC; A.N. Strahler, 1952). The shape of HC is used to infer the geomorphic development stage (Chen et al., 2003). The convex, S-shaped and concave-shaped curves represent the youthful stage (related to weakly eroded basin), mature and old-peneplain stage (highly eroded basin) of basin development, respectively (Amine et al., 2020a). The values of HI close to 1 indicate high incision with negligible plateau erosion and young landforms due to active tectonics, while moderate to low values indicate evenly dissected watersheds (El Hamdouni et al., 2008). The HC for all the basins is calculated using spatial analyst tools in ArcGIS 10.8 (Rabii et al., 2017). The tectonic influence in a watershed can be inferred by evaluating possible tectonic tilting of the basins (Keller & Printer, 2002). The Af shows the tectonic tilting in the basin in the transverse direction of flow (Hare & Gardner, 1985). For stream in the stable setting, the Af will be close to 50, and if Af is larger or less than 50, it suggests tilt and influence of active tectonics (Pérez-Peña et al., 2010). TTSI also determines the tilt in the drainage basins due to neotectonics and is calculated as per Cox (1994). It is estimated along the mainstream of each basin at multiple locations and averaged (Tsodoulos et al., 2008). TTSI value approaches 0 for symmetrical basins, and as the stream moves laterally away from the basin centre, the value increases. TTSI close to 1 shows a highly asymmetrical and possibly tilted basin (Keller & Printer, 2002). In tectonically active regions, the basin shape is quantified using BSI (Bull & Mcfadden, 1977). The high values of BSI reflect elongated basins and low values for more circular basins with stable settings. In tectonically active regions, the drainage basin widths are narrower near the mountain fronts where the high stream energy is primarily involved in downcutting against the continuous upliftment. In contrast, the stable setting permits the widening of drainage basins upstream of the mountain front (Ramírez-Herrera, 1998). The Vf index identifies recent uplift and tectonic quiescence areas and discriminates narrow, U-and V-shaped valleys (El Hamdouni et al., 2008). The low Vf values (deep V-shaped valleys) are associated with rapid upliftment and higher incision due to active tectonics. The broad U-shaped valleys associated with large Vf values show attainment of base-level erosion and are subjected to lateral erosion due to relative tectonic quiescence (Keller & Printer, 2002). The intermediate values represent low displacement rates governing moderately active fronts.
The SLGI is a quantitative geomorphic index that correlates to stream power governing erosional and depositional processes in the specified channel reach and possible active tectonics (Hack, 1973). This index expresses the relation among channel slope, rock resistance and tectonic activity (Keller & Printer, 2002). It is calculated by dividing the stream into multiple segments of equal intervals using the DEM dataset, and the average value is considered. The SSI is defined as the ratio of the stream channel length and the length of the straight line joining two ends of the channel. It relates to the hydraulic and morphological characteristics of the stream and records tectonic changes (Gomez & Marron, 1991).

Relief parameters
Relief parameters influence flood patterns and sediment-carrying capacity of the stream and help understand the basin's denudational characteristics as low basin relief and Rr are distinctive attributes of low resistant rocks with high erosional tendencies (Schumm, 1956). The basin relief (km) varies from 0.065 (basin 34) to 1.847 (basin 4), and Rr varies from 0.00353 (basin 34) to 0.10007 (basin 3; Table 4). The basins in the Khasi Hills region (Basins 1, 2, 4-6, 19 and 20) mostly show high relief values (R > 1.5), signifying high active tectonics (Figure 4a). The larger relief values result from the neotectonic regime of the region (Thomas et al., 2010 Figure 4b).
The Rn values range between 0.090 (basin 34) and 2.438 (basin 1; Table 4). Ten basins (basins 1-7, 19, 20 and 40) covering ~42% area, show higher Rn values (Rn > 1.5) and classified under high active tectonic class (Figure 4c). The high Rn values suggest that these basin patches are more susceptible to soil erosion and have inherent structural complexity in relation to relief and drainage density (Anand & Pradhan, 2019).

Hypsometric curve and hypsometric integral (HI)
The hypsometric analysis explains the different landscape evolution stages and erosional landforms (A.N. Strahler, 1952). The calculated HI values for the study area vary from 0.16 (basin 38) to 0.72 (basin 11; Table 5) and are classified into different active tectonic classes (Figure 5d; Amine et al., 2020b). To compare the spatial distribution of the HI value, the hypsometric curve is also plotted for each basin (Figure 5a-c). The basin with a high HI value (>0.5), e.g., basins 2, 4, 6 and 7, shows a convex curve (Figure 5a). The basin with an intermediate HI value (0.4-0.5), with complex S-shaped curves (Figure 5b), is found to be randomly distributed over the study area ( Figure 4d) and located in moderately dissected hills and valleys. Most of the basins (basins 25 to 43, covering ~39% area), in the western portion (Garo Hills region), between Dauki, Dhubri and Dudhnai Faults, are found to have low HI values (<0.4), suggesting old stage of the development process (Figure 4d). These tracts are mostly eroded and least affected by active tectonics. A similar inference is also evident from the hypsometric curve (concave-shaped curve) and subdued relief of those basins (Figure 4a and 5c).

Asymmetry factor (Af) and transverse topographic symmetry factor (TTSI)
The Af is calculated for all 43 basins, and the difference between the observed Af and 50 (AF = |Af-50|) is obtained in absolute terms (Table 5) and plotted in a GIS environment (Figure 6b). The value of AF ranges from 0.05 (basin 20) to 30.55 (basin 11). A total of 21 basins (covering ~53% area) show higher values (AF > 15; Figure 6b), denoting a highly asymmetric pattern and belonging to the high active tectonic class (Class 1, Table 1; Zhang et al., 2019). In comparison, 10 basins (covering ~11% area) consist of low AF values (<7), suggesting a stable setting (Class 3) of these tracts. The tilt direction of the basins is shown in Figure 6a. The basins of the western part that belong to Class 1 or 2 are moderate to highly asymmetric. In contrast, the eastern portion has more variable asymmetry classes. For all the basins, TTSI varies from 0.14 (basin 24) and 0.59 (basin 12; Table 5), showing the asymmetric nature of the basins in the study area and the influence of neo-tectonics (Tsodoulos et al., 2008). The spatial distribution of TTSI shows that most of the basins have considerable asymmetry (TTSI ≥0.2) except basins 1 and 24 (Class 1 and 2; Figure 6c). The basin along the southern escarpment and in the northeastern part of the region is tilted in the south-eastern direction except for a few exceptions (e.g. basins 6 and 7; Figure 6b) due to the proximity of the E-W trending Dauki Fault and NE-SW trending Barapani Shear zone (Sharma & Sarma, 2017). Overall, no particular trend is observed in the basin tilting direction which may be attributed due to the plateau-type landscape of the region. Though AF and TTSI provide information about drainage tilting, direct evidence of ground tilting cannot be obtained from these two indices.

Basin shape index (BSI)
In tectonically active places, the young basins tend to have an elongated shape, normal to the topographic gradient (Ramírez-Herrera, 1998 (Figure 6d). The BSI value larger than 3.5 indicates an elongated basin, while the value between 2.0 and 3.5 indicates a moderately elongated shape (Zhang et al., 2019). A maximum elongation is observed in the northwestern part of basin 28 between Dhubri and Samin Faults, followed by basins 16 and 13 (Table 5). The lowest value of 0.91 for basin 11 (Table 5) in the eastern portion (in the Jaintia Hill region) is observed, suggesting a stable, mature stage (Figure 6d).

Valley floor width to height ratio (Vf)
The Vf is calculated in basins at more than one location ( Figure 7a) and averaged using the DEM data. The Vf ranges between 0.19 (basin 4) to 7.41 (basin 14; Table 5), where low values (Vf < 0.5) indicate V-shaped, deeply incised valleys with higher upliftment rates (Mahmood & Gloaguen, 2012). Basins with a low Vf value, signifying a high active tectonic class, are distributed in the central portion of the study area ( Figure 7b). It mainly consists of higher relief  ( Figure 4a), with deeply incised V-shaped valleys representing the young stage of basin development and active plateau region (Sarma et al., 2015). Moreover, the basin near the southern escarpment (basins 1, 2, 4-6), draining across the Dauki Fault, shows the maximum incision (lowest Vf values). These basins are located in moderately to highly dissected plateau and hills and valley geomorphological units. The basins (7, 13, 14, 28, 32-35, 37, 41 and 43) have large Vf values (Vf > 1; signifying low active tectonics), representing flatfloored U-shaped valleys showing the dominance of erosional and depositional processes. These basins generally consist of alluvial deposits in the lower portions near mountain fronts with low erosional resistance and spreading laterally. However, the upper reaches of these basins have a more erosion-resistant Table 6. Assigned active tectonic classes of geomorphic indices and obtained indices of relative active tectonics (IRAT) based on average of classes of the areal parameter (AP), relief parameter (RP) and geomorphic indices (GI).  capacity (sedimentary rock of Epeiric sea formation; Figure 2a). According to Vf values, the study region falls under the moderate to high active tectonic class (Table 6 & Figure 7b).

Stream length gradient index (SLGI) and stream sinuosity index (SSI)
The high peaks in SLGI represent an abrupt change in channel slope .  (Dar et al., 2014). The basins in the central portion (Khasi Hills region) (basins 1, 2, 4-7, 19-21) are Class 1, indicating a strong tectonic influence (Figure 7c). Despite having more or less similar geological units in the western part than the central portion (Figure 3a), lower SLGI values are observed in the northwestern region, which may be attributed to the subdued topography of these basins (Figure 1). In contrast, the basins dominated by soft sedimentary rocks (ES, Figure 2a) in the southwestern and northeastern parts show consistent results and lower values (Figure 7c). The SSI ranges from 1.19 (basin 8) to 1.65 (basin 38), showing the sinuous character of the streams and active tectonics. The classified map shows that all the basins have moderate to low value of SSI (≤2.5), signifying moderate to high active tectonics (Figure 7d; Table 5). An inverse relation between channel slope and stream sinuosity is observed. Tectonic uplift and strike-slip movement are recorded in the sinuosity index as variation in stream velocity occurs in response to gradient modification, governing the erosional and depositional character of the stream (Gomez & Marron, 1991). The class numbers associated with different basins of different indices are utilised to produce relative tectonic activity classes (Table 6).
Comparing the spatial distribution of different classes of different parameters with the geological setting of the study area revealed that landscape evolution is mainly influenced by tectonic activity. The basins with the same geological setting fall under the different classes of the same parameters. Basins 4 and 6 have Palaeozoic era formations underneath (Figure 2a) but fall under different indices such as BSI, AF, TTSI and others ( Figure 4). As per hypsometric analysis, the convex shape hypsometry curve of basins with high HI values in high topographic regions suggests higher erosional resistance in conjunction with the varying rock strength from moderate to very strong in these tracts (Figure 2a & 4d). Considering the uniformity in climatic conditions in central and western Meghalaya, the HI and SLGI results that reflect both climate and rock strength suggest that local geomorphology and drainage development are affected by the tectonic uplifting (Figure 7c). At the same time, the deformation zone may have been partially impacted by climate, such as the central-southern zone.

Index of relative active tectonics (IRAT)
The average of measured morphometric parameters and geomorphic indices of 43 basins is calculated through spatial analysis and data integration and utilised for the spatial distribution of IRAT (Table 6; Anand & Pradhan, 2019;Mahmood & Gloaguen, 2012). The basins with high relief generally show high to very high active tectonics (Figure 4a and 8a) and cover ~66.5% of the study area (14,924 km 2 ). The basins of the Khasi Hills region (basins 1, 2, 4, 16 and 19-22), bounding between Dauki Fault in the south and Oldham Fault in the north, are identified with very high (IRAT <1.851) IRAT class (Figure 8a). Similarly, most of the basins in the Jaintia Hills regions (basins 6-8, 12, 13 and 15), associated with Dauki and Tluh Faults, represent high to very high relative active tectonics. The basins possess mixed IRAT classes (classes 2, 3 and 4). The basins of lower reaches with less relief are identified with moderate to low level relative active tectonics (basins 24, 26, 30-39, 41-43; mostly in the southwestern portion), while the basins 25, 27-29 and 40, covering most of the Garo Hills region, are showing high class (1.851-2.130) of IRAT due to presence of structural features such as Dapsi Thrust, Chedrang, Darugiri, Dudhani and Samin Faults. Overall, the basins falling under classes 3 and 4 (moderate to low) of IRAT cover only 4288 km 2 ( Figure 8a). Thus, two-thirds of the study area is classified as class 1 or 2 of very high or high tectonic activity in terms of evident geomorphic response. IRAT tends to increase along Dauki, Kulsi, Tluh, Oldham Faults and Barapani Shear zone, showing that tectonic activity is currently high in the region.
Seismic activity is generally linked with rapid tectonic movement and is associated with active deformation zones (Softa et al., 2018). Over the last 230 years, the study region has experienced more than 300 mutually exclusive earthquakes of Mw 3.5 or more. Many events are found in the central and northwestern parts along the diagonal axis ( Figure 2a) and are mainly associated with Dhubri, Dauki, Khulsi, Dudhnai, Darungiri, Oldham, Samin Faults and Barapani shear zone. The results are also coherent with this trend, with high IRAT values along the NW-SE (increasing west to east) of Meghalaya. Structural discontinuities are the geomorphological expression of the lineaments that developed due to tectonics representing the structural deformation in a region (Prakash et al., 2017). A high lineament density reflects highly fractured fault zones (Bhat et al., 2020). In the study area, the localities of high lineament density are generally found at high altitudes, which may be attributed to hard rocks in these reaches, such as Gneissic or Granitoid rocks. Large clusters of seismic events are also observed in the areas having high lineament density, supporting the high tectonic activities and their control over the landscape evolution of the study area.

Conclusion
The present study aims to identify the tectonic activity of the Meghalaya region, India. Drainage basins and corresponding stream networks are delineated based on the SRTM-DEM (30 m resolution). Morphometric parameters and geomorphic indices for each 43 drainage basins are calculated and analysed further. The values of each index are grouped into Classes 1, 2 and 3, signifying different tectonic activity levels (high, moderate or low). The result shows that rapid uplift and active tectonic deformation have played a significant role in landscape evolution. As evident from morphometry analysis, the high value of SLGI and HI along the southern escarpment and higher river incision indicates relative rapid uplifting of the Khasi and Jaintia Hills regions. At the same time, smaller values of geomorphic indices in the Garo Hills region reflect relatively slow uplift, which is coherent with the reported differential rate of movement of ~3 mm/year to ~6 mm/ year, increasing from west to east along the Dauki Fault. The results obtained from other parameters have also endorsed this finding and confirmed the active tectonic deformation and differential uplift of the Meghalaya.
Further, the integrated spatial analysis of IRAT computed from different morphometric and morphotectonic parameters reveals that most of the basins covering the Khasi and Jaintia Hills region and partially Garo Hills region of the study area (covering ~66.5% of the area) fall under high to very high rate of active tectonic deformation. The majority of the Khasi and Jaintia Hills basins are primarily identified with very high IRATs. These basins show a strong correlation with structural features in the region (such as the Dauki Fault, Barapani shear, Kulsi, Oldham and Dudhani Faults) and have high lineament density confirming the findings of IRAT.
The present study will help in the identification of gradual-temporal changes in the landscape due to endogenic geomorphic processes and zonation of landslides and seismic-hazard-prone areas.