**2. General geomorphology and seismicity of Wagad Kachchh**

The WH is second largest uplifted block of Kachchh basin, after mainland of Kachchh, covering an area of ~2432 km2 , and is bounded by GF to the north and SWF to the south [11, 16]. The area is drained by numerous ephemeral streams; flow direction regularly spaced around the upper planation surface [23, 24]. From north to south, the WH comprises of three E-W trending active faults, namely the GF between Deshalpar and Fatehgarh area, the North Wagad Fault (NWF) north of Bharudia and the SWF between Mai and east of Chitrod (**Figure 1A**).

Geomorphologically the WH is divided into 3 units; (i) the upper planation surface (Mesozoic) with juvenile streams, (ii) the middle incised slopes with piedmont (Tertiary), and (iii) the low-lying areas representing Quaternary deposits [23, 25]. The upper surface represents an early Quaternary erosional event, whereas the middle incised slopes with terraces were developed during late Quaternary [26]. These two geomorphic units provide sediments to the lower peripheral areas. Suvai, Bhimguda, Narelawali, Dhadawali, Karaswali, Malan, Baniyo, and Dabhodanwari are six ephemeral rivers that flow northward and originate from the WH, following the regional slope and drain into the Great Rann of Kachchh [23]. Along their longitudinal length, these rivers cross several E-W oriented faults (**Figure 2**).

process. The digital elevation model extracted from the SRTM was validated with the Survey of India topographic map (1:50,000) scale. To extract drainage network DEM data is used and 27 northward and south ward flowing rivers basins were generated. We calculated several tectonic attributes namely stream length-gradient Index (SL); steepness index (Ks), hypsometric integral (HI), asymmetric factor (AF) and Basin shape (BS). Based on results obtained from above analysis, spatial distributions of relative index of active tectonics (RIAT) are estimated for North Wagad/Bharudia, Gedi and Island fault zones. The dimensions of these drainage

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The map of local relief in the present study is produced from River-Tool by subtracting arithmetically a sub-envelope surface that describes the general pattern of valley bottoms elevations from an envelope surface (that connects peaks elevations) [28]. We obtained such surfaces by smoothing the minimum and maximum topography of the SRTM DEM by a 20 km wide circular moving window (**Figure 1C**). We chose the value of 20 km since it is the average spacing of the main valleys (5th, 6th and 7th Strahler order with respect to a critical

We have considered five swath profiles across the study area to describe and quantify the topographic trend of the northern WH. The results show the trend of minimum, maximum and mean elevation into a single plot [29, 30] (**Figure 1D**). The statistical analyses such as maximum, minimum and mean elevations were calculated along each swath profile within a GIS platform. (**Figure 1D**). A rectangular swath of 300 m width was chosen to extract a series of parallel profiles that are separated by 1-cell (5 m). The width of the swath profile has been used to condense both elevated surfaces and streams. The higher elevation in swath depicts maximum elevation corresponds to the ridgelines; whereas, the lower elevation curve for the minimum elevation represents the valley floors. The Incision by river can be measured by the arithmetic difference between the maximum and minimum elevations within the longitudinal

The SL index is one of the quantitative geomorphic parameters included in morphotectonic assessment (Hack, [34]). This index will increase in value as rivers and streams flow over active uplifts and may have lesser values when flowing parallel to structures such as valleys made by strike-slip faulting [32]. The SL index seems to be a valid tool to detect local uplift as well as the incipient local response to regional processes [33]. Conventionally the SL index shows a quantitative approach to differential geomorphic studies related to erosion and depositional processes that include the river channel, long profile, and valley morphology as well

as tectonically derived features such as fault scarps. This index was defined by [32] as:

). This allowed us to remove small valleys, in effect operating like a low-pass

basins are given in **Table 1**.

filter that highlights the regional-scale features.

distance of the swath rectangle [31].

**3.3. Stream length gradient index (SL)**

**3.1. Map of local relief**

area of ~4 km2

**3.2. Swath profiles**

**Figure 2.** (A) Geological map of Wagad area shows especial distribution of SL along various geological units. Spatial distribution of SL class contour map of northern Wagad region. The higher activity is marked by higher order color (B) especial distribution of Ks along various geological units. Distribution of Ks class contour of northern Wagad region. Fault lines are shows by solid black line; dykes are marked by green lines; and bedding slope direction is highlighted by small black arrow. (C) Spatial variation of topography and statistics estimation for values of basin-wide hypsometric integral. The hotspots of higher uplift are marked by higher color values of hypsometric integral. (D) Relationship between amounts of stream offset along the fault and upstream length from the faults (F1–F10). *For generation of* **Figure 1A** and **B** *used Arc-GIS-10.4, Global mapper 18 software's and the final editing and contouring has been done in Surfer-11 software. We used River tool 3.0 for generation of hypsometric curves. The contour values of hypsometry Integral (HI) has been generated in Global mapper 18 and finally the contouring has been done in Surfer 14 software. We used excel for generation of* **D**.

The aftershocks of the January 26, 2001 Bhuj earthquake (Mw 7.7) are still continuing [15]. Distribution of the hypocenter of these aftershocks suggests that they are distributed mainly towards NE and SW directions. It has been observed that the WH is pronounced activated after the 2001 mainshock [12, 15, 27]. It is testified by a large number of aftershocks (Mw ≥ 2.5) occurred in the WH with focal depths ≥10 km. A few moderate earthquakes also occurred along the GF. Among these earthquakes, the most recent are the February 2006 (Mw 5.0); February 2006 (Mw 4.8); March 2006 Mw 5.7 and April 2008 Mw 4.1 [27] (**Figure 1B**). In the GF zone some 30 earthquakes (Mw 3.0–5.7) have been recorded at Seismic Network of Gujarat (SesisNetG) at shallow focal depths (≤ 20 km) during the period of 2006–2013 (**Figure 1B**).
