Geodetic characterization of active Katrol Hill Fault (KHF) of Central Mainland Kachchh, western India

Donupui Suriu , Rkesh K. Dumk , Joyeep Pikry , Girish Ch. Kothyri ,Mhesh Thkkr , Kni V. Swmy , Ajy K. Tloor , Snip Prjpti

a Institute of Seismological Research, Raysan, Gandhinagar, Gujarat, 382009, India

b Department of Earth and Environmental Science, KSKV University, Bhuj, Kachchh, India

c Adikavi Nannaya University, RajahMundary, A.P, India

d Department of Remote Sensing and GIS, University of Jammu, Jammu, India

ABSTRACT After the M7.7 earthquake in 2001, the Kachchh rift basin became the focus of various geological and geophysical researches on the western Indian plate. As an essential technology, the Global Navigation Satellite System (GNSS) has been utilized to study the deformation pattern in the central mainland Kachchh.We select the east-west striking Katrol Hill Fault(KHF)as the study area and analyze the crustal deformation pattern using the datasets from 2014 to 2019. The geodetic results along the KHF reveal a mean deformation of about 2.1 mm per year,which is higher in the eastern part and lower in the central and western parts. The investigation of deformation and derived strain reveals the segmented behavior of KHF,while the dominance of compressive strain(maximum 22 nanostrain/yr)in the eastern segment makes it the most active segment of the KHF. A higher deformation rate along the eastern KHF can be considered significant in terms of seismic hazard for this part of the Indian plate.© 2021 Editorial office of Geodesy and Geodynamics. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords:Geodesy GNSS Deformation Strain Indian plate

1. Introduction

The splitting of eastern Gondwanaland in Mesozoic created Kachchh,Cambay,and Narmada rift basins in western India[1-4].From north to south are the Kachchh and Narmada rifts,which are sub-parallel E-W trending rifts intersected by the NNW-SSE inclined rift of Cambay(Fig.1).This part of the Indian plate began to be compressed after colliding with the Eurasian plate [5,6]. The reversal of the stress state from extension to compression resulted in the reactivation of the faults in Kachchh [3]. This basin is bordered by two main east-west trending faults:the south-dipping Nagar Parkar Fault(NPF)in the north and the north-dipping North Kathiawar Fault(NKF)in the south[3,6].There are east-west faults in the basin, namely the Island Belt Fault (IBF), Kachchh Mainland Fault(KMF),South Wagad Fault(SWF),Katrol Hill Fault(KHF),Gedi Fault(GF),North Wagad Fault(NWF),and Vigodi Fault(VF),which had experienced persistent seismic activities in the region[3,6-10].In the last two centuries, major earthquakes such as M7.8 Allah Bund (1819), M7.0 Western Kachchh-Sunda (1845), M6.0 Anjar(1956),and M7.7 Bhuj(2001)earthquakes as well as several low to moderate earthquakes after 2001 have occurred [11-19]. Earthquakes in the Kachchh region are mainly caused by the accumulated strain from the continuous collision between the Indian and Eurasian plates [3]. It is believed that after the 2001 M7.7 earthquake, the faults towards N and NE Kachchh became more active and were responsible for the current enhanced seismicity[19-28].Hence,it is necessary to study the ongoing deformation process of individual faults in the Kachchh basin.Geodetic research using the continuous mode of GPS datasets is useful for precise measurements of deformation patterns. A study along the IBF in the north of Kachchh using GPS measurements indicates the deformation of 2.9 mm/yr and assesses the possibility of a maximum 6.0 magnitude earthquake [29]. Similarly, PSInSAR measurements in the eastern part of KHF show a maximum Line of Sight (LoS)displacement of 4.3 mm/yr [30]. And another research performed using the ALOS-PALSAR dataset suggests the deformation of 1.2-3.5 mm/yr along KMF [31].

Fig.1. The study area (rectangle) located in western India. The small blue circles along KHF indicate the location of GPS sites (refer to Table 1 for details). The locations of major earthquakes during the last two centuries are represented by red stars along with the magnitude and year of occurrence.

In order to measure the deformation after the 2001 Bhuj earthquake, the campaign mode GPS measurements and a few continuous mode studies were carried out in the Kachchh. After this earthquake,the measured horizontal deformation was 12 mm/yr and then decreased to 6 mm/yr, 3 mm/yr, 4 mm/yr [32-39]. As an intraplate region with low deformation,it is required to monitor the deformation pattern of various faults. In 2009, we started to deploy continuous mode GPS stations in the study area, and the results obtained so far indicate low deformation (up to 3.0 ± 0.5 mm/year) and long-standing compression (≈4 mm/yr)[39,40].The strain tensor analysis based on GPS data sets from 2009 to 2015 reveals the domination of N-S compression in Kachchh[32].Since a few earthquakes of magnitude ＜4.0 occurred along the KHF after the 2001 Bhuj earthquake,and considering the apparent displacement in Quaternary alluvial formation in the KHF zone,we focused the continuous mode GPS research on the faults crossing the Kachchh mainland.The GPS data were processed and analyzed in terms of deformation and strain rate to study the kinematic characteristics along KHF. Then we correlated the results with existing seismicity and available InSAR results to identify the zone of maximum deformation in the area.

2. Study area

The study area is dominated by an east-west trending intrabasinal Katrol Hill Fault (KHF) passing from the middle of mainland Kachchh (Fig.1). KHF divides the mainland Kachchh into two geographic domains,one sloping to the north and the other inclining to the south[41].The boundary of Cretaceous and Jurassic formation in this area is marked by KHF [42-44], which is defined as reverse fault [41]. The Ground Penetrating Radar (GPR) study defines the KHF as a south-dipping fault that is steep near the surface and vertical at depth[43,45].The fault overlapping offsets in the quaternary sediments display the periodic reactivation of KHF, and three reactivation events of Late Quaternary were acknowledged by the study based on GPR and geomorphology as well as the paleo-seismological trench investigation [46,47]. The optically stimulated luminescence(OSL)dating along Khari River in the vicinity of KHF identified three tectonic episodes and provided a slip rate of 0.23 mm/yr [48]. The electron spin resonance(ESR)technique recognized the reactivation of KHF at ～70 ka[49]and ～56 ka by improving the Alpha Efficiency calculation [50]. The segmented behavior represents active tectonic activities in different periods along the KHF [51]. KHF is laterally displaced at several places by northwest-southeast, northeastsouthwest directed transverse faults [43,44,52], and an annual deformation rate measured in the eastern segment of the KHF is greater than 4.0 mm[30,31].

3. Methodology and GNSS data processing

A total of eleven GPS stations (six continuous and five campaign modes) were established to observe the deformation along the KHF,in which the nine stations are equipped with Leica 1200 receivers and two stations are equipped with Topcon receivers.The continuous mode sites generate GPS data for all days of the year, while semi-continuous mode (campaign) sites generate GPS data for at least 100 days of the year. The antenna platform of each site was fixed on the Reinforced Cement Concrete(RCC)monument.The data observation rate of 30 s and the cut-off elevation mask angle of 15were fixed to the entire local GPS network. Continuous GPS stations measured 2-6 years of data,and semi-continuous stations (with an interval of 6 months between each epoch) measured 2-3 years of data.

In GPS data processing, the pre-processing part was accomplished by the Translation, Editing and Quality Check (TEQC),which is provided by University NAVSTAR Consortium (UNAVCO)[53]. After selecting sessions over 12 h and eliminating cycle slip data, all the generated raw data were transformed into the Receiver Independent Exchange (RINEX) format. The postprocessing of data was accomplished by GAMIT/GLOBK software 10.7[54,55].To generate a solution in the International Terrestrial Reference Frame (ITRF), about 21 International GNSS Services(IGS) sites were used [56]. The monument instability error was eliminated by the inclusion of 0.75 mm/yrrandom-walk noise to the positions of all the stations.The involvement of ocean tides eradicated by model FES2004 and GPT2 was applied as a local meteorological model,while the IERS2003 model was used for the solid earth displacement correction[57-61].And all these models have been applied during post-processing.Finally,the time series were generated according to the expected steps of velocity estimation[54,55].It is worth noting that the MOTH,KUKM,and NIGL sites showed a large number of movements, so we did not consider the results of these three sites in the result interpretation.The ITRF frame was utilized for velocity estimation.Then the angular velocity and rotational pole (W= 0.335613 ± 0.0030,W=0.070437 ± 0.0114, and W=0.434185 ± 0.0036) [62] were utilized to estimate deformation of the study area (Table 1).

4. Results and discussion

This study is the first geodetic survey along the KHF to the central part of the Kachchh mainland. The results based on the dense network of the 11 GPS sites show that the average ITRF velocity along KHF is 49.68 ± 1.0 mm/yr with an uncertainty of a sigma (Fig. 2 and Table 1). The average northward and eastward ITRF velocities are 34.60 ± 1.0 mm/yr and 35.90 ± 1.0 mm/yr,respectively(Table 1).

4.1. Deformation results

The investigation of time series after removing the plate motion[62]indicates a significant amount of deformation in this part of the Kachchh. The component-wise analysis illustrates the dominance of NE-NNW directed movement along the KHF(Fig.3).According to the results of sites ADIP, ANJA, STPR, and NAG1, the eastern segment of the KHF yields an average displacement of 2.1±0.4 mm/yr northward and 0.98±0.4 mm/yr westward(Fig.4).The BHUJ, BALA, SAMT, and KROH sites located in the middle and western segment of the KHF show an average displacement of 1.08 ± 0.3 mm/yr northward and 1.46 ± 0.3 mm/yr westward,respectively.The variation among the eastern,middle,and western segments highlights the segmented characteristics of KHF and a variable amount of slip component along the fault (Fig. 4).

4.2. Strain results

The strain analysis conducted using the grid_strain program[63,64] provides the domination of compressive strain and an almost equal amount of extensional strain in the study area(Table 1). Further, the eastern segment of KHF accumulates higher compressive strain compared to the middle and western segments.An average of 22 nanostrain/yr is observed in the eastern segment along the KHF, while the central and western segments reveal the average of 18 and 12 nanostrain/yr, respectively(Figs. 5 and 6).

The segmented behavior of faults is associated with the individual faults in the Kachchh basin,i.e.,the IBF,SWF,KMF,and KHF[4,9,24,29,51]. The geodetic study along the IBF identified three different segments of the fault and presented variable slip associations along the Pachchham, Khadir, and Bela segments [29]. The segmented behavior based on the detailed geomorphological investigation highlighted the presence of double and single fault zones along the South Wagad Fault [9]. Similarly, KMF is also recognized as a segmented fault based on the paleo-seismological investigation [24].

Additionally,the distribution of earthquake epicenters(https://isr.gujarat.gov.in)(Fig.6)towards the hanging-wall side proves the active nature of the fault, which can be directly linked with the south-dipping KHF. An InSAR study indicated the active nature of KHF and estimated the maximum deformation of 4.0-5.0 mm/yr(LoS)in the east Kachchh[37,39,65].Similarly,another study using ALOS PALSAR data from 2007 to 2010 showed that the vertical deformation of this part was 6-7 mm/yr [65]. It can be seen that the deformation is continuously declining after the M7.7 earthquake in the Kachchh region.The GPS studies in Kachchh revealed 12 mm/yr of horizontal motion after the six months of the 2001 Bhuj earthquake and subsequently reduced to 6, 4, and 3 mm/yr[30,32,33,35-37,39].

The average deformation of about 2 ± 1 mm/yr in the current study area (Fig. 3 and Table 1) is low compared to the plate boundary region but may be significant for this part of the Indian plate [62,66-75]. The geodetic investigation based on the GPS dataset from 2009 to 2015 revealed an average annual deformation rate of 3.0±0.5 mm in the Kachchh[39].Similar studies based on SAR technology in the different parts of Kachchh showed that the annual displacement was up to 4.0 mm [30,31,76]. Therefore, the results of the present study are comparable in the Kachchh region.Based on the GPS-derived results of the central mainland Kachchh,it can be concluded that the eastern segment of KHF is more active than the central and western parts. The derived strain implies thepresence of almost N-S compression with maximum strain accumulation towards the eastern part of KHF.

Table 1 The ITRF14 and Indian plate velocities of sites with the values of compressive and extensional strain.

Fig. 2. The network of the 11 GPS sites and the ITRF velocities (blue arrows) along the KHF with one sigma uncertainty.

Fig. 3. The deformation and strain rate along the KHF are quantified with reference to the site motion estimated by the Euler pole [62]. The average motion of GPS sites is 2.1 ± 1.0 mm/yr, which is considered significant in the intraplate region.

Fig.4. The histogram of northward and eastward displacement of GPS stations.The sites located in the east indicate more N-S motion compared to the central and western parts of KHF.Similarly,the E-W motion is more in the sites of central and western parts compared to the sites of the eastern part.This kind of motion highlights the segmented behavior of KHF.

Fig.5. The longitudinal distribution of strain tensors.The red and blue columns indicate the compression and extension,respectively.The relative analysis of strain tensors suggests the domination of compressive strain and an almost equal amount of extensional strain in the study area. For strain magnitude, please refer to Table 1.

Fig. 6. The distribution of earthquake epicenters in the study area. The measured strain tensor at each GPS site indicates the compression (red line) and extension (blue line).

5. Conclusions

Based on the GPS derived deformation and strain analysis in the central part of mainland Kachchh,the following conclusions can be drawn: the geodetic study in the central mainland Kachchh shows the ITRF velocity of 49.6 ± 1.0 mm/yr; the maximum deformation along the south-dipping E-W trending KHF is estimated to be 2.1±1.0 mm/yr;the variable north-south and comparable east-west geodetic displacements along the strike highlight the segmented character of the KHF zone,and the dominance of compressive strain makes the eastern segment the most active part along the KHF; a maximum of 22 nanostrain/yr is calculated in the eastern segment of KHF,which is reflected in the form of current seismicity.

Author statement

All the authors of the manuscript entitled “Geodetic characterization of active Katrol Hill Fault (KHF) of Central Mainland Kachchh, western India” assures that the results are original and derived based on fieldwork, followed by data analysis and interpretation.All of us nominate the corresponding author and approve the submission of the manuscript to the journal of “Geodesy and Geodynamics”. The present manuscript is part of the Ph.D. thesis work of Mr. D Suribabu.

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We are grateful to the Director-General, ISR ＆ DST- Govt. of Gujarat, for the necessary support to carry out the research work.The study is part of Active Fault mapping of the Kachchh region,and for that RKD is thankful to MoES-New Delhi for the grant via Seismo-1/270/AFM/2015.