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_Journal of Structural Geology 32 (2010) 350–361_ Contents lists available at ScienceDirect Journal of Structural Geology journal homepage: www.elsevier.com/locate/jsg Paleoseismic evidence from trench investigation along Hajipur fault, Himalayan Frontal Thrust, NW Himalaya: Implications of the faulting pattern on landscape evolution and seismic hazard Javed N. Malik a,*, Ajit K. Sahoo a,1, Afroz A. Shah a,2, Dattatraya P. Shinde b, Navin Juyal b, Ashok K. Singhvi b Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur, UP, India b Physical Research Laboratory, Ahmedabad 380 009, Gujarat, India Article history: Received 8 February 2009; Received in revised form 31 December 2009; Accepted 6 January 2010; Available online 14 January 2010 Keywords: Active faults Lateral propagation Himalayan Frontal Thrust Paleoseismology Landscape change Seismic hazard Abstract The study area falls within the mesoseismal zone of the 1905 Kangra earthquake (Mw 7.8). Two parallel NNW–SSE striking active fault scarps named as Hajipur Faults (HF1 and HF2) along the northwestern end of the Janauri anticline in the foothill zone have displaced floodplain sediments of the Beas River. The HF1 and HF2 represent imbricate faults of the Himalayan Frontal Thrust (HFT), and are the result of lateral propagation of deformation from two fold segments i.e., JF1 and JF2 respectively in northwest direction along the strike. Ground Penetrating Radar (GPR) profiles and trenching across the HF2 reveal two low-angle thrust fault strands (F1 and F2). Displacements of ~7.5 m on F2 and ~1.5 m on the associated branching faults (fa, fb and fc) were observed. Total four stratigraphic units: unit A (gravel) – with a lens of medium sand (unit A0) is the oldest; overlain by units B – medium to coarse sand; unit C – fine to medium sand; and unit D – fine to medium sand with scattered gravel were observed in trench. Radiocarbon ages of the charcoal samples from unit B and unit D, optical ages of sediments from units A0, B and C, GPR data and trench log suggest two major events along F1 and F2 strands. Event I along F1 occurred during 2600–800 yr BP and Event II along F2 around 400 yr BP and before 300 yr BP. Given the uncertainty in dates it is suggested that the latest event occurred during 1500–1600 AD. Considering the oldest unit (unit A) exposed in trench with vertical displacement of 7.5–8 m, age of ~2600 ± 500 yr BP and net displacement of ~9 m during single event along low-angle fault (q ~ 25°), implies slip rate ~7.6 ± 1.7 mm/yr, uplift rate ~3.2 ± 0.6 mm/yr, shortening rate ~6.9 ± 1.4 mm/yr and recurrence interval ~1160 ± 250 yr for large-magnitude event with Mw >7.0. With the recurrence of 1100 yr, the penultimate event probably occurred at around 1400–1500 yr BP. Given the recent GPS based slip rate of 14 ± 1 mm/yr in Kangra reentrant (Baneerjee and Burgman, 2002), the present study suggests that about half of this slip is consumed along the HFT and that this fault is more active compared to those in the hinterland. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction The continued convergence between Indian and Eurasian plates has made the Himalayan arc a seismically active region that experienced moderate to large earthquakes. In last 100 years, the Himalaya has experienced three major large-magnitude events: during 1905 Kangra (Mw 7.8), 1934 Bihar (Mw 8.1) and 1950 Upper Assam (Mw 8.4) earthquakes (Seeber and Armbruster, 1981; Yeats et al., 1997; Ambraseys and Bilham, 2000; Ambraseys and Douglas, 2004). The recent October 8, 2005 Muzaffarabad earthquake (Mw 7.6) occurred along an earlier identified active fault named Balakot–Bagh fault causing extensive damage in Pakistan as well as in the Indian side (Nakata et al., 1991; Kaneda et al., 2008). Seismic hazard evaluation in Himalaya is one of the most crucial problems. Historic records and instrumental data available so far are not so comprehensive, and also little or no written records are available from much of the Himalayan belt, hence actual appraisal of hazard from this dataset is difficult (Iyengar and Sharma, 1999; Bilham et al., 2001). For proper seismic hazard estimation, identification of active faults bears significant importance, it is also necessary to know the accurate locations and geometry of active faults (Gross et al., 2002). Paleoseismic investigation is one of the most commonly adopted techniques towards identification cataloguing the historic and pre-historic earthquakes in tectonically active regions of the world (McCalpin, 1996). The studies carried out during several decades have provided important data on the ongoing crustal deformation in the Himalaya. However, not much effort is directed to site-specific studies (Nakata, 1989; Valdiya, 1992; Yeats et al., 1992; Wesnousky et al., 1999; Malik et al., 2003; Malik and Nakata, 2003). Recent paleoseismic investigations from India, Pakistan and Nepal along the Himalaya arc have added valuable information towards the occurrence of large-magnitude earthquake during recent historic past. Investigations along Sirmuri Tal fault in Dehra Dun valley along Main Boundary Thrust (MBT) suggest two major earthquakes have struck Dehra Dun region in the last 1000 years (Oatney et al., 2001). Paleoseismic investigations along Black Mango (Kala Amb) tear fault along the Himalayan Frontal Thrust (HFT) in the NW Himalaya have revealed evidence of two large earthquakes with surface ruptures during the past 650 years; subsequent to 1294 AD and 1423 AD, and yet another at about 260 AD (Kumar et al., 2001). Also studies from NW Himalaya have indicated major event at around ~1400–1500 AD along HFT (Kumar et al., 2006; Malik et al., 2008). Paleoseismic evidence from east central Nepal reveals a single earthquake rupture along the Frontal Thrust during ~1100 AD (Lave? et al., 2005). Trench investigation performed along Balakot–Bagh fault after the 2005 Muzaffarabad earthquake suggests recurrence interval of 1000–3300 yr and shortening rate of 1.4–4.1 mm/yr (Kaneda et al., 2008). Earthquakes along active faults are periodic (Yeats et al., 1997; McCalpin, 1996) and a proper seismic hazard assessment needs an active fault map with paleoseismic history. The Muzaffarabad 2005 event has raised more concerns towards the seismic hazard assessment in areas along Himalayan foothills, where practically no historic or no active fault-paleoseismic data is available. In this paper we document the geomorphic manifestation of newly identified active faults, named as Hajipur faults in the mesoseismal zone of 1905 Kangra earthquake (Mw 7.8) along the northwestern end of the Janauri anticline (Fig. 1a). These faults along the Himalayan front were identified using CORONA satellite (stereo pair) photos, Digital Elevation Model (DEM) generated from SRTM data followed by detailed field investigations (Figs. 2–4). GPR (Ground Penetrating Radar) profiling was conducted to understand the geometry of the faulting and to locate the appropriate site for further paleoseismic investigation. Paleoseismic investigation revealed occurrence of two major events during 2600–800 yr BP and another at around 400 yr BP. The 1905 Kangra and 2005 Muzaffarabad events are the only well-documented events from NW Himalaya (Iyengar and Sharma, 1999; Ambraseys and Jackson, Ключевые слова: major event, yr bp, fold, thrust, nature, evidence, uvial terrace, himalayan foothill, mmyr, soan dun, nepal, current, ad, journal structural geology, single event, suggested, gross, osl, oldest unit, society, radiocarbon, sediment sample, higher elevation, himalayan arc, active, hanging wall, time, paleoseismic, active deformation, surface, trench, suggests, charcoal sample, model, mccalpin, yeats, folding, ha, burbank, gravel, displacement, figs, geology, beas, southern tibet, marker, structural, gpr prole, kangra reentrant, main, table sample, marked, higher himalaya, large-magnitude earthquake, northern fringe, ground, mark, gure legend, bilham, major earthquake, paleoseismic evidence, elastic crack, tectonics, journal structural, delcaillau, press, hajipur, tectonophysics, recurrence interval, srtm data, zhao, frontal, structural geology, reverse faulting, low-angle fault, osl age, deposition, major, study, fault scarp, yr, late quaternary, total, geophysical, hajipur fault, fault-related-fold segment, foothill zone, mmyr kumar, active fault, lave, plate, sample location, himalayan, rate, bp, scarp height, scarp, frontal fault, seeber, anticline, age, kumar, slip, river proles, comprising medium, valdiya, mesoseismal zone, segment linkage, geological, south, detrital charcoal, observed, fault, earth, medium, propagate laterally, sediment, hodges, north, international, medium sand, hazard, rupture, rgmann, major fault, paleoseismic investigation, investigation, ? mm, beas river, area, latest event, convergence rate, geophysics, unit, geophysical letters, journal, mw, surface rupture, river, stratigraphic unit, overbank environment, address, wa, nakata, mm, berc, seismic, science, tertiary hill, india, gpr, calendar age, deformation, sand, variable dip, bilham ambraseys, slip rate, armbruster, journal geophysical, identi?ed, indo-gangetic plain, strand, coarse sand, kangra, historic event, seeber armbruster, lateral propagation, fault plane, hill range, elsevier, gudmundsson, mm yr, oodplain deposit, net displacement, nw, radiocarbon age, range, zone, letters, imbricated fault, event, hinterland fault, molnar, earthquake, occurred, arc, walsh, hft, large-magnitude event, total slip, large earthquake, janauri anticline, unit unit, left bank, frontal thrust, exposed trench, trench site, malik, america, sample, ambraseys, avouac, himalayan belt, highly diffused, cartwright, current science, janauri, gravel unit, doi, himalayan frontal, faulting, penultimate event, himalaya, location, propagation, lateral, data, stein, central