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Verma M.,National Center for Seismology | Sutar A.K.,Ministry of Earth science | Bansal B.K.,Ministry of Earth science | Arora B.R.,Ministry of Earth science | Bhat G.M.,Jammu University
Journal of Asian Earth Sciences

A moderate earthquake (ML 5.0, MW 4.9) occurred in the Kangra region of Himachal Pradesh on 21 August, 2014 (08:11UT). The earthquake attains significance as it occurred immediately northeast of the source zone of the large Kangra earthquake of 1905 (MW 7.8), the source mechanism of the later earthquake remains a subject of debate. Further, the seismic event is nucleated in a narrow block, where intense clustering of small and moderate events has been indicated by earlier campaign mode surveys. Taking advantage that recent earthquake is well recorded by a regional BBS network, the source parameters are estimated and interpreted to provide fresh constraint on the elements of seismotectonic model. The earthquake with its epicenter at 32.34°N and 76.52°E is seated on the Panjal Thrust, boundary between Panjal imbricate zone and the Chamba nappe. The travel time inversion and wave form inversion technique suggest focal depth no more than 5km. A stress drop of 92 bars and a source radius of 1.1km. The moment magnitude (MW) for this event is calculated as 4.9. The anomalous high value of stress drop compared to the generally low values prevailing over much of the Kangra-Chamba region indicates that the earthquake of 21 August 2014 is rooted in crustal blocks characterised by strong material strength to support accumulation of high strain during the earthquake building cycle. Fault plane solution of the event under study suggested that source fault is striking 323° with dip of 34°. The rake value of 105° indicated thrust movement with a very negligible right lateral movement. Synthesis of source parameters, especially the shallow focal depth, strike paralleling the Panjal thrust/MBT with steep dip, favour the seismotectonic model where moderate magnitude earthquake of 21st August 2014 is a typical example caused by the reverse fault displacement on the Panjal thrust fault. In the compressive regime of the Kangra Himalaya, such movements are facilitated by the stresses resulting in response to the southward sliding of the Chamba nappe and thus activating the contact zone between the nappe and Panjal imbricate zone. © 2015 Elsevier Ltd. Source

Gahalaut V.K.,National Center for Seismology | Kundu B.,National Institute of Technology Rourkela
Geomatics, Natural Hazards and Risk

Earthquakes in the Indo-Burmese wedge occur due to India-Sunda plate motion. These earthquakes generally occur at depth between 25 and 150 km and define an eastward gently dipping seismicity trend surface that coincides with the Indian slab. Although this feature mimics the subduction zone, the relative motion of Indian plate predominantly towards north, earthquake focal mechanisms suggest that these earthquakes are of intra-slab type which occur on steep plane within the Indian plate. The relative motion between the India and Sunda plates is accommodated at the Churachandpur-Mao fault (CMF) and Sagaing Fault. The 4 January 2016 Manipur earthquake (M 6.7) is one such earthquake which occurred 20 km west of the CMF at ∼60 km depth. Fortunately, this earthquake occurred in a very sparse population region with very traditional wooden frame houses and hence, the damage caused by the earthquake in the source region was very minimal. However, in the neighbouring Imphal valley, it caused some damage to the buildings and loss of eight lives. The damage in Imphal valley due to this and historical earthquakes in the region emphasizes the role of local site effect in the Imphal valley. © 2016 Informa UK Limited, trading as Taylor & Francis Group Source

Yadav R.K.,CSIR - Central Electrochemical Research Institute | Nankali H.,National Cartographic Center | Kundu B.,National Institute of Technology Rourkela | Patel P.,Dr Hari Singh Gour University | Gahalaut V.K.,National Center for Seismology
Journal of Asian Earth Sciences

We use coseismic offsets, derived from continuous GPS measurements at six nearby sites, due to the twin Varzaghan-Ahar earthquakes (northwest Iran) of 11 August 2012 (Mw 6.4 and 6.3) to constrain slip distribution on the ruptures of two earthquakes. We assume that slip during the two earthquakes occurred on conjugate faults. Majority of the slip occurred during the first earthquake which involved dextral slip on the east west trending vertical plane. The earthquake involved slip at shallow depth which reached up to ~0.9. m at the surface, consistent with the evidence of surface rupture and the observed offsets. During the second earthquake oblique slip occurred on a north-south rupture having steep dip towards east and extending towards north from the eastern edge of the first earthquake. Maximum slip of ~0.4. m occurred at depth of ~6-8. km. Derived moment magnitude of the first earthquake (6.45) from our analysis is consistent with the reported moment magnitude, while that of the second earthquake (6.1) is slightly underestimated from our analysis. © 2015 Elsevier Ltd. Source

Kundu B.,National Institute of Technology Rourkela | Vissa N.K.,National Institute of Technology Rourkela | Gahalaut V.K.,CSIR - Central Electrochemical Research Institute | Gahalaut V.K.,National Center for Seismology
Geophysical Research Letters

The Northwest Himalaya and its adjoining regions are one of the most seismically vulnerable regions in the Indian subcontinent which have experienced two great earthquakes [1902 Caucasus of magnitude MS 8.6 and 1905 Kangra, India of MS 8.6 (MW 7.8)] and several large damaging earthquakes in the previous century. In this study, time-dependent seismicity analysis is carried out in five main seismogenic zones in the Northwest Himalaya and its adjoining regions by considering earthquake inter-arrival times using a homogeneous and complete earthquake catalogue for the period 1900–2010 prepared by Yadav et al. (Pure Appl Geophys 169:1619–1639, 2012a). For this purpose, we consider three statistical models, namely Poisson (time independent), Lognormal and Weibull (time dependent). Fitness of inter-arrival time data is investigated using Kolmogorov–Smirnov (K–S) test for Lognormal and Weibull models, while Chi-square test is applied for the Poisson model. It is observed that the Lognormal model fits remarkably well to the observed inter-arrival time data, while the Weibull model exhibits moderate fitting. The parameters A and B of the time-dependent seismicity equation $$\ln {\text{IAT}} = A + BM \pm C$$lnIAT=A+BM±C (where ln IAT is the log of inter-arrival times of earthquakes exceeding magnitude M and C is the standard deviation), developed by Musson et al. (Bull Seismol Soc Am 92:1783–1794, 2002) are evaluated in each of the five main seismogenic zones considered in the region. The mean of the inter-arrival times for the Lognormal distribution is found to be linearly related to the lower-bound magnitude (Mmin). Values of the slope (B) of the mean vary from 2.34 to 2.57, while the parameter A ranges from −9.06 to −7.01 in the examined seismogenic zones with standard deviation ranging from 0.21 to 0.38. It is observed that the Hindukush–Pamir Himalaya and Himalayan Frontal Thrust exhibit higher seismic hazard (i.e., high seismic activity and low recurrence periods), while the Sulaiman–Kirthar ranges show the lowest. The variation in estimated seismicity parameters from one zone to another reveals high crustal heterogeneity and seismotectonic complexity in the study region. © 2015, Springer Science+Business Media Dordrecht. Source