• Irene Sarkar

      Articles written in Journal of Earth System Science

    • Estimation of hypocentral parameters of local earthquakes when crustal layers have constantP-velocities and dipping interfaces

      Irene Sarkar R Chander K N Khattri V K Gaur

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      The paper describes an algorithm for estimating the hypocentral coordinates and origin time of local earthquakes when the wave speed model to be employed is a layered one with dipping interfaces. A constrained least-squared error problem has been solved using the penalty function approach, in conjunction with the sequential unconstrained optimization technique of Fiacco and McCormick. Joint confidence intervals for the computed parameters are estimated using the approach of Bard for nonlinear problems. These results show that when a hypocentre lies outside the array of recording stations and head waves from a dipping interface are involved, then its inclination must be taken into account for dip angles exceeding 5°.

    • On the aftershock sequence of a 4.6 mb earthquake of the Garhwal Himalaya

      Irene Sarkar Ramesh Chander Dalia Chatterjee

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      Locally recorded data for eighteen aftershocks of a magnitude(mb) 4.6 earthquake occurring near Ukhimath in the Garhwal Himalaya were analysed. A master event technique was adopted to locate seventeen individual aftershock hypocentres relative to the hypocentre of the eighteenth aftershock chosen as the master event. The aftershock epicentres define an approximately 30 km2 rupture zone commensurate with the magnitude of the earthquake. The distribution of epicentres within this zone and the limited amount of first motion data support the view that a group of parallel, sub-vertical, sinistral strike-slip faults oriented N46°, transverse to the regional NW-SE trend of the Garhwal Himalaya, was involved in this seismic episode. Since the estimated focal depth range for aftershocks of this sequence is 3–14 km, we infer that this transverse fault zone extends through the upper crustal layer to a depth of 14 km at least.

    • A simulation of earthquake induced undrained pore pressure changes with bearing on some soil liquefaction observations following the 2001 Bhuj earthquake

      Irene Sarkar Ramesh Chander

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      The Bhuj earthquake of January 26th, 2001, induced wide spread liquefaction within the Kachch peninsula. It has been pointed out that inundation due to soil liquefaction was short lived in some parts than in others in the affected region. Several geological, seismological and hydrological factors would have cumulatively contributed to these observed changes.

      We simulate in this article, undrained or short-term change in pore pressure in a poroelastic half space, in response to a simplified model of the Bhuj earthquake source. We find that the regions of relatively shorter lived inundation due to soil liquefaction may fall in the region where pore pressure responsible for soil liquefaction attributable to strong ground shaking was counteracted by pore pressure changes due to undrained poroelastic effect and vice versa.

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