• H R Wason

      Articles written in Journal of Earth System Science

    • Estimation of the waiting time distributions of earthquakes

      S M J R Goel S K Malasi P S Moharir H R Wason K N Khattri V K Gaur

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      Whether the earthquake occurrences follow a Poisson process model is a widely debated issue. The Poisson process model has great conceptual appeal and those who rejected it under pressure of empirical evidence have tried to restore it by trying to identify main events and suppressing foreshocks and aftershocks. The approach here is to estimate the density functions for the waiting times of the future earthquakes. For this purpose, the notion of Gram-Charlier series which is a standard method for the estimation of density functions has been extended based on the orthogonality properties of certain polynomials such as Laguerre and Legendre. It is argued that it is best to estimate density functions in the context of a particular null hypothesis. Using the results of estimation a simple test has been designed to establish that earthquakes do not occur as independent events, thus violating one of the postulates of a Poisson process model. Both methodological and utilitarian aspects are dealt with.

    • Temporal and spatial variations in the magnitude of completeness for homogenized moment magnitude catalogue for northeast India

      Ranjit Das H R Wason M L Sharma

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      Northeast India region is one of the most seismically active areas in the world. Events data for the period 1897–2010, used in this study has been largely compiled from global ISC, NEIC and GCMT databases. Historical seismicity catalogue of Gupta et al (1986) and some events data from the bulletins of India Meteorological Department are also used. Orthogonal regression relations for conversion of body and surface wave magnitudes to 𝑀w,HRVD based on events data for the period 1978–2006 have been derived. An Orthogonal Standard Regression (OSR) relationship has also been obtained for scaling of intensity estimates to 𝑀_{w,NEIC} using 126 global intensity events with intensity VI or greater during the period 1975–2010.

      Magnitude of completeness and Gutenberg–Richter (GR) recurrence parameter values have been determined for the declustered homogenized catalogue pertaining to four different time periods namely, 1897–1963, 1964–1990, 1964–2000 and 1964–2010. The $M_c$ and ‘𝑏’ values are observed to decrease and increase, respectively, with addition of newer data with time. The study region has been subdivided into nine seismogenic zones keeping in view the spatial variations in earthquake occurrence and prevalent tectonics. $M_c$, ‘𝑏’ and ‘𝑎’ values have been estimated with respect to each zone, and the variations in the values of these parameters have been analysed.

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