Temporal and spatial variations of seismicity parameters for Northwest Himalaya

Abstract

Northwest Himalaya is one of the seismically most active regions of the world. For seismic hazard assessment, it is important to calculate the seismicity parameters for every source zones. Homogenous earthquake catalog is a basic input for seismic hazard calculation. General orthogonal regression relation is used to convert different magnitude scales into a single moment magnitude scale. Declustering method is used to remove any non-Poissonian behaviour from earthquake catalogue. The NW Himalaya and its adjoining region are divided into twenty two seismic source zones based upon the seismicity, tectonics of the region and fault plane solution. Entire Magnitude Range Method (EMR) is adopted to estimate the magnitude of completeness because this method is stable under most conditions and provides a comprehensive seismicity model. Earthquake dataset for the period 1964-2011 has been used to determine of Mc values for different seismic zones. The Mc value valid for the entire NW Himalaya region can be considered to be 4.7 for the catalogue period 1964-2011. The `b' value ranges between 0.67-1.33 for different source zones. The value of parameter `a' increases with the seismicity of the region. This homogenized earthquake catalog and seismicity parameters are the basic input for seismic hazard assessment.