Seismic microzoning of the Delhi metropolitan area, India— I: Seismicity modeling

Seismic activity parameters ( and values in a Gutenbdataer–Richter relationship, maximum magnitude , and predominant focal depths ) have been estimated for a grid of square cells of size 0.1° in latitudes and longitudes covering a large region bound by 24°−33°N and 72°−82°E to define input seismicity for microzoning of the Delhi metropolitan area. For this purpose, seven area types of seismic sources are first identified from a detailed seismotectonic evaluation of the region. Two of these sources form part of the Northwestern Himalaya and the remaining five encompass the intraplate area including and surrounding the National Capital Region. The seismic activity parameters are then estimated for each source zone by compiling a comprehensive catalog of 4483 past earthquakes with magnitudes of 2.0 or more covering the 1720–2020 period. All the grid cells in each source are initially assigned the same values of parameters , , and as those for the source zone; whereas parameter has been redefined for each grid cell using the cumulative occurrence rate of earthquakes above the minimum magnitude of completeness for the source zone. To account for possible uncertainties in past earthquake locations, values of the activity parameters thus assigned to all the grid cells in the region are spatially smoothed using an elliptical Gaussian kernel with a major axis along the predominant strike direction for the source zone of each grid cell. The grid cells across the source zone boundaries are also included in the smoothing process to normalize the effects of any subjectivity introduced in defining the source zone boundaries. Our estimations of seismic activity parameters thus obtained can be considered in the development of a robust and physically realistic seismicity model for practical engineering applications, which was made possible by our use of a sufficiently long duration of the earthquake catalog along with complete reporting of data up to magnitudes very close to the expected maximum magnitude in each source zone. We have also estimated the seismic activity parameters for the Hindu Kush subduction zone, which is then idealized by a point source.