A study of seismic activity in the northeast India and determination of its seismic potential

Abstract

In this research a study of seismic activity of northeast India has been made by considering various seismo-logical parameters such as energy release, temporal and spatial variation of seismicity, temporal variation of body wave travel time ratio, focal mechanism study, study of clustering and seismic gaps. The seismic potential of the region has also been determined qualitatively. Northeast India is seismically very active and several large earthquakes have occurred in this region. A sequence of moderate size earthquakes, their aftershock sequence and other clusters of small magnitude earthquakes indicate the formation of a major asperity complex in the region. The data for this study has been obtained from all available sources such as Earthquake Data File, Earthquake Data Report and Preliminary determination of Epicentre of U. S. Cost and Geodetic Survey, Bulletin of the International Seismological Centre, Local seismic networks of Regional Research Laboratory, Jorhat, and Gauhati University. The entire northeast India has been divided into three tectonic units based on geological, tectonics and seismic considerations. These are (1) Indo-Burma tectonic unit (2) Eastern Himalaya tectonic unit and (3) The tectonic unit covering Shillong plateau, Mikir hills massif and adjacent areas. By applying statistical test to the available data, three active regions and four quiet regions have been identified in northeast India. Statistical tests also show that the epicentral distribution of micro and macro earth-quakes of northeast India is not homogeneous. Three clustering activity areas have been identified in this region. The study of strain release characteristics of earth-quakes of the northeast India as a whole indicate a linear pattern of strain generation. Strain accumulation and relaxation curve of the region show that accumulated strain is maximum in and around Shillong plateau and also along the Kopili lineament. The accumulated strain, if released instantaneously, may give rise to an earthquake of magnitude...