Accuracy of determination of epicenter and origin time of small-magnitude earthquakes in the Indian subcontinent

Abstract

World seismicity maps prepared by plotting epicenters without considering their magnitude and the distribution of seismic stations may not represent true seismicity, since many earthquakes of small magnitude are not reported from regions having poor seismic networks. This situation is particularly noticeable in the Asian parts of the Alpide belt. Using the Monte Carlo method, errors of epicenter location and origin-time determination by the Indian network of seismic stations have been estimated for earthquakes in the Indian subcontinent. A simplified earth model has been used, and the calculations have been carried out for m_b values of 5.0, 4.5, and 4.0. The results are compared with similar error estimations for the Romanian region where a better network of seismic stations enables location of all earthquakes of m_b ≧ 4.2. This comparison shows that the errors for the central and the south Indian regions are comparable to those of Romania. However, the much larger errors in the north and northeastern regions show the necessity of establishing seismological observatories equipped with sensitive seismographs close to the foothills of the Himalayas.