Historical and future seismicity near Jaitapur, India

Although India has a long written record, the shaking intensity of few damaging earthquakes that occurred before AD 1800, can be quantified. Since reliable estimates of future shaking near planned nuclear power plants depend on the extrapolation of historical earthquake data spanning many centuries, estimates of seismic risk to the planned Jaitapur nuclear power plant assessed from a short dataset of only the past few centuries, may not, therefore, represent the true risk to the plant. Nuclear power stations can be engineered to withstand a high degree of shaking intensity, although the expense of the design increases with the severity and duration of the anticipated shaking. There is, therefore, significant interest in estimating the highest possible accelerations to be anticipated near Jaitapur, the proposed site of India’s largest 9900 MW nuclear power plant on the west coast (16°35′N, 73°20′E). Jaitapur, however, has no record of local seismicity in the past century, although several M ~ 3 events cluster towards the Koyna seismogenic area over 100 km to the northnorthwest. Specifically no earthquakes of M > 4.5 have occurred here since 1900, and definitely none since 1985 when good-quality local recordings became available. However, moderate earthquakes such as the M 6.4 Koyna earthquake of 1967 at distances <30 km and large ones at distances >100 km can also produce significant shaking. Indeed, Jaitapur has frequently experienced intensity VII shaking from such earthquakes. This level of shaking can be easily accommodated by most nuclear power plants, but a consideration of the tectonic setting of earthquakes in India suggests that Jaitapur lies in a similar setting to Latur and Koyna where earthquakes of Mw ≈ 6.5 have occurred within the past half century, resulting in local accelerations exceeding intensity VIII. Such an earthquake in the close vicinity of Jaitapur may not occur for many thousands of years, but although unlikely, it could occur within the lifetime of the nuclear power plant.