Volcanic and seismic hazards at a proposed nuclear power site in central Java

A nuclear power plant site has been proposed near the base of Mount Muria, a long-dormant volcano in Indonesia. Over a period of eight years the volcanic and seismic hazards were investigated, first by the contractor and later by a joint team of Indonesian geologists and consultants to the International Atomic Energy Agency. In order to assess the risk posed by a large volcano for which there is no record of historical eruptions, it was necessary to determine the age of the last activity by geological and geochronological means and to deduce from this whether the volcano posed a credible risk. Similarly, because there was no adequate record of seismic activity, the seismic hazards were investigated mainly by geological, geomorphological, and geophysical methods that identified and characterized potential seismogenic sources related to the volcano or tectonic movements (i.e. active/capable faults). Muria Volcano has not erupted since about two thousand years ago, but the last activity was sufficiently recent to rule out any assumption that the volcano is extinct. Detailed studies indicated that the proposed site may be vulnerable to the effects of air-borne tephra, pyroclastic flows and surges, debris flows, lahars, and opening of new vents. A more serious factor, however, was the poor geotechnical properties of the foundation material that required a careful analysis of the seismic hazards. Although the project was suspended, the study proved useful, because it provided an opportunity to develop procedures and techniques that could be applied in similar studies elsewhere.