Seismic microzonation and assessment of earthquake hazard for the construction sites of sea-based facilities in low seismicity water areas

Abstract

This paper reports the results from a study on earthquake hazard assessment for the northwestern part (until now considered to have been a low seismicity area) of the northern Caspian Sea around Morskoi Ivan-Karaul Island where oil-producing facilities are to be built. This earthquake hazard assessment is based on the traditional approach by analysis and summary of geological and geophysical data (primarily fault tectonics and geophysical fields). Seismic microzonation was carried out by the dynamic method based on the comparison of ground motion spectral amplitudes at a reference site and at other sites in the water area of interest. The basic data were records of aftershocks of teleseismic events made by OBSs. The experiment in dynamic microzonation turned out to be unique, in the sense that it was conducted in very shallow water (1–5 m), where the level of seismic noise is affected, not only by currents, but also by sea waves. We stress the importance of seismic monitoring during the operation period of the oil-gas facilities to provide checks on the technological process and to ensure the ecological safety of the environment.