General Concepts and PSHA Background

Abstract

The first step in building the PSHA model is the collection of geological, geophysical, geotechnical and seismological data from published and unpublished documents, theses, and field investigations. These data are integrated to develop a coherent interpretation of a seismotectonic framework for the study region. Its size can vary depending on the purpose. The international practice for a site-specific study is to distinguish between the investigations at a regional, near regional and site vicinity level (e.g. 300 km, 25 km and 5 km radius in IAEA SSG-9, IAEA (2010)). In order to include all features and areas with significant potential contribution to the hazard, it may also be necessary to include information in a radius up to 500 km (e.g. for subduction zones). This framework provides the guiding philosophy for the identification of seismic sources. Furthermore, the framework should address the important issues that each expert expects to influence the identification and characterisation of seismic sources in the region. The main topics to be addressed in the seismotectonic framework include: Use of pre-existing geological structures to provide a basis for defining the present and future seismicity. Tectonic models that are applicable to contemporary processes, the observed seismicity, and are compatible with seismic sources. Spatial distribution of the seismicity in three dimensions, and associated focal mechanisms and their relation to potential seismic sources. Implications of contemporary stresses and strains (e.g. earthquake focal mechanisms, geodetics, other kinematic constraints) for defining sources. Use of historical and instrumental seismicity and seismic source delineation to provide a basis for defining the locations of future earthquake activity.