Developments in studies of earthquake risk
Following recent developments in geophysics, analyses of earthquake risk should take full account of the tectonic setting of the regions concerned, of variations in soil properties, and of source characteristics of the earthquakes. New theories of global tectonics differentiate among various types of geophysically active areas. In particular. New Zealand's environment is closer to that of Japan and other west Pacific countries than to that of California, which is tectonically one of the least typical parts of the Pacific margin. The limitation of Californian earthquakes to depths in the upper crust, and their often established close lineations along surface traces of geological faults have resulted in the development of a refined process of quantitative risk analysis there, the techniques of which may not be appropriate in other areas. Small scale variations in soil characteristics cause variations in earthquake response which are often more significant in the evaluation of earthquake risk than regional differences in seismicity. Recent developments in seismic source theory show that a single parameter such as magnitude is not adequate to define source characteristics closely. With the additional determination of seismic moment, source parameters such as fault radius, fault displacement and stress drop can all be estimated. These source parameters define the expected shape of the source spectra, and thus the frequency characteristics of earthquakes that may be expected in different parts of an active area such as New Zealand.
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Copyright (c) 1975 R. D. Adams
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