Application of the ESI 2007 scale to two large earthquakes: South Island, New Zealand (2010 mw7.1), and Tohoku, Japan (2011 mw9.0)

Abstract

Application of the ESI 2007 Scale is implemented by compilation of reports and quantification of the surface effects on the geological environment (i.e., length and width of ground fractures, width of lateral spreading, diameter of mud/ sand/gravel boils) during two recent large earthquakes: South Island, New Zealand (3 September 2010 Mw7.1, referred to here as the New Zealand earthquake [NZE]) and Tohoku, Japan (11 March 2011 Mw9.0, referred to here as the Japan earthquake [JPE]). These two earthquakes occurred on different types of faults and in different geological and tectonic settings: the NPE was oblique to the Alpine fault, a strike-slip fault segment that is part of the tectonics between the Australian and Pacific plates that involves compressional regime and dextral component of motion, and the JPE occurred along the subduction zone between the Pacific and Okhotsk plates at the latitude of the Japan trench. From secondary information mined from various sources (including reports of reconnaissance campaigns, published papers, satellite imagery and photographs, and local reports from the affected areas), a database was compiled containing surface environmental effects of the two earthquakes to determine intensity levels and to construct preliminary isoseismal maps. In the case of NZE, intensities reached degree XI and reports were concentrated in the surroundings of the Christchurch district, whereas, in the case of JPE, reports were distributed along the Tohoku and Kanto regions in northeastern Honshu and intensities reached degree XII. The isoseismal maps constructed based solely on the environmental effects are a good complement to other estimates of intensity for both earthquakes.