Abstract
New Zealand?s tectonic setting, astride an obliquely convergent tectonic boundary, means that it has experienced many large earthquakes in its 200-year written historical records. The task of identifying and studying the largest early instrumental and pre-instrumental earthquakes, as well as identifying the smaller events, is being actively pursued in order to reduce gaps in knowledge and to ensure as complete and comprehensive a catalogue as is possible. The task of quantifying historical earthquake locations and magnitudes is made difficult by several factors. These include the range of possible earthquake focal depths, and the sparse, temporally- and spatially-variable historical population distribution which affects the availability of felt intensity information, and hence, the completeness levels of the catalogue. This paper overviews the procedures and tools used in the analysis, parameterisation, and recording of historical New Zealand earthquakes, with examples from recently studied historical events. In particular, the 1855 M 8+ Wairarapa earthquake is discussed, as well as its importance for the eminent 19th century British geologist, Sir Charles Lyell, and for future global understanding of the connection between large earthquakes and sudden uplift, tilting and faulting on a regional scale.
Highlights
New Zealand’s tectonic setting, astride the obliquely convergent tectonic boundary between the Pacific and Australian plates, means that it experiences a high rate of small to moderate earthquakes, many large earthquakes and occasionally, great earthquakes
Beneath the North Island and Northern South Island, the Pacific Plate descends beneath the Australian Plate, the maximum depth of earthquakes generally
Over 300 active faults, exhibiting a range of rupture styles and characteristics, many capable of producing large to great earthquakes, have been identified throughout the country
Summary
New Zealand’s tectonic setting, astride the obliquely convergent tectonic boundary between the Pacific and Australian plates, means that it experiences a high rate of small to moderate earthquakes, many large earthquakes and occasionally, great earthquakes (figs. 1 and 2a,b). The subduction interfaces in the North and South of the country are considered capable of large earthquakes, no large events have been unequivocally identified along the Hikurangi margin in the historical record. The records of historical earthquakes, landslides, tsunami and volcanic events play important roles in the development of the probabilistic. The recent move to introduce time dependence into probabilistic seismic hazard models means that the record of large shallow earthquakes becomes even more important. There is a paucity of data on the effects of strong shaking on the modern built environment, and on «lifelines» (water, gas, electricity distribution systems, road and rail systems, etc.) in major population centres This makes the development of robust relationships between wellconstrained earthquake parameters (magnitude, location, depth and mechanism), intensity of shaking, and engineering parameters difficult. The 1855 earthquake is of importance as New Zealand’s largest historical earthquake, and, it is of international interest because of its significance for the eminent British geologist of the 19th century, Sir Charles Lyell
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