Abstract:

The geological effects of the 1855 Wairarapa New Zealand earthquake with an estimated magnitude of Mw 8.2–8.4 provided Charles Lyell with direct evidence of the relationship between earthquakes, fault rupturing, regional uplift and subsidence. The scientific importance of the earthquake is that it was the breakthrough event that led to the first recognition of active fault tectonics and therefore changed the course of geological thinking and understanding. Following the observations by Darwin of coastal uplift during the 1835 Chilean earthquake, the 1855 event in New Zealand also provided further crucial evidence for the Uniformitarian principle promulgated by Lyell in that geological features of the landscape could be explained as the cumulative sum of small incremental changes rather than cataclysmic events involving much larger amounts of crustal movement, thus laying the foundations for future understanding of regional seismotectonics and geomorphological changes accompanying an earthquake. Details of the effects of the 1855 earthquake derived from Lyell's unpublished notes and correspondence and the inferences he made from them are presented and discussed. Comparison is made with the results of subsequent work that, although in broad agreement with Lyell's account, also indicate greater localized uplift, less subsidence, variable vertical displacement along ‘Lyell's' fault, the nature of the fault contact and horizontal displacement on the fault.

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