Abstract:
The Alpine Fault is the largest fault-line in New Zealand, spanning the entire length of the South Island, and recent studies have estimated a mean earthquake recurrence interval of 291 ± 23 yr, based on recorded historic earthquake activity in a variety of different locations. These studies, however, each have limitations preventing the complete accuracy of earthquake age estimates. International studies like Forti & Postpischl (1986) in Mexico and Postpischl et al. (1991) in Italy have shown that stalagmites in caves have the potential to record historic earthquake events either through the change of drip point location or how the stalagmite sits. The Hollywood 1 stalagmite collected from North Westland, New Zealand has identifiable physical growth direction changes that align with estimated earthquake events recorded by past studies over the past 4000 years. Chemical variations down the length of the stalagmite were also identified as potential indicators of earthquake activity under the postulation that the seismic activity could open new pathways through the karst environment, allowing leeching of aquifer, host rock or organic elements. Particular patterns can be observed in the ratios of elements at estimated earthquake boundaries, but no clear pattern could be identified at every single boundary that confirmed with certainty that the chemical variations alone could preserve earthquakes, but once combined with the physical growth direction changes and past research provide certainty of paleo-seismic activity.
