Journal article
Strong proximal earthquakes revealed by cosmogenic 3He dating of prehistoric rockfalls, Christchurch, New Zealand
BH Mackey, MC Quigley
Geology | Published : 2014
DOI: 10.1130/G36149.1
Abstract
The 2011 rupture of previously undetected blind faults beneath Christchurch, New Zealand, in moment magnitude (Mw) 6.2 and 6.0 earthquakes triggered major rockfalls that caused fatalities and infrastructure damage. Here we use field, geospatial, seismologic, numerical modeling, and cosmogenic 3He data to provide first evidence for prehistoric rockfall ca. 8-6 ka, and a possible preceding event ca. 14-13 ka, at a site where extensive rockfall occurred in the Christchurch earthquakes. The long (~7 ± 1 k.y.) time intervals between successive rockfall events and the high peak ground velocity thresholds required for rockfall initiation at this site (~20-30 cm/s) preclude earthquakes from major id..
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Funding Acknowledgements
This research was funded by a Rutherford Foundation Postdoctoral Fellowship to Mackey. The NZ Earthquake Commission provided financial support. We thank K. Farley and the California Institute of Technology Noble Gas Lab for <SUP>3</SUP>He analysis. B. Bradley provided peak ground velocity data and insightful commentary. Constructive criticisms from S. Stacey, S. Brocklehurst, and T. Stahl improved the manuscript. G. Stock, M. Stirling, and an anonymous reviewer provided insightful reviews of an earlier version of this manuscript. We thank the residents of Rapaki for access to the site, and L. Vick for modern rockfall data. Plots in Figure 3 were made from the Camelplot.m code written by Greg Balco.