SCEC Award Number 11027 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Fragile Geologic Features in New Zealand: Improved Age Constraints, and Post Earthquake Reconnaissance
Name Organization
Mark Stirling GNS Science (New Zealand)
Other Participants Dylan Rood
SCEC Priorities B2, B4, B6 SCEC Groups GMP, SHRA, EFP
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
Our SCEC funded efforts in the year 2011 have been threefold. The first focussed on gaining age control for PBRs in temperate (non-desert) environments. The case study PBR Clyde-6 is located less than 5km from the Dunstan Fault, a major active reverse fault. Samples collected from a vertical profile of Clyde-6 have been used to interpret the rate of exhumation and thus an age for the PBR. The results suggest that the age at which the rock was exhumed and free to topple is ~40 ka. In other words PBRs in non-desert environments may be of similar age to their desert counterparts.

Our second activity was a visit to the epicentral area of the devastating M6.2, February 22 2011 Christchurch New Zealand earthquake to examine damaged and undamaged FGFs formed in hard volcanic rock. Strong motion records show the earthquake to have produced rock PGAs of about 1g in the epicentral region. Shag Rock, a sea-stack FGF in the epicentral region of the earthquake was intensely damaged, whereas FGFs located about 15km from the epicentral region were undamaged.

Our third activity was attending the SCEC Annual meeting and presented the poster “New age constraints for precarious landforms in New Zealand: A temperate analog for North America” (authors Stirling, Rood, Balco and Zondervan). We also went on a two day fieldtrip to the Solitario Canyon (western) side of Yucca Mountain to visit PBR sites and discuss the progress made and issues encountered during FGF studies for the ExGM project.
Intellectual Merit Our PBR case study stands as a first demonstration of the age of PBRs within temperate (non-desert) environments. The study shows the PBRs may be of similar age to their desert counterparts, despite the commonly-perceived differences in rock weathering between the two environments. This is an important result in the context of using PBRs for constraining seismic hazard models at long return periods, outside of desert environments.
Broader Impacts The project has significantly enhanced the utility of fragile geologic features for testing seismic hazard models. This will produce more reliable seismic hazard maps for the benefit of society.
Exemplary Figure Figure 1. Clyde-6 PBR (left), in which the PBR is in contact with the pedestal at the narrow neck near the top of the overall tor. The red and light-colored markers on the PBR mark the position of sample sites and key geometric nodes used for photogrammetry and DEM development. The Clyde-6 PBR is located less than 5km from the Dunstan Fault (right), a major active reverse fault and the focus of seismic hazard studies for a large dam safety review.