Changes in hot spring temperature and hydrogeology of the Alpine fault hanging wall, New Zealand, induced by distal South Island earthquakes

S. C. Cox (Corresponding Author), C. D. Menzies, R. Sutherland, P. H. Denys, C. Chamberlain, D. A. H. Teagle

Research output: Contribution to journalArticlepeer-review

68 Citations (Scopus)
13 Downloads (Pure)

Abstract

Thermal springs in the Southern Alps, New Zealand, originate through penetration of fluids into a thermal anomaly generated by rapid uplift and exhumation on the Alpine Fault. Copland hot spring (43.629S, 169.946E) is one of the most vigorously flowing, hottest of the springs, discharging strongly effervescent CO2‐rich 56–58°C water at 6 ± 1 l sec−1. Shaking from the Mw7.8 Dusky Sound (Fiordland) 2009 and Mw7.1 Darfield (Canterbury) 2010 earthquakes, 350 and 180 km from the spring, respectively, resulted in a characteristic approximately 1°C delayed cooling over 5 days. A decrease in conductivity and increase in pH were measured following the Mw7.1 Darfield earthquake. Earthquake‐induced decreases in Cl, Li, B, Na, K, Sr and Ba concentrations and an increase in SO4 concentration reflect higher proportions of shallow‐circulating meteoric fluid mixing in the subsurface. Shaking at amplitudes of approximately 0.5% g Peak Ground Acceleration (PGA) and/or 0.05–0.10 MPa dynamic stress influences Copland hot spring temperature, which did not respond during the Mw6.3 Christchurch 2011 aftershock or other minor earthquakes. Such thresholds should be exceeded every 1–10 years in the central Southern Alps. The characteristic cooling response at low shaking intensities (MM III–IV) and seismic energy densities (approximately 10−1 J m−3) from intermediate‐field distances was independent of variations in spectral frequency, without the need for post‐seismic recovery. Observed temperature and fluid chemistry responses are inferred to reflect subtle changes in the fracture permeability of schist mountains adjacent to the spring. Permanent 10−7–10−6 strains recorded by cGPS reflect opening or generation of fractures, allowing greater quantities of relatively cool near‐surface groundwater to mix with upwelling hot water. Active deformation, tectonic and topographic stress in the Alpine Fault hanging wall, where orographic rainfall, uplift and erosion are extreme, make the Southern Alps hydrothermal system particularly susceptible to earthquake‐induced transient permeability.
Original languageEnglish
Pages (from-to)216-239
Number of pages24
JournalGeoFluids
Volume15
Issue number1-2
Early online date19 Sept 2014
DOIs
Publication statusPublished - Feb 2015

Bibliographical note

Samples from the Westland National Park were collected under Department of Conservation permit WC‐22994‐GEO. This project was funded under GNS Science's ‘Impacts of Global Plate Tectonics in and around New Zealand Programme’ (PGST Contract C05X0203). Geochemical analyses were funded by a Natural Environmental Research Council‐CASE PhD studentship award NE/G524160/1 to CDM (GNS Science CASE Partner) and NERC grants NE/H012842/1, NE/J024449/1 and IP‐1187‐0510 to DAHT. We acknowledge the New Zealand GeoNet project and its sponsors EQC, GNS Science and LINZ, as well as the late John Beavan, for providing data used in this study. We wish to thank our colleagues John Townend, Jim Cousins, John Haines, Carolin Boese, Rachael James, Dave Craw, Delia Strong and Agnes Reyes for discussions and helpful comments, although not necessarily implying they agree with all of our interpretations and conclusions.

Keywords

  • Copland hot spring
  • earthquake
  • fluid flow
  • orogenic geothermal systems
  • permeability change
  • Welcome Flat

Fingerprint

Dive into the research topics of 'Changes in hot spring temperature and hydrogeology of the Alpine fault hanging wall, New Zealand, induced by distal South Island earthquakes'. Together they form a unique fingerprint.

Cite this