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Likelihood Phase

Graphic representing earthquake probability

Schematic representation, using a Russian roulette analogy, of the 100 year conditional probability of rupture of the Wellington-Hutt Valley segment of the Wellington Fault. Results from It’s Our Fault research indicate that the chance of having a large (magnitude ~7.5) Wellington Fault earthquake is significantly lower than previously thought – about a 10% chance of rupture in the next 100 years (B), compared to pre-It’s Our Fault estimates of 30% (A) (Rhoades & others 2011; Rhoades & others 2010).

At the outset of the It’s Our Fault programme we suspected that Wellington’s reputation for “being overdue for the Big One” was overstated, and so we went about examining this proposition. Initial work aimed at addressing this focused on:

  • Geological investigations to better explain past earthquakes on the region’s major fault lines;
  • Global Positioning System (GPS) studies to understand the movement of the large tectonic plates under Wellington;
  • Computer modelling of the complex forces that affect the different faults in central New Zealand.

 The timing of any earthquake is a matter of probability – it could happen tomorrow. But the latest results from this research indicate the chance of having a large (magnitude ~7.5) Wellington Fault earthquake is significantly lower than previously thought. This is because the interval between large Wellington Fault earthquakes appears to be longer, the most recent rupture of the fault is younger, and the 1855 AD earthquake on the Wairarapa Fault de-stressed the Wellington Fault. This is an important shift in our understanding. Given these results, then more frequent, moderate-sized local earthquakes (magnitude 6.0–7.0), or larger distant earthquakes, may be more important in terms of planning and preparedness than infrequent large local events.

A brochure outlining the results of these earlier phases of work can be viewed here.

There are a number of publications (including journal articles, conference abstracts, progress reports and task completion reports) that document the research undertaken within the Likelihood Phase of It’s Our Fault. Click here to access the publications listed below.

PUBLICATIONS LIST

Project Overview

  • Van Dissen & others. 2009. It’s Our Fault: Better Defining the Earthquake Risk in Wellington - Results to Date & a Look to the Future. (Conference abstract).
  • Van Dissen & others. 2010. It’s Our Fault: better defining earthquake risk in Wellington. (Conference abstract).

Geological Investigations

Wellington Fault overview

  • Begg & others. 2008. Wellington Fault: Neotectonics and Earthquake Geology of the Wellington-Hutt Valley Segment. (Field trip guide).

Wellington Fault paleoearthquake characterisation

  • Langridge & others. 2009. It’s Our Fault – Wellington Fault Paleo-Earthquake Investigations: Final Report. (Task completion report).
  • Langridge & others. 2011. Five Thousand Years of Surface Ruptures on the Wellington Fault, New Zealand: Implications for Recurrence and Fault Segmentation. (Journal article).

Wellington Fault single-event displacement characterisation

  • Little & others. 2010. Coseismic strike slip at a point during the last four earthquakes on the Wellington fault near Wellington, New Zealand. (Journal article).

Wellington Fault slip-rate characterisation

  • Ninis & others. 2010. The Wellington Fault - Holocene displacements and slip rates at Emerald Hill, Wellington, New Zealand: Progress Report. (Progress report).
  • Ninis & others. 2013. Slip Rate on the Wellington Fault, New Zealand, during the Late Quaternary: Evidence for Variable Slip during the Holocene. (Journal article).

Wairarapa Fault overview

  • Little & others. 2008. Southern Wairarapa Fault and Wharekauhau Thrust (Palliser Bay). (Field trip guide).

Wairarapa Fault paleoearthquake characterisation

  • Little & others. 2009. Late Holocene surface ruptures on the southern Wairarapa fault, New Zealand: Link between earthquakes and the uplifting of beach ridges on a rocky coast. (Journal article).

Wairarapa Fault slip-rate characterisation

  • Carne & others. 2011. Using displaced river terraces to determine Late Quaternary slip rate for the central Wairarapa Fault at Waiohine River, New Zealand. (Journal article).
  • Villamor & others. 2008. It’s Our Fault – Wairarapa Fault Slip Rate Investigations Task: Completion Report – Is the Wairarapa Fault slip rate decreasing to the north? (Task completion report).

Wharekauhau Fault overview

  • Schermer & others. 2009. Quaternary deformation along the Wharekauhau fault system, North Island, New Zealand: Implications for an unstable linkage between active strike-slip and thrust faults. (Journal article).

Ohariu Fault paleoearthquake characterisation

  • Litchfield & others. 2010. Post c. 300 year rupture of the Ohariu Fault in Ohariu Valley, New Zealand. (Journal article).
  • Litchfield & others. 2010. It’s Our Fault – Ohariu Fault Paleoearthquake Investigations: Final Report. (Task completion report).

Detailed mapping offshore Cook Strait faults

  • Barnes & others. 2008. Structure and paleoearthquake records of active submarine faults, Cook Strait, New Zealand: Implications for fault interactions, stress loading, and seismic hazard. (Task completion report).
  • Barnes and Pondard 2010. Derivation of direct on-fault submarine paleoearthquake records from high-resolution seismic reflection profiles: Wairau Fault, New Zealand. (Journal article).
  • Pondard and Barnes 2010. Structure and paleoearthquake records of active submarine faults, Cook Strait, New Zealand: Implications for fault interactions, stress loading, and seismic hazard. (Journal article).

Past Subduction Zone ruptures

  • Cochran, U.A.; Litchfield, N.J.; Clark, K.J.; Ries, W.; Villamor, P.; Howarth, J.; Watson, C.; Strong, D. 2015. Improved Age Control for a Fourteenth Century Earthquake and Tsunami from Okupe Lagoon, Kapiti Island, GNS Science Report 2015/28. 83 p
  • Clark & others. 2011. Investigating subduction earthquake geology along the southern Hikurangi margin using palaeoenvironmental histories of intertidal inlets. (Journal article).
  • Hayward & others. 2011. Ecological distribution of the foraminifera in a tidal lagoon–brackish lake, New Zealand, and its Holocene origins. (Journal article).
  • Wilson and Cochran 2008. It’s Our Fault – Past Subduction Zone Ruptures: Task Progress Report 2007-08. (Progress report).

Wellington Geodetic & GPS Studies

  • Beavan and Wallace 2008. It’s Our Fault – Wellington geodetic studies task completion report – Fault coupling results from inversion of new and reprocessed GPS campaign data from the Wellington region. (Task completion report).
  • Wallace & others. 2012. The kinematics of a transition from subduction to strike-slip: An example from the central New Zealand plate boundary. (Journal article).

Synthetic Seismicity Modelling

  • Robinson & others. 2009. t’s Our Fault – Synthetic Seismicity of the Wellington Region: Final Report. (Task completion report).
  • Robinson & others. 2011. Using synthetic seismicity to evaluate seismic hazard in the Wellington region, New Zealand. (Journal article).

Wellington Fault Conditional Probability of Rupture

  • Rhoades & others. 2010. It’s Our Fault: Re-evaluation of Wellington Fault conditional probability of rupture. (Conference abstract).
  • Rhoades & others. 2010. It’s Our Fault – Conditional probability of rupture of the Wellington-Hutt Valley segment of the Wellington Fault. (Task completion report).
  • Rhoades & others. 2011. Re-evaluation of conditional probability of rupture of the Wellington-Hutt Valley segment of the Wellington Fault. (Journal article).

Wairarapa Fault and Ohariu Fault Conditional Probabilities of Rupture

  • Van Dissen & others. 2013. Conditional probability of rupture of the Wairarapa and Ōhariu faults, New Zealand. (Journal article).

Aftershock hazard

  • Christopherson & others. 2013. Sensitivity study of aftershock occurrence for a Wellington Fault earthquake. (Conference abstract).
  • Christopherson & others. 2014. Time-varying and long-term mean aftershock hazard in Wellington. (Conference abstract).
  • Rhoades & others. 2012. It’s Our Fault – Contribution of Wellington Fault rupture aftershocks to long-term earthquake hazard: A Progress Report. (Progress report).

Tsunami Hazard Modelling

  • Mueller & others. 2014. Investigating the effects of earthquake complexity on tsunami inundation hazard in Wellington Harbour. (Task completion report).