The 2010 National Seismic Hazard Model

The latest version of the National Seismic Hazard Model (NSHM) for New Zealand provides probabilistic estimates of the strength of earthquake shaking that can be expected according to a user-defined time period and probability, e.g. the peak ground acceleration (PGA) that has a 10% of happening in any 50 year time window. Probabilistic Seismic Hazard Analysis (PSHA) uses the location, recurrence behaviour, and predicted ground motions of earthquake sources to estimate the hazard at a site, or across a grid of sites as shown in the map below for Class C (shallow soil) site conditions.

The NSHM is an algorithm that draws upon several component models to calculate its results. It uses a fault model that combines New Zealand’s active fault database, which includes 536 fault sources, and the 170 year historical earthquake catalogue. The background model is comprised of a multi-layered background seismicity grid.

Ground Motion Prediction Equations (GMPEs) are also an important component of the NSHM. The standard GMPE in use in New Zealand outside of the Christchurch region is the McVerry et al. (2006) GMPE. 

The source model files can be downloaded here F501115B.DAT and here NZBCK615.DAT
See below for a list of relevant source model citations.

Fault Source Model (file = F*.DAT)

Rows 1-3: Ignore
Row 4: Abbreviated fault source name and slip type
       rv, rs = reverse
       sr = strike-slip and reverse
       ss = strike-slip
       sn = strike slip and normal 
       nn, ns = normal
       nv = normal-volcanic
       if = subduction interface
Row 5: Number of digital straight-line sections (n) making up the source
Row 6: Dip, dip direction, depth to base, depth to top
Row 7: Endpoints of fault source in degrees and mins, characteristic Mw, and mean/preferred recurrence interval
Rows 8 to (8+n-1): Endpoints of digital straight line sections making up fault source (one row per digital section)
Row 8+n-1: End of fault source delimiter

Background Source Model (File = NZBCK*.txt)

Row 1:

Columns 1-6: Three “subcatalogues”, giving min magnitudes and time periods of completeness; i.e.
4.0 46 = M>4.0 for the time period 1964-2009 inclusive
5.0 24 = M>5.0 for the time period 1940-1963 inclusive
6.5 100 = M>6.5 for the time period 1840-1939 inclusive
Column 7: Magnitude increment (0.1)

Rows 2 to end of file:

Columns 1-3: “Nvalues” for the three subcatalogues above, i.e.
N(M>4 for 46 years) N(M>5 for 24 years) N(M>6.5 for 100 years)
Column 4: b-value
Column 5: Maximum magnitude for point source
Column 6*: Percentage crustal events
Column 7: Slip type (same as fault model, listed above)
Column 8*: Percentage slab events
Column 9*: Percentage interface events
Column 10-12: Latitude, longitude, and depth of point source. Note that the point sources are spaced evenly in lat, lon, and depth, and the N values are defined for a volume that has boundaries equidistant between the point source and the immediate neighbours.

* The values in these columns should sum to 1 (100%).

Seismic hazard pga graphic

This map shows one output of the National Seismic Hazard Model from Stirling et. al. (2012): PGA (units of g) with a 10% probability of exceedance in 50 years on Class C (shallow soil) sites.
























Relevant Citations 

Stirling, M.W.; McVerry, G.H.; Gerstenberger, M.C.; Litchfield, N.J.; Van Dissen, R.J.; Berryman, K.R.; Barnes, P.; Wallace, L.M.; Villamor, P.; Langridge, R.M.; Lamarche, G.; Nodder, S.; Reyners, M.E.; Bradley, B.; Rhoades, D.A.; Smith, W.D.; Nicol, A.; Pettinga, J.; Clark, K.J.; Jacobs, K. 2012 National seismic hazard model for New Zealand : 2010 update. Bulletin of the Seismological Society of America, 102(4): 1514-1542; doi: 10.1785/0120110170

Stirling, M.W.; McVerry, G.H.; Berryman, K.R. 2002. A new seismic hazard model for New Zealand, Bulletin of the Seismological Society of America, 92(5):1878-1903.

McVerry, G.H.; Zhao, J.X.; Abrahamson, N.A.; Somerville, P.G. 2006. New Zealand Acceleration Response Spectrum Attenuation Relations for Crustal and Subduction Zone Earthquakes, Bulletin of the New Zealand Society for Earthquake Engineerng, 39(1): 1-58.
NOTE: A correction was made to the site class term equation (equation 4) this paper. We will make the correction available as soon as possible.