NSHM: Alaska 2007

NOTE: This model is preliminary and for review purposes only. It is intended for use with an updated USGS earthquake hazards codebase: nshmp-haz. It is currently under review and does NOT represent an official release or product. For official release products please see the USGS Earthquake Hazards website.

For details on the format of this U.S. Geological Survey (USGS) National Seismic Hazard Model (NSHM), see the nshmp-haz wiki.

See also the 2007 USGS Alaska Earthquake Hazard Maps & Data.

Implementation Details

Notable implementation details (in fortran source and inputs) that set Alaska 2007 apart from later COUS models and this updated nshmp-haz implementation of the Alaska model:

• Grid and slab optimization tables use discretization of 2km out to 200km.
  • nshmp-haz: discretization = 1km
• Grid and slab sources use the Wells & Coppersmith (1994) magnitude-length scaling relation.
  • nshmp-haz: slab sources use Youngs et al. (1997) (aka 'geomatrix'; consistent with 2014 COUS NSHM)
• Grid and slab sources randomize strike at M≥6.
  • nshmp-haz: uses point-source distance corrections for M≥6 (in relations above; consistent with 2014 COUS NSHM)
• Ground motion models do not impose one-sided 3σ upper truncation on exceedances.
  • nshmp-haz: no change
• Other details:
  • nshmp-haz: grid source maxDepth = 15 km
• Focal mechansim variations are encoded into coefficients supplied with each input file; flavors for strike-slip and mixed strike-slip/reverse were ported from the 2002 COUS model.
  • nshmp-haz: point sources generate focal mechanism specific ruptures with appropriate rake that are processed independently, consistent with 2014 COUS NSHM
• Aleatory uncertainty was added in the 2002 COUS model and was carried over here as a moment-balanced Gaussian distribution on mMax of M±0.15 discretized over 5 values with σ=0.12. The 2008 COUS model increased the width of the distribution to M±2σ and increased the discretization to 11 values. Both implementations require custom code; the more recent approach is more straightforward with the distribution a function of σ.
  • nshmp-haz: uses more recent (11-point; ±2σ) aleatory uncertainty model
• Hazard curves are not truncated at 3σ.
  • nshmp-haz: no change

Other Notes

• Consistent with 2008 and 2014 COUS models, slab and grid Gutenberg-Richter MFD magnitudes bins are centered on 0.05; interface MFD bins are centered on 0.1.