The 2008 USGS Seismic Hazard Model for the Conterminous U.S.


The 2008 national seismic hazard model for conterminous U.S. is described in detail by Petersen et al. (2008). This model is an update of previous work (Frankel et al., 1996; Frankel et al., 2002). Here we describe the OpenQuake-engine implementation of the 2008 model.

To reproduce earthquake activity in various tectonic settings, the seismic source model employs two main source typologies: gridded seismicity and fault sources. Gridded seismicity is used to model spatially variable seismicity (obtained through a smoothed seismicity approach) as well as zones of uniform seismicity. Fault sources are instead used to model shallow crustal faults and large subduction interface faults.
The full source model can be divided into a number of sub-models:

  • Western U.S. active shallow crust gridded seismicity
  • Western U.S. subduction intraslab (deep) gridded seismicity
  • Western U.S. crustal faults
  • Cascadia subduction interface faults
  • Central and eastern U.S. stable continental crust gridded seismicity
  • Central and eastern U.S. faults
  • Charleston gridded seismicity model

Gridded seismicity models are implemented as collections of point sources (following the NRML pointSource definition). For shallow seismicity (in both western and eastern U.S.) the hypocentral depth is fixed at 7.5 km and the seismogenic layer is assumed to extend from 0 to 15 km. Deep (subduction intraslab) seismicity is instead associated to an hypocentral depth equal to 50.0 km with a seismogenic layer extending from 50 to 100 km. In case a model defines uncertain rupture strikes, ruptures in a point source are distributed over multiple strike angles, otherwise a single strike is defined. Depending on the model, ruptures can be vertical (strike-slip) or inclined (dip angle assumed equal to 50 degrees).

Shallow crustal faults are implemented as simple fault sources (NRML simpleFaultSource) or as characteristic fault sources with simple geometry (NRML characteristicFaultSource (with simple geometry)). Large subduction interface events are instead implemented as complex fault sources (NRML complexFaultSource) or as characteristic fault sources with complex geometry (NRML characteristicFaultSource (with complex geometry)).

The map below depicts the annual occurrence rate per source (between minimum and maximum magnitudes) for the different source models included in the hazard model. Click the show map layers icon to view different source models and base layer maps.

operating instructions

Various functions are available as part of the map.

mouse/touch operation
  • moving by grabbing the map with a mouse-click you can move the map around
  • overview map using the + button in the bottom right of the map you can expand an overview map
  • zooming in and out using the + and - buttons in the top left of the map you can obtain more or less detail in the map
  • switching themes or maps clicking on the ≡ icon on the right-hand side of the map you can view and select available maps and themes
  • retrieving information the map may contain elements that contain more information, by clicking these a popup will show this information
  • fullscreen display using the ✈ button the map can be maximized to fullscreen display, use the ✕ button to return to page display.
keyboard operation

Keyboard operation becomes available after activating the map using the tab key (the map will show a focus indicator ring).

  • moving using the arrow keys you can move the map
  • overview map using the + button in the bottom right of the map you can expand an overview map
  • zooming in and out using the + and - buttons in the top left of the map or by using the + and - keys you can obtain more or less detail in the map
  • switching themes or maps clicking on the ≡ icon on the right-hand side of the map you can view and select available maps and themes
  • retrieving information the map may contain elements that contain more information, using the i key you can activate a cursor that may be moved using the arrow keys, pressing the enter will execute an information retrieval. press the i or the escape key to return to navigation mode
  • fullscreen display using the ✈ button the map can be maximized to fullscreen display, use the ✕ button to return to page display.

It's possible that some of the functions or buttons describe above have been disabled by the page author or the administrator

 

Total occurrence rate
(number of events / year)
  • < 1e-6
  • 1e-6 - 1e-5
  • 1e-5 - 1e-4
  • 1e-4 - 1e-3
  • 1e-3 - 1e-2
  • 1e-2 - 1e-1
  • 1e-1 - 1
  • 1 - 10
  • >= 10







The ground motion model distinguishes between four main tectonic regions:

  • Active Shallow Crust (western U.S.)
  • Stable Continental Crust (eastern U.S.)
  • Subduction Interface (Cascadia)
  • Subduction Intraslab (northern California and Oregon/Washington)

For each tectonic region, various GMPEs are used to account for epistemic uncertainties. For each tectonic region, the model considers multiple ground motion prediction equations organized in a logic tree structure.

Active Shallow Crust Weight
Boore and Atkinson 2008 0.333
Campbell and Bozorgnia 2008 0.333
Chiou and Youngs 2008 0.333
Subduction Interface Weight
Zhao et. al. 2006 0.5
Atkinson and Boore 2003 0.25
Youngs et. al. 1997 0.25

Reference site condition

The NEHRP B/C site condition is assumed to be the reference site conditions for the 2008 U.S. national seismic hazard model. This is equivalent to a Vs30 (shear wave velocity in the uppermost 30 meters) = 760 m/s. Almost all GMPEs utilized in the western U.S. accept Vs30 as prediction variable. The remaining GMPEs are used with coefficients already calibrated for the B/C site conditions.

Comparison against USGS-NSHMP results

We present here a number of comparisons between the hazard results (e.g. hazard maps/curves) provided by the United States Geological Survey - National Seismic Hazard Mapping Project (USGS-NSHMP) and by the OpenQuake-engine implementation.

To properly judge the comparison it is worth noticing that the current the OpenQuake-engine implementation of the 2008 U.S. model does not reproduce exactly all the features as defined in the original model. In particular, the current implementation does not include the cluster model for the New Madrid zone (only the unclustered model is implemented) nor epistemic uncertainties on GMPE median ground motion values for shallow crustal sources in the western US. Moreover differences may arise because of the different ways earthquake ruptures are modeled in the two software used for the calculations.

The maps below represent hazard maps for PGA (10% in 50 years) as computed by the USGS-NSHMP and by the the OpenQuake-engine.
The visual comparison reveals an overall agreement. The difference map below shows in a more quantitative way the differences between the two maps.
The figures below represent comparisons of hazard curves for a number of selected sites in western and central U.S.

  • Ellsworth, W., 2003, Appendix D—Magnitude and area data for strike slip earthquakes, in Working Group on California Earthquake Probabilities, Earthquake probabilities in the San Francisco Bay region—2002–2031: U.S. Geological Survey Open-File Report 03–214, 6 p. Report
  • Frankel, A.D., Petersen, M.D., Mueller, C.S., Haller, K.M., Wheeler, R.L., Leyendecker, E.V., Wesson, R.L., Harmsen, S.C., Cramer, C.H., Perkins, D.M., Rukstales, K.S. (2002). Documentation for the 2002 update of the National Seismic Hazard Maps: U.S. Geological Survey Open-File Report 2002–420, 39 p. Report
  • Frankel, A., Mueller, C., Barnhard, T., Perkins, D., Leyendecker, E., Dickman, N., Hanson, S., and Hopper, M., (1996). National Seismic Hazard Maps—Documentation June 1996: U.S. Geological Survey Open-File Report 96–532, 110 p Report
  • Hanks, T.C., and Bakun, W.H., 2002, A bilinear source-scaling model for M–log A observations of continental earthquakes: Bulletin of the Seismological Society of America, v. 92, p. 1841–1846. Journal Article
  • Petersen, M.D., A.D. Frankel, S.C. Harmsen, C.S. Mueller, K.M. Haller, R.L. Wheeler, R.L. Wesson, Y. Zeng, O.S. Boyd, D.M. Perkins, N. Luco, E.H. Field, C.J. Wills, and K.S. Rukstales (2008). Documentation for the 2008 Update of the United States National Seismic Hazard Maps. U.S. Geological Survey, Open-File Report 2008–1128.Report
  • Wells, D.L., and Coppersmith, K.J., 1994, New empirical relationships among magnitude, rupture length, rupture width, and surface displacements: Bulletin of the Seismological Society of America, v. 84, p. 974–1002. Journal Website

This table summarises the main characteristics of the original implementation of this model

1 Datasets availability
1.1 Earthquake catalogue Available here
1.2 Geological database Faults database here
1.3 Strong-motion database Not available
1.4 Site characterization database Not available
Notes
2 Methodology for model development
2.1 Scientific participation (SSHAC levels) and review process Level 3
2.2 Documentation describing model preparation Petersen et al., 2008
2.3 Codes used for model preparation Availablehere
Notes
3 PSHA input model
3.1 Seismic Source Model
3.1.1 Area sources Included (background)
3.1.2 Grid sources Included
3.1.3 Crustal faults Included
3.1.4 Subduction faults Included (Cascadia subduction zone)
3.1.5 Non-parametric ruptures Not included
3.1.6 Magnitude-area scaling relationships Ellsworth (2003), Hanks and Bakun (2002), Wells and Coppersmith (1994)
3.2 Ground Motion Model
3.2.0 Tectonic regionalisation Included
3.2.1 Models for active shallow seismicity Included
3.2.2 Models for subduction interface Included (Cascadia subduction zone)
3.2.3 Models for subduction intraslab Included (Cascadia subduction zone)
3.2.4 Models for stable continental regions Included
3.2.5 Models for deep non-subduction sources Included
3.2.6 Models for volcanic areas Not included
3.3 Site Response Model
3.3.1 Based on GMPEs Yes, hazard is computed for a reference soil condition corresponding to NEHRP B/C boundary (Vs30=760 m/s)
3.3.2 Based on site-response analysis Not included
3.4 Epistemic uncertainties
3.4.1 Seismic Source Model Included
3.4.2 Ground Motion Model Included using a logic tree (see the ground motion model section)
3.4.3 Site Response Model Not included
Notes
4 Hazard Input Description
4.1 Hazard input document Not available
4.2 Input files Availablehere
Notes
5 Calculation
5.1 Software Suite of Fortran and C codes
5.2 Results
5.2.1 Hazard curves Available for a grid of geographic pointshere
5.2.2 Hazard maps Available for a grid of geographic pointshere
5.2.3 Uniform hazard spectra Not considered
5.2.4 Disaggregation Not considered
5.2.5 Stochastic event sets Not considered
5.2.6 Ground motion fields Not considered
Notes

The OpenQuake-engine input model (NRML format) can be downloaded at the link provided below - Please read the license and disclaimer attached to the model.

N.B. This is a model adapted by GEM to the OpenQuake-engine from the original model developed by the USGS. This explains minor differences you might encounter between the results presented in the OpenQuake platform and those disseminated by the original Organisation.

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  • usgs2008_intro.txt
  • Last modified: 2016/10/07 09:31
  • by Armando Scarpati