SeisRisk III

This is an older version of the hazard software. It was used for earlier versions (pre-1996) of the hazard maps. It was not used for the 1996 or newer hazard maps.

• SeisRisk III (47.6 MB)
• SeisRisk III (modified by R. LaForge, February 1996) (62 kB)

Background Information

Seisrisk III is the last published version of a series of programs used to produce probabilistic earthquake ground motion hazard maps for the United States from 1972 to 1992. Though it has been superseded in the US Geological Survey by a more flexible program allowing for sources based on smoothing of historical seismicity, Seisrisk III is still being used as a teaching tool in academia and for hazard mapping in other countries. In the past decade, Seisrisk III has been used for hazard mapping in Italy, Turkey, Iran, in the Mediterranean countries as a whole, and in the West Indies, for example.

Because of this continuing interest, we are continuing to host the source code and references to publications on the structure and the use of Seisrisk III, including auxiliary programs for the construction of input. However, except for answering a few helpful questions, we are no longer providing support or advice for users. We are also hosting a set of program modifications to Seisrisk III written by a colleague in the Bureau of Reclamation. We are aware that other modifications exist, for instance, one version adapted to use intensity and its uncertainties instead of parametric ground motions, and another adapted to use non-circular isoseismals for point sources. These can be found by diligent search of the internet.

Known Issues

We are aware of some known issues with the software however we have no plans to fix any of the following or other issues:

• A “bug fix” exists that has not yet been incorporated in any published version of SEISRISK III. This fix is to ensure a proper interpolation for values which involve the “last box” in the ground-motion annual-rate accumulators. This bug does not usually cause a problem, because most users scale the ground motions such that the interpolation primarily is taking place in the lower range of accumulator boxes.
• A “loose end” exists in subroutine inside. The subroutine has a trap which does not permit a calculation when a site point lies too close to a quadrilateral corner point. When such a point is discovered in the course of a run, the run is terminated. If this happens, it is easy to adjust the “equator” by a very slight amount, thus moving the site point away from the corner point. Because rather a good deal of calculation can go past before such a site is discovered by the program, it would be desirable to permit the program to continue rather than terminate. We have not worked on a version to do this, because we encounter the problem rather infrequently in our usage. However, users with complex sources or small site-grid spacing may find the simple adjustment merely induces a failure at a different site.