USGS 2023 National Seismic Hazard Model Project (NSHMP) Update: What Have We Observed and Learned?

It was a privilege that the U.S. Geological Survey (USGS) selected Moody’s RMS headquarters in Newark, California, to host their public workshop for the 2023 USGS National Seismic Hazard Model Update, held on May 3-4, 2023.

The purpose of the workshop was for the USGS to present the results of the 2023 National Seismic Hazard Model Project (NSHMP) Update covering the fifty states of the contiguous U.S. and to provide a chance to review the latest hazard results.

The 2023 U.S. 50-State National Seismic Hazard Model - Overview Version 1.1 document running to some 65 pages – and full of new insights, is available here, with results from Version 2 of the document shown at the workshop.

I have to say that hosting the workshop on behalf of the USGS really represented a modest gesture from us, as the USGS National Seismic Hazard Model is such an invaluable resource for Moody’s RMS, as it is for the wider seismology scientific community and practicing engineers.

The two-day workshop provided opportunities for all stakeholders, from several government organizations to private companies, to review the updated hazard results, ask questions, share their experiences, and provide feedback.

It cannot be understated how vital this update to the USGS model, as with previous updates, is to us as an organization. It represents the very latest view of risk and we heavily depend on this model and the insights it provides for updating the Moody’s RMS U.S. Earthquake Model.

2023 National Seismic Hazard Model Project - Preliminary Results

But what did the USGS NSHMP preliminary results show? In its Version 1.1 conclusion, the USGS states that overall the 2023 NSHM provides important new data, models, and methods that improve the hazard characterization and usefulness of the new model.

It acknowledges that changes across the country are generally larger than in previous models because the 2023 NSHM update models and techniques are significantly different from models applied in previous NSHMs.

The USGS also recognizes that it needs to ensure that the new changes are better than previous models or it needs to consider logic trees that allow for a broad range of possibilities.

One major finding is that the 2475-year return period (or the two percent probability of exceedance in 50 years) hazard is increasing by more than 50 percent in many parts of the low seismic hazard region in the central and eastern U.S, particularly in the coastal plains where the new NSHM amplification model is influential.

However, for the western U.S., the changes reveal a mix of both an increase and a reduction of the hazard. Examining more closely, in some areas, changes are driven by the update of the modeling data, while in other areas, the change is due to improvements in hazard calculation methodology.

As a member of the USGS Steering Committee and the Earthquake Rupture Forecast (ERF) Review Panel, I had the opportunity to review the preliminary results of this update before the workshop. But what the workshop gave me was the opportunity to hear comments from the user community.

Since the objective of the update to the NSHM is to ensure the best science is deployed, across the various Scientific Review Panels there were in-depth discussions on the definition of what represents the best available science or the best applicable science for updating the model.

The ERF Review Panel and the Ground-Motion Review Panel both presented an in-depth review of their specific model components, which are likely to be adopted by USGS, based on the USGS guideline.

Overall, the preliminary model update suggests that USGS has made significant updates to the various source and ground-motion components of the model. We are looking forward to seeing the final version of the model updates.

I am curious to see the impact of these NSHM updates on U.S. seismic risk although we are seeing a significant impact on the location-level hazard results at long return periods. In terms of incorporating this latest update, Moody’s RMS has always ensured that its U.S. Earthquake Models are as up-to-date as possible.

From this workshop and the review of the NSHM, as the USGS has made significant updates to the model, to ensure that Moody’s RMS reflects the changes, as with previous updates, it does take significant time and resources for us for incorporating these important updates into our models.  

Thanks again to the USGS for the opportunity to host the workshop at Moody’s RMS, and as always, we will keep our clients and the market informed on the progress of the NSHM updates and subsequent revisions to Moody’s RMS U.S. Earthquake models.

For more information on Moody's RMS U.S. Earthquake models, click here.