A comparison of the 2017 USGS South America seismic hazard model with the Global Seismic Hazard Assessment Program (GSHAP) model and the 2010 USGS preliminary model was made to see how the models differ. The comparisons were made as ratios of PGA at 10% probability of exceedance in 50 years. Ratio maps of each comparison are included as a geo-referenced tiff (GeoTIFF).
Seismic hazard curves were determined using the USGS seismic hazard model for South America. The curves represent the annual rate of exceedance versus peak horizontal acceleration or horizontal spectral response acceleration for 0.2- or 1.0-second periods, for a grid of points with a spacing of 0.1 degrees in latitude and longitude. The hazard curves were used to prepare maps and gridded data that portray peak horizontal acceleration and horizontal spectral response acceleration for 0.2- and 1.0-second periods with a 2%, 10%, and 50% probability of exceedance in 50 years, and a uniform site condition (Vs30) of 760 m/sec. MMI maps for 2%, 10%, and 50% probability of exceedance in 50 years were derived from PGA...
Based on the USGS probabilistic seismic hazard model for South America, earthquake ground motion "design" maps were prepared, using the same procedures used to prepare seismic design maps for the U.S. and its territorries. The design maps for the U.S. and its territories have been adopted by U.S. building codes and consist of two parts: 1) Risk-targeted maximum considered earthquake (MCER) spectral acceleration maps at periods of 0.2 and 1.0 seconds, and 2) maximum considered earthquake geometric mean (MCEG) PGA maps. Both types of maps are derived in accordance with the site_specific ground motion procedures of the NEHRP Recommended Seismic Provisions for New Buildings and Other Structures (BSSC, 2015) and...
Disaggregation of the seismic hazard for peak ground acceleration having a 2 percent probability of exceedance in 50 years is given for several major cities in South America. These disaggregation plots and reports show the relative contribution of individual sources to the seismic hazard (aggregated by magnitude and distance).
The 2017 USGS South American seismic hazard model is based on: a uniform seismicity catalog, a smoothed (gridded) seismicity model, a subduction model, crustal fault model, and ground motion models that are described below. These models are combined to account for ground shaking from earthquakes on known faults as well as earthquakes on faults not included in the model.
These maps and data portray the spatial potential for damaging ground shaking quantified as slight (MMI ≥ VI), moderate (MMI ≥ VII), and considerable (MMI ≥ VIII) in 100 years. The maps and data are based on the average of the results obtained from pga and 1.0-second horizontal spectral acceleration. Site specific soil factors based on Vs30 shear wave velocities were implemented using a simple topographic proxy technique (Allen and Wald, 2009). Allen, T.A. and Wald, D.J. 2009,. On the use of high-resolution topographic data as a proxy for seismic site conditions (VS30), Bulletin of the Seismological Society of America 99, 935-943.
The probabilistic hazard models are used in conjunction with the USGS Prompt Assessment of Global Earthquakes for Response (PAGER) empirical vulnerability relationships (Jaiswal and Wald, 2010, 2011) to calculate seismic risk. The vulnerability relationships are country specific and were used to estimate fatalities and economic losses from earthquake ground shaking. These relationships are highly approximate and are a proxy approach to quantifying earthquake losses. Accuracy can vary by an order of magnitude for places that lack empirical loss data. Jaiswal, K. S., and Wald, D.J., 2010, An empirical model for global earthquake fatality estimation, Earthquake Spectra 26, 1017-1037. Jaiswal, K. S., and Wald,...
