Worldwide Seismic Design Values - Documentation & Help
Motivation for this tool
The USGS has received numerous requests for SS and S1 values at sites around the world, not just in the U.S. and its Territories. The Worldwide Seismic Design Values tool collects published SS and S1 values from local, regional, and global studies and makes them available from one tool.
The SS and S1 values provided by this tool should be consistent with those from a local study. Nonetheless, the design values in this tool never supersede those in the governing building code or from a site-specific analysis.
The seismic design procedures of local or national building codes might require design parameters other than SS and S1. The user is responsible for knowing what seismic design parameters are required by the applicable building code.
Help using the tool
The user interface of the Worldwide Seismic Design Values tool is a Google Map. A user can pan and zoom the map, like any other Google Map, either by using the pan and zoom controls, by dragging the map, or by double-clicking on a location. If the red "location marker" is no longer visible after panning or zooming, the location marker automatically moves to the center of the new viewport.
Shaded red boxes indicate regional, gridded datasets. The Global Seismic Hazard Assessment Program data are not indicated by a red box as they cover most locations of the globe.
SS and S1 values are available in an information window by querying the map in several ways:
- Pins with gray stems and red, ball tops indicate data at particular locations. Click on a pin to view the information window.
- The "location marker" is a large red arrow and can be moved to any location on the map. Drag the marker to the location of interest and drop it to show the information window.
- A latitude and longitude pair can be entered in the search box at the top of the map. Latitudes should be in the range -90 to 90 decimal degrees, with negative values for the Southern Hemisphere. Longitudes should be in the range -180 to 180 decimal degrees, with negative values for the Western Hemisphere. The location marker will move to the latitude and longitude entered, and the information window will appear.
- An address or partial address (for example, city or ZIP code) can be entered at the top of the map instead of a coordinate. Click on the link "Enter Address Instead," and an address input box will replace the coordinate input boxes. The location marker will move to the address entered, and the information window will appear. For a partial address, Google Maps finds a single point consistent with the partial address, and the Worldwide Seismic Design Values tool reports the SS and S1 values at that single point. The user can switch back to the coordinate input boxes by clicking "Enter Lat and Lon Instead."
- The user's computer can provide its approximate location. In the address input bar, select "Geolocate Me." The location marker will move to the approximate location, and the information window will appear.
Each information window shows SS and S1 values at the selected location from all available datasets.
Error message: "No point data exists for this location" - There is no dataset covering the selected site. This is most likely to occur in ocean areas and near the poles, where even GSHAP data are unavailable.
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Sources of SS and S1 values
|Region||Dataset||Grid spacing (deg)||Number of locations||Notes|
|Worldwide||Global Seismic Hazard Assessment Program, adjusted using Unified Facilities Criteria methodology||0.1||5,369,091||These data are not an exact copy of the GSHAP database. The USGS
convertedt the 10% probability of exceedance in 50 years PGA values provided
by GSHAP to SS and S1 by:
|Worldwide||Global Seismic Hazard Assessment Program, adjusted using Eurocode 8 methodology as refined by Lubkowski (2010)||0.1||5,369,091||These data are not an exact copy of the GSHAP database. The USGS converted the 10% probability of exceedance in 50 years PGA values provided by GSHAP to SS and S1 by using the Eurocode 8 methodology as refined in: Lubkowski, Z.A., 2010. “Deriving the Seismic Action for Alternative Return Periods According to Eurocode 8”|
|Worldwide||GS of Canada Open File 5814||NA||173||The SS and S1 values are reproduced from Table 7 of the GSC OF 5814 report. At sites in Canada, the GSC based the SS and S1 values on the 2005 National Building Code of Canada. At sites in the U.S., the GSC used SS and S1 values from the 2009/06 International Building Code. At sites outside Canada and the U.S., the GSC estimated SS and S1 values from the Global Seismic Hazard Assessment Program.|
|Outside the U.S. & its Territories||UFC 3-310-01, Change 2||NA||441||The SS and S1 values reported here are reproduced from Tables D-2 and E-1 of Unified Facilities Criteria 3-310-01, Change 2. The data are not provided on a regular grid but rather given at selected locations outside the U.S. and its Territories. The SS and S1 values may have been approximated from peak ground acceleration values with a 10% probability of exceedance in 50 years, as described in the Approximate SS and S1 Values Section below.|
|Haiti||2010 USGS OFR 1067||0.05||24,341||The USGS derived SS and S1 values following the procedure defined in the 2009/06 International Building Code. Each SS and S1 value is the minimum of probabilistic and deterministic hazard values.|
|Afghanistan||2007 USGS OFR 1137||0.1||34,881||The SS and S1 values are spectral accelerations with a 2% probability of exceedance in 50 years. The USGS has not calculated deterministic values in this region, which would be used according to the International Building Code procedure to cap these probabilistic values.|
|Southeast Asia||2007 USGS Administrative Report||0.1||66,581||
Approximate SS and S1 values
Some datasets provide peak ground acceleration (PGA) values with a 10% probability of exceedance in 50 years. For the Global Seismic Hazard Assessment Program dataset and some sites in the Unified Facilities Criteria dataset, the Worldwide Seismic Design Values tool provides approximate SS and S1 values derived from PGA values. This tool uses the following approximations. PGA values with a 2%-in-50-year exceedance are approximately twice the PGA values with a 10%-in-50-year exceedance. The SS value is 2.5 times the 2%-in-50-year PGA value, and the S1 value is roughly equivalent to the 2%-in-50-year PGA value. Thus, SS is approximately 5.0 times the 10%-in-50-year PGA, and S1 is approximately 2.0 times the 10%-in-50-year PGA.
Multiple SS and S1 values
At many sites around the world, SS and S1 values are available from several datasets. The Worldwide Seismic Design Values tool reports SS and S1 values from all available datasets in an unordered list. The dataset listing in the information window does not imply preference for one dataset over another. Also, the variability (or consistency) in SS and S1 values is not equivalent to the uncertainty in the SS and S1 value at a site. Some datasets adopt values from existing studies. In this case, at least two datasets will have the same SS and S1 values in the information window, but these are not independent reports of the design values.
If there are multiple SS and S1 values available at the site of interest, the user should choose the most appropriate source of information for the design project. The user might consider choosing the dataset that is the most specific to the site. For example, the USGS performed a seismic hazard analysis specifically for Afghanistan, but the Global Seismic Hazard Assessment Program dataset also covers the country. The SS and S1 values from the USGS dataset would be more specific to sites in Afghanistan than the values from the GSHAP dataset. Similarly, if two or more country-specific datasets overlap (for example, near an international border), the SS and S1 values from the dataset associated with the country where the project will be built would be more specific to the site than any dataset associated with another country.
The Global Seismic Hazard Assessment Program dataset is the primary source used for unpopulated areas (as well as many populated areas). Though this dataset does not cover the entire world, it does cover a significant portion of it.
Example gridded dataset (black dots) and the four types of requested locations (red dots).
If a user selects a location with one or more underlying datasets on a grid, the application uses a bilinear interpolation method to return the SS and S1 values associated with the location from each gridded dataset. A selected location falls into one of four categories (labeled in the figure at right):
- Exact Grid Point (P1). The requested location is at a grid point in the underlying dataset. The application returns the exact SS and S1 values at the grid point in the dataset.
- Between Two Longitudes (P2). The requested location shares a latitude in the gridded dataset, but the location is between two gridded longitude values. The application returns SS and S1 values linearly interpolated between the two gridded points with the same latitude on either side of the location.
- Between Two Latitudes (P3). The requested location shares a longitude in the gridded dataset, but the location is between two gridded latitude values. The application returns SS and S1 values linearly interpolated between the two gridded points with the same longitude on either side of the location.
- Bounded by Four Grid Points (P4). The requested location is inside an imaginary box defined by four grid points in the dataset. The application performs a bilinear interpolation. First the SS and S1values are linearly interpolated between the northern pair of grid points and between the southern pair. Then these interpolated values are again interpolated to find the SS and S1 values at the requested latitude.
- Add data from:
- Canada (GS of Canada Open File 5813)
- New Zealand (NZ Standard 1170.5:2004)
- Mexico (2008 Manual of Civil Structures)
- Add batch-mode functionality
- Indicate the precision of SS and S1 values in the information window