Soil amplification maps for estimating earthquake ground motions in the Central US

Bauer, Robert A.; Kiefer, John D.; Hester, Norm

doi:10.1016/s0013-7952(01)00045-x

Cited by 23 publications

(26 citation statements)

References 6 publications

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“…The amplification factors for NEHRP site classifications in that document are given in Table 1-6 and Table 1-7. The USGS PSHA maps and the preliminary PSHA maps that incorporate site effects are presented on a quadrangle scale, with the contour interval corresponding to the criteria set for the seismic hazard levels defined in the proposed LRFD guidelines and thus illustrate the impact of the criteria on the spatial distribution of hazard for both 1 Hz and 5 Hz ( We create the following summary maps and tables by applying the proposed LRFD guidelines criteria to the results, which takes the maximum of the seismic hazard level at 1 Hz or 5 Hz: With most of the counties in Indiana having NEHRP Class D or Class E NEHRP classification [Bauer et al, 2001], there is a great impact in applying the amplification factors in the recommended LRFD guidelines even if the only information known is that provided in the USGS 2002 maps. This can be seen by comparing the seismic hazard levels from the USGS 2002 map (Figure 1-43) with the USGS 2002 map with Class D site effects (Figure 1-44).…”

Section: Resultsmentioning

confidence: 99%

“…These future maps will provide information at the level necessary for planning and budgeting, though site specific studies will still be needed for engineering. Average velocity of all S-wave measurements made in the surficial material type found at grid point (from [Bauer et al, 2001] and this report) or velocity from Table 1-2.…”

Section: Discussionmentioning

confidence: 99%

“…Map symbol and description refer to the mapped units from [Gray, 1989]. Values assigned for specific gravity were taken from [Rockaway, 1997].. 1-14 Table 1-2 Indiana surface bedrock units [Gray, 1989] and assigned surficial shear wave velocity values for similar Illinois bedrock units [Bauer et al, 2001] Table 1-4 Data used to determine column shear wave velocity averaged by unit type from borehole velocity measurements. Map symbol and description refer to the mapped units from [Gray, 1989].…”

Section: Methodsmentioning

confidence: 99%

“…Each grid point is assigned the average shear wave velocity from Table 1-1 for the geologic material within which the grid point falls. Shear wave velocities for grid points where bedrock is mapped at the surface are taken from values compiled for similar Illinois bedrock units [Bauer et al, 2001] (Table 1-2).…”

Section: Geologic Datamentioning

confidence: 99%

“…More recent studies have attempted to provide more detailed soil amplification classifications for the central U.S. These are described by [Bauer et al, 2001] and [Street et al, 2001]. A new methodology has been developed to incorporate soil profile site effects into the probabilistic calculation Cramer et al, 2003].…”

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An Analysis of Seismic Hazards in Indiana

Haase¹,

Nowack²,

Park³

et al. 2004

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Prepared in cooperation with the Indiana Department of Transportation and Federal Highway Administration. AbstractCurrent USGS probabilistic seismic hazard estimates (Frankel et al., 2002) show a higher seismic hazard in southwestern Indiana than for the rest of the state. This is expected based on past work documenting large pre-historic events in the Wabash Valley, and also based on isoseismal levels of shaking from the New Madrid 1811-1812 earthquakes. When assessing the hazard on a county by county basis, the local soil conditions produce amplification of shaking in regions with soft or unconsolidated sediments relative to firm-rock sites. We have reproduced the probabilistic seismic hazard calculation following the USGS methodology for the state of Indiana and provided details for the shaking level on each county of the state. Here we compare the 1996 and 2002 versions of the seismic hazard maps Frankel et al., 2002]. We also compare the results with an assumed maximum magnitude for the New Madrid earthquake of 7.3. This produces significantly lower acceleration levels. The USGS probabilistic maps were constructed assuming firmrock sites. Versions of the maps were produced assuming other NEHRP classification levels, however no information was provided specific to the state of Indiana that suggests which site classification is appropriate for a given location. More recent studies have attempted to provide more detailed soil amplification classifications for the central U.S. These are described by [Bauer et al., 2001] and [Street et al., 2001]. A new methodology has been developed to incorporate soil profile site effects into the probabilistic calculation Cramer et al., 2003]. We demonstrate the usefulness of this approach by applying it to a low resolution near-surface velocity model based on a limited amount of soil profile data in Indiana, and we report on the relative amplification and deamplification expected given the available data. The results show particular regions of amplification on the order of 2 or greater for both the 1 Hz and the 5 Hz spectral acceleration with 2% probability of being exceeded in 50 years, between the standard NEHRP B/C site and the probabilistic site effect calculation. For the 1 Hz maps, this occurs in the central and central northern part of the state including the Indianapolis metropolitan area, where the surficial units of glacial tills are particularly thick because of the sediments that both fill the bedrock Teays Valley and that overlie it in thickness up to 1,370 meters. Lower amplitudes are noted for much of the south central part of the state because bedrock crops out or is present near the surface. These results are useful because they give a first order estimate that illustrates the potential effect of geology. They are demonstration maps that lack the detailed data required for practical use, but serve as a proof-of-concept for the probabilistic site effect methodology. Even with these approximate maps it is clear that there is a significant variation in the numb...

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Geologic Datamentioning

confidence: 99%

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