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Surface Seismic Refraction/Reflection Measurement Determinations of Potential Site Resonances and the Areal Uniformity of NEHRP Site Class D in Memphis, Tennessee (2003)

Williams, R. A. ; Wood, S. ; Stephenson, W. J. ; [et al.]

Sage Publications

In: Earthquake Spectra. 2003; 19(1): 159-189. Published 2003 Feb 01. doi: 10.1193/1.1543161.

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Publication Date: 2003-02-01

Description: We determined S-wave velocities (Vs) to about 40-m depth at 65 locations in the Memphis-Shelby County, Tennessee, area. The Vs measurements were made using high-resolution seismic refraction and reflection methods on the ground surface. We find a clear difference in the Vs profiles between sites located on the Mississippi River flood plain and those located to the east, mostly covered by loess, in the urban areas of Memphis. The average Vs to 30-m depth at 19 sites on the modern Mississippi River floodplain averages 197 m/s (±15 m/s) and places 17 of these sites at the low end of NEHRP soil profile category type D (average Vs 180-360 m/s). The two remaining sites are type E. Vs to 30-m depth at 46 sites in the urban areas east of the modern floodplain are more variable and generally higher than the floodplain sites, averaging about 262 m/s (±45 m/s), still within category D. We often observed the base of the loess as a prominent S-wave reflection and as an increase in Vs to about 500 m/s. Based on the two-way travel time of this reflection, during an earthquake the impedance boundary at the loess base may generate resonances in the 3- to 6-Hz range over many areas of Memphis. Amplitude spectra from four local earthquakes recorded at one site located on loess indicate consistent resonance peaks in the 4.5- to 6.5-Hz range.

Print ISSN: 8755-2930

Electronic ISSN: 1944-8201

Topics: Architecture, Civil Engineering, Surveying , Geosciences

Published by Sage Publications on behalf of Earthquake Engineering Research Institute.

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The Influence of the Coastal Plain Sedimentary Wedge on Strong Ground Motions from the 1886 Charleston, South Carolina, Earthquake (1990)

Chapman, M. C. ; Bollinger, G. A. ; Sibol, M. S. ; [et al.]

Sage Publications

In: Earthquake Spectra. 1990; 6(4): 617-640. Published 1990 Nov 01. doi: 10.1193/1.1585589.

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Publication Date: 1990-11-01

Description: The effect of Atlantic Coastal Plain sediments on ground motion from the 1886 Charleston, South Carolina, earthquake was studied using linear regression analysis and ground motion modeling. Statistical tests applied to 264 Modified Mercalli intensity reports at epicentral distances less than 400 km showed that intensities within the Lower Coastal Plain (near the coast) averaged from 0.5 to 1.0 units less than intensities within other areas over comparable distances. Simulated ground acceleration time histories were generated along two profiles: one trending northeast from the epicenter along the coast and another trending northwest toward the Fall Line. The modeling results (which assume linear behavior) indicate that the thick coastal sediments attenuate high frequency motions (〉3-10 Hz), while amplifying lower frequency motions. In contrast, locations on thinner sediments to the northwest experience amplification of high frequency motions. The overall effect is that peak acceleration decays more slowly with distance in the thinning sediments to the northwest of the epicenter than in the thick sediments along the coast.

Print ISSN: 8755-2930

Electronic ISSN: 1944-8201

Topics: Architecture, Civil Engineering, Surveying , Geosciences

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Surface Seismic Measurements of Near-Surface P- and S-Wave Seismic Velocities at Earthquake Recording Stations, Seattle, Washington (1999)

Williams, Robert A. ; Stephenson, William J. ; Frankel, Arthur D. ; [et al.]

Sage Publications

In: Earthquake Spectra. 1999; 15(3): 565-584. Published 1999 Aug 01. doi: 10.1193/1.1586059.

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Publication Date: 1999-08-01

Description: We measured P- and S-wave seismic velocities to about 40-m depth using seismic-refraction/reflection data on the ground surface at 13 sites in the Seattle, Washington, urban area, where portable digital seismographs recently recorded earthquakes. Sites with the lowest measured Vs correlate with highest ground motion amplification. These sites, such as at Harbor Island and in the Duwamish River industrial area (DRIA) south of the Kingdome, have an average Vs in the upper 30 m (V¯s30) of 150 to 170 m/s. These values of V¯s30 place these sites in soil profile type E (V¯s30 〈 180 m/s). A “rock” site, located at Seward Park on Tertiary sedimentary deposits, has a V¯s30 of 433 m/s, which is soil type C (V¯s30: 360 to 760 m/s). The Seward Park site V¯s30 is about equal to, or up to 200 m/s slower than sites that were located on till or glacial outwash. High-amplitude P- and S-wave seismic reflections at several locations appear to correspond to strong resonances observed in earthquake spectra. An S-wave reflector at the Kingdome at about 17 to 22 m depth probably causes strong 2-Hz resonance that is observed in the earthquake data near the Kingdome.

Print ISSN: 8755-2930

Electronic ISSN: 1944-8201

Topics: Architecture, Civil Engineering, Surveying , Geosciences

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