MAGNITUDES OF PREHISTORIC EARTHQUAKES FROM A STUDY OF PALEOLIQUEFACTION FEATURES

by

HU KE and SARAH L. GASSMAN, Ph.D.

University of South Carolina

Department of Civil and Environmental Engineering

Columbia, SC 29208

phone: 803-777-8160; fax: 803-777-0670

gassman@engr.sc.edu

 

PRADEEP TALWANI, Ph.D

University of South Carolina

Department of Geological Sciences

Columbia, SC 29208

 

ABSTRACT

The purpose of this work is to assess the ground motions (magnitudes) of prehistoric earthquakes in the South Carolina Coastal Plain and improve the fundamental understanding of the processes leading to liquefaction. Three sites were investigated: Ten Mile Hill north of the Charleston Air Force Base, and Gapway and Sampit in Georgetown county. The work involves three phases: soil profiling, assessment of paleo-acceleration magnitudes, and the effect of underlying clay layers on the amplification of ground motions. The soil profiling is conducted primarily based on the current soil classification methodology using CPT, SPT, and shear wave velocity data assimilated with geotechnical laboratory index properties including relative density and fines content. Then, the paleo-acceleration magnitude is estimated using three different methods currently in use: (1) Seed et al. (1985) method, (2) Ishihara (1985) method and (3) Martin and Clough (1994) method and the results are compared. At last, a parametric study is performed using a two-dimensional equivalent-linear site response analysis program ProShake to evaluate the amplification from underlying clay layers and their contribution to liquefaction events. Preliminary results from this study indicate that these current methodologies agree well in back-calculating the paleo-acceleration magnitude. At both the Gapway and Sampit sites, this study indicates that a peak ground acceleration of 0.2g can induce liquefaction if M=7.5 is assumed and 0.25g if M=6.0 is assumed. At Ten Mill Hill, the peak ground acceleration was found to be 0.22g at M=7.5 and 0.3 g at M=6.0.

 

 

 

This is a student paper.