The Earthquake Engineering Online Archive

Analysis of local variations in free field seismic ground motion

Chen, Jian-Chu; Lysmer, John; Seed, H. Bolton

UCB/EERC-81/03, Earthquake Engineering Research Center, University of California, Berkeley, 1981-01, 281 pages (450/C478/1981)

It is generally assumed that near-surface motions consist only of vertically propagating waves. To test the validity of this assumption for engineering design, nearsurface motions produced by horizontally propagating waves were theoretically investigated. The motions investigated include inclined P-, SV-, and SH-waves, Rayleigh waves, and Love waves in horizontally layered sites over a viscoelastic halfspace. The research involved five phases: (1) review of current knowledge, (2) development of a new method of site response analysis, (3) application to site response analysis, (4) application to soil-structure interaction analysis, and (5) evaluation of the relative importance of horizontally propagating waves in engineering design. The new method of site response analysis involves a finite element-type discretization of the site in the vertical direction which is essentially linear and works in the frequency domain. Nonlinearities are handled by an equivalent linear method. Transient motions are handled by Fourier techniques. The method is essentially the same for inclined body waves and surface waves. The procedures have been implemented in two computer codes, SITE and LOVE. These codes can produce the complete transient field of motion based on knowledge of the motion at a certain point and the type of wave field producing the motion. The procedure has been applied to a number of sites (rock, sand, and alluvium) assuming different types of wave fields; the motions produced by these fields are then compared with those produced by vertically propagating waves. Examples of soil-structure interaction analyses are provided for a structure on rock, a structure on sand, and a large retaining wall on an alluvial site.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-81-03.pdf (14 MB)