NEHRP Clearinghouse

Title
Resonance Zones on the Surface of a Dipping Layer Due to Plane SH Seismic Input.
File
PB80107907.pdf
Author(s)
Wojcik, G. L.
Source
National Science Foundation, Washington, DC. Engineering and Applied Science., January 1979, 99 p.
Abstract
This is an analytical study of the local effects of lateral geologic inhomogeneity on surface ground motion during earthquakes. The model is a surface dipping layer overlaying a halfspace, with plane SH waves incident from the halfspace in the downdip direction. Surface motion over the layer is calculated for transient (time domain) and harmonic (frequency domain) inputs. In the frequency domain constructive interference on the surface produces a standing wave pattern with spatial zones of resonance where translational motion is on the order of 6-15 times that if the dipping layer were not present. Rotational motion is amplified to a greater extent, on the order of 20-50 times, and relative motion between spatially separated points, on the order of 10-20 times. The amplification mechanism is total reflection of multiple reflected plane waves between the free surface and halfspace. In the time domain a transient input is converted to a series of transients on the surface. Depending on the natural frequency and location of the layer, structural or instrument response to a transient input is amplified to the same degree that surface motion is amplified in the frequency domain. An extension of the analysis, suitable for Love wave excitation, is described. Applications include seismic zonation, critical facility siting, building rehabilitation and ground failure.
Keywords
Dynamic response; Ground motion; Earthquake engineering; Love waves; Earthquakes; Plane waves; Time domain; Earth movements; Frequency domain; Mathematical models; Seismic waves