Peak Strong Motion Attenuation Relations for Horizontal and Vertical Ground Displacements

The attenuation of the maximum shear wave for strong ground displacements in large earthquakes (5.4 < M_w < 7.2) in California was studied from a seismological viewpoint. Smooth regression curves of attenuation were statistically fitted to measurements made personally on each seismogram. The curves were computed for two different geological classifications of the recording location (rock or soil), and two different fault mechanisms of the seismic source (strike-slip or reverse-fault). The sample consisted of eight strike-slip and four reverse-fault mechanism earthquakes with 237 soil and 92 rock peak ground displacement measurements.

The peak ground-motion displacements were measured from the S body-wave portion of the seismograms (frequencies between 0.2 and 1 Hz) after discrimination of the seismic wave types. The peak displacement from any surface wave train was not considered in this analysis. An attenuation distance H_slip was used as the distance from the recording station to the location on the fault plane of largest slip. Two sub-samples were formed consisting of the transverse (SH) and vertical (SV) measurements.

The set of ground-displacement attenuation curves predict greater amplitudes at sites classified as soil sites compared to rock sites, and for SH versus SV motion for both types of seismic source mechanisms.