Earthquake-induced transient ground strains from dense seismic networks

Earthquake-induced transient ground strain are evaluated based on the records obtained by two dense seismic networks, namely the Parkway Valley, New Zealand, and the UPSAR, California, arrays. The calculations are based on the spatial interpolation of the recorded displacements and a numerical differentiation to obtain the strain tensor at ground surface. The computed peak ground strains show an important dependence on azimuth, by a factor of about two. Furthermore, the relationship of the peak ground strains as a function of the most common measures of ground motion severity, such as peak ground acceleration, velocity and displacement, is explored. Our results are in reasonable agreement with other published relationships and with some of the few available direct records of strain. However, they point out the limitations of the simplified evaluations used in the engineering practice, which uniquely consider the wave passage effect on the ground strain evaluation, and tend to significantly underestimate the observations