Methods for Calculation of Ground Response During Strong Earthquakes

Since the 1920s, seismologists have been developing quantitative methods to assess the influence of local site conditions on the parameters of ground motion. This chapter analyzes the current state of knowledge in this field, describes physical mechanisms of local site effects and the situations in which they appear. Linear transformations of seismic waves in subsurface soils, such as, amplification of the waves in the upper softer layers, resonant phenomena and topographic effects have been intensively studied in recent decades and are now quite well understood and taken into account in practice of engineering seismology. Significant progress was also made in studying the nonlinear response of subsurface soils. Seismic observations indicate that during strong earthquakes, significant distortions occur in the waveforms and spectra of seismic waves propagating in soil layers. Seismic waves travel from the earthquake sources tens to hundreds kilometers in dense materials of the Earth’s crust and only meters in soils, but often the soils mostly determine parameters of motion on the surface. In Russia and abroad, nonlinear soil behavior during strong ground motion has been studied in laboratory and field experiments. This chapter provides an overview of these studies, describes numerical methods for calculating soil response and the results of testing various methods on earthquake records in situ. Two-and three-dimensional methods are usually the extensions of the corresponding one-dimensional methods.