Energy flow in shallow depth based on vertical array records during recent strong earthquakes (supplement)

Based on subsurface wave energy flows calculated in the previous paper for strong motion records at 30 vertical array sites by assuming vertical propagation of SH waves, upward energy ratios between layers have been correlated to corresponding impedance ratios. This indicates that the upward energy tends to decrease almost in proportion to the power of 0.70 of the impedance ratio from deep-seated stiff rock (equivalent to seismological bedrock) to soft soil near ground surface. The upward energies at the seismological bedrock have been estimated from the observed energy at the deepest level for all vertical array sites by using this relationship and plotted versus hypocentral distances.

► Upward energy ratios between layers are correlated to corresponding impedance ratios α. ► Upward energy Eu decreases in proportion to the power of 0.70 of α. ► Possible to evaluate the energy in shallow layers from the energy at seismological bedrock. ► Eu at seismological bedrock is estimated from the energies at vertical array base layers.