EFFECTS OF SEDIMENTARY LAYERSON DIRECTIVITY PULSE AND FLING STEP

摘要

Effects of sedimentary layers on the long-period directivity pulse and the fling step are investigatedusing the theoretical method developed by Hisada and Bielak [1]. First, basic physics of the directivitypulses and the fling step are investigated using a simple strike-slip fault model in a homogeneous halfspace.Next, the method is applied to the strong motion recorded at the Lucerne valley during the 1992Landers earthquake, using the fault model and the local layered structure model by Wald and Heaton [2].It was confirmed that the maximum amplitude of the velocity and displacement was inclined to the faultplane at 30 – 50 degree due to the combined effect of the long-period pulse and the fling. The inclusion ofsedimentary layers increases greatly both amplitudes and durations of the directivity pulses, whereas itdoes not affect those of the slip pulses. This is because the directivity pulses are the body and surfacewaves excited in the sedimentary layers from wide range of faults (the nearest fault to the furthest fault),whereas the fling steps are generated by the slip of the nearest surface fault.