Abstract
AbstractAmethod for decomposing anSH-wave at the surface into the instantaneous power of shearing strain associated with rays in a homogeneous half space as a function of lapse timetand depth time τ, which is the travel time for the depth direction, is demonstrated. The instantaneous power in the (t, τ) space shows local maxima at the intersections of up-coming and down-going rays, which correspond to the velocity boundaries of the real layered structure beneath the site. Thus, the proposed method provides a tool for estimating the velocity boundaries of real layered structure from only surface recordings. The estimated results obtained by applying the proposed method to strong-motion data recorded at two Kanto sediment sites are in good agreement with the velocity boundaries previously determined by means of down-hole methods.
Highlights
IntroductionThis nonstationarity is due to the nonstationarity of the fault rupture process itself emitting seismic waves and due to modulation effects that occur along the propagation paths, which generate various transient phases
The instantaneous power is represented as a function of lapse time t and depth time τ, which is defined as the travel time of the wave associated with a ray, from the surface in the depth direction
This means that the surface recordings are decomposed into the intrinsic seismic waves associated with rays in terms of the instantaneous power in the (t, τ ) space, which is demonstrated as nonstationary ray decomposition
Summary
This nonstationarity is due to the nonstationarity of the fault rupture process itself emitting seismic waves and due to modulation effects that occur along the propagation paths, which generate various transient phases This limits the application of Fourier analysis and second-order stationary time series analyses, such as correlation or spectral analyses, to seismic signals. The instantaneous power is represented as a function of lapse time t and depth time τ , which is defined as the travel time of the wave associated with a ray, from the surface in the depth direction This (t, τ )-type nonstationary representation of instantaneous power for a multi-layered structure is calculated in terms of the Wigner-Ville distribution (Claasen and Mecklenbrauker, 1980a), and the (t, τ )-type representation is estimated for a homogeneous half space using seismograms recorded at the surface. Despite the ray decomposition into the homogeneous half space, this nonstationary
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