Abstract
Heuristic approach is made to derive the seismic directivity for short-waves. Since seismic wavelengths for engineering concerns are very short, such waves are inevitable to be distorted due to heterogeneities near the source region. The excitation of the short-waves is also controlled by the small-scale fault irregularities such as fault patches, asperities and harriers.Unilateral rupture along fault length L is considered. Fault patches are uniformly distributed on the fault with a number density of m per unit area. Since the fracture of fault patches is assumed to be random, the energy of short-waves would be additive. The maximum amplitude of short-waves is, therefore, expected to be amax=[mL2r2/Td]1/2F(K) where r2is a narrow-band average energy from one fault patch and Td is rupture time over fault length L as Td=L/c[c/v-cosθ] K corresponds to the number of peaks and troughs of the wave train considered, mL2, and F(K)=[lnK2/2π-lnlnK2/2π]1/2 The theory predicts seismic directivity for short-wave amplitudes as (c/v-cosθ)-1/2 whereas (c/v-cosθ)-1 is known for long-waves. Our previous result suggests that r2 is related to L, so that amax would increase in proportion to L.
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Schedule a callMore From: Zisin (Journal of the Seismological Society of Japan. 2nd ser.)
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