S-PHASE WAVE PROPAGATION THROUGH MISSISSIPPI EMBAYMENT SEDIMENTS

CHIU, S.C., LANGSTON, C.A.; WITHERS, M.; CERI, The University of Memphis, Memphis, TN 38152, USA, scchiu@memphis.edu.

S body waves from microearthquakes in the New Madrid Seismic Zone (NMSZ) are investigated at selected broadband station sites to understand wave propagation through the Mississippi embayment sediments. Earthquake body waveforms display distinctive features that constrain the nature of the body wave local site response and wave propagation within the unconsolidated Mississippi embayment sediments. S-wave resonance effects may infer near-site conditions. Site resonance effects change between individual receivers because of velocity heterogeneity. Travel times of observed S-phases such as S, Sp, and SsShs (the first S-wave reverberation) can be used to estimate the average S-wave slowness and Poisson's ratio within the embayment sediments. An average Poisson's ratio in the range of 0.34 to 0.45 is obtained for selected sites within the central NMSZ. Use of well log data in wave calculations shows that 1-D heterogeneity can be the first-order influence on seismic wave propagation within the Mississippi embayment sediments.