Near-surface Vs Profiling in the New Madrid Seismic Zone Using Surface-wave Methods

Abstract

Surface-wave tests were performed at eleven sites in Shelby County and Memphis, Tennessee and northeast Arkansas representing soil deposits of differing types and ages to determine near-surface shear-wave velocity (V~) profiles for siteresponse analyses. Active surface-wave tests were conducted using a harmonic source and an irregular linear array of receivers. At two of the eleven sites, a two-dimensional array of receivers was used to record surface waves generated by passive sources including microtremors and cultural noise. Dispersion curves for both types of tests were calculated using frequency-wavenumber methods and were inverted using an algorithm that encourages smoothness of the resulting V~ profile. The surface-wave test results compare well with profiles obtained by other researchers using a variety of methods. We believe that most observed differences are due to the nature of surface-wave propagation and the characteristics of the inversion algorithm. At the Mud Island B site, we obtained a profile to a depth of 170 rn by combining active and passive dispersion data to form a composite dispersion curve. The combination of active and passive data significantly enhances the capabilities of surface-wave test procedures. Finally, the measured V~ profiles were used to calculate linear amplification spectra, which clearly indicate differences in site response between Holocene-and Pleistocene-age deposits.

Local Earthquake Wave Propagation through Mississippi Embayment Sediments, Part I: Body-Wave Phases and Local Site Responses

“…Techniques include use of small-scale seismic reflection and refraction (e.g., Street et al, 2001), small-scale surface wave dispersion (e.g., Romero and Rix, 2001;Rix et al, 2002), and geotechnical cone-penetration tests (e.g., Schneider et al, 2001). These studies uniformly show that shear-wave velocities near the surface are quite low at 150-300 m/sec.…”

Combined active-passive surface wave measurements at five sites in the Western and Southern US

“…In this study, the frequency domain beamforming method (Lacoss et al, 1969;Tokimatsu, 1995;Rix et al, 2002) was employed to obtain Rayleigh wave dispersion curves from measurements of vertical particle motion during testing. This method typically utilizes multiple receivers arranged in a one-dimensional array for active measurements or a two-dimensional array for passive measurements.…”

“…Passive surface waves such as those of microtremors and cultural noise may be utilized as an alternative to overcome this limitation because passive waves typically contain greater energy at low frequencies than most active surface waves. In addition, active and passive measurements may be combined to enable V S profiling to greater depths without sacrificing nearsurface resolution (Rix et al, 2002;Yoon and Rix, 2004;Liu et al, 2005;Park et al, 2005).…”

Geotechnical Reconnaissance of the 2002 Denali Fault, Alaska, Earthquake

“…This is performed using a non-biased numerical approach that iterates toward a constrained least-squares fit between the theoretical and experimental data , Rix et al 2002. The liquefaction assessment of the ground using shear-wave velocity is a process in which the soil capacity to resist liquefaction is compared with the estimated loads put on the soil mass by earthquake shaking.…”