Near-surface anisotropic structure characterization by Love wave inversion for assessing ground conditions in Urban Areas

Abstract

In many geophysical applications, neglecting of anisotropy is somehow an oversimplification. The mismatch between prediction based on isotropic theory and near-surface seismic observations indicates the need for the inclusion of medium anisotropy. In this paper, surface wave (Love wave) dispersion properties are used to estimate the anisotropic structure of the near-surface layered earth, which is modeled as media possess vertical transverse isotropy (VTI), a reasonable assumption for near-surface sedimentary layers. Our approach utilizes multi-mode surface waves to estimate both the velocity structure and the anisotropy structure. This approach consists of three parts. First, the dispersion analysis is used to extract dispersion curves from real data. Second, the forward modeling is carried out based on the dispersion equation of Love wave in a multi-layered VTI medium. Dispersion curves of multi-modes, which are the numerical solutions of the dispersion equation, are obtained by a graphic-based method. Finally, the very fast simulated annealing (VFSA) algorithm is used to invert velocity structure and anisotropy structure simultaneously. Our approach is verified by the synthetic dispersion curve generated by a VTI medium model. The estimation of shear wave velocity and anisotropy structure of surface wave data acquired at Rentschler Field, an urban center site on sediments in the Connecticut River valley reveals a simple structure of the sediment layer over a bedrock half space. The results are verified by other inversion results based on different data set obtained on the same site. The consistency of inversion results shows the feasibility and efficiency of the approach.

Keywords

Love wave / dispersion / multi-modes / anisotropy / very fast simulated annealing

References

[1] Anderson D. L. Elastic Wave Propagation in Layered Anisotropic Media. Journal of Geophysical Research, 1961, 66(9): 2953-2963.

[2] Anderson D. L. Love Wave Dispersion in Heterogeneous Anisotropic Media. Geophysics, 1962, XXVII(4): 445-454.

[3] Bear L. K., Dickens T. A., Krebs J. R., . Integrated Velocity Model Estimation for Improved Positioning with Anisotropic PSDM. The Leading Edge, 2005, 24: 622-634.

[4] Gassmann F. Elastic Waves through a Packing of Spheres. Geophysics, 1951, 16(4): 673-685.

[5] Haskell N. A. The Dispersion of Surface Waves on Multilayered Media. Bulletin of the Seismological Society of America, 1953, 43: 17-34.

[6] Hayati H. Characterizing Liquefaction Resistance of Aged Sand Deposits: [Dissertation], 2009 South Carolina: Clemson University, 113-118.

[7] Ingber L. Very Fast Simulated Re-Annealing. Mathematical Computer Modelling, 1989, 12(8): 967-973.

[8] Ke G., Dong H., Kristensen A., . Modified Thomson-Haskell Matrix Methods for Surface-Wave Dispersion-Curve Calculation and Their Accelerated Root-Searching Schemes. Bulletin of the Seismological Society of America, 2011, 101(4): 1692-1703.

[9] Layat C., Clement A. C., Pommier G., . Some Technical Aspects of Refraction Seismic Prospecting in the Sahara. Geophysics, 1961, 26(4): 437-446.

[10] Liu L. B., White E., Urin F., . Microtremor Surveys Crossing the Connecticut River Valley. Seismological Society of America Eastern Section Annual Meeting, Boston, 2010

[11] Liu L. B., Chen Q.-F., Wang W. J., . Ambient Noise as the New Source for Urban Engineering Seismology and Earthquake Engineering: A Case Study from Beijing Metropolitan Area. Earthquake Science, 2014, 27(1): 89-100.

[12] Luo Y. H., Xia J. H., Liu J. P., . Joint Inversion of High-Frequency Surface Waves with Fundamental and Higher Modes. Journal of Applied Geophysics, 2007, 62(4): 375-384.

[13] Park C. B., Carnevale M. Multichannel Analysis of Surface Waves (MASW). Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP), Boston, 2014

[14] Schleicher K., Cramer J., Gerrard C., . Model Building for Tilted Transverse Anisotropic Depth Migration of the Crystal, Gulf of Mexico Wide Azimuth Survey. 72nd Conference and Exhibition, EAGE, Expanded Abstracts, Barcelona, 2010, 253.

[15] Thomsen L. Weak Elastic Anisotropy. Geophysics, 1986, 51(10): 1954-1966.

[16] White J. E., Sengbush R. L. Velocity Measurements in Near-Surface Formations. Geophysics, 1953, 18(1): 54-69.

[17] Xia J. H., Miller R. D., Park C. B., . Inversion of High Frequency Surface Waves with Fundamental and Higher Modes. Journal of Applied Geophysics, 2003, 52(1): 45-57.

[18] Xia J. H., Xu Y. X., Chen C., . Simple Equations Guide High-Frequency Surface-Wave Investigation Techniques. Soil Dynamics and Earthquake Engineering, 2006, 26(5): 395-403.

[19] Xie H. Anisotropic Earth Structure Revealed by Simulated Annealing Inversion of Seismic Waves: [Dissertation], 2014 Connecticut: University of Connecticut, 37-44.