by Sri Atmaja P. Rosyidi* & Susy K. Ariestianty*
*Jurusan Teknik Sipil, UMY
**Puslitbang Jalan dan Jembatan, Banlitbang, Kementerian Pekerjaan Umum Bandung
Shear wave velocity is one of the most important input parameters in modeling of soil behavior under cyclic load. By acquiring the value, the dynamic soil properties such as shear modulus and damping ratio can be derived. The measurement of a shear wave velocity can be performed employing a seismic method where some receivers are placed on the ground to record the propagation of surface waves. Multi-channel Analysis of Surface Wave (MASW) that was developed by Park , uses multi receivers (12 – 48 receivers). The earlier method uses only two receivers is known as Spectral Analysis of Surface Wave [4, 5]. The MASW method is faster and effective costly. Pattern recognition of seismic events, mode separation and noise can be evaluated and diminished in data processing with more accuracy and reliability [2, 3, 8]. The dispersion curve, obtained from multiple seismic data recorded at different distances from the source . This curve is smoother and more accurate over a wide range the interested frequencies, particularly in low frequencies measurements . The MASW method is also applied to obtain the correction between shear wave velocities profile of the soils and bearing capacity of soil, i.e., Standard Penetration Test (SPT).
Twenty four low frequency geophones (4.5 Hz) are utilized to record the propagation of surface wave. A sledge hammer is used as the source to generate the wave. Appropriate field configuration is chosen so that the aim and interest of investigation are obtained. The important parameters that have to be considered carefully are total spread length of geophones, source distances to the first geophone, geophone spacings and the record length . The total spread length of geophones determines the maximum depth of investigation. The geophone spacing (dx) of 1 m and 2 m are usually selected with the source distance to the first geophone (x1) of 5 m and 10 m selected. A record length of 1000 ms is chosen to cover investigations of soft to hard material. Consecutive shots gathered for each configuration are obtained by moving the adopted source-receiver configuration several times.
Subsequently, all the seismic records are processed into two main steps in the data processing. First, the determination and construction of dispersion curve and second, the inversion process to generate shear wave velocity profile with depth.
 Foti S., “Multi-Station Methods for Geotechnical Characterisation Using Surface Waves,” PhD Diss., Politecnico di Torino, 229 pp, 2000.
 Ivanov, J., Park, C.B., Miller, R.D., Xia, J., and Overton, R., “Modal Separation before Dispersion Curve Extraction by MASW method:,” Proceedings of the SAGEEP 2001, Denver, Colorado, SSM-3, 2001.
 Ivanov, J., C.B. Park, R.D. Miller, and J. Xia, “Analyzing and filtering Surface Wave Energy by Muting Shot Gathers,” Journal of Environmental & Engineering Geophysics, v. 10, no. 3, p. 307-322, 2005.
 Nazarian, S., “In situ determination of elastic moduli of soil deposits and pavement systems by spectral-analysis-of-surface-waves method,” Ph.D. Dissertation, the University of Texas, Austin, 1984.
 Nazarian, S., and Stokoe II, K.H., “In situ Shear Wave Velocities from Spectral Analysis of Surface Wave,” Proceeding of the World Conference on Earthquake Engineering, Vol. 8, San Fransisco, Calif., July 21-28, 1984.
 Park, C. B., “Characterization of Geotechnical Sites by Multichannel Analysis of Surface Waves,” Proceedings of the Korean Ground Society, 95th annual meeting, Seoul, Korea, 15-21, 1995.
 Park, C.B., Miller, R.D., and Xia, J., “Imaging dispersion curves of surface waves on multi-channel record” [Expanded Abstract]: Soc. Explor. Geophys., 1377-1380. 1998.
 Park, C.B., Miller, R.D., and Miura, H., “Optimum field parameters of an MASW survey,” [Exp. Abs.]: SEG-J, Tokyo, May 22-23, 2002.
 Penumadu, D., and C.B. Park, “Multichannel analysis of surface wave (MASW) method for geotechnical site characterization,” Proceedings of the Geo-Frontiers Conference, Austin, Texas, January 23-26, 2005.