From surface wave inversion to seismic site response prediction: Beyond the 1D approach |
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| Institution: | 1. Università di Padova, Dipartimento di Geoscienze, 35122 Padova, Italy;2. King Fahd University of Petroleum and Minerals, Earth Sciences Department, 31261 Dhahran, Saudi Arabia;1. Department of Architecture, Design and Urban Planning, University of Sassari, Piazza Duomo n.6, 07041 Alghero (SS), Italy;2. Dept. of Civil, Construction-Architectural & Environmental Engineering, University of L’Aquila, Via Giovanni Gronchi 18, Zona industriale di Pile, 67100 L''Aquila (AQ), Italy;3. Department of Engineering and Architecture, University of Trieste, Piazzale Europa n.1, 34127 Trieste (TS), Italy;1. Institute of Seismological Research, Raisan, Gandhinagar, Gujarat, India;2. Seismology Division, Ministry of Earth Sciences, Prithvi Bhawan, New Delhi, India;1. School of Earth and Space Sciences, University of Science and Technology of China, 230026 Hefei, Anhui, PR China;2. Department of Earth and Space Sciences, Southern University of Science and Technology, 518055 Shenzhen, Guangdong, PR China;1. Department of Civil Engineering and Construction Management, California State University, Long Beach, 1250 Bellflower Blvd, Long Beach, CA 90850, USA;2. Department of Civil Engineering, Cankaya University, Eski?ehir Yolu 29.km, 06810 Ankara, Turkey;3. Arup, 12777?W Jefferson Blvd # 200, Los Angeles, CA 90066, USA;4. Department of Civil Engineering, University of Bristol, Bristol BS8 1TR, UK;5. Department of Civil Engineering, University of Patras, Rio 26504,? Greece;6. Department of Civil and Environmental Engineering, University of California, Los Angeles, 420 Westwood Plaza, 5731 Boelter Hall, Los Angeles, CA 90095, USA;1. CEA, DEN, DANS, DM2S, SEMT, Laboratoire d’Etudes de Mécanique Sismique, F-91191 Gif-sur-Yvette, France;2. EDF, DR&D, Acoustics and Mechanical Analysis Department, 1, avenue du Général de Gaulle, F-92141 Clamart, France;3. EDF, SEPTEN, Dynamic and Earthquake Engineering Group, 12-14, avenue Dutriévoz, F-69628 Villeurbanne, France;4. Institute of Mechanical Sciences and Industrial Applications, EDF-CNRS-CEA-ENSTA UMR 9219, 1, avenue du Général de Gaulle, F-92141 Clamart, France |
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| Abstract: | Surface wave methods consist of the extraction and inversion of the Rayleigh wave phase-velocity dispersion curve to recover the (usually 1D) shear-wave velocity profile. In the literature, uncertainty due to data error has not received much attention, but the discussion about uncertainty due to model error is even poorer. Even with an unrealistic noise-free dataset and an exact forward model, an inappropriate parameterization can generate solutions very far from the actual soil structure. In general, the model used for the dispersion curve interpretation is 1D. Hence, when the velocity distribution is laterally heterogeneous, model errors can have significant consequences on the reliability of the resulting shear-wave velocity distribution. From a poor velocity reconstruction, an unsatisfactory, and often dangerous site response analysis follows. In fact, shear wave measurements play a relevant role in seismic ground motion amplification estimation. In this paper, we discuss the possibility of processing the seismograms using a multi-offset phase analysis (MOPA), in order to derive soil elastic parameters for weak motion predictions. This technique allows the detection and location of the lateral discontinuities, and a better model parameterization. In fact, once the discontinuities are identified, we can split the profile into several, truly 1D, parts. The use of the standard 1D dispersion curve extraction and inversion for each side of the heterogeneity generates velocity profiles that we can put side by side to get correct 2D reconstructions of the shear-wave distributions. From 2D velocity reconstruction, we can calculate the site response that may be significantly different from the site response generated from a traditional 1D analysis of the same seismograms. In this work, we discuss the site responses of two synthetic examples with lateral heterogeneities. We show how misleading a 1D analysis may be if applied to a truly 2D velocity distribution, particularly in terms of site response prediction. |
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