Analyst A: Alternatives in Analysis of the UTexas1 Surface Wave Dataset

In February of 2011 an earthquake event caused significant damage and loss of life in Christchurch, New Zealand. Such an event serves as motivation for improved foundation design and characterization of the shallow subsurface. In January of 2013, University of Texas engineers acquired surface wave data which has been made available to the ASCE GeoInstitute Geophysical Engineering Committee for a benchmark project. Participants were invited to process and interpret the common data set. This paper reports the results designated as those of “Analyst A”. The active vibroseis and sledgehammer data were combined to produce a composite Rayleigh wave dispersion curve. Alternative soil profile representations were considered. The resulting image is of low velocity zone sandwiched between a faster surface zone and a faster profile down to 30 meters depth. INTRODUCTION The UTexas1 SurfaceWave Dataset was acquired in Christchurch, New Zealand. The site was located approximately 1.5 km from the coast. The Geophysical Engineering Committee of the ASCE GeoInstitute has organized a benchmark project in which participating geophysical engineers have been invited to process and interpret this common data set with tools of their own choosing. The instructions were to work as much or as little of the data as each participant desired. The available data include both active-source and ambient noise sets. This participant has chosen to only work the active-source data. The vibrator data were processed in the frequency domain, the hammer data in the time domain. The resulting dispersion curves were then combined to provide a composite dispersion curve. Inversion of the composite dispersion curve was done employing a 1-D-gradational soil profile in which the objects of the inversion are control points whose depth and shear-wave velocity assignment may vary. The reader is referred to Michaels (2011) for another example of this representation. page 1 This is an author-produced, peer-reviewed version of this article. The final, definitive version of this document can be found online at Geo-Congress 2014: Technical Papers and Keynote Lectures, published by the American Society of Civil Engineers. Copyright restrictions may apply. doi: 10.1061/9780784413272.074