The Consortium of Organizations for Strong Motion Observation Systems (COSMOS) supported blind trials using passive microtremor array data for shear-wave velocity site characterization. The trials included data from four sites in order to consider limitations imposed by differing geologies, differing sparse array geometries, and differing interpretation methodologies. The trials used a four-phase approach in order to evaluate changes in blind interpretation as each phase introduced additional array data. The microtremor array data were incrementally released to approximately a dozen analysts in four phases: (1) 2-station linear arrays; (2) sparse triangular arrays; (3) complex nested triangular or circular arrays; (4) all available geological control including drillhole data. While data from one site consisted of recordings from 3-component sensors, the other three sites consisted of data from vertical-component sensors only. The sites covered a range of noise source distributions, ranging from one site with a highly directional microtremor wave field, to others with distributed or omni-directional wave fields. The four sites were located in: 1) San Jose, California, USA, 2) Trois Rivieres, Quebec, Canada, 3) La Salle, Italy, and 4) Carson, California, USA. At each site ambient noise microtremor analysis was conducted using differing geophones: Site 1) Guralp three-component CMG 40T, 2) Sercel 2 Hz vertical-component geophones, 3) I/O SM-6/U-B 4.5 Hz vertical-component geophones, and 4) Geospace GS-114D 4.5 Hz vertical-component geophones.
