The dataset for this investigation consists of microtremor array data collected at 11 sites in the Seattle basin, Washington State. Ten of the arrays consisted of seven Nanometrics Trillium Compact broadband sensors deployed in asymmetric nested triangles (sites ST01, BA02, SP04, LF05, UW06, SN07, RD08, EL09, CH10, and KG11) that recorded for up to six hours. The eleventh array, at site NW03, was supplemented with a smaller triangular array that recorded for about 1 hour before redeployment to a larger array. The inter-sensor distances varied from about 173 m to 2000 m. The data were recorded on Reftek RT-130 data loggers and converted to SAC binary format for archival. All three components were recorded from each sensor. Coordinates of each sensor location are provided in UTM zone 10N format, WGS84 datum. Field logs describing the sensor locations and instrumentation are also provided.