Calibration of USArray-TA Stations using Earth Tides

Full deployment of the 400 stations comprising the transportable array (TA) portion of the USArray component of the NSF Earthscope program was accomplished during the summer of 2007 and equipment rollover to new sites has become a reality. These stations currently form a grid covering the continental US from the Pacific coast to the eastern state borders of Arizona, Utah and Idaho. Seismic data from TA stations is transmitted from the field to the Array Network Facility (ANF) located at UCSD and then onwards to the IRIS Data Management Center which distributes it to the scientific community at large. The current and future data collected by this mostly homogeneous network, consisting of 3-component broadband seismometers and high dynamic range digitizers installed within weather-proof shallow vaults with sensors deployed about 2 m below the surface, will constitute a great data set for years to come. Currently the instrument response of TA stations is derived from the specifications of the equipment manufacturers, which is believed to be reliable. However, in attempt to assess the accuracy of the published response information of these stations we will measure the amplitude and phase of the Earth's tides recorded by TA stations by comparing these measurements with values expected from the models of the elastic, solid earth derived from tidal and free oscillation measurements and from modern ocean tidal models based upon analysis of satellite data. We will present results from stations with continuous recordings of at least 60 days from each station in which the earth's tides are observed.