Observations of seismometer calibration and orientation at USArray stations, 2006-2015

We use an empirical approach to assess the amplitude calibration and sensor orientation of 1857 seismographic stations for the full duration of the USArray deployment across the conterminous United States. Long-period seismograms recorded at each operating station during the 10-year period 2006-2015 are compared with synthetic waveforms for more than 3000 earthquakes of M (sub w) > or =5.7. Optimal scaling factors between observed and synthetic seismograms are determined and averaged for each station, component, and response epoch. The orientation of the seismometer is estimated from the combined optimal fit of longitudinal and transverse components and is averaged for each station and response epoch. We observe large and geographically coherent variations in amplitude scaling and correct for these variations. Residual scaling-factor anomalies following correction are smaller than 10% for more than 90% of the stations. Average seismometer orientations show no large-scale anomaly pattern across the continent. Orientation anomalies are 3 degrees or smaller for 88% of the stations. Several stations with outlying calibration or orientation are identified. The high quality of the calibration and sensor orientation of the USArray network argues for further exploitation of the details of the recorded wavefield in the mapping of elastic and anelastic structure across the North American continent.