The M2 Tidal Tilt Results from USArray Seismic Data from the Western United States

We explore the detectability of M-2 tidal tilt in the western part of the United States, using seismic velocity data from 40 stations in the EarthScope Transportable Array (TA) network. We augment these data with data from two additional stations both collocated at the Pinon Flats Observatory (PFO) in southern California (networks TA and Incorporated Research Institutions for Seismology [IRIS] International Deployment of Accelerometers [IDA]). We find a good agreement between the acceleration-tilt derived from the TA seismic data with the theoretical model (body Earth and ocean loading for M-2). These results are also consistent with prior studies using borehole tiltmeters operated at PFO (Wyatt and Berger, 1980; Wyatt et al., 1982). We find statistically significant M-2 tilt anomaly responses that correlate with large lateral variations in rock properties in Yellowstone National Park, which stem from volcanic sources in the region. We also examined deviations in the M-2 tidal tilt mode in regions with other geological features including the Cascades volcanic range and a large plutonic body located in Idaho and eastern Oregon. Of these, only the Cascadia data show evidence of lateral variances of elastic properties, similar to that of the Yellowstone Caldera (YC). We conclude that tilt measurements from seismic noise data can successfully identify relatively large structural changes in elastic properties of the crustal Earth (e.g., the YC) and significant change in the elastic properties (e.g., Cascadia subduction zone). But, when the features are smaller and/or have a more muted variation in the elastic properties (e.g., the plutonic body in Idaho and eastern Oregon), the induced changes in the tilt values are too small to be detected using TA data.