Benchmarking Automated Rayleigh-Wave Arrival Angle Measurements for USArray Seismograms

Surface wave arrival angles are an important secondary set of observables to constrain Earth's 3-dimensional structure. These data have also been used to refine information on the alignments of horizontal seismometer components with the geographic coordinate system. In the past, particle motion has been inspected and analyzed on single 3-component seismograms, one at a time. But the advent of large, dense seismic networks has made this approach tedious and impractical. Automated toolboxes are now routinely used for datasets where station operators cannot determine the orientation of a seismometer upon deployment, such as conventional free-fall ocean bottom seismometers. 

In a previous paper, we demonstrated that our automated Python-based toolbox DLOPy compares favorably with traditional approaches to determine instrument orientations. But an open question has been whether the technique also provides  individual high-quality measurements for an internally consistent dataset to be used for structural imaging. For this feasibility study, we compared long-period Rayleigh-wave arrival angles at frequencies between 10 and 25 mHz for 10 earthquakes during the first half of 2009  that were recorded at the USArray Transportable Array (TA), a component of the EarthScope program. After vigorous data vetting, we obtained a high-quality dataset that compares favorably with an arrival angle database compiled using our traditional interactive screen approach, particularly at frequencies 20 mHz and above. 

On the other hand, the presence of strong Love waves may hamper the automated measurement process as currently implemented. 
While the proper choice of the start time of the analysis window may depend on a particular geographic location of a seismic network, our observations for USArray data suggest that a slightly later start time than is currently used may yield more high-quality Rayleigh wave measurements.