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Mapping Near-Surface Rigidity Structure using Co-located Pressure and Seismic Sensors from the EarthScope Transportable Array

Jiong Wang, & Toshiro Tanimoto

Published August 14, 2018, SCEC Contribution #8570, 2018 SCEC Annual Meeting Poster #102

For frequencies below 0.05 Hz, Sorrells (1971) and Sorrells et al. (1971) proposed a promising model in which moving pressure waves on the surface of the Earth generate low-frequency seismic signals. By using Sorrells model, we can study the pressure-ground interaction via co-located pressure and seismic sensors. Taking advantage of the EarthScope Transportable Array (TA) stations, which have pressure sensors attached since 2011 (Tytell et al. (2016)), we analyze surface-pressure induced ground motions recorded at frequencies 0.01 and 0.02 Hz. Adopting the homogeneous half-space model, we estimate the near-surface rigidity within 50-100 meters from the surface at 458 TA stations, by taking ratios of horizontal seismic PSDs and pressure PSDs. We compare our calculated rigidity with the USGS Global Vs30 model, where we find good regional agreement with the surface geology at unique locations, for example, in the Appalachian Mountains and the Mississippi Alluvial Plain. Co-located stations in TA provide new data to retrieve near-surface structure information, which is important for ground-motion prediction studies.

There are 9 stations located in PiƱon Flats Observatory Array (PY) that have co-located barometers since late 2015. We have computed rigidity from data of frequencies that range from 0.01 to 0.05 Hz with an increment of 0.005 Hz for 9 PY stations. Different frequencies correspond to different depths that seismic motions can extend; thus making it possible to study layered structure. Tanimoto and Wang (2018) showed that retrieved rigidities tend to be a bit higher for 0.01 Hz results comparing to 0.02 Hz results, which suggests an increase of rigidity with depth. We also show the relationship between the observed seismic noise and the structure property of the underlying medium. Station with higher near-surface rigidity will require larger surface pressure to generate significant seismic signals, especially vertical signals, that could be separated visually from other sources such as ocean waves.

Wang, J., & Tanimoto, T. (2018, 08). Mapping Near-Surface Rigidity Structure using Co-located Pressure and Seismic Sensors from the EarthScope Transportable Array. Poster Presentation at 2018 SCEC Annual Meeting.

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