Shallow Earth Structure from Wind-Induced Ground Motion

Jiong Wang, & Toshiro Tanimoto

Published August 13, 2017, SCEC Contribution #7550, 2017 SCEC Annual Meeting Poster #033 (PDF)

Recently, earth scientists from different fields, such as seismology, climate studies and regular weather monitoring, have become increasingly interested in wind-induced ground motion. Due to developments of high-quality seismic network with co-located seismometers and barometers, we can learn the characteristics of the background seismic noise in a more systematic manner. We will point out that data analysis on long-term data such as seasonal or annual data can indeed provide insights into the nature of seismic noise, generated by atmospheric effects.

In this study, we use Southern California CI stations and Earthscope TA (Transportable Array) stations and primarily focus on the wind-induced ground motion recorded at specific stations with co-located seismometers and barometers between 0.01-0.05 Hz. All TA stations after mid-2011 have been equipped with barometers and infrasound sensors, which provide continuous stream of ground motions and surface pressure data.

We analyze data for multiple years from two networks. There are two major components in our results: (i) shallow structure information from ground motion-pressure ratio and (ii) daily variation in ground motion.

Based on equations introduced by Sorrell et al (1971,1973), we derive a series of equations to calculate rigidity of the shallow structure and associated wind velocity near the surface based on the ratio between different ground motion components and pressure. We only select data section with clean positive slopes between ground motion and pressure to obtain more consistent ratios, which means we only use data where atmospheric pressure is controlling the local ground motion (Tanimoto and Valovcin, 2016). These results at shallow depths can be an independent check on seismic structure for the upper layer (~ 1 km) of the earth and may be useful for ground motion prediction studies.

We have noticed daily variations in stacked 24-hour ground motion PSD plots for most stations. In general, all three ground motion components have higher amplitude at noon and lower amplitude at midnight. Pressure and wind velocity show similar trends, which support that this pattern may be caused by the wind velocity change. Separation of the dataset between day and night may be beneficial for making cross-correlations (and thus Green’s function generations) much more efficient. We are exploring such possibilities by understanding noise-sources better using surface pressure.

Key Words
shallow structure, background noise, barometer seismometer, daily variation, rigidity, elastic parameters

Citation
Wang, J., & Tanimoto, T. (2017, 08). Shallow Earth Structure from Wind-Induced Ground Motion. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology