Theory for deriving shallow elasticity structure from co‐located seismic and pressure data

Toshiro Tanimoto, & Jiong Wang

Published May 30, 2019, SCEC Contribution #9968

Colocated seismic and pressure data are available at many seismic stations in the world. For frequencies approximately between 0.01 and 0.05 Hz, colocated data show evidence of strong coupling between the atmosphere and the solid Earth, especially when pressure is high. Coherence between vertical seismic data and pressure is often higher than 0.9. Such data provide information for shallow structure in the upper 50–100 m because they show how the Earth responds to surface pressure changes. We present the basic theory and an inversion scheme for shallow structure using surface observables η(f)=Sz/Sp where f is frequency and Sz and Sp are the power spectral densities of vertical seismic data and of surface pressure data. A vertically heterogeneous medium is assumed beneath a station where density, P wave velocity, and S wave velocity change with depth. We show that the integration of the minors for the equations of motion gives a fast algorithm to compute η(f). Using numerical differentiation, we derive depth sensitivity kernels for η(f) with which we invert η(f) for shallow structure, just like we invert phase velocity of surface waves for the Earth structure. Depth sensitivity kernels show that if we take density, bulk modulus, and rigidity as independent parameters, η(f) has no sensitivity to density structure, making it mainly a function of two elastic constants. We present examples of inversion based on this formulation.

Citation
Tanimoto, T., & Wang, J. (2019). Theory for deriving shallow elasticity structure from co‐located seismic and pressure data. Journal of Geophysical Research: Solid Earth,. doi: 10.1029/2018JB017132.