Seismic Detection of Oceanic Internal Gravity Waves from Terrestrial
Observations
Abstract
Oceanic internal gravity waves propagate along density stratification
within the water column and are ubiquitous. They can propagate thousands
of kilometers before breaking in shoaling bathymetry and the ensuing
turbulent mixing affects coastal processes and climate feedbacks.
Despite their importance, internal waves are intrinsically difficult to
detect as they result in only minor amplitude deflection of the sea
surface; the need for global detection and long time series of internal
waves motivates a search for geophysical detection methods. The pressure
coupling of a propagating internal wave with the sloping seafloor
provides a potential mechanism to generate seismically observable
signals. We use data from the South China Sea where exceptional
oceanographic and satellite time series are available for comparison to
identify internal wave signals in an onshore passive seismic dataset for
the first time. We analyze potential seismic signals on broadband
seismometers in the context of corroborating oceanographic and satellite
data available near Dongsha Atoll in May-June 2019 and find a promising
correlation between transient seismic tilt signals and internal wave
arrivals and collisions in oceanic and satellite data. It appears that
we have successfully detected oceanic internal waves using a terrestrial
seismometer. This initial detection suggests that the seismic detection
and amplitude determination of oceanic internal waves is possible and
can potentially be used to expand the historical record by capitalizing
on the existing terrestrial seismic network.