Seismic detection of oceanic internal gravity waves from subaerial seismometers

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 amplitudedeflection 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 data set 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 subaerial seismometer. This initial detection suggests that the
onshore seismic detection and amplitude determination of oceanic internal
waves is possible and can potentially be used to expand the historical
record by capitalizing on existing island and coastal seismic stations.