The world's oceans absorb 90% of the thermal energy which global warming collects. That is increasing the energy of ocean waves whose passing and mutual interference create low frequency pressure waves on the sea floor, detectable by the world's seismometers as a background hum. That hum has been getting louder.
And the referenced study (open access)
How global warming shakes the Earth: Seismic data show ocean waves gaining strength as the planet warms
The same instruments used to measure earthquakes pick up vibrations as ocean waves put pressure on the sea floor. Four decades of data tell a story about ocean storms.
theconversation.com
And the referenced study (open access)
Increasing ocean wave energy observed in Earth’s seismic wavefield since the late 20th century - Nature Communications
Ocean waves induce geographically extensive seafloor forces that excite a continuous and globally detectable seismic wavefield. This study infers global near-coastal average wave energy intensification at a rate of 0.27% per year since the late 1980’s, and 0.35% per year since January 2000.
www.nature.com