Landslide

• As oceans waves rise and fall, they apply forces to the sea floor below and generate seismic waves.
• These seismic waves are so powerful and widespread that they show up as a steady thrum on seismographs, the same instruments used to monitor and study earthquakes.

What seismology has to do with ocean waves

• These highly sensitive instruments continuously record an enormous variety of natural and human-caused seismic phenomena, including volcanic eruptions, nuclear and other explosions, meteor strikes, landslides and glacier-quakes.
• However, the most globally pervasive of seismic background signals is the incessant thrum created by storm-driven ocean waves referred to as the global microseism.

Two types of seismic signals

• A second way in which ocean waves generate global seismic signals is called the primary microseism process.
• These signals are caused by traveling ocean waves directly pushing and pulling on the seafloor.
• The primary microseism signal is visible in seismic data as a steady hum with a period between 14 and 20 seconds.

What the shaking planet tells us

• We found that 41 (79%) of these stations showed highly significant and progressive increases in energy over the decades.
• The results indicate that globally averaged ocean wave energy since the late 20th century has increased at a median rate of 0.27% per year.

• But these results show that North Atlantic waves have intensified the fastest in recent decades compared to historical levels.
• The decadeslong microseism record also shows the seasonal swing of strong winter storms between the Northern and Southern hemispheres.

Together, these and other recent seismic studies complement the results from climate and ocean research showing that storms, and waves, are intensifying as the climate warms.

A coastal warning

• Our results offer another warning for coastal communities, where increasing ocean wave heights can pound coastlines, damaging infrastructure and eroding the land.
• And they emphasize the importance of mitigating climate change and building resilience into coastal infrastructure and environmental protection strategies.

Richard Aster receives funding from the U.S. National Science Foundation.