Seismic waves, commonly associated with earthquakes, are also generated by the motion of ocean waves. As these waves rise and fall, they exert forces on the seafloor, producing a steady seismic signal detectable by seismographs.
Recent research, published in Nature Communications, reveals that these seismic signals from ocean waves have intensified over the last four decades, indicating a rise in wave energy and storminess linked to global temperature increases.
This study utilized global seismographic networks, which are primarily known for monitoring earthquakes but are sensitive enough to record a variety of natural and human-caused seismic phenomena. These include volcanic eruptions, meteor strikes, landslides, and human activities, such as the reduction in seismic noise during the coronavirus pandemic lockdowns.
The study focused on the global microseism, a persistent seismic background signal created by storm-driven ocean waves. Microseismic signals are generated in two ways: the secondary microseism, which is more energetic and occurs when ocean waves interfere with each other, creating pressure variations on the seafloor, and the primary microseism process, caused by ocean waves directly impacting the seafloor in shallower water regions.
Researchers analyzed primary microseism intensity data from 52 long-term seismograph sites worldwide, dating back to the late 1980s. The findings were striking: 41 of these stations (79%) showed significant increases in energy over the decades. Since the late 20th century, the globally averaged ocean wave energy has increased by a median rate of 0.27% per year, with this rate accelerating to 0.35% per year since 2000. The Southern Ocean regions near Antarctica displayed the highest overall microseism energy, but the most rapid increase was observed in the North Atlantic waves, consistent with research indicating rising storm intensity and coastal hazards in this area.
This long-term microseism record also captures seasonal shifts in storm intensity between the hemispheres, effects of Antarctic sea ice changes, and variations linked to El Niño and La Niña cycles. These findings align with climate and ocean research, confirming that storms and waves are growing more intense with climate warming.
The study serves as a warning for coastal communities, highlighting the threat posed by increasing ocean wave heights and more potent storms. These challenges, exacerbated by sea level rise and land subsidence, underscore the urgency of climate change mitigation and the need to enhance coastal infrastructure resilience and environmental protection strategies.