As ocean waves rise and fall, they impact the seafloor and create seismic waves. These seismic waves are so powerful and widespread that they appear as a constant hum on seismographs, the same devices used to monitor and study earthquakes.
This wave signal has become increasingly intense in recent years, reflecting increasingly large storm waves and high ocean turbulence at sea. A new study published in the journal Nature CommunicationMy colleagues and I have followed this growth worldwide over the past four decades.
These global data, along with other ocean, satellite and regional seismic studies, show an increase in wave energy over the decades coinciding with the increase in storms associated with rising global temperatures.
What does seismology have to do with ocean waves?
Global seismographic networks are known for monitoring and studying earthquakes, as well as allowing scientists to create images of the planet’s deep depths. These highly sensitive instruments continuously record a wide range of natural and anthropogenic seismic events, including volcanic eruptions, nuclear and other explosions, meteorite impacts, landslides and glacial earthquakes.
They also constantly receive seismic signals from wind, water and human activities. For example, seismographic networks have observed a global recession in human-induced seismic noise as quarantines were implemented around the world during the coronavirus outbreak. But the most common of the seismic background signals globally is the continuous small wave generated by ocean waves caused by storms, called global microseismism.
Two types of seismic signals
Ocean waves produce microseismic signals in two different ways. The more energetic of the two, known as secondary microseima, vibrates for a period of approximately eight to 14 seconds. As wave groups move in different directions in the oceans, they interact with each other and create pressure fluctuations on the seafloor. However, disturbing waves are not always present, so in this sense they are an imperfect indicator of overall ocean wave activity.
The second way ocean waves produce global seismic signals is called the primary microseismic process. These signals originate from moving ocean waves that directly push and pull on the seafloor.
This occurs in areas where the water depth is less than 1,000 feet (about 300 meters), as the movement of water in waves decreases rapidly with depth. The primary microseismic signal can be seen in the seismic data as a steady hum with a period of 14 to 20 seconds.
What the trembling planet tells us
In our study, we estimated and analyzed historical primary microseismic intensity through the late 1980s in 52 seismographic sites worldwide with a long history of continuous recording. We found that 41 of these stations (79 percent) showed very significant and progressive increases in energy over the decades.
The results show that global average ocean wave energy has increased by an average of 0.27 percent per year since the late 20th century. However, since 2000, this rate increase on the global average has increased by 0.35 percent per year.
We found the highest total energy of microseismics in very stormy regions of the Southern Ocean near the Antarctic Peninsula. However, these results show that North Atlantic waves have strengthened most rapidly in recent years compared to historical levels.
This is consistent with recent research suggesting that North Atlantic storm intensity and coastal hazards are increasing. One record-breaking example was Storm Ciaran, which hit Europe in November 2023 with strong waves and hurricane-force winds.
Decadal microseismic records also show seasonal differences in severe winter storms between the Northern and Southern Hemispheres. It captures the wave-absorbing effect of growing and shrinking Antarctic sea ice, as well as the multi-year highs and lows associated with El Niño and La Niña cycles and their long-term effects on ocean waves and storms. These and other recent seismic studies complement findings from climate and ocean studies that show storms and waves are increasing as the climate warms.
coastal warning
Oceans have absorbed nearly 90 percent of the excess heat associated with increases in greenhouse gas emissions from human activities in recent decades. This excess energy can turn into more destructive waves and stronger storms. Our results are another warning for coastal communities where rising ocean waves can crash into shorelines, damaging infrastructure and eroding land.
The effects of increased wave energy are exacerbated by climate change and ongoing sea level rise due to subsidence. They also highlight the importance of mitigating climate change and building resilience into coastal infrastructure and environmental protection strategies. Source
Source: Port Altele
