Seismic waves are produced when ocean waves rise and fall and exert forces on the sea floor below. Seismographs, which track and analyze earthquakes, display these seismic waves as a constant thrum due to their great forceand vast distribution.
In recent decades, that wave signal has become more strong, reflecting increased ocean swell and more stormy seas.
I monitored that growth globally over the past 4 years with colleagues, and we published our findings in the journal Nature Communications. These worldwide data demonstrate a decades-long rise in wave energy that is consistent with growing storminess linked to rising global temperatures, as do further ocean, satellite, and regional seismic investigations.
What the relationship between ocean waves and seismology
The ability of global seismographic networks to track and analyze earthquakes and produce images of the planet's deep interior is what makes them most famous
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. They also capture persistent seismic signals from wind, water and human activity. For example, seismographic networks observed the global quieting in human-caused seismic noise as lockdown measures were instituted around the world during the coronavirus pandemic.
Numerous natural and man-made seismic events, such as volcanic eruptions, nuclear and other explosions, meteor strikes, landslides, and glacier earthquakes, are continuously recorded by these incredibly sensitive instruments. Additionally, they record continuous seismic signals from human activity, the water, and the wind. For instance, during the coronavirus pandemic, seismographic networks recorded a global quieting in seismic noise caused by humans as lockdown procedures were implemented globally.
But the most ubiquitous seismic background signal in the world is the constant roar produced by storm-driven ocean waves, known as the global microseism.
Two kinds of seismic data
There are two distinct ways in which ocean waves produce microseismic signals. The secondary microseism, which is the more intense of the two, pulses every eight to fourteen seconds. Pressure variations on the sea floor are caused by waves interfering with one another as they move across the oceans in different directions. It is an imperfect proxy for total ocean wave activity, though, because interfering waves aren't always present.
The primary microseism process is the second way that global seismic signals are produced by ocean waves. The seafloor is directly pushed and pulled by traveling ocean waves, which is what causes these signals. This happens in areas where the water depth is less than 1,000 feet (about 300 meters), as the motions of the water within the waves diminish quickly as one descends deeper. Seismic data reveals the main microseism signal as a continuous hum with a duration of 14–20 seconds.
The planet's shaking message to us
In this work, we examined and estimated historical primary microseism intensity at 52 global seismograph sites with extensive records dating back to the late 1980s. We discovered that over the decades, the energy levels of 41 (79%) of these stations exhibited highly significant and progressive increases.
The findings show that, since the late 20th century, the average global ocean wave energy has grown at a median annual rate of 0.27%. But that average annual growth rate has increased by 0.35% globally since 2000.
Intensification of ocean waves since the late 1980s: Each circle represents a seismic station, and its size is proportionate to the Earth's vertical acceleration at that station, smoothed over a period of three years. Periods where ground motions are greater than the historical median are indicated by red circles, and periods when they are smaller are indicated by blue circles. The graph that is synchronized displays the median vertical acceleration anomaly across all stations, which is indicative of El Niño cycles and a notable rise in the past few years.
The extremely stormy Southern Ocean regions close to the Antarctic Peninsula are where we detected the highest total microseism energy. However, these findings demonstrate that, in comparison to historical levels, North Atlantic waves have intensified at the quickest rate in recent decades. This is in line with new research that indicates an increase in coastal hazards and storm intensity in the North Atlantic. One instance of a record-breaking storm was Storm Ciarán, which struck Europe in November 2023 with hurricane-force winds and enormous waves.
The seasonal swing of powerful winter storms between the Northern and Southern hemispheres is also depicted in the decades-long microseism record. It records the long-range effects of El Niño and La Niña cycles on ocean waves and storms, as well as the wave dampening effects of growing and shrinking Antarctic sea ice and their multi-year highs and lows. Hurricane Nicole's powerful waves in November 2022 eroded the ground beneath a number of Daytona Beach, Florida, homes.
The findings from studies on the ocean and climate that indicate storms and waves are getting stronger as the climate warms are supported by these and other recent seismic investigations. A coastal alert Ninety percent of the excess heat linked to rising greenhouse gas emissions from human activity in recent decades has been absorbed by the oceans. Greater waves and stronger storms may result from that extra energy.
You must be logged in to post a comment.