Earthquakes

Beyond traditional earthquakes, the ocean floor experiences a rich variety of seismic signals that reveal different processes happening inside the Earth. In volcanic settings, we detect long-period events that result from magma movement and volcanic tremor that indicates sustained fluid migration. These signals can tell us whether a volcano is filling with new magma or whether seawater is infiltrating the volcanic system, which can make eruptions more explosive.

We also detect short-duration events in gas or fluid-bearing sediments, signals from hydrothermal circulation where hot fluids rise through the seafloor, and seismicity induced by human activities such as resource extraction or carbon storage. Each type of event has its own distinctive signature, and learning to recognise these patterns helps us understand what's happening kilometres beneath the seafloor. It's information that's impossible to gather any other way.

Earthquakes beneath the ocean pose significant hazards to coastal communities worldwide through both direct ground shaking and tsunami generation. When powerful earthquakes occur beneath the sea, they can trigger tsunamis that travel across entire ocean basins, threatening coastlines thousands of kilometres from the source. These waves can arrive with devastating force, and understanding the earthquake processes that generate them is essential for early warning systems that protect millions of people living in coastal areas.

But the importance of earthquake research extends well beyond hazard assessment. Earthquakes can also trigger underwater landslides down steep submarine slopes, which themselves can generate tsunamis whilst damaging fragile seafloor habitats. Understanding where and when these events are likely to occur helps us protect both human communities and marine ecosystems.

The movement of fluids through the seafloor, particularly the circulation of seawater through hot rock at mid-ocean ridges, profoundly influences ocean chemistry. When we use seismic monitoring to map where and how these fluids move, we're gaining insights into chemical exchanges that affect the ocean's ability to support life. The chemistry of seawater influences everything from which organisms can thrive to how the ocean absorbs carbon dioxide from the atmosphere.

These hydrothermal systems, which we detect and map using seismic methods, support extraordinary chemosynthetic ecosystems that exist in complete darkness, deriving energy from chemical reactions rather than sunlight. Understanding the chemical composition of fluids emerging from these systems also tells us about the Earth's interior and helps explain why different volcanic regions produce different types of eruptions and associated hazards. The interplay between Earth's interior and ocean chemistry shapes both the geological and biological character of our ocean planet.

Seismic waves travelling through the Earth act as a natural imaging system, revealing the planet's layered structure in ways no other tool can match. When an earthquake occurs, it generates waves that travel through different materials at different speeds, bending and reflecting as they encounter boundaries between layers. By recording these waves at multiple locations and analysing their arrival times and characteristics, we can map the Earth's interior. This technique has revealed that the Earth's core is liquid, has shown us how the crust forms and evolves, and continues to unveil new details about the deep structure beneath ocean basins.

This isn't just about satisfying curiosity about Earth's interior. Understanding how new oceanic crust forms at mid-ocean ridges and how it's recycled at subduction zones helps us comprehend the fundamental processes that shape our planet. These processes control everything from the distribution of mineral resources to the long-term regulation of atmospheric carbon dioxide through the carbon cycle, making earthquake research relevant to understanding Earth as a system.

Beginning next year, NOC will participate in a new project at the Lucky Strike hydrothermal field on the Mid-Atlantic Ridge. This site is particularly interesting because it sits directly on the boundary where two tectonic plates are pulling apart and new oceanic crust is forming. We'll conduct two expeditions to deploy and then recover ocean bottom seismometers and electromagnetic instruments that will help us investigate how heat flows from the Earth's interior, how hydrothermal fluids circulate through the newly formed crust, and how this circulation affects the chemical exchange between Earth and ocean.

Mid-ocean ridges are where new seafloor is born, and hydrothermal systems at these ridges play outsized roles in ocean chemistry despite occupying relatively small areas. The fluids emerging from these vents carry dissolved minerals and support unique ecosystems that derive energy from chemistry rather than sunlight. By understanding the seismic and electromagnetic signatures of these systems, we gain insights into fundamental processes that shape both the solid Earth and the ocean that covers it. The Lucky Strike project exemplifies how earthquake monitoring reveals processes operating across the interface between geology, oceanography, and biology.

Whilst much of our work involves placing instruments on the seafloor, we also conduct complementary research in the laboratory. In NOC's Rock Physics Laboratory, researchers investigate the fundamental processes that govern how earthquakes nucleate, that critical moment when stress overcomes friction and a fault begins to slip. We study how human activities can trigger earthquakes, knowledge that's essential for safely managing subsurface operations from resource extraction to carbon storage.

The laboratory work focuses on understanding how rocks behave under the extreme pressures and temperatures found deep within the Earth. At what point do rocks deform elastically, storing energy that might later be released in an earthquake? When do they fail catastrophically? These laboratory insights help us interpret the earthquakes we record on the seafloor and inform how we assess and manage induced seismicity. The combination of field observations and controlled laboratory experiments provides a more complete understanding than either approach could achieve alone.

When we conducted the Santorini expedition in March 2025, the BBC joined us aboard RRS Discovery for a day at sea. Their coverage brought marine geophysics research to a broad audience, showing how scientists actually work to monitor active volcanic systems. The BBC's article about the expedition captures both the technical challenges and the scientific excitement of seafloor seismic monitoring.

We're also planning to present the first results from the Santorini project at the American Geophysical Union conference in December 2025, in a special session focused specifically on Santorini volcano. This conference presentation will mark the first public sharing of what we learned from the seismic swarm captured by our instruments. Beyond these formal channels, we use audio processing to make earthquake recordings audible, creating sensory experiences that help people connect with Earth processes they can't normally perceive. There's something powerful about actually hearing an earthquake, even though it's been artificially sped up. It makes abstract geophysical data suddenly vivid and real.