Scuba Safety: What to Do in an Underwater Earthquakes & Tsunamis

The global diving community operates in a delicate balance: human physiology is sustained by life-support equipment against the crushing weight of the ocean. Most of our training assumes the environment is relatively stable and predictable. But the ocean sits on top of some of Earth’s most geologically active boundaries—subduction zones, transform faults, and spreading ridges.

When a major seismic event happens underwater, the risks to divers are not simply “earthquake risks, but wet.” They are a distinct and dangerous mix of hydroacoustic shock, rapid pressure oscillations, and violent hydrodynamic surge. Understanding those invisible forces—and responding with a calm, physics-based plan—can be the difference between survival and catastrophe.

This guide moves beyond generic advice like “stay calm.” It explains what actually happens during underwater earthquakes, how tsunami energy behaves at different depths, and why certain injuries (inner ear trauma, pulmonary barotrauma, decompression illness) become more likely during chaotic “yo-yo” profiles. It finishes with a clear, step-by-step protocol you can integrate into dive briefings, training, and emergency action plans.

Note: This is educational content, not medical advice. If a dive injury is suspected, contact emergency services and consult qualified dive medicine professionals. For broader risk planning and preparedness content, see DIVEVOLK’s diving safety resources.

1. Introduction: The Tectonic Interface of the Underwater World

Earth’s oceans are not a calm “lid” over the planet. They are a dynamic layer above active tectonic systems. When geological stasis is shattered, the underwater environment can change instantly. For a diver, the hazard profile includes:

• Hydroacoustic shock (pressure waves that transmit efficiently through water and tissue)
• Barometric and pressure oscillation injury risk (air spaces can be compressed/expanded without changing depth)
• Hydrodynamic violence (surge, downwellings, and “washing machine” turbulence from tsunami effects near shore)
• Post-disaster contamination (sewage, fuel, pathogens, and chemical runoff in the littoral zone)

Survival is contingent on understanding what you can’t see: pressure oscillations, orbital wave motion, and secondary hazards like debris fields and contamination. Later in this post you’ll find a quick checklist you can print or add to your dive operator’s EAP.

Related reading: for dive planning and gear readiness, visit Dive Planning Essentials and Emergency Gear Checklist.

2. Geophysical Mechanics of Subsea Seismic Events

To protect yourself, you have to understand the mechanism. An underwater earthquake is not just “the ground shaking.” It’s the instant conversion of seawater into a conductor of high-intensity energy. Because water transmits pressure waves extremely well, the ocean can preserve—and deliver—seismic energy with lethal fidelity.

2.1 Seismic Wave Propagation and the T-Phase

When a fault ruptures beneath the sea, it releases energy as seismic waves. Underwater, the interaction is more complex than on land because of acoustic coupling between the seabed and the water column.

• P-Waves (Compressional Waves): Fast (roughly 6–8 km/s in crust). When they hit the seabed, they can generate a hydroacoustic pressure wave in the water. Divers often describe this as a sudden shock—like an explosion or collision.
• S-Waves (Shear Waves): Slower (roughly 3–4 km/s). Water cannot support shear stress, so S-waves don’t propagate directly in water, but they strongly disturb the seabed and contribute to secondary mechanisms discussed below.
• The T-Phase (Tertiary Wave): A hydro-seismic phenomenon: seismic energy can couple into the ocean’s acoustic channels and travel long distances. To a diver it can present as a sustained, intense rumble after the initial shock.

Key implication: water preserves sound energy far better than air. Even if a boat crew feels “only a mild tremor,” a submerged diver may experience significant acoustic energy and tissue-level transmission.

External reference (high authority): NOAA tsunami basics and wave behavior are explained in NOAA’s educational resources. NOAA: Tsunami Propagation

2.2 The Cavitational Mechanism and Pressure Oscillation

The most profound danger to a submerged diver comes from rapid seabed displacement. In significant events, the seafloor can act like a piston. When the seabed accelerates faster than the overlying water can follow, transient cavities (bubbles) can form and collapse, releasing intense acoustic shock.

That’s why survivors often describe not “shaking,” but a deafening roar—similar to piling operations or a massive propeller overhead.

Crucially, the risk is not just sound. Rapid pressure oscillations can force involuntary compression and expansion of air-filled spaces—lungs, sinuses, ears, and even buoyancy compensators—without a change in depth. This is why “just stay at the same depth” is not a guaranteed shield.

Practical takeaway: In a seismic event underwater, treat pressure waves as a real physical injury risk—similar in some ways to blast exposure—but delivered efficiently through water and tissue.

2.3 Acoustic Impedance and Bodily Transmission

In water, injuries occur differently than in air because of acoustic impedance. The acoustic impedance of human tissue is similar to water, which means sound energy passes through the body efficiently. But air spaces (lungs, sinuses, middle ear) create a dramatic mismatch, causing energy to deposit at tissue-air boundaries.

This is the physics behind immersion blast-style injuries: damage concentrates at gas-tissue interfaces, stressing delicate membranes and alveolar walls.

For dive medicine context, Divers Alert Network (DAN) provides reputable education on ear injuries and diving medicine: DAN: Ear Injuries

2.4 Seabed Liquefaction and Topographic Collapse

Seismic energy can raise pore water pressure in sediments, leading to liquefaction—the seabed temporarily behaves like a fluid. This can trigger:

• Structure collapse: wrecks, coral heads, and heavy moorings may sink or shift suddenly.
• Turbidity currents: visibility can drop from clear to zero in seconds due to sediment clouds and submarine landslides.
• Reef disintegration: walls can shed debris; overhangs or caves may become deadly.

If you’re diving with camera equipment, consider how you’ll protect both safety and gear. For example, if you need both hands stable for ascent control, it may be safer to clip off accessories and keep your hands free. For equipment carry strategies, see Gear Rigging & Clip-Off Techniques.

3. Hydrodynamics of Tsunami Generation

Earthquakes create the initial hazard. A tsunami can become the secondary, mass-movement phase—especially near coastlines. Many divers misunderstand tsunamis as “big waves.” In reality, tsunami physics are different: they are long-wavelength waves whose energy can involve the entire water column.

3.1 The Physics of Orbital Wave Motion

Wind waves are surface-dominant; their energy decays with depth. Tsunamis often have wavelengths so large that, in a geophysical sense, they behave like shallow-water waves even in deep ocean. That means orbital motion can extend very deep compared to wind waves.

For a clear explanation of how tsunamis travel and transform, NOAA’s resources are a strong baseline: U.S. Tsunami Warning Centers FAQ

3.2 Depth vs. Safety: The Myth of the “Safe Stop”

“Are we safe at 15 meters?” It depends on where you are.

• Deep/open water: If you are mid-water over a deep abyss, a tsunami passing above may be subtle and slow. Remaining below the surface can sometimes be safer than surfacing into debris and chaos.
• Shallow/coastal reef: If total depth is 20–30 meters, you may be in the danger zone. As the wave shoals, energy compresses and surge currents can reach 5–10 knots, creating violent, sustained movement.

Key idea: A tsunami near shore often isn’t “a wave hitting you from above”—it’s a powerful horizontal conveyor belt that turns the reef into a moving hazard field.

3.3 The “Washing Machine” Effect and Drawback

Survivors of major tsunami events have described the underwater experience as being inside a “washing machine.” For divers, the major components are:

1. The surge: a forceful shoreward current that drags divers across reef structure, increasing impact injury risk.
2. The drawback: rapid withdrawal of water from the coast can pull divers seaward or cause sudden depth changes.
3. Turbulence: eddies, downwellings, and cross-currents can separate teams instantly and dislodge regulators.

4. Physiological Trauma Profile

The combination of high-pressure acoustics and violent surge creates a distinct injury profile. The most critical risks include auditory/vestibular trauma, pulmonary barotrauma and arterial gas embolism, decompression sickness from yo-yo profiles, and (near the epicenter) immersion blast injuries.

4.1 Auditory and Vestibular Trauma

The ear is often the “canary in the coal mine” for underwater seismic injury. Pressure spikes and bone-conducted vibration can overload the inner ear. A dangerous reflex is to attempt aggressive equalization (like a forceful Valsalva) when the ear feels “full”—that can worsen injury if membranes are already stressed.

Symptoms may include sudden vertigo, roaring tinnitus, and hearing loss. Underwater, severe vertigo is life-threatening because it destroys orientation and triggers panic responses.

4.2 Pulmonary Barotrauma and Arterial Gas Embolism (AGE)

Violent surge can create involuntary depth excursions. If a diver is lifted rapidly and holds their breath—even briefly—the expanding gas can rupture alveoli. Gas bubbles can then enter arterial circulation, causing an AGE with stroke-like symptoms immediately upon surfacing.

For a reputable medical overview of dive-related injuries, the CDC provides helpful guidance: CDC: Dive-Related Injuries

4.3 Decompression Sickness (DCS) from “Yo-Yo” Profiles

Repeated fast ascents and descents can increase bubble formation risk. Even if lung rupture is avoided, the “yo-yo” pattern can elevate odds of neurological and vestibular DCS—especially when stress, exertion, and disorientation are high.

4.4 Immersion Blast Injuries

Close to the epicenter, the shockwave behaves more like an underwater blast. Injury can occur without any ascent due to spalling at tissue-air interfaces (lungs, intestines). This is rare for recreational divers but relevant for proximity scenarios.

Table 1: Differential Diagnosis of Seismic Dive Injuries

5. Procedural Response: The “Seismic Survival Algorithm”

This protocol is designed to be practical under stress. It follows a clear logic: stabilize, protect your airway, avoid hazards, and manage ascent risk.

5.1 Phase 1: The Event (0 to 60 Seconds)

1. STOP and HOVER: Immediately stop swimming and establish neutral buoyancy. Don’t touch the bottom—liquefaction and debris risk.
2. Move to Open Water: Swim laterally away from walls, caves, overhangs, and wreck penetration zones. Rockfall and collapse are major hazards.
3. Assume a Protective Posture: If vibration is intense, tuck into a compact “turtle” position to protect head and abdomen.
4. Trust Your Instruments: Vertigo can lie. Your depth gauge doesn’t. Use it as your objective reference.
5. Airway Management: Keep your regulator in. If you feel depth fluctuations or strong movement, begin continuous exhalation (a steady hum) to keep your airway open and reduce lung injury risk.

5.2 Phase 2: Assessment and Decision (1 to 5 Minutes)

Now tsunami risk becomes the priority.

• Deep/open water: If you are in blue water with deep bottom (e.g., >100 meters), staying at a controlled depth may be safer than surfacing into debris and surface chaos.
• Shallow/coastal: If you are on a shallow reef (<30 meters total depth), you may be in the high-risk surge zone. However, a panicked ascent creates near-certain injury risk. The goal is a controlled swimming ascent, not a bolt.

Consensus protocol: Begin a controlled ascent (about 9 m/min). Avoid a buoyant emergency ascent. If the surface is violent, pause at ~5 meters and reassess. If current is dangerous, shelter behind sturdy, non-living structure (like a massive pinnacle or mooring block) if available—otherwise drift and protect your head.

Safety stop guidance: Unless the environment is physically collapsing, don’t automatically skip the safety stop. Stress and exertion can complicate decompression dynamics; a controlled stop can reduce risk of adding DCS on top of trauma.

5.3 Phase 3: Surfacing and Boat Interaction

1. Look Up Before You Break the Surface: Rotate and check for debris. Extend one arm above your head as a bumper.
2. Establish Positive Buoyancy Immediately: Fully inflate your BCD on surfacing.
3. Expect the Boat May Not Be There: In tsunami warnings, vessels often move to deep water to avoid capsizing. Plan to self-manage survival at the surface until rescue returns.

Group survival: Stay together. Clip buddy lines or hold BCDs to form a visible cluster. Deploy DSMBs immediately—bright surface markers can be critical in debris-filled seas.

For official guidance on boats and tsunami response planning, see the International Tsunami Information Center: ITIC: If I Have a Boat

6. Post-Disaster Environment: Contamination Hazards

Surviving the quake and surge doesn’t end the danger. Coastal destruction can release a “toxic soup” into nearshore water: sewage, fuel, pathogens, and industrial runoff.

6.1 Biological and Chemical Hazard

• Pathogens: ruptured sewage lines can introduce bacteria that cause severe infections if aspirated or introduced into wounds.
• Chemicals: fuels, pesticides, heavy metals, and other contaminants can adhere to wetsuits and remain in contact with skin.

6.2 Decontamination and Medical Prophylaxis

• Keep airway protection on until you’re in a clean zone when possible.
• Rinse and decon gear with fresh water and appropriate cleaning solutions.
• Be cautious with ear drops if eardrum rupture is suspected (pain/vertigo).

For diving hygiene best practices, DAN offers additional education: DAN: Aural Hygiene

7. Operational Preparedness and Legal Responsibilities

For dive professionals and operators, preparation is both ethical and operationally essential. In seismic regions, an EAP that ignores tsunami procedures is incomplete.

7.1 Emergency Action Plans (EAPs)

• Recall systems: Standard signals may be ineffective in chaos. Plan multiple recall methods.
• Deep-water assembly point: Define a GPS coordinate in deeper water where the boat will relocate during tsunami warnings.
• Diver expectation management: Brief divers clearly: the vessel may move to safety, and rescue may return when conditions stabilize.

For building or improving your action plan, see: DIVEVOLK Dive Operator EAP Template

7.2 Training and Liability

• Briefing drills: Add a 30-second “Seismic Safety” segment during briefings in high-risk regions.
• Monitoring alerts: Operators should monitor reputable alert sources and avoid launching during active warnings where applicable.

8. Equipment Considerations for Seismic Zones

Standard recreational gear may have limitations in disaster scenarios. Consider these baseline recommendations:

• Reliable regulators: choose high-performance systems that behave predictably under stress and turbulence.
• Surface signaling for every diver: DSMB, whistle, and (when appropriate) mirror or dye markers.
• Full-face masks (specialized use): public safety divers working in contaminated water environments may require them.

If you routinely dive with a phone for underwater navigation or content capture, ensure your setup supports hands-free safety priorities. Explore underwater phone protection options at DIVEVOLK Underwater Housing Collection, and consider bundled configurations at SeaTouch 4 Max Kits.

9. Conclusion

An underwater earthquake is a low-probability, high-impact event that dismantles the normal rules of diving. The ocean becomes a transmitter of shock and a conveyor belt of kinetic energy.

Survival depends on following physics-based priorities:

1. Respect the energy: the “roar” is a pressure wave capable of damaging air spaces.
2. Protect the airway: continuous exhalation helps prevent pressure-related lung injuries during rapid fluctuations.
3. Manage the ascent: panic ascents are a leading killer; controlled movement is the goal.
4. Prepare for the aftermath: signaling, drift management, and decontamination matter as much as surfacing.

By integrating this protocol into training and briefings, divers can replace panic with an actionable plan—turning an unthinkable scenario into a survivable one.

Quick Reference: Seismic Diver Survival Checklist