Underwater Earthquake Tsunami: The Most Common Tsunami on Earth

Various circumstances can trigger tsunamis. However, the most common trigger for tsunamis is the undersea earthquake. Underwater earthquake tsunami occurs more frequently than the eruption-triggered or landslide-triggered tsunamis.

Tsunamis generated by this earthquake varied from small, harmless ones to massive waves. People throughout history have witnessed the latter several times. Huge tsunamis can destroy large coastal areas and kill many people. Thankfully, early warning systems can detect signs of tsunamis and alert people.

How Does an Underwater Earthquake Tsunami Occur?

A tsunami is not a single wave. It was a train of waves. Moreover, they move quickly and have long wavelengths. The wave height can reach 30 m when they reach coastal areas. The combination of the force, speed, and height of those waves has killed thousands of people in the last century.

Tsunamis typically occur after a strong underwater earthquake. However, undersea landslides, volcanic eruptions, and meteorite falls can also cause this natural hazard. Below is a summary of how the earthquake-triggered tsunami occurs.

1. Earthquake Mechanism

Earthquakes can occur anywhere, on land or underwater. The latter can generate a tsunami if it causes the sea floor to shift vertically. In other words, earthquakes that move the ocean plate horizontally cannot generate tsunamis.

The vertical shift of the seabed will cause waves to appear surrounding the epicenter of the underwater earthquake. However, not all undersea earthquakes are strong enough to displace seawater.

Typically, earthquakes can cause tsunamis if their magnitude is above 6.5 on the Richter scale. Moreover, the depth of the epicenter must be less than 70 km below the ocean floor.

2. Tsunami Formation

The waves caused by the earthquake will travel in all directions, crossing the ocean at high speed. The speed of these waves can reach hundreds of kilometers per hour. 

Therefore, it may sweep nearest coastal areas in minutes and may reach the other side of the ocean in less than 24 hours. In the sea, those deathly waves seem to have low heights. However, they go deep to the ocean floor. 

Moreover, tsunami wavelengths are extremely long, reaching hundreds of kilometers. After reaching coastal areas, the underwater earthquake tsunami will turn into a gigantic series of waves because the wavelength shortens and the height increases.

In addition, the forces of those deathly waves remain, but the speed decreases when reaching shallow waters. Therefore, tsunamis can sweep coastal areas with a strong force. Moreover, they may cause deep inundation over large low-lying areas near the coast.

Signs of Tsunamis

In the last two decades, 200,000 people in the Pacific Ring of Fire died due to earthquake-triggered tsunamis. This zone is extremely vulnerable to earthquake-triggered tsunamis. Approximately 80% of tsunamis in the world occur in this zone.

Therefore, people living in or visiting countries of the Ring of Fire must know the signs of an underwater earthquake tsunami.

• Strong Earthquake in Coastal Areas: People typically experience a strong earthquake in coastal areas before a tsunami. This earthquake may occur 5 minutes before the first wave of the tsunami. Therefore, people on the beach must immediately go to higher places after the quake.

• The Vacuum Effect: Shortly before the tsunami hits the shore, people will see the seawater suddenly withdraw from the shore. Experts call this phenomenon the vacuum effect. During this condition, the sea floor near the coast may be visible.

• Loud Ocean Roar: Another sign of a tsunami is loud ocean sound. This strange sound comes from the movement of the displaced seawater. The moving water is in a vast volume. That’s why its sound is loud.

Tsunami Early Warning Systems

In many cases, people in the tsunami-prone zones do not experience the shaking of the earth because the earthquake epicenter is far from their locations. Moreover, some people do not recognize tsunami cues. Therefore, countries that are vulnerable to tsunamis must have a tsunami early warning system.

This system utilizes various equipment, e.g., sensors, analytical tools, and communication systems. The sensors can detect earthquakes and changes in seawater levels. They will send data to the TEWS center via satellites after identifying those two occurrences.

Moreover, the analytical technology in the TEWS center will analyze the data to check whether or not an undersea earthquake triggers a tsunami. When underwater earthquakes generate tsunamis, the TEWS center will disseminate tsunami warning alerts via wireless cell broadcasts, sirens, and TV/radio broadcasts.

Therefore, all people in coastal areas will receive the alerts and be able to evacuate from their locations. Consequently, tsunami early warning systems can help governments minimize the number of tsunami victims. 

The underwater earthquake tsunami can be extremely destructive. However, those who are in low-lying coastal areas can recognize earthquake-triggered tsunamis. Authorities can also use TEWS to alert those people about the incoming waves. To have an effective TEWS, authorities must have cell broadcasters from smsbroadcaster.com.