Understanding Underwater Earthquakes

Earthquakes are a reminder that nature is powerful. The realization that Earth constantly moves and changes is apparent when an earthquake occurs. What people see as a deadly occurrence is a part of geologic function that has continued for millions of years.

Tectonic plates are constantly moving. They grind past each other, the plates slide underneath each other, plates separate from each other. The movement of plates builds up stress. When the stresses finally exceed the strength of the rock, an earthquake occurs. When the earthquake occurs on the sea floor, the consequences are tsunamis.

A Closer Examination of the Four Plate Boundaries

1. Divergent boundaries occur when plate boundaries pull away from each other.

When the plates pull apart, a new crust is made by magma pushing up from the mantle.

2. Convergent boundaries occur when one plate dives under another and the crust is destroyed. The plates head toward each other on a collision course. When they hit, it causes an earthquake.

3. Transform boundaries occur when the plates slide horizontally past each. The crust is not affected.

4. Plate boundary zones are not defined and the effects of plate interaction are not known.

Example of Earth’s Core, Mantle and Crust and Lithosphere

Imagine a peach cut in half. The core is the seed. The skin out the outside represents the crust. The seed in the center represents the core of the earth. The fleshy part has the most mass. This is the mantle. The upper mantle nearest the crust and the crust is where the lithosphere is located. The lithosphere is the interconnection of plates that move constantly.

The most recent undersea earthquake occurred 80 miles east of the island of Honshu, Japan. The tectonic plate that lies under the Pacific Ocean is constantly moving. It moves at a rate of 3 inches per year. The movement caused stress along the plate boundary. The stress had to be relieved and brought on the earthquake of 9.0 magnitude.

The Earthquake Brings on the Tsunami

The earthquake occurred 15 miles under the Earth’s surface. This caused the ocean floor to lift suddenly. This lift displaced the water and created a deep wave (starting at the bottom of the ocean) and the wave moved quickly. It hit the shallow water near the land, This is what caused the tsunami to increase in height and expand outward. The momentum of the original wave ends up spreading over the land.

An earthquake is stored energy in the Earth’s crust that suddenly releases because of shifting tectonic plates. The Earth’s lithosphere move plates constantly. The plates move so slowly that people do not feel them. When the plates lock up at boundaries, frictional stress occurs. When the strain is too much, the rocks give away, break off, and slide down along the fault lines. This displaces the crust when the pent-up energy releases and seismic waves cause tremors.

Jian Lin, a scientist at MIT/Woods Hole Oceanographic Institution Joint Program (WHOI), reports that it is easier to find fault lines below sea level than on land. The ultimate purpose of studying fault lines is to forecast earthquakes on land. According to Lin, land earthquakes cause more damage and cause more deaths than undersea earthquakes.

The more researchers learn about earthquakes, the better the chances to avoid devastation from surprise earthquakes.