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Why Did the Earthquake Occur Here?
A shaking intensity map for the Honshu earthquake. Click here to learn what the colors mean.
The earthquake occurred off the coast of the island of Honshu, approximately 129 km (80 miles) east of the community of Sendai.
- Click here to see the epicenter of the earthquake.
- Click here to see the tectonic plates in this area.
- What tectonic plates act on Japan? Japan sits on the boundaries of four tectonic plates; the Pacific plate, the Philippine plate, the Okhotsk plate and the Eurasian plate.
Earthquakes are often caused by the interaction between tectonic plates.
- Click here to zoom in on the tectonic plates in the immediate neighborhood of the earthquake.
- What two plates most likely caused the earthquake? The interaction of the Pacific plate and the Okhotsk plate most likely caused the earthquake.
- Click here to display the fault lines.
- What kind of fault line exists between these two plates? A convergent fault exists between the Pacific plate and the Okhotsk plate.
- Click here to add in velocity vectors for our plates.
- Which of our two plates is moving faster? The Pacific plate is moving much faster than the Okhotsk plate. As a matter of fact, the Pacific plate is the fastest moving plate on the surface of the Earth.
- Click here to add in an historical overview of earthquakes in the area.
- Which plate is being subducted here? Explain your reasoning. The Pacific plate is being subducted under the Okhotsk plate. We know this because of the pattern of historical earthquake data. Almost all of the earthquakes occur on the Okhotsk plate. The only way this could occur is if the Pacific plate is sliding under the Okhotsk plate.
Continued friction between the plates in the subduction zone has resulted in an ongoing series of aftershocks.
- Click here to see some of the aftershocks.
Interactive animation showing the rapid release of stored energy that causes an earthquake. The Honshu earthquake occurred along a reverse (thrust) fault. A reverse (thrust) fault is formed along convergent plate boundaries.
The movement of the Pacific plate under the Okhotsk plate has resulted in the formation at the plate boundaries of a deep oceanic trench known as the Japan Trench. The Japan Trench has a maximum depth of 9,000 m (19,500 ft).
- Click here to see the Japan Trench.
- Briefly explain in your own words why the earthquake occurred here. The earthquake occurred in this area as a result of the collision between two plates, the Pacific plate and the Okhotsk plate. The Pacific plate is sliding under the Okhotsk plate since it is denser than the Okhotsk plate. At some point, these two interacting plates became stuck. Pressure slowly built up in the locked area. Eventually the pressure became too great, and the locked section of the plates abruptly broke apart. It was the rapid release of pressure between the two plates that caused the March 11 earthquake. (Note: The energy released by the sudden movement of the plates was so great that the island of Honshu actually moved 2.4 metres to the east.)