On Nov. 14, 2015, tectonic plates off the coast of Nakanoshima, Japan, shifted, causing an earthquake with a magnitude of 7.0. The earthquake caused a small tsunami wave.
The wave in question measured only 30 centimetres in height and was not significant enough to affect the coast of the country that sits on the world’s largest ocean.
The U.S. Geological Survey (USGS) said that the epicenter of the shallow quake, which struck at 5:51 a.m. local time, was about 160 kilometres (100 miles) from the town of Makurazaki. According to both the USGS and the Japan Meteorological Agency, the earthquake’s focus was about 10 kilometres under the ocean floor.
Earthquakes are caused by the motion of tectonic plates—the large pieces of rock that make up the Earth’s crust. Tectonic plates are not stable and regularly slide into, past, or away from each other as they float on the Earth’s molten mantle. The shifting and gliding of the tectonic plates causes motion on the surface, which results in the shaking of the Earth beneath our feet. Earthquakes can range from ground shaking to devastating surface ruptures that can change the way we see the Earth. There are a few things that determine how much damage an earthquake can do. The distance beneath the surface of the crust matters.
If a part of a plate shifts far down below, or beneath the ocean, the outcome can be very different than if it was in the middle of a land mass.
The other determinant is how much power the quake has and how much energy it produces; both of these variables are measured by the Momentum Magnitude Scale (MMS). The MMS is a modern scale system used to determine the strength, energy, and power of Earth movements. The MMS succeeds the Richter scale—the older way of determining the power of a quake. Like the MMS, the Richter scale was a 10-point, exponential scale that measured the energy released through tectonic plate motion. The Richter scale was abandoned in the 1970s for a more reliable, more accurate scale.
The MMS measures quakes exponentially as well. The lower the number, the less damage a quake is likely to cause. Lower-rated earthquakes can be so similar that it can be difficult to tell the difference until about halfway up the scale. A magnitude 7.0 earthquake—like the one that occurred off the coast of Japan—can be dangerous, and is cause to implement national warnings about tsunamis or aftershocks, like Japan put in effect, following the Nov. 13 earthquake.The Japanese government has not reported any damages or injuries.
For now, it appears that the quake was deep enough and far enough off the coast to have no dramatic, sudden, or lasting effects on the country.