18 years ago today - the Kobe Earthquake - Japan

Eighteen years ago to the day the Kobe earthquake shook Japan.  The Great Hanshin earthquake occurred on Tuesday, January 17, 1995, at 05:46 JST in the southern part of Japan. It measured 6.8 on the moment magnitude scale (USGS), and Mj7.3 (adjusted from 7.2) on JMA magnitude scale.  The tremors lasted for approximately 20 seconds. The focus of the earthquake was located 16 km beneath its epicentre, on the northern end of Awaji Island, 20 km away from the city of Kobe.

An earthquake is a quick release of energy in the Earth’s crust, creating seismic waves. The Earth’s crust is made up of tectonic plates. The tectonic plate edges move against each other all the time, but sometimes they get stuck. When this happens energy builds up to a point of rupture and the seismic energy is released.

The depth of an earthquake is very important.  If it is shallow it will cause much more structural damage to buildings than a deep one. On the Earth’s surface an earthquake will manifest itself by shaking buildings and the ground moving. If an earthquake occurs at sea it can move and displace the seabed. The water on the seabed of an ocean or large lake is normally very still, with waves only occurring near the surface, but if the seabed moves it can cause a deep and harmful that can result in a tsunami as happened in Japan in 2011.

In the Kobe earthquake, approximately 6,434 people lost their lives (final estimate as of December 22, 2005); about 4,600 of them were from Kobe.

A section of the Nojima Fault

The Great Hanshin earthquake belonged to a third type, called an "inland shallow earthquake". Earthquakes of this type occur along active faults. Even at lower magnitudes, they can be very destructive because they often occur near populated areas and because their hypocenters are located less than 20 km below the surface. The Great Hanshin earthquake began north of the island of Awaji, which lies just south of Kobe. It spread toward the southwest along the Nojima Fault on Awaji and toward the northeast along the Suma and Suwayama faults, which run through the center of Kobe. Observations of deformations in these faults suggest that the area was subjected to east-west compression, which is consistent with previously known crustal movements.

The earthquake proved to be a major wake-up call for Japanese disaster prevention authorities. Japan installed rubber blocks under bridges to absorb the shock and rebuilt buildings further apart to prevent them from falling like dominoes. The national government changed its disaster response policies in the wake of the earthquake, and its response to the 2004 Chūetsu earthquake was significantly faster and more effective.  The earthquake and tsunami of 2011 though was much larger than anything that had been seen before causing almost 16,000 deaths.  There was little that could be done to stop such a force of nature.

A large amount of data was collected after the tsunami of 2011 that provides "the possibility to model in great detail what happened during the rupture of an earthquake." The effect of this data is expected to be felt across other disciplines as well, and this disaster will "provide unprecedented information about how buildings hold up under long periods of shaking – and thus how to build them better.

Earthquakes can strike at any time and are unpredictable in their nature.  Fortunately these types of earthquake are not that common.  Early warning systems are in place for many countries around earthquake hot spots so as to try and give people time to get to safety.

See also:-
http://en.wikipedia.org/wiki/Japan_tsunami
http://en.wikipedia.org/wiki/Kobe_earthquake
http://www.bbc.co.uk/learningzone/clips/a-geological-explanation-of-earthquakes/6736.html