Monday, March 14, 2011

The “Shindo” Scale Used for Earthquakes in Japan

I cannot attest as to the validity of the following information, but it explains fairly clearly the difference between the “Shindo” scale used in Japan and the Richter scale.  This was useful for me because I've never been able to understand why an earthquake reported on Japanese TV as a “2” felt more like a “3” or “4” to me.

Japan experiences about 1,000 earthquakes each year of a magnitude sufficient to be felt. While the rest of the world uses the Richter scale to measure earthquakes, the Japan Meteorological Agency uses a seismic intensity scale - used also in Taiwan - known as the shindo (literally 'tremor') scale. Whereas the Richter scale measures a quake at its epicenter, the 'shindo scale' measures it at a specific location where the quake is felt. Therefore the effects of a single earthquake have a variable 'shindo scale' reading depending how far the affected area is from the epicenter.

A Shindo Scale 1 quake is the lightest, while a 7 is the most severe.
In detail, the points on the scale are defined as follows:

  • 0: Goes unnoticed by humans. Speed of shock waves on the ground is less than 0.008 m/s².

  • 1: Barely noticable, but only if inside. Ground speed of 0.008–0.025 m/s².

  • 2: Noticable if inside, and sufficient to wake some sleepers. Ground speed of 0.025–0.08 m/s².

  • 3: Felt by most people if inside. Sufficient to inspire fear in some people. Ground speed of 0.08–0.25 m/s².

  • 4: Sufficient to inspire fear in many people, wake most sleepers, and prompt some people to seek escape. Ground speed of 0.25–0.80 m/s².

  • 5−: Prompts most people to seek escape, but strong enough to prevent some people from moving. Ground speed of 0.80–1.40 m/s².

  • 5+: Strong enough to cause the collapse of a few unreinforced concrete-block walls and gravestones. Driving difficult or impossible. Ground speed of 1.40–2.50 m/s².

  • 6−: Will cause collapse of wall tiles and windowpanes in some buildings. Ground speed of 2.50–3.15 m/s².

  • 6+: In many buildings, wall tiles and windowpanes are damaged and fall. Strong enough to cause the collapse of some unreinforced concrete-block walls and gravestones. Ground speed of 3.15–4.00 m/s².

  • 7: Wall tiles and windowpanes are damaged and fall in most buildings. Even reinforced concrete-block walls may collapse. Ground speed of over 4 m/s².

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