Earthquake Measures

Yesterday (4.12) I had the occasion to spend the day at home; between 8:00am and 6:00pm, there were three earthquakes that could be sensed. Later, looking on the Japan Yahoo page, I saw the following data:
8:08am M6.3, Highest shindo 5- (Chiba offshore)
2:07pm M6.3, Highest shindo 6- (Fukushima coast)
4:14pm M4.4, Highest shindo 4 (Nagano inland)

(Just FYI, between 8:08 and 4:14, there was a total of about 25 aftershocks. Most of them, of course, could not be felt.)

For the record, these followed the big one yesterday, April 11:
5:16pm M7.1, Highest shindo 6- (Fukushima coastline).

Two measuring systems, magnitude and shindo, are used to indicate earthquake strength in Japan. Magnitude "measures the seismic energy released by an earthquake" (Wikipedia). Magnitude is represented by a single value (number) taken at the epicenter of the earthquake. The East Japan earthquake on March 11 was Magnitude 9.0, but of course that force of energy was not felt everywhere the earthquake could be sensed.

Japan's original earthquake measurement system is called "shindo" 震度. Shindo measures "seismic intensity, lit. 'degree of shaking'" (Wikipedia). The shindo scale "describes the degree of shaking at a point on the Earth's surface. As a result, the measure of the earthquake varies from place to place, and a given quake may be described as 'shindo 4 in Tokyo, shindo 3 in Yokohama, shindo 2 in Shizuoka'" (Wikipedia). There are over 600 meters in Japan, resulting in reports of intensity according to particular area. The shindo scale runs from 1 to the highest value of 7. March 11 was Shindo 7.

The shindo scale is as familiar to Japanese people as magnitude is to Americans. (It can be confusing: two people talking about an earthquake could be referring to different measures of "5," for example. It is almost like a foreign language.)