User:Wolf20482/sandbox/Japan Meteorological Agency seismic intensity scale

The Japan Meteorological Agency (JMA) Seismic Intensity Scale (known in Japan as the Shindo seismic scale) is a seismic intensity scale used in Japan to categorize the intensity of local ground shaking caused by earthquakes.



The JMA intensity scale should not be confused or conflated with magnitude measurements like the moment magnitude (Mw) and the earlier Richter scales, which represent how much energy an earthquake releases. Much like the Mercalli scale, the JMA scheme quantifies how much ground-surface shaking takes place at measurement sites distributed throughout an affected area. Intensities are expressed as numerical values called "seismic intensity" (震度); the higher the value, the more intense the shaking. Values are derived from peak ground acceleration and duration of the shaking, which are themselves influenced by factors such as distance to and depth of the hypocenter (focus), local soil conditions, and nature of the geology in between, as well as the event's magnitude; every quake thus entails numerous intensities.

The data needed for calculating intensity are obtained from a network of 670 observation stations using "Model 95" strong ground motion accelerometers. The agency provides the public with real-time reports through the media and Internet giving event time, epicenter (location), magnitude, and depth followed by intensity readings at affected localities.

History
The Tokyo Meteorological Observatory, which in 1887 became the Central Meteorological Observatory first defined a four-increment intensity scale in 1884 with the levels faint (微), weak (弱), strong (強), and violent (烈). In 1898 the scale was changed to a numerical scheme, assigning earthquakes levels 0–7.

In 1908, descriptive parameters were defined for each level on the scale, and the intensities at particular locales accompanying an earthquake were assigned a level according to perceived effect on people at each observation site. This was widely used during the Meiji period and revised during the Shōwa period with the descriptions seeing an overhaul.

Following the Great Hanshin Earthquake of 1995, the first quake to generate shaking of the scale's strongest intensity (7), intensities 5 and 6 were each redefined into two new levels, reconfiguring the scale into one of 10 increments: 0–4, 5-lower (5–), 5-upper (5+), 6-lower (6–), 6-upper (6+), and 7. This scale has been in use since 1996.

Scale overview
The JMA scale is expressed in levels of seismic intensity from 0 to 7 in a manner similar to that of the Mercalli intensity scale, which is not commonly used in Japan. Real-time earthquake reports are calculated automatically from seismic-intensity-meter measurements of peak ground acceleration throughout an affected area, and the JMA reports the intensities for a given quake according to the ground acceleration at measurement points. Since there is no simple, linear correlation between ground acceleration and intensity (it also depends on the duration of shaking  ), the ground-acceleration values in the following table are approximations.

Measurement system
Since April 1997, Japan has been utilizing automated seismic observation instruments to measure and report the seismic intensity of earthquakes, a shift from the traditional method that relied on physical sensations and damage assessment.

The first seismic intensity meters, known as "Model 90", were installed in 1991. These initial models lacked the capability to record waveforms. In 1994, the "Model 93" seismic intensity meter was introduced, which had an enhanced ability to record digital waveforms on a memory card. Later, the "Model 95" seismic intensity meter was developed, offering significant improvements such as more than doubling the maximum observable acceleration, doubling the sampling rate, and other enhancements. As of now, the JMA uses "Model 95" seismic intensity meters exclusively.

Model 95 seismic intensity meter specifications:


 * Observation components: NS (North-South), EW (East-West), UD (Up-Down); three components (seismic intensity is a composite of three components)
 * Measurement range: 2048gal to -2048gal
 * Sampling: 100Hz rate, 24-bit
 * Recording criteria: Seismic intensity of 0.5 or higher (collected in one-minute intervals)
 * Recording medium: IC memory card

As of the end of 2009, the JMA had installed approximately 4,200 seismic intensity meters, which increased to 4,313 by August 2011. This was a significant increase from the initial 600 units when the switch to measuring seismic intensity was made. This indicates that Japan's seismic observation network is one of the densest in the world. Of these, about 600 are managed by the JMA, about 800 are managed by the National Research Institute for Earth Science and Disaster Resilience (NIED), and about 2,900 are installed by local public bodies, including prefectures, cities, towns, villages, and other administrative agencies.

The seismic intensity meters used by the Japan Meteorological Agency (JMA) are installed with the goal of placing at least one seismometer in each municipality as it was before the major mergers of the Heisei era. In island and depopulated areas, the aim is to install even more. This has resulted in almost complete coverage

Intensity 7
The Intensity 7 (震度7, Shindo 7) is the maximum intensity in the Japan Meteorological Agency seismic intensity scale, covering earthquakes with an instrumental intensity (計測震度) of 6.5 and up. At Intensity 7, it becomes impossible to move at will. The intensity was created following the 1948 Fukui earthquake. It was observed for the first time in the 1995 Great Hanshin earthquake. A list of Intensity-7 earthquakes follows.

Comparison with other seismic scales
A 1971 study that collected and compared intensities according to the JMA and the Medvedev–Sponheuer–Karnik (MSK) scales showed that the JMA scale was more suited to smaller earthquakes whereas the MSK scale was more suited to larger earthquakes. The research also suggested that for small earthquakes up to JMA intensity 3, a correlation between the MSK and JMA values could be calculated with the formula MSK = JMA1.5 + 1.5, whereas for larger earthquakes the correlation was MSK = JMA1.5 + 0.75.