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

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Not to be confused with Japan Meteorological Agency magnitude scale.
Japan Meteorological Agency seismic intensity scale

The Japan Meteorological Agency (JMA) Seismic Intensity Scale[1] (known in Japan as the Shindo seismic scale)[2] is a seismic intensity scale used in Japan to categorize the intensity of local ground shaking caused by earthquakes.

Map of Japan showing the distribution of maximum JMA Seismic Intensities by prefecture for the 2011 Tōhoku Earthquake

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 shindo (震度, "seismic intensity"); 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.[3][4] The agency provides the public with real-time reports through the media and Internet[5] giving event time, epicenter (location), magnitude, and depth followed by intensity readings at affected localities.

History[edit]

The Tokyo Meteorological Observatory, which in 1887 became the Central Meteorological Observatory[6] first defined a four-increment intensity scale in 1884 with the levels bi (微, faint), jaku (弱, weak), kyō (強, strong), and retsu (烈, violent). In 1898 the scale was changed to a numerical scheme, assigning earthquakes levels 0–7.[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.[7]

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.[7]

Scale overview[edit]

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[8][9][10]), the ground-acceleration values in the following table are approximations.[better source needed]

JMA Seismic Intensity Scale[11][12][13]
Intensity Instrumental Intensity Effects on:
People 		Indoors Outdoors Residential buildings Other structures Utilities Ground and slopes Peak ground acceleration[14] Mercalli equivalent (appr.)
0 0–0.4 Imperceptible to most people. Indoor objects will not shake. No damage <0.008 m/s2 I
1 0.5–1.4 Perceptible to some people in the upper stories of multi-story buildings Objects may sway or rattle. No damage 0.008–0.025 m/s2 I–II
2 1.5–2.4 Perceptible to most people indoors. Awakens light sleepers. Hanging objects sway. Shaking without damage. No damage 0.025–0.08 m/s2 II–III
3 2.5–3.4 Perceptible to everyone indoors. Frightens some people. Objects inside rattle noticeably and can fall from raised surfaces. Overhead power lines sway. Perceptible to people outdoors. Houses may shake intensely. Light damage possible to homes with low earthquake resistance. Light damage to older buildings with low earthquake resistance. Light damage possible to earthquake-resistant buildings. Unaffected 0.08–0.25 m/s2 III–IV
4 3.5–4.4 Most people are frightened by the shaking. Some seek escape. Most sleepers are awoken. Hanging objects swing and dishes inside cupboards rattle. Unsecured objects topple over. Moving objects produce loud noises. Power lines sway. Tremors are perceptible to people outside. Light damage to less earthquake-resistant homes. Most homes shake intensely and walls may crack. Apartment buildings will shake. Light damage to non-residential buildings. Little damage to earthquake-resistant structures. Interruptions (esp. electricity) are possible. No landslides or ground cracking 0.25–0.80 m/s2 IV–VI
5− (5弱) 4.5–4.9 Most people are frightened, and feel the need to hold on to something stable to support themselves. Some may try to escape from danger by running outside. Some people find it difficult to move. Hanging objects swing. Most unsecured objects topple. Dishes fall from cupboards and books on shelves fall to the ground. Unsecured furniture will move. Utility poles swagger. Windows may break or fall, unreinforced cinderblock walls topple, some road damage Wall and column damage to low earthquake-resistant residential structures Wall cracks in low earthquake-resistant buildings. Light damage to regular and earthquake-resistant structures Automatic valves cut residential gas. Some water supply interruptions. Blackouts. Soft ground may crack. Rockfalls and small slope failures possible 0.80–1.40 m/s2 V–VII
5+ (5強) 5.0–5.4 Many people are considerably frightened and find it difficult to move. Most road users will stop their vehicles, as the shaking makes it extremely difficult to drive. Most dishes in a cupboard and most books on a bookshelf fall. Occasionally, a TV set on a rack falls down, heavy furniture such as drawers fall over, and sliding doors slip out of their grooves. Due to earthquake-induced deformation of doorframes, it may become impossible to open or close interior doors after the shaking stops. Unreinforced concrete-block walls can collapse and tombstones overturn. Poorly installed vending machines can fall over. Less earthquake-resistant homes and apartments suffer heavy/significant damage to walls and pillars and can lean. Medium to large cracks are formed in walls. Crossbeams and pillars of less earthquake-resistant buildings and even highly earthquake-resistant buildings also have cracks. Gas pipes and water mains are damaged. (Gas service and/or water service are interrupted in some regions.) Cracks may appear in soft ground. Rockfalls and small slope failures would take place. 1.40–2.50 m/s2 VI–VIII
6− (6弱) 5.5–5.9 Difficult to keep standing. A lot of heavy and unanchored furniture moves or falls. Due to earthquake-induced deformation of doorframes, it is impossible to open interior doors in many cases. All objects will shake violently. Strongly and severely felt outside. Light posts swing, and electric poles can fall down, causing fires. Less earthquake-resistant houses collapse, and walls and pillars of earthquake-resistant buildings homes are damaged. Apartment buildings can collapse from their floors falling down onto each other. Less earthquake-resistant buildings easily receive heavy damage and may be destroyed. Even highly earthquake-resistant buildings have large cracks in walls and will likely be moderately damaged, at the very least. In some buildings, wall tiles and windowpanes are damaged and fall. Gas pipes and/or water mains will be damaged. Gas, water and electricity are interrupted. Small to medium cracks appear in the ground, and larger landslides take place. 2.50–3.15 m/s2 VII–IX
6+ (6強) 6.0–6.4 Impossible to stand; cannot move without crawling. Most heavy and unanchored furniture moves or becomes displaced. Trees can fall down due to violent shaking. Bridges and roads suffer moderate to severe damage. Less earthquake-resistant houses will collapse or be severely damaged. In some cases, highly earthquake-resistant residences are heavily damaged. Multi-story apartment buildings will fall down partially or completely. Many walls collapse, or at least are severely damaged. Some less earthquake-resistant buildings collapse. Even highly earthquake-resistant buildings suffer severe damage. Occasionally, gas and water mains are damaged. (Electrical service is interrupted. Occasionally, gas and water service are interrupted over a large area.) Cracks can appear in the ground, and landslides take place. 3.15–4.00 m/s2 VIII–X
7 >6.5 It is impossible to move at will due to the intense shaking, which can throw those who do not secure themselves around. Most heavy and unanchored furniture moves or becomes displaced. In most buildings, wall tiles and windowpanes are damaged and fall. In some cases, reinforced concrete-block walls collapse. Most or all residences collapse or receive severe damage, no matter how earthquake-resistant they are. Most or all buildings (even earthquake-resistant ones) suffer severe damage. Electrical, gas and water service are interrupted. The ground is considerably distorted by large cracks and fissures, and slope failures and landslides take place, which can change topographic features. >4 m/s2 IX–XII

Measurement of seismic intensities[edit]

Measurement system[edit]

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.[15][16]

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[edit]

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.[17] At Intensity 7, it becomes impossible to move at will.[13] 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.

Earthquake[18] Date Magnitude Area of Intensity 7
1995 Great Hanshin earthquake January 17, 1995 6.9 Mw[19] Kobe, Nishinomiya, Ashiya, Takarazuka, Tsuna, Hokudan, Ichinomiya (Hyogo)
2004 Chūetsu earthquake October 23, 2004 6.6 Mw Kawaguchi (Niigata)
2011 Tōhoku earthquake March 11, 2011 9.0 Mw Kurihara (Miyagi)[20]
2016 Kumamoto earthquakes April 14, 2016 6.2 Mw Mashiki (Kumamoto)
April 16, 2016 7.0 Mw Nishihara, Mashiki (Kumamoto)
2018 Hokkaido Eastern Iburi earthquake September 6, 2018 6.6 Mw Atsuma (Hokkaido)
2024 Noto earthquake January 1, 2024 7.5 Mw Shika (Ishikawa)

Comparison with other seismic scales[edit]

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.[21]

See also[edit]

References[edit]

  1. ^ This is the official name; see http://www.jma.go.jp/jma/en/Activities/earthquake.html and http://www.jma.go.jp/jma/en/Activities/inttable.html, both of which treat it as a proper noun.
  2. ^ ""A closer look at the shindo seismic scale" (in Japanese)". 2018-06-27. Retrieved 2020-03-25.
  3. ^ ""About The JMA's strong ground motion monitoring" (in Japanese)". Retrieved 2019-01-22.
  4. ^ "List of current and past JMA seismic intensity observation points (in Japanese)". Retrieved 2019-01-22.
  5. ^ "Japan Meteorological Agency – Earthquake Information".
  6. ^ "History". Japan Meteorological Agency. JMA. Retrieved 2021-10-13.
  7. ^ a b c Ishibashi, Katsuhiko (April–June 2004). "Status of historical seismology in Japan". Annals of Geophysics. 47 (2/3): 352.
  8. ^ How seismic intensity is calculated (Japanese) Archived 2008-09-17 at the Wayback Machine
  9. ^ "Seismic intensity and acceleration (Japanese)". Archived from the original on 2008-07-05.
  10. ^ Agency, 気象庁 Japan Meteorological. "気象庁 – 計測震度の算出方法".
  11. ^ "JMA seismic intensity scale".
  12. ^ "気象庁 | 震度について". www.jma.go.jp. Retrieved 2021-07-23.
  13. ^ a b "気象庁 | 気象庁震度階級関連解説表". www.jma.go.jp. Retrieved 2021-07-23.
  14. ^ "The Great Hanshin Earthquake Disaster". 2006-09-09. Archived from the original on 2006-09-09.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
  15. ^ "強震観測について". Japan Meteorological Agency (in Japanese). Archived from the original on 2024-01-02. Retrieved 2024-01-17.
  16. ^ "3 観測と地震予知". www.bousaihaku.com. Archived from the original on 2016-03-06. Retrieved 2016-03-06.
  17. ^ "気象庁 | 計測震度の算出方法". www.data.jma.go.jp. Retrieved 2021-07-23.
  18. ^ "【図解】最大震度7を観測した地震（Yahoo!ニュース オリジナル THE PAGE）". Yahoo!ニュース (in Japanese). Retrieved 2022-04-04.
  19. ^ ISC (2015), ISC-GEM Global Instrumental Earthquake Catalogue (1900–2009), Version 2.0, International Seismological Centre
  20. ^ 日本放送協会. "3.11東日本大震災 最大震度7と大津波 巨大地震の衝撃 - NHK". www3.nhk.or.jp. Retrieved 2022-04-04.
  21. ^ 広野卓蔵; 佐藤馨 (1971). "MSK震度と気象庁震度の比較". 気象研究所研究報告 (in Japanese). 22. 気象庁気象研究所: 177–193. Archived from the original (PDF) on 2013-03-20.

External links[edit]


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