Earth:Strong ground motion

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Short description: Type of earthquake
ShakeMap for the 2001 Nisqually earthquake

In seismology, strong ground motion is the strong earthquake shaking that occurs close to (less than about 50 km from) a causative fault. The strength of the shaking involved in strong ground motion usually overwhelms a seismometer, forcing the use of accelerographs (or strong ground motion accelerometers) for recording. The science of strong ground motion also deals with the variations of fault rupture, both in total displacement, energy released, and rupture velocity.

As seismic instruments (and accelerometers in particular) become more common, it becomes necessary to correlate expected damage with instrument-readings. The old Modified Mercalli intensity scale (MM), a relic of the pre-instrument days, remains useful in the sense that each intensity-level provides an observable difference in seismic damage.

After many years of trying every possible manipulation of accelerometer-time histories, it turns out that the extremely simple peak ground velocity (PGV) provides the best correlation with damage.[1][2] PGV merely expresses the peak of the first integration of the acceleration record. Accepted formulae now link PGV with MM Intensity. Note that the effect of soft soils gets built into the process, since one can expect that these foundation conditions will amplify the PGV significantly.

"ShakeMaps" are produced by the United States Geological Survey, provide almost-real-time information about significant earthquake events, and can assist disaster-relief teams and other agencies.[3]

Correlation with the Mercalli scale

The United States Geological Survey created the Instrumental Intensity scale, which maps peak ground velocity on an intensity scale comparable to the felt Mercalli scale. Seismologists all across the world use these values to construct ShakeMaps.

Instrumental
Intensity
Velocity
(cm/s)
Perceived shaking Potential damage
I < 0.0215 Not felt None
II–III 0.135 – 1.41 Weak None
IV 1.41 – 4.65 Light None
V 4.65 – 9.64 Moderate Very light
VI 9.64 – 20 Strong Light
VII 20 – 41.4 Very strong Moderate
VIII 41.4 – 85.8 Severe Moderate to heavy
IX 85.8 – 178 Violent Heavy
X+ > 178 Extreme Very heavy

Notable earthquakes

PGV
(max recorded)
Mag Depth Fatalities Earthquake
318 cm/s[4] 7.7 33 km 2,415 1999 Jiji earthquake
183 cm/s[5] 6.7 18.2 km 57 1994 Northridge earthquake
170 cm/s[4] 6.9 17.6 km 6,434 1995 Great Hanshin earthquake
152 cm/s[4] 6.6 10 km 11 2007 Chūetsu offshore earthquake
147 cm/s[4] 7.3 1.09 km 3 1992 Landers earthquake
145 cm/s[4] 6.6 13 km 68 2004 Chūetsu earthquake
138 cm/s[4] 7.2 10.5 km 356 injured 1992 Cape Mendocino earthquakes
117.41 cm/s 9.1[6] 29 km 19,747 2011 Tohoku earthquake and tsunami
108 cm/s[7] 7.8 8.2 km 8,857 April 2015 Nepal earthquake
38 cm/s[8] 5.5 15.5 km 0 2008 Chino Hills earthquake
20 cm/s (est)[9] 6.4 10 km 115-120 1933 Long Beach earthquake

See also

References

  1. "INSTRUMENTAL SEISMIC INTENSITY MAPS". http://pasadena.wr.usgs.gov/shake/pubs/shake/node7.html. 
  2. Wu, Yih-Min; Hsiao, Nai-Chi; Teng, Ta-Liang (July 2004). "Relationships between Strong Ground Motion Peak Values and Seismic Loss during the 1999 Chi-Chi, Taiwan Earthquake". Natural Hazards 32 (3): 357–373. doi:10.1023/B:NHAZ.0000035550.36929.d0. 
  3. "ShakeMaps". https://earthquake.usgs.gov/earthquakes/shakemap/. 
  4. 4.0 4.1 4.2 4.3 4.4 4.5 "How Fast Can the Ground Really Move?". INSTITUTE FOR DEFENSE ANALYSES. https://apps.dtic.mil/sti/pdfs/AD1131695.pdf. 
  5. "ShakeMap Scientific Background". https://earthquake.usgs.gov/earthquakes/shakemap/background.php. 
  6. "M9.1 - Tohoku, Japan". United States Geological Survey. https://earthquake.usgs.gov/earthquakes/eventpage/official20110311054624120_30/origin/detail. 
  7. Takai, Nobuo; Shigefuji, Michiko; Rajaure, Sudhir; Bijukchhen, Subeg; Ichiyanagi, Masayoshi; Dhital, Megh Raj; Sasatani, Tsutomu (26 January 2016). "Strong ground motion in the Kathmandu Valley during the 2015 Gorkha, Nepal, earthquake. Earth Planets Space 68, 10 (2016).". Earth, Planets and Space (Takai, N., Shigefuji, M., Rajaure, S. et al.) 68 (1): 10. doi:10.1186/s40623-016-0383-7. 
  8. "M5.5 - Greater Los Angeles area, California". USGS. https://earthquake.usgs.gov/earthquakes/eventpage/usp000gddf#general_region. 
  9. Hough, S. E.; Graves, R. W. (22 June 2020). "Nature:The 1933 Long Beach Earthquake (California, USA) Ground Motions and Rupture Scenario". Scientific Reports 10 (1): 10017. doi:10.1038/s41598-020-66299-w. PMID 32572047. 

Sources