Earth:Peak ground acceleration

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Short description: Maximum ground acceleration during an earthquake at a location

Peak Ground Acceleration (PGA) is equal to the maximum ground acceleration that occurred during earthquake shaking at a location. PGA is equal to the amplitude of the largest absolute acceleration recorded on an accelerogram at a site during a particular earthquake.[1] Earthquake shaking generally occurs in all three directions. Therefore, PGA is often split into the horizontal and vertical components. Horizontal PGAs are generally larger than those in the vertical direction but this is not always true, especially close to large earthquakes. PGA is an important parameter (also known as an intensity measure) for earthquake engineering, The design basis earthquake ground motion (DBEGM)[2] is often defined in terms of PGA.

Unlike the Richter and moment magnitude scales, it is not a measure of the total energy (magnitude, or size) of an earthquake, but rather of how hard the earth shakes at a given geographic point. The Mercalli intensity scale uses personal reports and observations to measure earthquake intensity but PGA is measured by instruments, such as accelerographs. It can be correlated to macroseismic intensities on the Mercalli scale[3] but these correlations are associated with large uncertainty.[4] See also seismic scale.

The peak horizontal acceleration (PHA) is the most commonly used type of ground acceleration in engineering applications. It is often used within earthquake engineering (including seismic building codes) and it is commonly plotted on seismic hazard maps.[5] In an earthquake, damage to buildings and infrastructure is related more closely to ground motion, of which PGA is a measure, rather than the magnitude of the earthquake itself. For moderate earthquakes, PGA is a reasonably good determinant of damage; in severe earthquakes, damage is more often correlated with peak ground velocity.[3]

Geophysics

Earthquake energy is dispersed in waves from the hypocentre, causing ground movement omnidirectionally but typically modelled horizontally (in two directions) and vertically. PGA records the acceleration (rate of change of speed) of these movements, while peak ground velocity is the greatest speed (rate of movement) reached by the ground, and peak displacement is the distance moved.[6][7] These values vary in different earthquakes, and in differing sites within one earthquake event, depending on a number of factors. These include the length of the fault, magnitude, the depth of the quake, the distance from the epicentre, the duration (length of the shake cycle), and the geology of the ground (subsurface). Shallow-focused earthquakes generate stronger shaking (acceleration) than intermediate and deep quakes, since the energy is released closer to the surface.[8]

Peak ground acceleration can be expressed in fractions of g (the standard acceleration due to Earth's gravity, equivalent to g-force) as either a decimal or percentage; in m/s2 (1 g = 9.81 m/s2);[6] or in multiples of Gal, where 1 Gal is equal to 0.01 m/s2 (1 g = 981 Gal).

The ground type can significantly influence ground acceleration, so PGA values can display extreme variability over distances of a few kilometers, particularly with moderate to large earthquakes.[9] The varying PGA results from an earthquake can be displayed on a shake map.[10] Due to the complex conditions affecting PGA, earthquakes of similar magnitude can offer disparate results, with many moderate magnitude earthquakes generating significantly larger PGA values than larger magnitude quakes.

During an earthquake, ground acceleration is measured in three directions: vertically (V or UD, for up-down) and two perpendicular horizontal directions (H1 and H2), often north–south (NS) and east–west (EW). The peak acceleration in each of these directions is recorded, with the highest individual value often reported. Alternatively, a combined value for a given station can be noted. The peak horizontal ground acceleration (PHA or PHGA) can be reached by selecting the higher individual recording, taking the mean of the two values, or calculating a vector sum of the two components. A three-component value can also be reached, by taking the vertical component into consideration also.

In seismic engineering, the effective peak acceleration (EPA, the maximum ground acceleration to which a building responds) is often used, which tends to be ⅔ – ¾ the PGA[citation needed].

Seismic risk and engineering

Study of geographic areas combined with an assessment of historical earthquakes allows geologists to determine seismic risk and to create seismic hazard maps, which show the likely PGA values to be experienced in a region during an earthquake, with a probability of exceedance (PE). Seismic engineers and government planning departments use these values to determine the appropriate earthquake loading for buildings in each zone, with key identified structures (such as hospitals, bridges, power plants) needing to survive the maximum considered earthquake (MCE).

Damage to buildings is related to both peak ground velocity (PGV) and the duration of the earthquake – the longer high-level shaking persists, the greater the likelihood of damage.

Comparison of instrumental and felt intensity

Peak ground acceleration provides a measurement of instrumental intensity, that is, ground shaking recorded by seismic instruments. Other intensity scales measure felt intensity, based on eyewitness reports, felt shaking, and observed damage. There is correlation between these scales, but not always absolute agreement since experiences and damage can be affected by many other factors, including the quality of earthquake engineering.

Generally speaking,

  • 0.001 g (0.01 m/s2) – perceptible by people
  • 0.02  g (0.2  m/s2) – people lose their balance
  • 0.50  g (5  m/s2) – very high; well-designed buildings can survive if the duration is short.[7]

Correlation with the Mercalli scale

The United States Geological Survey developed an Instrumental Intensity scale, which maps peak ground acceleration and peak ground velocity on an intensity scale similar to the felt Mercalli scale. These values are used to create shake maps by seismologists around the world.[3]

Instrumental
Intensity 		Acceleration
(g) 		Velocity
(cm/s) 		Perceived shaking Potential damage
I < 0.000464 < 0.0215 Not felt None
II–III 0.000464 – 0.00297 0.135 – 1.41 Weak None
IV 0.00297 – 0.0276 1.41 – 4.65 Light None
V 0.0276 – 0.115 4.65 – 9.64 Moderate Very light
VI 0.115 – 0.215 9.64 – 20 Strong Light
VII 0.215 – 0.401 20 – 41.4 Very strong Moderate
VIII 0.401 – 0.747 41.4 – 85.8 Severe Moderate to heavy
IX 0.747 – 1.39 85.8 – 178 Violent Heavy
X+ > 1.39 > 178 Extreme Very heavy

Other intensity scales

In the 7-class Japan Meteorological Agency seismic intensity scale, the highest intensity, Shindo 7, covers accelerations greater than 4 m/s2 (0.41 g).

PGA hazard risks worldwide

In India, areas with expected PGA values higher than 0.36 g are classed as "Zone 5", or "Very High Damage Risk Zone".

Notable earthquakes

PGA
single direction
(max recorded) 		PGA
vector sum (H1, H2, V)
(max recorded) 		Mag Depth Fatalities Earthquake
3.23 g [11] 7.8 15 km 2 2016 Kaikoura earthquake
4.36 g [12] 6.9/7.2 8 km 12 2008 Iwate–Miyagi Nairiku earthquake
1.92 g [13] 7.7 8 km 2,415 1999 Jiji earthquake
1.82 g [14] 6.7 18 km [15] 57 1994 Northridge earthquake
1.81 g[16] 9.5 33 km 1,000–6000 1960 Valdivia earthquake
1.51 g [17][18] 6.2[19] 5 km 185 February 2011 Christchurch earthquake
1.47 g [20] 7.1 42 km[21] 4 April 2011 Miyagi earthquake
1.26 g [22][23] 7.1 10 km 0 2010 Canterbury earthquake
1.25 g[24] 6.6 8.4 km 58–65 1971 Sylmar earthquake
1.04 g [25] 6.6 10 km 11 2007 Chūetsu offshore earthquake
1.0 g[26] 6.0 8 km 0 December 2011 Christchurch earthquake
0.98 g [27] 7.0 21 km 119 2020 Aegean Sea earthquake
0.91 g 6.9 16 km 5,502–6,434 Great Hanshin earthquake
0.78 g [28][29] 6.0 6 km 1 June 2011 Christchurch earthquake
0.65 g [30] 8.8 23 km[31] 525 [32] 2010 Chile earthquake
0.6 g [33] 6.0 10 km 143 1999 Athens earthquake
0.51 g [34] 6.4 16 km 612 2005 Zarand earthquake
0.5 g [35] 7.0 13 km 100,000–316,000[36] 2010 Haiti earthquake
0.438 g [37] 7.7 44 km 28 1978 Miyagi earthquake (Sendai)
0.41 g[38] 6.5 11 km 2 2015 Lefkada earthquake
0.4 g [39] 5.7 8 km 0 2016 Christchurch earthquake
0.367 g [40] 5.1 1 km 9 2011 Lorca earthquake
0.18 g [41] 9.2 25 km 131 1964 Alaska earthquake

See also

References

  1. ↑ Douglas, J (2003-04-01). "Earthquake ground motion estimation using strong-motion records: a review of equations for the estimation of peak ground acceleration and response spectral ordinates". Earth-Science Reviews 61 (1–2): 43–104. doi:10.1016/S0012-8252(02)00112-5. Bibcode: 2003ESRv...61...43D. https://strathprints.strath.ac.uk/53451/1/Douglas_ESR_2003_Earthquake_ground_motion_estimation_using_strong_motion.pdf. 
  2. ↑ Nuclear Power Plants and Earthquakes, accessed 8 April 2011.
  3. ↑ 3.0 3.1 3.2 "ShakeMap Scientific Background. Rapid Instrumental Intensity Maps". Earthquake Hazards Program. U. S. Geological Survey. https://earthquake.usgs.gov/earthquakes/shakemap/background.php#intmaps. 
  4. ↑ Cua, G. (2010). "Best Practices" for Using Macroseismic Intensity and Ground Motion Intensity Conversion Equations for Hazard and Loss Models in GEM1. Global Earthquake Model. http://www.globalquakemodel.org/media/publication/GEM-TechnicalReport_2010-4.pdf. Retrieved 11 November 2015. 
  5. ↑ European Facilities for Earthquake Hazard & Risk (2013). "The 2013 European Seismic Hazard Model (ESHM13)". EFEHR. http://www.efehr.org:8080/jetspeed/portal/hazard.psml. 
  6. ↑ 6.0 6.1 "Explanation of Parameters". Geologic Hazards Science Center. U.S. Geological Survey. https://geohazards.usgs.gov/deaggint/2002/documentation/parm.php. 
  7. ↑ 7.0 7.1 Lorant, Gabor (17 June 2010). "Seismic Design Principles". Whole Building Design Guide. National Institute of Building Sciences. http://www.wbdg.org/resources/seismic_design.php. 
  8. ↑ "Magnitude 6.6 – Near the west coast of Honshu, Japan". Earthquake summary. USGS. 16 July 2001. https://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/us2007ewac.php#summary. 
  9. ↑ "ShakeMap scientific background. Peak acceleration maps". Earthquake Hazards Program. U. S. Geological Survey. https://earthquake.usgs.gov/earthquakes/shakemap/background.php#accmaps. 
  10. ↑ "ShakeMap Scientific Background". Earthquake Hazards Program. U. S. Geological Survey. https://earthquake.usgs.gov/earthquakes/shakemap/background.php. 
  11. ↑ Goto, Hiroyuki; Kaneko, Yoshihiro; Young, John; Avery, Hamish; Damiano, Len (4 February 2019). "Extreme Accelerations During Earthquakes Caused by Elastic Flapping Effect". Scientific Reports 9 (1): 1117. doi:10.1038/s41598-018-37716-y. PMID 30718810. Bibcode: 2019NatSR...9.1117G. 
  12. ↑ Masumi Yamada (July–August 2010). "Spatially Dense Velocity Structure Exploration in the Source Region of the Iwate-Miyagi Nairiku Earthquake". Seismological Research Letters v. 81; no. 4. Seismological Society of America. pp. 597–604. http://srl.geoscienceworld.org/cgi/content/extract/81/4/597. 
  13. ↑ "M 7.7 - 21 km S of Puli, Taiwan". USGS. https://earthquake.usgs.gov/earthquakes/eventpage/usp0009eq0/. 
  14. ↑ Yegian, M.K.; Ghahraman; Gazetas, G.; Dakoulas, P.; Makris, N. (April 1995). "The Northridge Earthquake of 1994: Ground Motions and Geotechnical Aspects". Third International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics. Northeastern University College of Engineering. p. 1384. http://www.coe.neu.edu/Depts/CIV/faculty/myegian/library/Thenorthridge%20Earthquake%20of%201994%20Ground%20Motions%20and%20Geotechnical%20Aspects.pdf. 
  15. ↑ "M 6.7 - 1km NNW of Reseda, CA". USGS. https://earthquake.usgs.gov/earthquakes/eventpage/ci3144585/executive/. 
  16. ↑ "M 9.5 - 1960 Great Chilean Earthquake (Valdivia Earthquake)". USGS. https://earthquake.usgs.gov/earthquakes/eventpage/official19600522191120_30/shakemap/analysis/. 
  17. ↑ "Feb 22 2011 – Christchurch badly damaged by magnitude 6.3 earthquake". Geonet. GNS Science. 23 February 2011. http://www.geonet.org.nz/news/feb-2011-christchurch-badly-damaged-by-magnitude-6-3-earthquake.html. 
  18. ↑ "PGA intensity map". Geonet. GNS Science. http://www.geonet.org.nz/var/storage/images/media/images/news/2011/lyttelton_pga/57159-2-eng-GB/lyttelton_pga.png. 
  19. ↑ "New Zealand Earthquake Report – Feb 22 2011 at 12:51 pm (NZDT)". Geonet. GNS Science. 22 February 2011. http://geonet.org.nz/earthquake/quakes/3468575g.html. 
  20. ↑ "Archived copy of USGS Shakemap usc0002ksa". https://earthquake.usgs.gov/earthquakes/shakemap/global/shake/c0002ksa/. 
  21. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named earthquake.usgs
  22. ↑ Carter, Hamish (24 February 2011). "Technically it's just an aftershock". New Zealand Herald (APN Holdings). http://www.nzherald.co.nz/opinion/news/article.cfm?c_id=466&objectid=10708275. 
  23. ↑ "M 7.1, Darfield (Canterbury), September 4, 2010". GeoNet. GNS Science. http://www.geonet.org.nz/earthquake/historic-earthquakes/top-nz/quake-13.html. 
  24. ↑ Cloud & Hudson 1975, pp. 278, 287
  25. ↑ Katsuhiko, Ishibashi (11 August 2001). "Why Worry? Japan's Nuclear Plants at Grave Risk From Quake Damage". Japan Focus (Asia Pacific Journal). http://www.japanfocus.org/-Ishibashi-Katsuhiko/2495. 
  26. ↑ NZ Herald Article – Violence of tremors stuns experts. (24 Dec 2011). [1]. Retrieved 24 December 2011.
  27. ↑ "EERI PERW 2021 – Part 1: Aegean Sea Earthquake". Earthquake Engineering Research Institute. https://slc.eeri.org/2021-sdc/perw/. 
  28. ↑ "Jun 13 2011 – Large earthquakes strike south-east of Christchurch". Geonet. GNS Science. 13 June 2011. http://www.geonet.org.nz/news/archives/2011/jun-2011-large-earthquakes-strike-south-east-of-christchurch.html. 
  29. ↑ "PGA intensity map". Geonet. GNS Science. http://www.geonet.org.nz/var/storage/images/media/images/news/2011/june_2_pga/58225-2-eng-GB/june_2_pga.png. 
  30. ↑ "Informe Tecnico Terremoto Cauquenes 27 de Febrero de 2010 Actualizado 27 de Mayo 2010". http://www.csn.uchile.cl/wp-content/uploads/2016/06/Informe_Terremoto_Cauquenes_2010.pdf. 
  31. ↑ "Archived copy of USGS Magnitude 7 and Greater Earthquakes in 2010". https://earthquake.usgs.gov/earthquakes/eqarchives/year/2010/2010_stats.php. 
  32. ↑ "Subsecretaría del Interior de Chile (31 January 2011). "Informe final de fallecidos y desaparecidos por comuna"". http://www.interior.gob.cl/filesapp/listado_fallecidos_desaparecidos_27Feb.pdf. 
  33. ↑ Anastasiadis A. N.. "The Athens (Greece) Earthquake of September 7, 1999: Preliminary Report on Strong Motion Data and Structural Response". Institute of Engineering Seismology and Earthquake Engineering. MCEER. http://mceer.buffalo.edu/research/Reconnaissance/greece9-7-99/. 
  34. ↑ "Earthquake Mw 6.3 in Iran on February 22nd, 2005 at 02:25 UTC". European-Mediterranean Seismological Centre. http://www.emsc-csem.org/Page/index.php?id=72. 
  35. ↑ Lin, Rong-Gong; Allen, Sam (26 February 2011). "New Zealand quake raises questions about L.A. buildings". Los Angeles Times. http://www.latimes.com/news/local/la-me-quake-california-20110226,0,1231448.story. 
  36. ↑ "Earthquakes with 50,000 or More Deaths". https://earthquake.usgs.gov/earthquakes/world/most_destructive.php.  U.S. Geological Survey, Earthquakes with 50,000 or More Deaths
  37. ↑ Brady, A. Gerald (1980). An investigation of the Miyagi-ken-oki, Japan, earthquake of June 12, 1978. National Bureau of Standards. pp. 123. https://books.google.com/books?id=qEuWntnoZzYC&pg=PA123. 
  38. ↑ Papaioannou, Christos; Karakostas, Christos; Makra, Konstantia; Lekidis, Vassilios; Theodoulidis, Nikos; Zacharopoulos, Stratos; Margaris, Basil; Rovithis, Emmanouil et al. (2018-06-21), THE NOVEMBER 17, 2015 MW6.4 LEFKAS, GREECE EARTHQUAKE: SOURCE CHARACTERISTICS, GROUND MOTIONS, GROUND FAILURES AND STRUCTURAL RESPONSE, https://www.researchgate.net/publication/326009944 
  39. ↑ "Large quake off the coast of Christchurch". http://info.geonet.org.nz/display/quake/2016/02/14/Large+quake+off+the+coast+of+Christchurch. 
  40. ↑ "Los terremotos paradójicos | España | EL PAÍS". http://www.elpais.com/articulo/espana/terremotos/paradojicos/elpepuesp/20110513elpepinac_4/Tes. 
  41. ↑ National Research Council (U.S.). Committee on the Alaska Earthquake, The great Alaska earthquake of 1964, Volume 1, Part 1, National Academies, 1968 p. 285

Bibliography



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