PHIVOLCS Earthquake Intensity Scale

The PHIVOLCS Earthquake Intensity Scale (PEIS) is a seismic scale used and developed by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) to measure the intensity of an earthquake.

It was developed as upon a specific response to the 1990 Luzon earthquake. PHIVOLCS cites seismic scale specifically developed for the Philippine setting, the different geography of each country and other "geological considerations" led to the development of PEIS. The scale measures the effect of an earthquake on a given area based on its relative effect to people, structures and objects in the surroundings.[1]

The PEIS was adopted in the Philippines in 1996 replacing the Rossi-Forel scale.[2]

Scales

The PEIS has ten intensity scales represented in Roman numerals with Intensity I being the weakest and Intensity X being the strongest.[2]

PHIVOLCS Earthquake Intensity Scale (PEIS)[2]
Intensity
Scale		 Description Equivalent to other
seismic scales[3]
Modified
Mercalli		 Shindo
I Scarcely perceptible
  • Delicately balanced objects are disturbed slightly.
  • Still water in containers oscillates slowly.
 I 0
II Slightly felt
  • Felt by few individuals at rest indoors.
  • Hanging objects swing slightly.
  • Still water in containers oscillates noticeably.
 II 1
III Weak
  • Felt by many people indoors, especially in upper floors.
  • Hanging objects swing moderately.
  • Still water in containers oscillates moderately.
  • Feels like a light truck passing by.
 III 2
IV Moderately strong
  • Felt generally by people indoors and by some people outdoors.
  • Hanging objects swing considerably.
  • Motorcars may rock slightly.
  • Liquids in containers are slightly disturbed.
  • Water in containers oscillates strongly.
  • A rumbling sound may sometimes be heard.
  • Feels like a heavy truck passing by.
 IV 3
V Strong
  • Felt by most people indoors and outdoors.
  • A strong shaking and rocking is felt throughout building.
  • Hanging objects swing violently.
  • Small, light, and unstable objects may fall or overturn.
  • Liquids spill from filled open containers.
  • Vehicles rock noticeably.
  • Leaves and twigs of trees shake.
 V 4
VI Very Strong
  • Furniture and other heavy objects are displaced.
  • Wall plaster may crack.
  • People may lose balance.
  • Small church bells may ring.
  • If on the road, it may feel like driving with flat tires.
  • Very old or poorly built houses and man-made structures are slightly damaged though well-built structures are not affected.
  • Limited rockfalls and rolling boulders occur in hilly to mountainous areas and escarpments.
  • Trees shake.
 VI 5-
VII Destructive
  • Heavy objects and furniture overturn or topple.
  • Difficulty standing on upper floors.
  • Old or poorly-built structures suffer considerable damage.
  • Some well-built structures are slightly damaged.
  • Some cracks may appear on dikes, fishponds, road surface, or concrete hollow block walls.
  • Limited liquefaction, lateral spreading and landslides are observed.
  • Trees shake noticeably.
 VII 5+
VIII Very Destructive
  • People will find it difficult to even stand outdoors.
  • Many well-built buildings are considerably damaged.
  • Concrete dikes and the foundations of bridges are destroyed by ground settling or toppling.
  • Railway tracks are bent or broken.
  • Utility posts, towers, and monuments may tilt or topple.
  • Water and sewer pipes may be bent, twisted, or broken.
  • Liquefaction and lateral spreading cause manmade structures to sink, tilt, or topple.
  • Numerous landslides and rockfalls occur in mountainous and hilly areas.
  • Boulders are thrown out from their positions particularly near the epicenter.
  • Fissures and faults rupture.
  • Trees shake violently.
  • Water splashes over dikes or the banks of rivers.
 VIII, IX 6-
IX Devastating
  • People are forced to the ground.
  • Most buildings are totally damaged.
  • Bridges and elevated concrete structures are toppled or destroyed.
  • Numerous utility posts, towers, and monuments are tilted, toppled, or broken.
  • Sewer pipes are bent, twisted or broken.
  • Landslides and liquefaction with lateral spreadings and sandboils are widespread.
  • The ground is distorted into undulations.
  • Trees are shaken very violently with some toppled or broken.
  • Boulders are commonly thrown out.
  • River water splashes violently or slops over dikes and banks.
 X, XI 6+
X Completely Devastating
  • Many trees are toppled, broken, and uprooted.
  • Practically all man-made structures are destroyed.
  • Massive landslides and liquefaction, large-scale subsidence and the uplifting of land forms and many ground fissures are observed.
  • Changes in river courses and destructive seiches in large lakes occur.
 XII 7

References
  1. "'Shaking Table' at Phivolcs helps Pinoys prepare for quakes". GMA News. 20 January 2010. Retrieved 12 February 2017.
  2. "Making sense of the PHIVOLCS earthquake intensity levels". Official Gazette of the Republic of the Philippines. Retrieved 12 February 2017.
  3. "Final Report" (PDF). Earthquake Impact Reduction Study for Metropolitan Manila, Republic of the Philippines. Japan International Cooperation Agency, Metropolitan Manila Development Authority, Philippine Institute of Volcanology and Seismology; Pacific Consultants International, OYO International Corporation, PASCO Corporation (consultants). 1 (Executive Study): 14. March 2004. Retrieved 12 February 2017.
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