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The Phivolcs Earthquake Intensity Scale: How each intensity feels
Thursday 9th of February 2012

TACLOBAN CITY, Leyte, February 10 (PIA) --  Even ordinary citizens can determine the intensity of the earthquake they are experiencing with the help of the Phivolcs Earthquake Intensity Scale (PEIS), Philippine Institute of Volcanology and Seismology (Phivolcs) Director Renato U. Solidum Jr. said in a chance interaction.

 
Dr. Solidum was a guests during the 25th Anniversary celebration of the Philippine Information Agency and it was at lunch when he obligingly answered the questions of several PIA directors.
 
The Philippine Institute of Volcanology and Seismology (Phivolcs) is the government agency that deals with tectonic and volcanic activities in the Philippines. One of the major concerns of this government agency is the monitoring of earthquakes that affects the country.
 
The Philippines is located at the rim of the Pacific Ring of Fire and the country experiences mild earthquakes every day because of this. With the many earthquakes that rock the country every day, how does Phivolcs determine if the earthquake is destructive or not? The answer to that is the Phivolcs Earthquake Intensity Scale.
 
 
The PEIS is felt on the relative effect of the earthquake to people, structures, objects, and surroundings. The scale starts from Intensity I, which is the weakest, to Intensity X, which is the strongest.
 
The PEIS flyer showed that an earthquake with: 
 
Intensity I is Scarcely Perceptible. It is scarcely perceptible to people under favorable circumstances. Delicately balanced objects are disturbed slightly. Still water in containers oscillates slowly. 
 
Intensity II is Slightly Felt. It is felt by few individuals at rest indoors. Hanging objects swing slightly. Still water in containers oscillates noticeably.
 
Intensity III is Weak. It is felt by many people indoors especially in upper floors of buildings. Vibration is felt like one passing of a light truck. Dizziness and nausea are experienced by some people. Hanging objects swing moderately. Still water in containers oscillates moderately. 
 
Intensity IV is Moderately Strong. It is felt generally by people indoors and by some people outdoors. Light sleepers are awakened. Vibration is felt like a passing of heavy truck. Hanging objects swing considerably. Dinner, plates, glasses, windows and doors rattle. Floors and walls of wood framed buildings creak. Standing motor cars may rock slightly. Liquids in containers are slightly disturbed. Water in containers oscillates strongly. Rumbling sound may sometimes be heard.
 
Intensity V is Strong. It is generally felt by most people indoors and outdoors. Many sleeping people are awakened. Some are frightened, some run outdoors. Strong shaking and rocking felt throughout building. Hanging objects swing violently. Dining utensils clatter and clink; some may be damaged.  Small, light and unstable objects may fall or overturn. Liquids spill from open containers. Standing vehicles rock noticeably. Shaking of leaves and twigs of trees are noticeable. 
 
Intensity VI is Very Strong. Many people become scared;  many may run outdoors. Some people lose their balance. Motorists feel like driving in flat tires. Heavy objects or furniture move or may be shifted. Small church bells may ring. Wall plaster may crack. 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 noticeably.
 
Intensity VII   is Destructive. Most are frightened and run outdoors. People find it difficult to stand in upper floors. Heavy objects and furniture overturn or topple. Big church bells may ring. Old or poorly-built structures suffer considerably damage. Some well-built structures may be damaged slightly. Some cracks may appear on dikes, fishponds, road surface, or concrete hollow block walls. Limited liquefaction, lateral spreading, and landslides are observed. Trees shake visibly. (Liquefaction is a process by which loose saturated sand lose strength during an earthquake and behave like liquid).
 
Intensity VIII is Very Destructive. People become panicky. People find it difficult to stand outdoors. Many well-built buildings are considerably damaged. Concrete dikes and foundation of bridges are destroyed by ground settling or toppling. Railway tracks are bent or broken. Tombstones may be displaced, twisted, or overturned. Utility posts, towers, and monuments may tilt or topple. Water and sewer pipes may be bent, twisted, or broken. Liquefaction and lateral spreading cause man-made structure to sink, tilt, or topple. Landslides and rockfalls occur in mountainous and hilly areas. Boulders roll out from their positions particularly those near the epicenter. Fissures and faults rapture may be observed. Trees violently shake. Water splash over dikes or banks of rivers.
 
Intensity IX is Devastating. People are forcibly thrown to ground. Many cry and shake with fear. Most buildings are totally damaged. Bridges and elevated concrete structures are toppled or destroyed. Numerous utility posts, towers, and monument are tilted, toppled, or broken. Water 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 on slops over dikes and banks.
 
Intensity X is Completely Devastating. Practically all man-made structures are destroyed. Massive landslides and liquefaction, large scale subsidence and uplifting of land forms and many ground fissures are observed. Changes in river courses and destructive seiches in large lakes occur. Many trees are toppled, broken and uprooted.
 
With the PEIS as guide, people will know the severity of the earthquake. (Erlinda Olivia P. Tiu - PIA 8)
 
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