Earthquakes

• The Philippines is a country located near the Pacific Ocean within the Ring of Fire.
• Earthquakes happen when there is a slip of rocks along the fault.
• We have a ripe fault line in Leyte called the Central Leyte Fault.
• Fault is a crack or break on the surface of the crust where two blocks of rocks slip
• The point where the earthquake happens is called the focus, and above it is called the epicenter.
• Three main types of faults:

  • Normal fault
  • Reverse fault
  • Strike-strip fault
• Normal fault is a fault in which the block above the fault has moved downward relative to the block below.
• A Reverse fault in which the upper block, above the fault plane, moves up and over the lower block.
• Strike-slip faults are vertical (or nearly vertical) fractures where the blocks have mostly moved horizontally.
• The Philippines uses the Richter scale in measuring the magnitude. It ranges from 1-10.
• To measure the intensity, the Philippines uses the PHIVOLCS Earthquake Intensity Scale (PEIS), which also ranges from 1 – 10.
• Another instrument that can be used in measuring the intensity of an earthquake and that is the Modified Mercalli Scale, which ranges from 1- 12.
• Phivolcs Intensity Scale:

  • I. Scarcely Perceptible
  • II. Slightly Felt
  • III. Weak
  • IV. Moderately Strong
  • V. Strong
  • VI. Very Strong
  • VII. Destructive
  • VIII. Very Destructive
  • IX. Devastating
  • X. Completely Devastating
• Scarcely Perceptible is when delicately balanced objects are disturbed slightly.
• Slightly felt is Felt by few individuals at rest indoors. Hanging objects swing slightly.
• Weak is felt by many people indoors especially in upper floors of buildings. Vibration is felt like one passing of a light truck.
• Moderately Strong is felt generally by people indoors and by some people outdoors. Light sleepers are awakened.
• Strong 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 and Hanging objects swing violently.
• Very strong is when many people are frightened; many run outdoors. Some people lose their balance and motorists feel like driving in flat tires.
• Destructive is when people find it difficult to stand in upper floors. Heavy objects and furniture over turn or topple. Old or poorly-built structures suffer considerably 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 are shaken strongly
• Very Destructive is when People are panicky. People find it difficult to stand even outdoors. Many well-built buildings are considerably damaged. Concrete dikes and foundation of bridges are destroyed by ground settling or toppling. Numerous landslides and rockfalls occur in mountainous and hilly areas.
• Devastating is when 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. 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.
• Completely Devastating is Practically all man-made structures are destroyed. Changes in river courses and destructive seiches in large lakes occur. Many trees are toppled, broken and uprooted.