SCI U1

• The Philippines is one of the countries in the world with high disaster risk index. It means that we are vulnerable to different natural hazards like storms, floods, and most of all seismic activities.
• Several earthquakes occur every day but most are weak and generally cannot be felt by people.
• Most of the earthquakes are caused by fault movements, while some are due to volcanic activity.
• Volcanoes and mountains are the most common landforms in the archipelago.
• According to the Philippine Institute of Volcanology and Seismology (PHIVOLCS), there are 23 active volcano and more than 400 mountains in the country.
• Active volcanoes


  that erupted within the last 10,000 years
• Types of volcanoes in the Philippines

  • Active
  • Potentially active
  • Inactive
• As of 2008, PHIVOLCS listed 23 active, 26 potentially active and 281 inactive volcanoes. Out of 23 active volcanoes, 21 had historic eruptions.
• Most volcanoes in the country are subduction-related although there are few exotic types.
• Mayon Volcano


  • Located in Albay
  • The most active volcano in the country
  • Famous for its almost perfect cone shape
• The Philippines is in a zone within the Pacific ocean that covers a collection of moving plate edges forming a "ring" of volcanoes that cause earthquakes. This region is called the Pacific Ring of Fire or the Circum-Pacific belt.
• Around 75% of the world's active and dormant volcanoes can be found in the Pacific Ring of Fire region.
• The Philippines is an archipelago surrounded by subducting plates that provide the ideal condition for volcanic formation resulting to highly active seismicity and volcanism in the country.
• Formation of volcanic arcs

  1. Subduction of an oceanic tectonic plate under another tectonic plate

  2. Oceanic plate saturated with water affects the melting point of the mantle

  3. Subduction goes deeper, increasing pressure, reducing water content

  4. Magma ascends to form an arc of volcanoes parallel to the subduction zone
• Volcanic arcs in the Philippines

  • Luzon Volcanic Arc
  • East-Philippine Volcanic Arc
  • Negros-Panay Arc
  • Sulu-Zamboanga Arc
  • Cotabato Arc
• Volcanic activity


  • Emission of gases
  • Flowing of lava outside the surface
  • Sudden violent explosive bursts
• Magma


  Buoyant molten rock that rises toward the surface, eventually forming a magma chamber
• Volcanic eruption


  When some of the molten materials ascend to the Earth's surface and are extruded as lava
• The Philippines is in a zone within the Pacific ocean that covers a collection of moving plate edges forming a "ring" of volcanoes and earthquakes called Pacific Ring of Fire
• Active volcanoes in the Philippines

  • Mayon (Albay Province)
  • Taal (Batangas)
  • Kanlaon (Negros Oriental)
  • Bulusan (Sorsogon)
• About 23 out of the 220 volcanoes in the Philippines are active according to the Institute of Volcanology and Seismology (PHIVOLCS)
• Active volcanoes


  • Mayon
  • Taal
  • Kanlaon
  • Bulusan
• Potentially active volcanoes do not have any historical record of any eruption but are considered as morphologically young. There are also suspected seismic activity and documented local ground deformation
• Some potentially active volcanoes in the Philippines

  • Apo
  • Corregidor
  • Isarog
  • Lapac
  • Malindig (Marlanga)
  • Mandalagan
  • Mariveles
  • Negron
  • San Cristobal
  • Silay
• Inactive volcanoes have not erupted for at least 10 000 years and are not expected to erupt again in the future. The morphology of these volcanoes was already modified by weathering and erosion
• Inactive volcanoes


  • Bolod
  • Bontes
  • Burgos
  • Calayan
  • Canipo
• Every day, there are records of several seismic activities in the Philippines. It is always possible that a strong earthquake may hit an area anywhere in the archipelago
• Buildings that can withstand high magnitude earthquakes have a broad base, and decreasing size as the building gets taller
• Fault


  Break in Earth's crust where rocks move or slide past one another
• Earthquake


  Occurs when rocks in the lithosphere rupture or move to release accumulated energy and stress
• Epicenter


  The surface directly above the hypocenter, where the greatest damage takes place during earthquakes
• Major faults in the Philippines

  • East Luzon Trough
  • Philippine Trench
  • Manila Trench
  • Negros Trench
  • Sulu Trench
  • Cotabato Trench
  • Philippine Fault or Philippine Fault Zone (PFZ)
  • Valley Fault System or Marikina Valley Fault
  • Macolod Corridor
  • Lubang-Verde Passage Fault System
  • Mindoro or Aglubang Fault
  • Sibuyan Sea Fault
  • Legaspi Lineament
  • Tablas Lineament
  • Mindanao Fault
  • Offshore Cebu-Bohol faults
• The Philippines is comprised of several subduction zones both on its eastern and western part, responsible for most of the significant earthquakes, terrible tsunamis, and some of the worst volcanic eruptions in the archipelago
• Intensity


  A measure of the degree of shaking experienced in an area, a combination of what people felt and the damage observed in structures
• Magnitude


  A quantitative measurement based on instruments, estimating the amount of energy released
• Historical accounts of earthquakes in the Philippines only started during the Spanish colonization in the late 15th century
• Instrumentally-derived parameters for earthquakes in the Philippines started in 1892 onwards
• There are millions of earthquakes that have occurred in the Philippines, some too weak or too deep to be felt, but a few have caused severe damages
• Destructive earthquakes in the Philippines

  • August 2, 1968 (magnitude 7.3, intensity VIII) in Casiguran, Aurora
  • March 17, 1973 (magnitude 7.0) in Ragay Gulf, Bicol Region
  • August 17, 1976 (magnitude 7.9) in Mindanao
  • June 14, 1990 (magnitude 7.1) in Panay
  • July 16, 1990 (magnitude 7.8) in Luzon
• The August 17, 1976 earthquake in Mindanao is considered the most destructive earthquake in the Philippines so far