Lecture 3

• Geological Hazards are those geologic conditions that present a risk to life (injury or death), of substantial loss or damage to property, or damage to the environment
• Natural disasters like earthquakes and tsunamis are linked to plate tectonics, the grinding movement of pieces of Earth's crust
• With the present state of technology, most geologic events cannot be prevented or even predicted with any precision
• Landslides are an exception: they can often be prevented
• Areas prone to such events can be identified as earthquake fault zones, active volcanoes, and coastal areas susceptible to tsunamis
• Geological Hazards

  • Earthquake Hazards
  • Volcanic Hazards
  • Landslide Hazards
• Earthquake


  also called temblors are weak to violent shaking of the ground produced by the sudden movement of rock materials below the earth's surface
• Focus


  Point inside the earth where the earthquake started, sometimes called the hypocenter

  
• Epicenter


  Point on the surface of the earth directly above the focus
• Magnitude


  Proportional to the energy released by an earthquake at the focus, calculated from earthquakes recorded by a seismograph, represented by Arabic numbers
• Intensity


  Strength of an earthquake as perceived and felt by people in a certain locality, a numerical rating based on the relative effects to people, objects, environment, and structures, represented by Roman numerals
• In the Philippines, the intensity of an earthquake is determined using the PHIVOLCS Earthquake Intensity Scale (PEIS)
• Types of earthquakes

  • Tectonic earthquakes
  • Volcanic earthquakes

  
• Tectonic earthquakes


  Produced by sudden movement along faults and plate boundaries

  
• Volcanic earthquakes


  earthquakes induced by rising lava or magma beneath active volcanoes
• The Philippine Institute of Volcanology and Seismology (PHIVOLCS) is a service institute of the Department of Science and Technology (DOST) that is principally mandated to mitigate disasters that may arise from volcanic eruptions, earthquakes, tsunami and other related geotectonic phenomena
• Earthquake Hazards


  • Ground Rupture
  • Ground Shaking
  • Liquefaction
  • Earthquake-induced Landslide
  • Tsunami
• Ground Rupture


  Deformation on the ground that marks the intersection of the fault with the earth's surface
• Ground Shaking


  Disruptive up, down and sideways vibration of the ground during an earthquake, can cause damage or collapse of structures and consequently hazards like liquefaction and landslide
• Liquefaction


  Phenomenon wherein sediments, especially near bodies of water, behave like liquid similar to a quicksand, causing sinking and/or tilting of structures above it, sandboils, and fissuring
• Sand boils


  • Created in the January 6, 2001 Bhuj, India earthquake (moment magnitude 7.6), caused by soil losing its internal cohesion during strong shaking
• Earthquake-induced Landslide


  Down slope movement of rocks, solid and other debris commonly triggered by strong shaking, causing erosion, burial and blockage of roads and rivers
• Tsunami


  Series of waves caused commonly by an earthquake under the sea, causing flooding, coastal erosion, and drowning of people and damage to properties
• 2011 Japan earthquake and tsunami


  • Magnitude 9.0 earthquake struck off Japan's northeastern shore, generating enormous tsunami waves that spread across miles of shoreline, climbing as high as 130 feet (40 meters), tearing apart coastal towns and villages, carrying ships inland, and damaging the Fukushima Daiichi Nuclear Power Plant
• Most Destructive Earthquakes in the Philippines

  • Moro Gulf Earthquake (1976 Mag. 8.1)
  • Luzon Earthquake (1990 Mag. 7.8)
  • Casiguran Earthquake (1968 Mag. 7.3)
  • Bohol Earthquake (2013 Mag. 7.2)
  • Panay Earthquake (1990 Mag. 7.1), Mindoro Earthquake (1994 Mag. 7.1)
  • Ragay Gulf Earthquake (1973 Mag. 7.0)
  • Davao del Sur Earthquake (2019 Mag. 6.9)
  • Palimbang Earthquake (2002 Mag. 6.8), Bohol Earthquake (1990 Mag. 6.8)
  • Negros Oriental Earthquake (2012 Mag. 6.7)
  • Surigao del Norte Earthquake (2017 Mag. 6.7)
• Top 5 Biggest Earthquake ever recorded

  • Valdivia, Chile (22 May 1960 Mag. 9.5)
  • Alaska, USA (27 March 1964 Mag. 9.2)
  • Sumatra (26 December 2004 Mag. 9.1)
  • Tohoku (11 March 2011 Mag. 9.1)
  • Kamchatka, Russia (5 November 1952 Mag. 9.0)
• Volcano


  A vent, hill or mountain from which molten or hot rocks with gaseous material have been ejected, also craters, depressions, hills or mountains formed by removal of pre-existing material or by accumulation of ejected materials
• The Philippines sits on a unique tectonic setting ideal to volcanism and earthquake activity, situated at the boundaries of two tectonic plates - the Philippine Sea Plate and the Eurasian plate - both of which subduct or dive beneath
• The 2011 earthquake recorded in Japan was the most powerful earthquake recorded to date. Its epicentre was located approximately 72km off the northeast coast of Honshu (the largest island of Japan) and was so powerful it was later estimated that the Earth had been shifted on its axis by between 10 and 25cm, while Honshu was moved 2.4m east.
• Geological Hazards


  • Earthquake Hazards
  • Volcanic Hazards
  • Landslide Hazards
• Volcano


  • A vent, hill or mountain from which molten or hot rocks with gaseous material have been ejected
  • Also craters, depressions, hills or mountains formed by removal of pre-existing material or by accumulation of ejected materials
• The Philippines sits on a unique tectonic setting ideal to volcanism and earthquake activity. It is situated at the boundaries of two tectonic plates – the Philippine Sea Plate and the Eurasian plate – both of which subduct or dive beneath the archipelago along the deep trenches along its east and west seaboard.
• Ring of Fire


  • also called Circum-Pacific Belt, a path along Pacific Ocean characterized by active volcanoes and frequent earthquakes.
  • length is approximately 40,000 kilometers (24,900 miles).
  • traces boundaries between tectonic plates— Pacific, Juan de Fuca, Cocos, Indian-Australian, Nazca, North American, and Philippine Plates.
• Seventy-five percent of Earth's volcanoes—more than 450 volcanoes—are located along the Ring of Fire. Ninety percent of Earth's earthquakes occur along its path, including the planet's most violent and dramatic seismic events.
• Volcanic hazards directly associated with eruption

  • Lava flow
  • Tephra fall or ashfall and ballistic projectiles
  • Pyroclastic density currents or PDCs (pyroclastic flow, pyroclastic surge, base surge)
  • Lateral blast
  • Volcanic gas
• Volcanic hazards indirectly associated with eruption

  • Lahar, flooding
  • Debris avalanche, landslide
  • Volcanic tsunami
  • Ground deformation (subsidence, fissuring)
  • Secondary explosion, PDCs and ashfall
• Volcano classification in the Philippines

  • Active Volcanoes
  • Potentially Active Volcanoes
  • Inactive Volcanoes
• Landslide


  The mass movement of rock, soil, and debris down a slope due to gravity. It occurs when the driving force is greater than the resisting force. It is a natural process that occurs in steep slopes. The movement may range from very slow to rapid. It can affect areas both near and far from the source.
• Landslide materials


  • Soil
  • Debris
  • Rock
• Landslide Triggers - Natural


  • Intense Rainfall
  • Weathering of Rocks
  • Ground Vibrations Created During Earthquakes
  • Volcanic Activity