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• Potential earthquake hazard

  Anything that includes a physical phenomenon associated with an earthquake that may produce adverse effects on human activities
• Earthquake magnitude

  • Measured at the epicenter - the point on the Earth's surface directly above the hypocenter
  • Measured on one of the scales based on the work of Charles Richter
  • Describes the total energy released by earthquake
• Factors that determine the amount of loss and destruction caused by an earthquake

  • Duration of shaking
  • Distance from the fault
  • Local conditions
  • Population density
  • Building quality
• Earthquake magnitude descriptors

  • Great (8 and higher)
  • Major (7-7.9)
  • Strong (6-.6.9)
  • Moderate (5-.5.9)
  • Light (4-4.9)
  • Minor (3-3.9)
  • Very minor (Less than 3)
• Great (8 and higher) magnitude earthquakes have 1 per year on average and have total destruction and high loss of life
• Major (7-7.9) magnitude earthquakes have 18 per year on average and have serious building damage and major loss of life
• Strong (6-.6.9) magnitude earthquakes have 120 per year on average and have large losses, especially in urban areas
• Moderate (5-.5.9) magnitude earthquakes have 800 per year on average and have significant losses in populated areas
• Light (4-4.9) magnitude earthquakes have 6200 per year on average and are usually felt with some instructional damage
• Minor (3-3.9) magnitude earthquakes have 49000 per year on average and are typically felt but usually little damage
• Very minor (Less than 3) magnitude earthquakes have 9000 per day on average and are not felt but recorded
• Earthquake intensity


  Measure of shaking at each location, and this varies from place to place, depending mostly on the distance from the fault rupture area
• Earthquake intensity is traditionally a subjective measure derived from human observations and reports of felt shaking and damage, but can now be calculated using instrumental data
• Primary earthquake hazards

  • Ground shaking
  • Ground rupture and fissuring
  • Liquefaction
  • Earthquake-induced landslide
  • Tsunami
  • Seiches
• Ground shaking


  • Hazard created by earthquakes and a trigger for another hazard such as liquefaction and landslides
  • Recorded in terms of velocity of the ground, acceleration of ground motion, frequency content of the shaking, and duration
• Ground rupture and fissuring

  Deformation on the ground that marks the interaction of the fault with the earth's surface
• Liquefaction


  Mixing of sand or soil and groundwater (water underground) during the shaking of a moderate or strong earthquake, a hazard in areas that have groundwater near the surface and sandy soil
• Earthquake-induced landslide


  Downslope movement of rocks, soil and other debris commonly triggered by strong shaking
• Tsunami


  Huge wave caused by an earthquake under the ocean, can be tens of feet high when they hit the shore and can do enormous damage to the coastline, a series of waves caused commonly by an earthquake under the sea
• Seiches


  Small tsunamis that occur on lakes that are shaken by the earthquake, usually only a few feet high but can still flood or knock down houses, and tip over trees
• Natural warning signs for a tsunami

  • Severe ground shaking from local earthquakes
  • Water receding from the coast, exposing the ocean floor, reefs and fish
  • Abnormal ocean activity, a wall of water, and an approaching tsunami create a loud "roaring" sound similar to that of a train or jet aircraft
• Lahar


  An Indonesian term that describes a hot or cold mixture of water and rock fragments flowing down the slopes of a volcano and river valleys
• Lahar


  • Its size affects how far it may flow
  • When lahar rushes downstream from a volcano, its size, speed, and the amount of water and rock affect its impact
• Lahar


  The surge of water and rock debris often erodes rock vegetation from the side of a volcano and along the river valley it enters
• Ash fall


  A rain of airborne ash resulting from a volcanic eruption
• Ash fall


  • It can have a serious detrimental effect on crops and livestock depending mainly on ash thickness, the type, and the growing condition of a crop
  • Fluorine poisoning and death can occur in livestock that graze on ash-covered grass if fluoride is present
• Pyroclastic flow


  Heavier than-air gas-particle emulsion that can attain temperatures over 1000C
• Pyroclastic flow


  • It ranges from high-density flows that move down and move across the water
  • Pyroclastic surge is a synonym for dilute pyroclastic flow
• Pyroclastic density currents


  Gravity-driven rapidly moving, ground-hugging mixtures of rock fragments and hot gasses
• Pyroclastic density currents


  • Temperatures may be as hot as 900 degrees Celsius, or as cold as steam
  • They are highly destructive owing to their mass, high temperature, high velocity, and great mobility
  • Deadly effects include asphyxiation, burial, incineration, and crushing from impacts
• Tephra Fall and Ballistic Projectiles


  • They can endanger life and property by the force of impact of falling fragments
  • Loss of agricultural lands
  • Producing suspensions of fine-grained particles in air and water
  • Carrying noxious gases, acids, salts, and close to vent, heat
• Mitigation of Tephra Fall and Ballistic Projectiles


  1. Clearing tephra from the roofs as it accumulates

  2. Designing roofs with steep slopes

  3. Strengthening roofs and walls

  4. Designing filters for machinery

  5. Wearing respirators or wet clothes over the mouth and nose

  6. Developing and releasing information about the incident
• Volcanic Gases


  • Magma contains dissolved gasses that are released in the atmosphere during the eruption and while the magma lies close to the surface and hydrothermal system
  • They are mostly noxious and smell bad, but can cause mass fatalities