Module 11A: Geologic Hazards - Earthquakes

• Hazard - any source of potential damage, harm or adverse health effects on something or someone
• Geohazards - any geological activity that poses harmful risks or damages
• Earthquake - any ground shaking activity due to fault movement, volcanic activity, combination of both, and other factors that deforms the Earth’s lithosphere or crust
• Focus - point within the earth where an earthquake rupture starts
• Epicenter - point on the surface vertically above the focus
• Magnitude - quantifies the energy of an earthquake

  Surface-wave Magnitude Scale

  Moment Magnitude Scale
• Intensity- strength of an earthquake felt by people in a certain locality
• Intensity - strength of an earthquake felt by people in a certain locality
• Seismic Waves - vibrations (waves of energy) generated by earthquakes
• Surface Waves - seismic waves that travel across the Earth’s surface
• Love waves - surface waves that move side-to-side or horizontally
• Rayleigh Waves - surface waves that move in a ”rolling motion”
• Body Waves - seismic waves that travel beneath the Earth’s surface
• Primary Wave - a body wave that can travel through gases, liquids, and solids
• Secondary Wave - a secondary body wave that cannot travel through fluids (gases and liquids)
• Volcanic-Tectonic Earthquake - caused by movement of faults or fractures beneath active volcanoes
• Tectonic Earthquake - caused by movement of faults or tectonic plates
• Fault - a surface where two blocks of rock slip past one another
• Volcanic Earthquake - caused by movement of magma or rock-fracturing beneath volcanoes
• Normal fault - a kind of fault where the hanging wall slips downwards with respect to the footwall
• Fault scarp - planar geomorphic feature formed by offset of Earth’s surface by earthquakes
• Reverse fault - a kind of fault where the hanging wall thrusts upwards with respect to the footwall
• Elastic Rebound Theory - Tectonic earthquakes occur via buildup of stress and strain, undergoing different stages of deformation until it results in brittle rupture

  
• Ground rupture - deformation on the ground that marks the intersection of the fault with the earth’s surface
• Liquefaction - occurs when underlying water-filled sediments during earthquake release liquids which makes the soil fluid-like
• Sinkhole - patches of the earth surface that collapse, forming an abyss
• Tsunami - occurs when an underwater earthquake becomes a source of energy in the ocean for large waves to form
• Ground Shaking - disruptive up, down and sideways vibration of the ground during an earthquake

  ... can lead, not only to infrastructure collapses, but fatalities as well

  ... can trigger the destabilization of a slope which leads to slope failure
• Why do earthquakes happen so often in the Philippines?

  Pacific Ring of Fire and Bounded by Trenches
• 1976 Moro Gulf Earthquake - "Midnight Killer" with a magnitude 7.9 Epicenter: Celebes Sea between Mindanao and Borneo Generated by Cotabato Trench
• 1990 Luzon Earthquake - Magnitude 7.8 Epicenter: Rizal, Nueva Ecija Generated by: strike-slip movements along Northwest segment of Philippine Fault Zone and its splay, Digdig Fault Zone
• What are the two Philvolcs Initiatives?

  HazardHunter PH

  Fault Finder
• The recommendations on how to improve disaster risk response on earthquakes all boil down to National, LGU, and Individual levels