Tectonic processes and hazards

• Tectonic hazard

  Anything that threatens human life or infrastructure because of the processes of plate boundaries and the movement of them
• Most earthquakes occur on plate boundaries
• The most powerful earthquakes occur at conservative plate boundaries
• Ocean fracture zone (OFZ)

  Earthquake activity along mid-ocean ridges
• Continental fracture zone (CFZ)

  Earthquake activity along mountain ranges
• The Pacific Ring of Fire is a very active area for volcanoes and earthquakes
• Intraplate earthquakes

  Earthquakes that occur inside the plate margins, usually weaker
• Volcanic hotspots

  Fractures in the crust where there is a magma plume rising through, creating islands over time
• Constructive margins

  1. Plates move apart, allowing magma to rise

  2. Can be oceanic-oceanic or continental-continental

  3. Eruptions are usually effusive and not very damaging
• Destructive margins

  1. Oceanic plate subducts under continental plate

  2. Forms mountain ranges, large earthquakes, and violent volcanic eruptions

  3. Can also be oceanic-oceanic or continental-continental
• Conservative margins

  1. Plates slide past each other, causing frequent shallow earthquakes

  2. Only occur between oceanic and continental plates
• Earth structure

  Crust, lithosphere, asthenosphere, mantle, outer core, inner core
• Mantle convection

  Convection currents in the mantle that drive plate movement
• Alfred Wegener's theory of continental drift proposed that all continents were once part of a supercontinent called Pangea
• Arthur Holmes proposed the idea of mantle convection as the driving force behind plate movement
• Harry Hess developed the theory of seafloor spreading and mid-ocean ridges
• Paleomagnetism provides evidence for plate movement and seafloor spreading
• Subduction

  Denser oceanic plate sinks under lighter continental plate, causing earthquakes and volcanoes
• Gravitational sliding

  Occurs at constructive margins, where rising magma creates a slight slope for the plates to slide apart
• Slab pull

  The dense, cold oceanic plate pulls itself into the mantle as it subducts
• Constructive margins

  1. Shallow, low-magnitude earthquakes

  2. Small, slow, effusive volcanoes with low gas content

  3. Example: Mid-Atlantic Ridge
• Destructive margins (oceanic-continental)

  1. Deep, high-magnitude earthquakes

  2. Violent, explosive volcanoes

  3. Forms mountain ranges
• Subduction

  • Plate is pulled into the mantle
• Plate boundary activities and hazards

  • Constructive plate margin
  • Destructive plate margin (oceanic-continental)
  • Destructive plate margin (oceanic-oceanic)
  • Collisional plate margin
  • Conservative plate margin
• Constructive plate margin

  • Shallow earthquakes less than 60km deep
  • Low magnitude earthquakes under 5
  • Small, slow volcanoes with low gas content and high viscosity
• Constructive plate margin

  • Mid-Atlantic ridge between Eurasian and North American plates
• Destructive plate margin (oceanic-continental)

  • Large earthquakes up to 9 magnitude
  • Frequent, violent volcanic eruptions of composite volcanoes with high gas and silica content
• Destructive plate margin (oceanic-continental)

  • Nazca and South American plate boundary (Chile 2010 earthquake)
• Destructive plate margin (oceanic-oceanic)

  • Frequent earthquakes but not as large as oceanic-continental
  • Violent volcanic eruptions creating volcanic islands
• Destructive plate margin (oceanic-oceanic)

  • 2018 Hawaii earthquake, 1984 Mauna Loa eruption
• Collisional plate margin

  • Large shallow fault line earthquakes, no volcanic eruptions
• Collisional plate margin

  • Andes in South America (4.9 magnitude earthquake in 2024)
• Conservative plate margin

  • High magnitude shallow earthquakes, very destructive
• Conservative plate margin

  • Pacific and North American plates (San Andreas Fault, 1989 near 7 magnitude earthquake)
• Earthquake hazards

  • Seismic waves (P-waves, S-waves, L-waves)
  • Crustal fracturing
  • Liquefaction
  • Landslides
• 1. waves

  • Fastest seismic waves, cause least damage
• 1. waves

  • Arrive after P-waves, shake ground violently and cause damage
• 1. waves

  • Arrive last, travel horizontally, cause significant damage including crustal fracturing
• Volcanic hazards

  • Pyroclastic flows
  • Ash fall
  • Lava flows
  • Gas eruptions
  • Lahars
  • Jökulhlaups
• Pyroclastic flows

  • Very large, dense, hot ash and gas clouds that flow rapidly down mountainsides