Hazards from Tectonic Processes 9.1 Flashcards
Where do Earthquakes occur?
- Clear linear chains along plate boundaries (Mid-atlantic ridge)
- Broad chains along subduction zones (Nazca plate)
- Few happen not on boundaries due to either hot spots or human activity
Where are volcanoes?
- 75% are along the ring of fire
- Hot spots
- Along Plate boundaries (Destructive and constructive only)
What Hazards are on Conservative Plate Boundaries?
- Intense Earthquakes due to friction (e.g. San-Andreas fault line)
- No volcanic eruptions
What hazards occur on Collision Plate Boundaries?
- Earthquakes due to collision and friction along the boundary
- No volcanic eruptions
What hazards occur on destructive plate boundaries?
- Shallow to deep earthquakes, inclined along the benioff zone where the slab pull occurs
- Explosive ashy viscous volcanic eruptions due to greater melting causing silica rich magma
What hazards are at Constructive plate boundaries?
- Moderate Earthquakes as a result of weak oceanic crust being moved by volcanic intrusions
- Fluid basaltic lava rises to form new oceanic crust
Why do volcanoes occur?
Tectonic plates move by convection currents but do not move smoothly due to intense friction, if they lock up huge amounts of tension builds up.
When tension is too great the plates slip causing a rapid release of pressure, a earthquake.
Name the two types of Body waves:
- Primary waves: incident compresses rock, causing a band of compression to move in direction of the wave
- Secondary waves: incident rock compresses sideways causing deformation in one direction and then adjacent layers to move in the opposite direction.
Important to note: P waves occur first followed by S waves at 60% speed, P waves can cause liquefaction
Name two types of Surface Waves:
- Raleigh waves: motion similar to water waves, the ground rolls bur particles rotate away from direction of travel
- Love waves: faster than Raleigh waves, propagate across the Earth’s surface, particles move side to side perpendicular to the path of the wave’s energy
Surface waves do the most damage in a earthquake event.
Two types of Seismic Scales
- Mercalli; the observed damage
- Richter scale; quantitative measurement of earthquake amplitude
What hazards do earthquakes cause?
Primary Hazards: Ground shaking and surface faulting (cracks)
Secondary Hazards: Landslides, Soil Liquefaction and Tsunami
What are the impacts on lives and property from Earthquakes?
Primary Impacts: Death, panic, shock and building and infrastructure collapse
Secondary Impacts: Homelessness, Disease (e.g. cholera) fires and floods and loss of communications
What are the impacts on Lives and property from Volcanoes?
Primary Impacts: Destruction and Injuries
Secondary Impacts: Flight disruption, atmospheric cooling, crop damage famine and homelessness.
PPM of Earthquakes
Prediction: Short term prediction is impossible, but strain cycles can be analysed to give approximate intervals.
Preparation/ Protection: Building design (shock absorbers cross bracing etc), safe houses and evacuation plans
Monitoring: Gas emissions, strain meters, lasers and ground tilt with seismometers
PPM of Volcanoes
Prediction: can be roughly predicted due to the run up prior to hazardous events; Satellite imaging, seismometers, Ultrasound and Chemical sensors.
Preparation/Protection: Possible to evacuate given lengthy prediction and measuring, lava dams and increased levees on outburst floodplains
Monitoring: Similar to prediction
