Tectonic Hazards EQ1 - Locations at risk from tectonic hazards Flashcards
What is a tectonic hazard?
A volcanic or seismic event that has the potential to impact people, the built environment, the economy and the living environment.
What is the global distribution of earthquakes?
The main earthquake zones are often found in clusters along plate boundaries - 90% of earthquakes are found at plate boundaries.
Some earthquakes are away from plate boundaries (intra-plate) but these are less common.
Most earthquakes occur around the Pacific Ring of Fire.
What is the global distribution of volcanoes?
Commonly found at the regions where plate margins occur, for example around the Pacific Ring of Fire. However they can occur away from plate boundaries, at ‘hotspot’ regions.
Volcanoes are most commonly found at divergent and convergent boundaries rather than conservative boundaries.
What is the global distribution of tsunamis?
Most tsunamis are generated along subduction zones, and 90% occur around the Pacific Basin
What happens at divergent plate boundaries?
Two plates are moving away from each other (can be continental or oceanic), leading to new crust being created by magma being pushed up from the mantle.
Magma produced here is basaltic (low viscosity). Eruptions tend to be less powerful (effusive).
What happens at convergent plate boundaries? (oceanic-continental)
Where two plates meet, the denser oceanic lithosphere is forced down and under the more buoyant continental lithosphere in the process of subduction. This leads to the formation of a deep sea trench.
The friction between the plates causes earthquakes along the surface of the subducting plate. This is the Benioff zone.
The subducting plate metls and produces Rhyolitic magma which is viscous and can cause powerful eruptions.
What happens at transform plate boundaries?
Two plates are sliding past each other, often at different speeds. This causes a build up of friction as they drag against each other. Responsible for high magnitude and shallow earthquakes.
Volcanism rare here.
What is a volcanic hotspot, and how do volcanoes form here?
A volcanic hotspot is an area of volcanic activity on the earths surface caused by a mantle plume deep in the earth. The mantle plume is abnormally hot rock that rises due to convection. As the tectonic plate moves over the hotspot like a conveyer belt, a series chain of volcanoes forms (e.g. Hawaii)
What are the properties of the two different types of crust?
Oceanic crust - thin, composed primarily of basalt but denser
Continental crust - thicker, composed primarily of granite and less dense
How do convection currents drive plate movement?
It is thought that convection currents only have a small impact on plate motion. Slab pull and ridge push are thought to be more significant.
How does slab pull drive plate movement?
The force of a cold, dense oceanic plate plunging into the mantle due to it’s own weight drives the movement of the plate
How does ridge push drive plate movement?
Rigid lithosphere slides down the hot, raised asthenosphere below mid ocean ridges, pushing plates away from each other
What is sea floor spreading?
The divergent motion of oceanic plates away from each other and the input of magma forming a mid ocean ridge, for example the Mid-Atlantic Ridge
What is paleomagnetism?
Paleomagnetism is the record of the Earth’s magnetic field in rocks, sediment and archaeological materials
How does paleomagnetism provide evidence for sea floor spreading?
Zones of magma ‘lock in’ the Earth’s magnetic polarity, when it changes every million or so years, so scientists can use this to create a ‘geo-timeline’
