Tectonics Flashcards
Seismic hazards
Generated when rocks within 700km of the Earths surface come under such stress that they break and become displaced
Volcanic hazards
Associated with eruption events
Intra-plate earthquakes
These occur in the middle or interior of tectonic plates and are much rarer than boundary earthquakes
Volcano
A landform that develops around a weakness in the Earths crust from which molten magma, volcanic rock and gases are ejected or extruded
Plate tectonics
Theory developed to explain the large scale movements of the lithosphere. It was based around the evidence from sea floor spreading and ocean topography marine magnetic anomalies paleomagnetism and geomagnetic field reversals. A knowledge of earths interior and outer structure is essential for understanding plate tectonics
Lithosphere
The surface layer of the Earth is a rigid outer shell composed of the crust and upper mantle. It is on average 100km deep. The lithosphere is always moving but very slowly fuelled by rising heat from the mantle which creates convection currents. The distinction between lithosphere and asthenosphere is one of physical strength rather than a difference in physical composition. The lithosphere is broken into huge sections which are the tectonic plates
Subduction zones
Broad areas where two plates are moving together often with the thinner more dense oceanic plate descending beneath a continental plate. The contact between the plates is sometimes called a thrust or megathrust fault. Where the plates are locked together frictional stress builds. When that stress exceeds a threshold a failure occurs along the fault plane that can result in a megathrust earthquake releasing strain energy and radiating seismic waves. It is common for the leading edge to lock under high friction. The locked fault can hold for hundreds of years building up enormous stress before releasing. The process of strain stress and failure is referred to as the “elastic-rebound theory”
Locked fault
A fault that is not slipping because the frictional resistance on the fault is greater than the shear stress across the fault is stuck. Such faults may store strain for extended periods that is eventually released in a large magnitude earthquake when the frictional resistance is eventually overcome. The 2004 Indian Ocean tsunami was the result of a megathrust locked fault with strain building up at around 20mm per year. It generated huge seismic waves and the devastating tsunami
Hypocentre
Is the focus point within the ground where the strain energy of the earthquake stored in the rock is first released. The distance between this and the epicentre on the surface is called focal length
Soil liquefaction
The process by which water-saturated material can temporarily lose normal strength and behave like a liquid under the pressure of strong shaking. Liquefaction occurs in saturated soils. An earthquake can cause the water pressure to increase to the point where the soil particles can move easily especially in poorly compacted sand and silt
Intensity
A measure of the ground shaking. It is the ground shaking that causes building damage and collapse and the loss of life from the hazard
Magnitude
The magnitude of an earthquake in related to the amount of movement or displacement in the fault which is in turn a measure of energy release. It’s measure at the epicentre
Epicentre
The location on the earth surface that is directly above the earthquake focus ie the point where an earthquake originates
Tsunami
Characterised by: Long wavelengths (150-1000km) Low amplitude (0.5-5m) Fast velocities (up to 600 kph in deep water)
Hazard
A perceived natural/geophysical event that has the potential to threaten both life and property
Disaster
The realisation of a hazard when it causes significant impact on a vulnerable population. CRED says a hazard become a disaster when:
10 or more people are killed
100 or more people are affected
Risk
The exposure of people to a hazardous event. More specifically it is the probability of a hazard occurring that leads to the loss of lives or livelihood
Resilience
In the context of hazards and disasters, resilience can be thought of as the ability of a system community or society exposed to hazards to resist absorb and recover from the effects of a hazard
Development
Development is linked to an improving society enabling people to achieve their aspirations. It includes the provision of social services acquisition of economic assets, improved productivity and reducing vulnerability to natural disasters. Low levels of development are closely associated with high levels of risk and vulnerability to natural disasters
Tectonic hazard profile
A technique used to try to understand the physical characteristics of different of different types of hazards. Hazard profiles can also be used to analyse and assess the same hazards which take place in contrasting locations or at different times. Looks at frequency, duration and speed of onset
Inequality
Usually refers to an unfair situation or distribution of assets and resources. It may also be used when people nations and non state players have different levels of authority competence and outcomes
Governance
The sum of the many ways individuals and institutions manage their common affairs. It is a continuing process through which conflicting or diverse interests may be accommodated and co-operative action may be taken. It includes formal institutions and regimes empowered to enforce compliance as well as informal arrangements that people and institutions have either agreed to or perceived to be in their interest
Disaster hotspot
A country or area that is extremely disaster prone for a number of reasons
