Earthquakes Flashcards

Question

What is the Benioff zone?

Answer 1

The area where friction is created between colliding tectonic plates, resulting in intermediate and deep earthquakes.

Answer 2

Oceanic plate is denser, so when the plates collide, the oceanic plate slides beneath the continental plate into the mantle and melts. Deep ocean trenches mark the place where oceanic plate starts to sink beneath the continental plate. The subduction also leads to the formation of fold mountains. Volcanic eruption are also generated as magma created by the melting oceanic plate pushes up through faults in the continental crust to reach the surface - where it causes explosive volcanic eruptions.

Answer 3

The denser or faster oceanic plate is subducted beneath the other. Deep ocean trenches form where this occurs, and the subducted plate then melts - creating magma, which rises up from the Benioff zone to form underwater volcanoes. The subduction also produces shallow- to deep-focus earthquakes - e.g. the 2004 Indian Ocean tsunami

Answer 4

A collision margin occurs. As both plates are about the same density, and are less dense than the asthenosphere beneath them, neither plate is actually subducted. Instead they collide and sediments between them are crumpled and forced up to form high fold mountains, like the Himalayas. However, there can be some subduction, caused when the compressed (therefore denser) sediments result in plate subduction beneath them. There is no volcanic activity, but any earthquakes are likely to have a shallow focus - increasing their severity.

Answer 5

As the two plates collide, the continental plate is folded and slowly pushed up, forming chains of fold mountains.

Answer 6

Over millions of years, these growing volcanoes rise above the sea level to form separate island volcanoes, which are usually found in curved lines called island arcs.

Answer 7

Two plates are moving apart

Answer 8

In oceans = mid-ocean ridges On continents = rift valleys

Answer 9

``` Mid-ocean ridges of underwater mountains extend for over 60,000km across the world’s ocean floors. Regular breaks (called transformer faults) cut across these ridges as they spread at different rates. ``` Shallow-focus earthquakes (less than 70km depth) occur, but they pose little risk to humans because the shocks are minor and occur underwater. Regular volcanic eruptions also create submarine volcanoes along these mid-ocean ridges, some of which grow above sea level to create new islands such as Iceland on the Mid-Atlantic ridge.

Answer 10

When plates move apart on contents, the crust stretches and breaks into sets of parallel cracks (faults). The land between these faults then collapses, forming steep-sided valleys called rift valleys.

Answer 11

The plates are sliding past each other where they meet at a fault. Sometimes the plates stick as they move past each other, causing stress and pressure to build until the two plates suddenly jerk past each other causing an earthquake and creating crumpled and ridged land. The San Andreas fault in California is an example.

Answer 12

No crust is made or destroyed, and there is no volcanic activity. However, this type is very tectonically active, and can be associated with powerful earthquakes.

Answer 13

Plates slide past each other

Answer 14

95% of earthquakes occur along tectonic plate boundaries. Many hazards occur around the ring of fire (around the Pacific Ocean)

Answer 15

The point inside the crust from which the pressure is released.

Answer 16

The point above the focus - this is where most shaking and damage occurs

Answer 17

Break in the crust | On a larger scale, which affects a wider area

Answer 18

This type of boundary is mostly found under the ocean where plates are moving apart. The gap created is filled by magma rising up from the mantle below, forming new crust and often forming volcanoes. Some volcanoes have become large enough to create islands such as Iceland.

Answer 19

How an earthquakes energy is released

Answer 20

These waves radiate out from the focus, like the ripples when a stone is thrown into a pond.

Answer 21

Primary waves and secondary waves are called body waves, because they travel through the earths body Love waves are surface waves, because they travel along the Earth’s surface.

Answer 22

Primary or pressure waves

Answer 23

These are the fastest and first to reach the surface. They travel through both solids and liquids (and shake in a backwards and forwards motion). They are only damaging in the most powerful earthquakes

Answer 24

Secondary or shear waves

Answer 25

These are slower (60% of the speed of P waves). They only travel through solids (and move with a sideways motion, shaking at right angles to the direction of travels). They do more damage than P waves.

Answer 26

Love waves

Answer 27

These are the slowest (last to arrive), but they cause the most damage (shaking the ground from side to side). They are larger and focus all of their energy on the Earth’s surface.

Answer 28

Seismometer - which detects and measures ground shaking

Answer 29

Magnitude and intensity

Answer 30

The amount of energy released at the epicentre.

Answer 31

Moment Magnitude Scale (MMS) - generally preferred, because it’s accurate and better at measuring large earthquakes.

Answer 32

The total energy released by an earthquake at the moment it occurs using the: - size of the seismic waves - amount of slipping or rock movement - area of the fault surface broken by the earthquake - resistance of the affected rocks

Answer 33

Goes from 1 (smallest) to 10 (can be infinite). It’s logarithmic - each number is ten times the magnitude of the number before.

Answer 34

An earthquakes effect on people, structure and the natural environment.

Answer 35

Modified Mercalli Intensity Scale - takes observations from people who experienced the earthquake and rates them on a scale from I (hardly noticed) to XII (catastrophic).

Answer 36

Primary | Secondary

Answer 37

Those that happen as a direct result of an earthquake

Answer 38

Ground shaking - causes infrastructure to collapse - killing or injuring those nearby. Crustal fracturing - when energy released during an earthquake causes the earths crust to crack - leaving gaps

Answer 39

The effects that occur directly as a result of this earthquake shaking and energy release.

Answer 40

Liquefaction Landslides/avalanches Tsunami

Answer 41

The violent shaking during an earthquake causes surface rocks to lose strength and become more liquid than solid. The subsoil loses its ability to support building foundations, so buildings and roads tilt or sink. It can make rescue efforts more difficult, and also disrupt underground power and gas lines (leading to fires).

Answer 42

The ground shaking places stress on slopes, so that they fail (resulting in landslides, etc). Many of these effects account for a large proportion of the damage and injuries caused by an earthquake.

Answer 43

Some underwater earthquakes generate tsunami that cause major problems for coastal areas.

Answer 44

For weeks, months or even years after an earthquake, other smaller earthquakes may follow

Answer 45

In the general area of the original earthquake

Answer 46

They’re the result of the earth ‘settling down’ or readjusting along the part of the fault that slipped at the time of the main earthquake. In general, the larger the earthquake, the larger and more numerous the aftershocks.

Answer 47

Earthquakes that occur in the middle of plates

Answer 48

Provides a percentage chance of a hazard happening, but cannot say exactly when.

Answer 49

Research today focuses on identifying ‘warning signs’, that may suggest a major earthquake is about to happen.

Answer 50

Foreshocks - small earthquakes that happen before a larger one. None have proved to be a reliable sign that an earthquake is about to happen.

Earthquakes Flashcards

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