1.2 Earthquakes

Complete the table on properties of seismic waves.

Complete the table to show how earthquakes are classified by the depth of the focus.

Earthquakes do not [blank_start]originate[blank_end] at depths greater than 720km because deeper, warm rocks are not [blank_start]brittle[blank_end] enough to [blank_start]fracture[blank_end] so [blank_start]faults[blank_end] do not occur.

What is the rigidity of a liquid?

The S wave shadow zone is found at: [blank_start]103[blank_end] degrees to [blank_start]103[blank_end] degrees. The P wave shadow zone is found at: [blank_start]103[blank_end] degrees to [blank_start]142[blank_end] degrees.

Body waves travel through the interior of the Earth.

Surface waves travel just below the Earth's surface.

L waves lose energy slowly with distance away from the epicentre.

Body waves are responsible for damage to buildings.

Focus = The point [blank_start]within[blank_end] the Earth at which the earthquake originates. [blank_start]Epicentre[blank_end] = the point on the Earth's surface, directly [blank_start]above[blank_end] the focus and shows where the greatest amount of [blank_start]damage[blank_end] is likely to occur.

Isoseismal line = A [blank_start]line[blank_end] on a map which joins up points of equal [blank_start]intensity[blank_end], separating zones of different intensities.

At the Gutenberg discontinuity P waves slow down and refract from their original path.

S waves can travel through liquids.

Mercalli Scale: - Measures the [blank_start]intensity[blank_end] of an earthquake based on the [blank_start]effects[blank_end] felt in a particular area. - It is a [blank_start]12[blank_end] point [blank_start]arbitrary[blank_end] scale.

Richter Scale: - Measures the [blank_start]magnitude[blank_end] of an earthquake by recording the [blank_start]amplitude[blank_end] of seismic waves. - The values are then converted into a [blank_start]logarithmic[blank_end] scale.

Define the term magnitude.

Define the term intensity.

Amplitude of L-waves in different types of rock: Solid, [blank_start]competent[blank_end] rocks allow vibrations to pass through easily. Waves are transferred with minimal damage to structures. L wave amplitude is [blank_start]low[blank_end]. [blank_start]Unconsolidated[blank_end] sediment [blank_start]oscillates[blank_end] freely. L wave amplitude [blank_start]higher[blank_end]. Intensity [blank_start]greater[blank_end] than on consolidated rock.

Define: Seismograph

Define: Seismometer

Define: Seismogram

Earthquakes occur in solid, [blank_start]brittle[blank_end], competent rocks as they suddenly [blank_start]fracture[blank_end] and move relative to each other. The seismic energy [blank_start]released[blank_end] is transmitted through the rocks as seismic [blank_start]waves[blank_end]. Weak incompetent rocks steadily [blank_start]deform[blank_end] under stress by folding or plastic flow. They do not [blank_start]fracture[blank_end] so earthquakes cannot occur.

How will intensity and damage to buildings change if underlying geology consists of unconsolidated sands? The intensity will [blank_start]increase[blank_end] as unconsolidated sands [blank_start]absorb[blank_end] the seismic waves, which decreases the wave [blank_start]speed[blank_end] and increases the wave [blank_start]amplitude[blank_end], resulting in greater [blank_start]damage[blank_end] to buildings.

The [blank_start]amplitude[blank_end] of seismic waves is larger in unconsolidated sediments resulting in greater [blank_start]damage[blank_end] to buildings. In consolidated sediment the seismic waves are [blank_start]dampened[blank_end].

Physical effects of earthquakes: Ground [blank_start]movement[blank_end] Damage to [blank_start]structures[blank_end] L[blank_start]iquefaction[blank_end] Land[blank_start]slips[blank_end] After[blank_start]shocks[blank_end] T[blank_start]sunamis[blank_end]

Social and economic effects of earthquakes: Infrastructure and c[blank_start]ommunications[blank_end] damaged affects how quickly people can respond to effects of earthquake. Damaged water pipes can affect supply of clean water and lead to risk of disease spreading. D[blank_start]eath[blank_end] and i[blank_start]njury[blank_end] of people impacting families. Loss of p[blank_start]ower[blank_end] supply.

How do earthquakes cause liquefaction?

How do earthquakes cause tsunamis? A large [blank_start]volume[blank_end] of water is displaced as a result of the earthquake being at a shallow depth below the sea.

How can the impact of an earthquake be reduced on built structures? Flexible pipes and electricity [blank_start]cables[blank_end] - prevents pipes from [blank_start]fracturing[blank_end] / stops [blank_start]fires[blank_end] Cross-bracing - [blank_start]strengthens[blank_end] building Mass on roof of tall buildings / [blank_start]damping[blank_end] - acts as a counterbalance as the building [blank_start]sways[blank_end] [blank_start]Pyramid[blank_end] shaped structure - more stable due to [blank_start]wider[blank_end] base Base [blank_start]isolation[blank_end] - [blank_start]absorbs[blank_end] ground vibrations Reinforced [blank_start]foundations[blank_end] - provides greater [blank_start]support[blank_end] and firmer base