Seismicity

Question 1

What is sesimicity

Answer 1

Movements within the earths crust cause stress to build up at points of weakness and rocks to deform. When the stress finally exceeds the strength of the rock, it fractures. The stored energy is suddenly released as an earthquake. Seismic waves spread out.

Question 2

What is the hypocentre

Answer 2

The focus. The more shallow the more damaging

Question 3

What is the focal length

Answer 3

The distance between the epicentre and the focus

Question 4

Primary waves

Answer 4

Arrive at the detector first. They are longitudinal waves which means vibrations are along the same direction as the direction of travel (forward movement)

Question 5

Secondary waves

Answer 5

Arrive at the detector second. They are transverse waves which mean the vibrations are at right angles to the direction of travel (vertical movement)

Question 6

Love/Long waves

Answer 6

Surface waves - do not travel through liquid
Faster than secondary waves
Travels horizontally (side to side)

Question 7

What can influence the impact of seismic activity

Answer 7

• geological conditions
• distance from epicentre
• time of day
• depth of earthquake
• preparation and education
• population density

Question 8

Liquefaction

Answer 8

Process by which water saturated sediment temporarily loses strength and acts like a liquid
Earthquake shaking increases water pressure in the soil, the spaces between soil particles become filled with water which causes soil to lose strength and flow like a liquid

Question 9

Mercalli Scale

Answer 9

This measures how much damage is caused by the earthquake based on observations
It is measured on a scale bwtween I and XII
This is a measure of intensity and changes according to which area you are measuring - damage nearer the epicentre would usually be greater than further away

Question 10

Moment magnitude scale

Answer 10

Based on the total moment release of the earthquake. It can be used for any kind of earthquake, near or far.
Magnitudes are based on a logarithmic scale (base 10). What this means is that for each whole number you go up on the magnitude scale, the amplitude of the ground motion recorded by a seismograph goes up ten times
Can describe earthquakes so small it has negative numbers and the scale has no upper limit

Question 11

Richter Scale

Answer 11

A logarithmic scale used to measure the magnitude of an earthquake
Goes from 1-10

Question 12

How does a tsunami work

Answer 12

1 - a plate shifts abruptly causing an earthquake and displaces water
2 - waves are generated and move out in all directions across the ocean, some travelling as fast as 600mph
3 - as waves enter shallower water they compress, their speed slows and they build in height
4 - the wave height increases and associated currents intensify, becoming a threat to life and property

Question 13

Indications that an earthquake will occur

Answer 13

• micro quakes
• bulging of the ground
• raised groundwater levels
• curious animal behaviour
• electrical and magnetic changes within local rocks

Question 14

Prediction, Planning and Prevention

Answer 14

Prediction - impossible, understanding of plate tectonics help, micro quakes before main tremor, only vague predictions can be made

Preparedness - earthquake warning systems, evacuation, adaptation

Prevention - not possible, mitigation and adaptation methods

Question 15

Contingency Planning

Answer 15

Individuals, organisations, local authorities, governments and internation aid agencies prepare for hazards in advance which aids management. eg special building designs, evacuation plans, practice drills, stock food and water, medical supplies