Earthquakes

Question 1

Define earthquake

Answer 1

Sudden movement of the earth’s crust causing tremors. It is caused by a release of energy that has built up over time

Question 1

Where do earthquakes occur?

Answer 1

99% percent occur at fault lines at divergent, convergent and transform plate boundaries.
1% occur at ancient fault lines

Question 2

Name and explain the three types of earthquakes

Answer 2

Shallow:
Foci less than 70km deep
Very damaging as seismic waves are close to the surface
Eg: Sichuan, China, 2008. Magnitude 8 - foci 19km deep

Intermediate:
Foci between 70-300km deep

Deep:
Foci 300km+ depth at subduction zones
Eg: Japan earthquake, 2011 Magnitude 9

Question 3

Name and explain the four main causes of earthquakes

Answer 3

Elastic Rebound:
Theory that energy builds up at plate
boundaries between plates. It gets released in the form of an earthquake and then energy begins to build up once again

Subduction:
Earthquake caused by plate collision as one plate is forced into mantle. This can cause large earthquakes

Glacial melting:
Isostatic rebound - When a large weight is removed from land (glacier) the land begins to rise triggering earthquakes

Ancient fault lines:
Due to continental drift many countries have changed position. Places that were once plate boundaries have changed. These can be ancient faults.

Question 4

Define focus

Answer 4

The location deep inside the earth where the earthquake begins - where the rock first breaks under stress

Question 5

Define epicentre

Answer 5

The point on the earth’s surface directly above the focus. Where the earthquake’s effects are felt the strongest.

Question 6

Define seismic waves

Answer 6

Energy waves or tremors that travel through the earth during an earthquake

Question 7

What are the different types of seismic waves?

Answer 7

Primary waves, secondary waves and surface waves

Question 8

What are the main locations on the earth where earthquakes happen?

Answer 8

Pacific Ring of Fire - Most destructive plate boundaries
San Andreas Fault, California - Transform boundary
Mid Atlantic Ridge - Constructive boundary, not powerful

Question 9

Explain with reference to examples that you have studied, how the Theory of Plate Tectonics helps us to explain the distribution of earthquakes around the world

Answer 9

See notes

Question 10

Draw a diagram of an earthquake

Answer 10

N/A

Question 11

Define magnitude

Answer 11

Magnitude measures the size or energy released by an earthquake

Question 12

Define Richter Scale

Answer 12

A logarithmic scale used to measure the magnitude of an earthquake. Each +1 on the scale = x10 increase in amplitude of seismic waves and x31.6 more energy released

Question 13

Define Moment Magnitude Scale (Mw)

Answer 13

A more accurate and modern method of measuring the size and energy of earthquakes. It calculates total energy released by considering seismic moment.

Question 14

Define Mercalli Intensity Scale

Answer 14

Measures the effects and damage causes by an earthquake based on human perception and observed damage. Qualitative scale ranked from I (not felt) - XII (total destruction).

Question 15

Define foreshocks

Answer 15

Smaller earthquakes that sometimes occur before main earthquake.

Question 16

Define aftershocks

Answer 16

Smaller earthquakes that follow the main earthquake. They occur as the crust adjusts to the changes in stress caused by the main shock.

Question 17

Define fault line

Answer 17

A fracture/zone of fractures in the earth’s crust along which movement has occurred.

Question 18

Define seismograph

Answer 18

An instrument used to detect and record the vibrations caused by seismic waves during an earthquake. This data helps scientists determind magnitude, location, and depth of an earthquake

Question 19

Define tsunami

Answer 19

A series of ocean waves causes by the displacement of a large amount of water typically due to an undersea earthquake or volcanic eruption.

Question 20

Define liquefaction

Answer 20

Liquefaction occurs when the shaking of an earthquake causes loosely packed, water saturated soil to behave like a liquid. This can lead to buildings above it sinking or collapsing

Question 21

Define Seismic Hazard

Answer 21

Seismic hazard refers to the probability of an earthquake occurring in specific location, and the potential consequences in terms of ground shaking and damage

Question 22

Give some examples of major earthquakes

Answer 22

1960 Valdivia Earthquake (Chile)
2004 Indian Ocean Earthquake (Sumatra-Andaman)
2011 Tōhoku Earthquake and Tsunami
1964 Great Alaska Earthquake
2010 Maule Earthquake (Chile)

Question 23

Give details about a earthquake you have studied

Answer 23

1960 Valdivia Earthquake (Chile)

Magnitude: 9.5 (largest earthquake ever recorded)
Location: Near Valdivia, Chile
Plate Boundary: Nazca Plate subducting under South American Plate (Convergent Boundary)
Effects:
* Massive tsunami affecting Chile, Hawaii, Japan, the Philippines, New Zealand and Alaska causing hundreds of deaths
* ~5700 deaths in Chile and widespread destruction of buildings, infrstructure and homes
* Caused landslides and flooding
* Significant economic losses
Tsunami height: Up to 25m along Chilean coast

Question 24

Define seismometer

Answer 24

The part of the seismograph that detects the movement

Question 25

Define seismologist

Answer 25

A scientist who uses data from seismographs and seismometers to study earthquakes and seismic waves

Question 26

How are earthquake predicted?

Answer 26

Seismic Hazard Assessment
Historical data: Analysing the historical records of earthquakes in a region to identify patterns and recurrence intervals of seismic activity
Seismic gaps: Identifying areas along known fault lines that have not experienced recent earthquakes (seismic gaps) and are therefore considered potential sites for earthquakes
Paleoseismology: Studying geological evidence of past earthquakes (eg. trenching studies along faults) to extend the historical record and understand long term seismic behaviour

Seismic Monitoring Networks
Seismometer Networks: Deploying dense networks of seismometers to continuously monitor ground vibrations. They help detect foreshocks.
GPS and InSAR: To measure ground deformation. Slow movements or strain accumulation can indicate increasing stress along faults

Statistical and Probabilistic Models
Probabilistic Seismic Hazard Assessment: Combing historical earthquake data, geological information and statistical models to estimate the probability of different levels of seismic shaking occurring in a region of a specific period.
Earthquake Forecasting: Developing short term and long term forecasts based on statistical patterns of earthquake occurrences. They provide probabilities but do not predict specific events

Early Warning Systems
Earthquake Early Warning (EEW): Networks of seismic sensors used to detect the inital, less damaging P-waves (primary waves) of earthquake. Early warning can be issued before more destructive S-waves (secondary waves) and surface waves by -
* Automatic Alerts - Systems that automatically send alerts to public via mobile phones, radio, TV etc.
* Automated Safety Measures - Early warnings can trigger automated responses eg. shutting down gas lines, stopping trains and opening fire station doors.

Geophysical and Geochemical Monitoring
Groundwater changes: Changes in groundwater levels and chemistry can sometimes precede earthquake due to stress changes in earth’s crust
Radon emissions: Measuring radon gas emissions from the ground, as increased emissions sometimes happen before earthquakes

Question 27

What are some ways the effects of earthquakes can be reduced?

Answer 27

Building design and construction
Seismic resistant structures: By using flexible materials, reinforced concrete and steel frames to absorb and dissipate energy
Base Isolation systems: Allow building to move independently of its foundations reducing shaking of structure
Retrofitting: Retrofit buildings (especially older ones) by adding bracing, reinforcing walls and improving foundations to better resist seismic forces

Urban planning and land use
Zoning regulations: Enforce zoning laws that prevent contruction on fault lines, unstable slopes, or areas prone to liquefaction
Land use planning: Develop open space, parks and wide roads that can serve as emergency evacuation routes and gathering points during earthquakes.
Lifeline infrastructure: Design critical infrastructure (hospitals, fire stations, bridges, utilities) to be earthquake resistant and ensure they are not all clustered in same high risk area

Early Warning Systems
Seismic sensors: Deploy network of seismic sensors to detect inital tremors and provide early warning before main shaking so people can take cover. Automated systems to shut down critical infrastructure
Public Alerts: Use mobile alerts, sirens etc to warn public quickly

Community Education and Preparation
Public awareness campaigns: Educate public about earthquake risks, safe practices during earthquake and the importance of preparation
Drills and training: Conduct regular earthquake drills in schools, workplaces and communities
Emergency kits: Encourage people to prepare emergency kits with essential supplies like water, food, medications and first aid materials

Emergency Response Planning
Disaster response plans: Develop comprehensive emergency response plans that outline roles and responsibilities for government agencies, emergency services and community organisations.
Coordination: Ensure effective communication and coordination among local, regional and national emergency services and agencies
Resilient infrastructure: Design resilient buildings and areas than can serve and shelters and command centres during earthquake

Question 28

Explain how the occurrence of earthquakes are monitored, predicted and their effects reduced

Answer 28

See notes

Question 29

What are the three main types of seismic waves?

Answer 29

P waves, S waves and surface waves

Question 30

How can scientists monitor plate movement

Answer 30

Tiltmeters, lasers etc.

Question 31

What indicates the possibility of an earthquake occurring

Answer 31

Slow tilting of land and foreshocks

Question 32

Write an essay on the study and prediction of earthquakes

Answer 32

N/A

Question 33

Explain some negative effects of an earthquake and use examples

Answer 33

1. Damage to Infrastructure
   * Seismic waves cause buildings and bridges to sway and collapse
   * Falling debris from collapsing infrastructure can crush/suffocate people causing death
   * Rescue workers must then search through rubble to find survivors and recover bodies
   * Causes economic losses

Example: 1994 Northridge Earthquake, California, USA
-6.7M
-Several freeway overpasses collapsed
-Thousands of buildings in Los Angeles area damaged

2. Loss of Life
   * Due to collapsing structures, falling debris, etc.
   * The instensity of an earthquake and level of preparedness incluences number of casualties

Example: 2010 Haiti Earthquake
-7.0M
-160,000 people killed - one of the deadliest earthquakes in the 21st century

3. Tsunami
   * Occur due to earthquakes at sea
   * Subducting plate can cause overlying plate to be forced suddenly upwards
   * This upward movement creates excess hump of water on ocean surface
   * This hump collapses and spreads all directions, travelling at up to 970km/h
   * As tsunami gets to coastline, the bottom of the wave comes in to contact with the shore and slows down due to friction, causing the rest of the wave to stand upwards and crash into the coastline at speed

Example: 2004 Indian Ocean Earthquake
- 9.1-9.3M
- Massive tsunami affecting countries across Indian Ocean
- 230,000 deaths and devastation along coastlines

Liquefaction
* During earthquake, the ground shaking forces groundwater upwards and saturates the soil
* In certain soil types, the soil can take on the properties of a liquid
* Soil affected by liquefaction is unable to support buildings, causing them to collapse
* Can also cause gas and sewage pipelines to sink and break leading to fires or contamination of water supplies

Example: 1923 Great Kanto Earthquake, Japan
- Tokyo and Yokohama experienced liquefaction causing buildings to sink

Question 34

What are some factors affecting earthquake effects?

Answer 34

Magnitude
* Magnitude or an earthquake refers to the amount of energy it releases
* Larger magnitude earthquakes cause more damage
* M5-M7= moderate
* M7+ = major

Depth of Focus
* Refers to where earthquake occurs beneath surface
* Shallow focus = more damage as shaking close to surface

Rock Type
* Some rocks have natural cracks/joints eg. sedimentary
* They can fracture easier

Time of Day
* Earthquakes at rush hour can affect a lot of people
* Earthquake at night means people are asleep to have slower reactions

Location
* High population density areas - more people affected
Eg: 39m people line in California, 4m live along San Andreas Fault
* Low population density = less people affected
Eg: Alaska 1960 - largest every earthquake recorded 760,000 population, 100 deaths

HIC vs LIC
-High Income Country
Eg: Japan, New Zealand
* Wealthy
* Very good infrastructure
* Very good response plans
* Building regulations
* Less people die due to this

-Low Income Country
Eg: Nepal, Pakistan
* Less money for infrastructure
* More people die due to this