Earthquakes Flashcards
Define earthquake
Sudden movement of the earth’s crust causing tremors. It is caused by a release of energy that has built up over time
Where do earthquakes occur?
99% percent occur at fault lines at divergent, convergent and transform plate boundaries.
1% occur at ancient fault lines
Name and explain the three types of earthquakes (where in the crust they occur) and give examples
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
Name and explain the four main causes of earthquakes
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.
Define focus
The location deep inside the earth where the earthquake begins - where the rock first breaks under stress
Define epicentre
The point on the earth’s surface directly above the focus. Where the earthquake’s effects are felt the strongest.
Define seismic waves
Energy waves or tremors that travel through the earth during an earthquake
What are the different types of seismic waves?
Primary waves, secondary waves and surface waves
What are the main locations on the earth where earthquakes happen?
Pacific Ring of Fire - Most destructive plate boundaries
San Andreas Fault, California - Transform boundary
Mid Atlantic Ridge - Constructive boundary, not powerful
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
See notes
Draw a diagram of an earthquake
N/A
Define magnitude
Magnitude measures the size or energy released by an earthquake
Define Richter Scale
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
Define Moment Magnitude Scale (Mw)
A more accurate and modern method of measuring the size and energy of earthquakes. It calculates total energy released by considering seismic moment.
Define Mercalli Intensity Scale
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).
Define foreshocks
Smaller earthquakes that sometimes occur before main earthquake.
Define aftershocks
Smaller earthquakes that follow the main earthquake. They occur as the crust adjusts to the changes in stress caused by the main shock.
Define fault line
A fracture/zone of fractures in the earth’s crust along which movement has occurred.
Define seismograph
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
Define tsunami
A series of ocean waves causes by the displacement of a large amount of water typically due to an undersea earthquake or volcanic eruption.
Define liquefaction
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
Define Seismic Hazard
Seismic hazard refers to the probability of an earthquake occurring in specific location, and the potential consequences in terms of ground shaking and damage
Give some examples of major earthquakes
1960 Valdivia Earthquake (Chile)
2004 Indian Ocean Earthquake (Sumatra-Andaman)
2011 Tōhoku Earthquake and Tsunami
1964 Great Alaska Earthquake
2010 Maule Earthquake (Chile)
Give details about a earthquake you have studied
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
Define seismometer
The part of the seismograph that detects the movement
Define seismologist
A scientist who uses data from seismographs and seismometers to study earthquakes and seismic waves
How are earthquake predicted?
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
What are some ways the effects of earthquakes can be reduced?
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
Explain how the occurrence of earthquakes are monitored, predicted and their effects reduced
See notes
What are the three main types of seismic waves?
P waves, S waves and surface waves
How can scientists monitor plate movement
Tiltmeters, lasers etc.
What indicates the possibility of an earthquake occurring
Slow tilting of land and foreshocks
Write an essay on the study and prediction of earthquakes
N/A
Explain some negative effects of an earthquake and use examples
-
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
-
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
-
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
What are some factors affecting earthquake effects?
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
