Seismic hazards revision :) Flashcards
Name 3 facts about PRIMARY waves
Fastest
least destructive
go through the centre of the Earth
longitudinal waves
Name 3 facts about SHEAR/SECONDARY waves
1/2 as fast as primary waves
only travel through SOLIDS (not Earth’s core)
Transverse waves
What are Ray-leigh waves?
What are Love waves?
Ray-leigh and Love =
- most destructive waves
- Slowest waves
What is an earthquake?
Shaking of Earth’s surface.
Result of sudden energy release in the lithosphere.
This creates seismic waves.
Where can you find earthquakes?
Found at ALL plate boundaries.
Divergent plate boundaries:
North American and Eurasian plates separating.
Convergent plate boundaries
(Nazca and South American plate)
Continental + continental = India and Asia colliding along Himalayas.
East African Rift Valley
Mid Atlantic ridge.
Transform plate boundaries
San Andreas fault - pacific plate moving faster than north american plate.
What is the plate boundary at Haiti?
North American plate and caribbean plates are moving side by side.
TRANSFORM.
Define a fault line
A weakness within the lithosphere.
What is a focus?
THe point within the crust where the energy of the earthquake is released.
Transferred across the crust in seismic waves.
What is the name of the point directly above the focus?
The epicentre.
Where the intensity of the Earthquake is likely to be strongest because it is the nearest point to the surface. The seismic waves have lost the least energy at this point.
What are the differences between earthquake storms and earthquake swarms?
Storm:
Earthquake activity moves along a fault line over years. One earthquake has built up stresses on the fault.
Swarm:
lots of earthquake activity of same magnitude happening around the same time. Usually a result of volcanic activity - impending eruptions.
How is a Earthquake storm different from an aftershock?
storm is earthquakes do not trigger another one, just transfer stress. Storm earthquakes also happen multiple years apart.
What is an example of an earthquake storm?
1999 Turkish Earthquake on North Anatolian Fault.
WHat is an example of an earthquake swarm?
Indonesia:
Island of Lombok hit by 29 earthquakes over 4 on the Richter scale.
What is the Moment Magnitude Scale?
Measures energy released during an earthquake
Logarithmic
uses seismometers to record ground motion and calculate magnitude
open ended.
Modified Mercalli INTENSITY:
Measures effects
based on observed effects
Scale from I to XII
Values vary with distance from epicentre
Only useful in inhabited areas.
MMS (moment magnitude scale) and MMI (modified mercalli intensity) can vary. Give an example of this in the 2011 Japanese quake.
2011 Japan Tohoku quake:
MMS = 9
MMI = IX
Give an advantage and disadvantage of the Richter scale
Advantage: Based off accurate recordings
scientists can compare strength at different times
Disadvantage:
seismograph have limitations - can underestimate energy released, calculated with one type of seismic wave.
give 3 primary hazards of seismic activity
Ground shaking
ground rupture
buildings collapse
Give some secondary hazards of seismic activity:
Fires
Shockwaves
avalanches (Nepal 2015)
Landslides (2021 Haiti, 14th August)
Tsunami (2004, December Boxing Day Tsunami)
Liquefaction (palu - indonesian- earthquake of 2018.
Environmental impacts
short term?
Long term?
ST: ruined habitats, flooding, fires, landslides,
LT: Changed landscapes
Social impacts?
Short term?
Long term?
ST: Disease, injury, death, looting, increased tax (2011 Japan = 10% tax raise to pay for rebuild)
disrupted transport, food, water, sanitation decrease.
LT: Rebuilding, disease and death, tax, homelessness, education disruption
Political impacts
Short term:
Long term:
ST: Loose faith in gov.
LT: Better mitigation programmes developed
Economic impacts of quakes:
Short term?
Long term?
ST: income lost, unemployment,
LT: income lost, unemployment, shops/businesses destroyed, £ needed to rebuild.
How do we respond to seismic hazards?
PREPARATION:
Emergency plans
supply kit
education of public
safe spaces e.g bunkers
group hubs (to ensure everyone’s accounted for in a hazard event)
How do we respond to seismic hazards?
MITIGATION:
Prediction
Authorities can allert public through technology (Haicheng, China - 90,000 people saved from 7.3 quake)
Emergency services are up to scratch.
How do we respond to seismic hazards?
PREVENTION:
Disaster plan
create specialised infrastructure - Japan = shock absorbers (buildings built on rubber blocks)
strengthen existing infrastructure - wire mesh
checks for damage after event to prevent after effects,
How do we respond to seismic hazards?
ADAPTION:
Heavy breakable objects on lower shelves
Specialised infrastructure.
Land use planning
How do we predict seismic hazards?
Detect changes in:
Radon + Thoron levels
ground surveying (movement)
upwelling of water
seismometer - monitor prequakes
tiltometer/magnetometer
sonar dishes - detect changes along fault line.
What are the limitations of predicting earthquakes?
NOT reliable
Evacuations can be very disruptive
some warning signs only recognisable in hindsight.
distrust in gov / scientists if quake doesn’t happen.
2009 L’Aquila earthquake, Italy, 6 scientists + 1 government official jailed for giving ‘overly-reassuring’ advice.
In an LEDC, it is more difficult to adapt, prevent, predict, prepare and mitigate. Why?
Lack of money, lack of tech, large populations (leading to urban sprawl so land use zoning is hard)
How are Tsunamis detected?
Seabed monitors - detect changes in pressure.
What are the three ps of hazard management?
Prediction
protection
preparedness.
Protection of earthquakes:
Computer controlled weights on roof to reduce movement, foundations in bedrock, rubber shock absorbers, fire resistant building materials, automatic shutters (stop broken glass travelling), ‘bird cage’ interlocking steel frame.
CORRUPTION can cause building codes to be bypassed!
Need to ‘retrofit’ original infrastructures.
Preparedness in earthquakes
The great shakeout (earthquake drill in America)
Phrases - Drop! Cover! Hold on! (USA)
‘Go-Bags’ - bags containing essential supplies in evacuation times.
Drills - boring, create false sense of security
LEDCS - limited access to tech and low literacy = barrier.
How did tech help the response in the 2010 Haiti earthquake?
Openstreetmap - enabled a good map to be created through satellite imaging.
In Nepal 2015 - shelter areas popped up on openstreetmap.
Why are phones effective in earthquakes?
GPs tracking and mapping areas
show where damage and blockage is - good for rapid response units.
What factors can impact the effectiveness of a response?
economic development
resource base
antecedent conditions / extenuating circumstances like previous natural hazards.
governance of an area
How do tsunamis form?
over-riding plate of a convergent plate boundary springs up - water above is displaced.
what might influence the effects of a Tsunami?
Population density
coastal relief / morphology
land use
How might we mitigate against a Tsunami?
Pacific Tsunami Warning system
Gives hours of notice
uses sea bed monitors to detect changes in pressure.
True or false - Tsunamis are a singular wave?
FALSE.
Multiple waves. The first one may not necessarily be the biggest wave.
40% of wave energy is transferred back out to sea so waves keep gaining energy.
