1.3a waves Flashcards
Three types of seismic waves
- Primary waves(fast)
- Secondary waves (slower)
- Rayleigh and Love (surface)
Seismometers
measures seismic waves and detects ground movement.
By knowing speed of different waves, by measuring at different locations around the world, we can calculate, time, location and size
Primary waves
Waves from the focus.
Caused by compression, they are the fastest (8km/sec) and first to reach the surface.
Travel through both solids and liquids (mantle, core and crust) and push in a forwards/backwards motion. Only damaging in very powerful earthquakes.
Secondary Waves
Slower waves from focus due to their longer wavelength (50% slower than P waves – approx. 4km/sec).
Only travel through solids (crust and mantle) and move in an up/down motion shaking at a right angle to direction of travel.
Do more damage than P waves.
Surface Waves
Rayleigh and Love
Both shake earth’s crust away from epicentre. Overall severity of an earthquake is linked to amplitude and frequency of waves – ground surface may be displaced horizontally, vertically or obliquely during an earthquake depending on strength of waves.
S and L waves are move destructive as they have a larger amplitude and energy force
Measuring Earthquakes
Moment Magnitude Scale (MMS)
Modified Mercalli Intensity Scale
Measuring Earthquakes: Moment Magnitude Scale (MMS)
Measures total amount of energy released by all shockwaves at the moment it occurs using the amplitude/size of the seismic waves including the amount of slippage or rock movement, the area of fault surface broken, and the resistance of the affected rocks.
Measuring Earthquakes: Modified Mercalli Intensity Scale
Takes observations from people who experienced the earthquake and rates them from 1 (hardly noticed) to 12 (catastrophic).
What is a Hazard
Something that has a negative impact on people in any way. Can both be human and physical
Hazards are either primary or secondary
Primary Hazards of earthquakes
Ground shaking
Causes buildings, bridges, roads, and infrastructure to collapse – killing and injuring
Crustal fracturing
When energy released during an earthquake causes earths crust to crack leaving gaps
Secondary Hazards of earthquakes
Liquefaction
Happens cuz soft sediment often behaves like quicksand during an earthquake. Shaking brings water to surface. Buildings often topple over or sink into ground as result of this.
Mexico City earthquake 1985 so bad cuz city built on old lake sediments and these had effect of amplifying shock waves
Landslides
China case study
