Earthquakes and tsunamis Flashcards
What is a focus of an earthquake?
The breaking point of the earthquake
What is an epicentre?
The point on the surface above the focusWa
What are the 4 different types of seismic shockwaves?
P (primary/pressure) waves
S (secondary/shear) waves
L (surface love) waves
R (rayleigh) waves
Describe P waves.
- the fastest waves and reach the surface first
- high frequency
- push through crust, mantle and core
Describe s waves.
- reach the surface after p waves
- high frequency
- shake through crust and mantle
Describe L waves
- the slowest waves
- moves side to side
- cause the most damage
Describe R waves
- radiate up and down from the epicentre
What generally creates tsunamis?
earthquakes
How small is the wave height of tsunamis?
less than 1m but can rise to over 25m once it reaches the shore
What is the wavelength of tsunamis?
very long- anything between 100 and 1000km
What is the speed of tsunamis?
quickly- anything between 640 and 960km per hour
Is there only one tsunami at a time?
usually consists of a series with the first not always being the biggest
What are the warning signs that an earthquake is imminent?
- microquakes
- bulging of the ground
- raised ground water levels
- electrical and magnetic changes within local rocks
- curious animal behavior
- increased argon gas
- decrease in radon gas
How can the risk of tsunamis and earthquakes be reduced?
- Geographic information systems
- Earthquake preparation skills
- Earthquake drills
- Reinforce infrastructure
What is the Modified Mercalli intensity scale?
- measures the actual intensity of damage caused
- numbers between 1 and 12:
1- tiny
5-moderate
7- destructive
12- catastrophic
Describe the global distribution of earthquakes.
- mostly occur along the NW side of the ring of fire
- nearly all take place along a plate margin
Describe an earthquake at a constructive plate margin
close to the surface and narrowly concentrated
Describe an earthquake at a conservative plate margin
narrow zone of usually shallow-depth earthquakes
Describe an earthquake at a destructive plate margin
has shallow and deep earthquakes
Why do tsunamis get bigger when they reach the shore?
The sea bed starts to interfere with the wave motion and slows it down, making the wave length shorter
Where is the ring of fire located?
Pacific plate/ ocean
How do you make a building earthquake proof?
- rolling weights on roof
- rubber shock absorbers at base
- interlocking steel frame
What is liquefaction?
when saturated soil loses its strength and stiffness as a result of shaking and causes it to behave like liquid
