Earthquakes Flashcards
What is an earthquake?
Vibrations of the Earth’s crust caused by movement at plate boundaries and major fault lines
What is the epicentre?
The point on the earth’s surface directly above the focus of an earthquake
What is a fault line?
A line on the earth’s surface that traces a geological fault
What is a focus?
The point in the earth’s crust where the earthquake happens
What is stress and release?
When pressure builds between two plates, stress is placed on the fault line and when it builds up it is released
What is the Mercalli Scale measure?
The intensity of the earthquake
What is used to measure a magnitude?
A seismometer
What scale does the Mercalli Scale use and how does it work?
Logarithmic scale, e.g. size 6 is 10x larger than 5 and 100x larger than 4
What are primary waves?
They arrive first and fast, moving through solid rock and fluids, pushes and pulls in the direction of travel
How do primary waves travel?
At about 8km/s and transfer energy from the focus to the epicentre
What are secondary waves?
They move slower than primary waves; only move through solid rock in an up and down motion
How do secondary waves travel?
At about 4km/s and transfer energy from the focus to epicentre
What are love waves and how do they move?
They arrive 20-30 secs after the P&S waves, only travel through the surface crust in a rolling motion which results in the ground moving side to side, shaking it
How do Rayleigh waves move?
They only travel through the surface of the crust, fastest waves move up and down
Why did the 2010 earthquake occur in Haiti?
- It is on a conservative fault
- Small depth (8-10km)
- Port-au-Prince only 15km away from the epicentre
