2.1 plate tectonics Flashcards
what are earthquakes?
earthquakes are vibration of the Earth’s surface caused by the sudden release of energy stored in the crust.
how do earthquakes form?
most earthquakes occur along these faults.
Along a fault, when rock masses on either side of the fault are pushed back by tectonic forces, friction causes hemispheres to get locked.
This causes stress to build up
When the stress exceeds the strength of the fault, the rocks snap or suddenly move to a new position.
seismic waves are then released, causing ground to shake.
what is a focus?
focus is the source of the earthquake
what is an epicentre?
point on earth’s surface directly above the focus
what is the relationship between focus and epicentre/ earthquake?
shallower focus that originates near the earth’s surface results in stronger earthquakes because the vibrations reaches the Earth’s surface quickly.
deeper focus results in weaker earthquake experienced on Earth’s surface.
how are earthquakes measured?
A seismometer measures the seismic waves released by an earthquake and determines magnitude.
which scale used to rate magnitudes of earthquake is better? why?
moment magnitude scale (Mw) is better. the Mw scale rates earthquake along magnitude based on total energy released during the earthquake. It estimates total energy released during an earthquake. the Richter scale calculates earthquake magnitude using height of the largest seismic wave recorded. However, because it rates an earthquake with a single drastic spike in wave energy as having a higher magnitude than a long earthquake with many large intense waves, it underestimates longer earthquakes which releases more energy overall by rating them as having lower magnitudes even though they will likely do more damage. hence Mw scale is more accurate.
