Earthquakes Flashcards
What is an Earthquake?
An Earthquake is a shock wave that moves throughout the Earth, often causing shaking of the Earth’s surface. It is usually caused by fault lines.
How do Earthquakes occur?
- Movement at fault lines (a crack on the Earth’s surface) causes a build up of pressure
- Eventually the pressure becomes too much
- All the built up energy is released in the form of seismic waves which pass through everywhere
- This causes violent shaking called ‘earthquakes’
What is the focus?
The focus refers to the origin of an Earthquake (AKA Hypocentre) within Lithosphere.
What is a epicentre?
The epicentre refers to the place where maximum friction happens on the crust, 90 degrees above the focus.
What is a fault line?
The fault line refers to a crack on the Earth’s crust along which displacement of crust occurs (vertically or horizontally). Generally in m or km.
What are seismic waves?
The seismic waves refers to the release of energy in waves due to friction between two tectonic plates.
What are aftershocks?
The aftershock refers to the smaller earthquakes that occur after an Earthquake, caused by resetting of masses at the fault line.
How do we measure earthquakes?
- Seismometers - instruments used to measure the motion of the ground including those of seismic waves generated by Earthquakes, volcanic eruptions, and other seismic sources
- Seismographs - another term used to mean seismometers however it is more applicable to the older instruments.
- Seismogram - the recorded graphical output from a seismometer/seismograph
Describe the mercalli scale.
- The Mercalli scale is a scale which measures the intensity of an Earthquake based on its observed effects.
- Range of intensity - I to XII
Describe the richter scale.
- The Richter scale is a scale which describes the Earthquake’s magnitude by measuring the seismic waves that causes the Earthquake
- Range of intensity - 1 to 10
- Logarithmic scale (Magnitude 5 is 10x bigger than magnitude 6)
