Earth Science: Earthquakes

Study Notes

An earthquake is a sudden shaking of the ground that occurs when masses of rock change position below Earth's surface.
Shifting masses send out shock waves that can alter the surface, creating cliffs and opening cracks in the ground.

Earthquakes occur almost continuously, but most are detected only by sensitive instruments called seismographs.
Some earthquakes cause major catastrophes, resulting in destroyed cities, broken dams, landslides, tsunamis, and volcanic eruptions.
On average, about 10,000 people die each year as a result of earthquakes.

Most earthquakes are associated with changes in the shape of Earth's outermost shell, particularly the crust.
Tectonic earthquakes are generated by the rapid release of strain energy stored within the rocks of the crust.
Human activity, such as dynamite or atomic explosions, can cause mild earthquakes.
The injection of liquid wastes and pressures from holding water in reservoirs can trigger minor earthquakes.

The strongest and most destructive quakes are associated with ruptures of crust, known as faults.
Faults are present in most regions, but not all earthquakes are associated with them.
Pressures from within Earth strain the tectonic plates, causing them to move along faults, releasing energy.

The shifting rock in an earthquake causes shock waves, or seismic waves, to spread through the rock in all directions.
There are two broad classes of seismic waves: body waves and surface waves.
Body waves travel within the body of Earth, including P (primary) waves and S (secondary) waves.
P waves compress and expand the rock, vibrating in the same direction as the wave travel.
S waves vibrate at right angles to the direction of wave travel, causing the "shake" waves.

Seismographs can pick up shock waves on the other side of the world.
By comparing the arrival times of P and S waves at seismological observatories, scientists can determine the location of an earthquake.

An earthquake is a sudden shaking of the ground that occurs when masses of rock change position below Earth's surface.
Shifting masses send out shock waves that can alter the surface, creating cliffs and opening cracks in the ground.

Earthquakes occur almost continuously, but most are detected only by sensitive instruments called seismographs.
Some earthquakes cause major catastrophes, resulting in destroyed cities, broken dams, landslides, tsunamis, and volcanic eruptions.
On average, about 10,000 people die each year as a result of earthquakes.

Most earthquakes are associated with changes in the shape of Earth's outermost shell, particularly the crust.
Tectonic earthquakes are generated by the rapid release of strain energy stored within the rocks of the crust.
Human activity, such as dynamite or atomic explosions, can cause mild earthquakes.
The injection of liquid wastes and pressures from holding water in reservoirs can trigger minor earthquakes.

The strongest and most destructive quakes are associated with ruptures of crust, known as faults.
Faults are present in most regions, but not all earthquakes are associated with them.
Pressures from within Earth strain the tectonic plates, causing them to move along faults, releasing energy.

The shifting rock in an earthquake causes shock waves, or seismic waves, to spread through the rock in all directions.
There are two broad classes of seismic waves: body waves and surface waves.
Body waves travel within the body of Earth, including P (primary) waves and S (secondary) waves.
P waves compress and expand the rock, vibrating in the same direction as the wave travel.
S waves vibrate at right angles to the direction of wave travel, causing the "shake" waves.

Seismographs can pick up shock waves on the other side of the world.
By comparing the arrival times of P and S waves at seismological observatories, scientists can determine the location of an earthquake.