Natural Hazards - Earthquakes
What Are Earthquakes?
An Earthquake is when the Earth's surface shakes or vibrates. This usually occurs near fault lines or plate boundaries. Earthquakes can happen without warning and if they strike populated areas can cause massive destruction.
What Causes Earthquakes?
The Earth's surface is broken up into 'Tectonic Plates' which are constantly moving due to convection currents beneath the plates. Tectonic Plates typically move only a few centimetres per year.
Earthquakes usually occur at fault lines, the major fault lines are at the plate boundaries where stress and strain builds up between the adjacent plates resulting in a sudden movement of rock which releases seismic energy causing an earthquake. The point of where the movement of rock occurs is called the "focus" and directly above it on the earths surface is called the "epicentre".
There are three different Tectonic Plate Boundaries:
Convergent/Destructive Plate Boundary
A Convergent or Destructive Plate Boundary is when two plate boundaries meet and one plate moves underneath the other.
Divergent/Constructive Plate Boundary
A Divergent or Constructive Plate Boundary is when two plates boundaries are moving away from one another forming new crust.
Transform Plate Boundary
A Transform Plate Boundary is when two plates slide past one another.
List of the Earth's Tectonic Plates:
- African Plate
- Antarctic Plate
- Australian Plate
- Eurasian Plate
- North American Plate
- South American Plate
- Pacific Plate
Where Can Earthquakes Occur?
Earthquakes can actually occur anywhere, but are more likely to happen near two fault boundaries where it is likely two plates will meet.
History of Recent Earthquakes
San Francisco Earthquake (1906)
Between 7.7 and 8.3 magnitudes; killed approximately 3,000 people and caused around $400 million in damage; most devastating earthquake in California and U.S. history.
Great Kanto earthquake (1923)
On the Japanese island of Honshu, killing over 140,000 in Tokyo and environs.
1935 Balochistan earthquake at Quetta, Pakistan
measuring 7.7 on the Richter scale. Anywhere from 30,000 to 60,000 people died
Loma Prieta earthquake (1989)
Severely affecting Santa Cruz, San Francisco and Oakland in California. This is also called the World Series Earthquake. It struck as Game 3 of the 1989 World Series was just getting underway at Candlestick Park in San Francisco. Revealed necessity of accelerated seismic retrofit of road and bridge structures.
Bam Earthquake (2003)
Over 40,000 people are reported dead.
Sumatra-Andaman Earthquake (26 December 2004)
Second largest earthquake in recorded history, registering a moment magnitude of 9.3. Epicentered off the coast of the Indonesian island of Sumatra, triggered a series of gigantic tsunamis that hit many surrounding countries causing around 300,000 fatalities.