An earthquake is the result of a sudden release of energy in the Earth's top 700 km that creates seismic waves. These waves are detected with seismometers and amplified electronically so they can be displayed as a function of time by a seismograph as a seismogram. The size of an earthquake is given by its open ended logarithmic scale of magnitude, often referred to as the Richter scale. Shocks smaller than magnitude 2.5 are usually not felt and those with magnitude 7 cause serious damage over large areas. Intensity of shaking is measured on the modified Mercalli scale, ranging from 1 far from the epicenter to a maximum near it, which can reach 12 in the strongest earthquakes..
At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacement of the ground. When the epicenter of a large earthquake is located offshore, the seabed sometimes is uplifted enough to cause a tsunami. The shaking in earthquakes can also trigger landslides and occasionally volcanic activity. (read more...)
A propagation of seismic waves.
Seismology (from the Greekseismos (σεισμός) = earthquake and λόγος (logos) = knowledge) is the scientific study of earthquakes and the propagation of elastic waves through the Earth. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, and artificial processes (explosions). A related field that uses geology to infer information regarding past earthquakes is paleoseismology.
The 2002 Bou'in-Zahra earthquake occurred on June 22, 2002 in northwestern Iran, which is crossed by several major fault lines. The earthquake's epicenter was near the small village of Bou'in-Zahra in the Qazvin Province, an area known for destructive earthquakes. Measuring 6.5 on the Richter scale and 6.3 on the Moment magnitude scale, the quake killed at least 261 people and injured 1,300 more. According to the International Institute of Earthquake Engineering and Seismology (IIEES), the earthquake was felt as far away as the capital city of Tehran, approximately 180 miles (290 km) east of the epicenter. Over 20 aftershocks followed the earthquake. There was great public anger due to the slow official response for villagers to receive supplies. Residents of the village of Avaj resorted to throwing stones at the car of a government minister.