Earthquake

An earthquake (also known as a quaketremor or temblor) is the result of a sudden release of energy in the Earth’s crust that creates seismic waves. The seismicity or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time.

Effects/impacts of earthquakes

Shaking and ground rupture

Shaking and ground rupture are the main effects created by earthquakes, principally resulting in more or less severe damage to buildings and other rigid structures. The severity of the local effects depends on the complex combination of the earthquake magnitude, the distance from the epicenter, and the local geological and geomorphological conditions, which may amplify or reduce wave propagation.[30] The ground-shaking is measured by ground acceleration.

Specific local geological, geomorphological, and geostructural features can induce high levels of shaking on the ground surface even from low-intensity earthquakes. This effect is called site or local amplification. It is principally due to the transfer of the seismic motion from hard deep soils to soft superficial soils and to effects of seismic energy focalization owing to typical geometrical setting of the deposits.

Ground rupture is a visible breaking and displacement of the Earth's surface along the trace of the fault, which may be of the order of several metres in the case of major earthquakes. Ground rupture is a major risk for large engineering structures such as dams, bridges and nuclear power stations and requires careful mapping of existing faults to identify any likely to break the ground surface within the life of the structure.

Landslides and avalanches

Earthquakes, along with severe storms, volcanic activity, coastal wave attack, and wildfires, can produce slope instability leading to landslides, a major geological hazard. Landslide danger may persist while emergency personnel are attempting rescue.

Fires

Earthquakes can cause fires by damaging electrical power or gas lines. In the event of water mains rupturing and a loss of pressure, it may also become difficult to stop the spread of a fire once it has started. For example, more deaths in the 1906 San Francisco earthquake were caused by fire than by the earthquake itself.

Soil liquefaction

Soil liquefaction occurs when, because of the shaking, water-saturated granular material (such as sand) temporarily loses its strength and transforms from a solid to a liquid. Soil liquefaction may cause rigid structures, like buildings and bridges, to tilt or sink into the liquefied deposits. This can be a devastating effect of earthquakes. For example, in the 1964 Alaska earthquake, soil liquefaction caused many buildings to sink into the ground, eventually collapsing upon themselves.

Deadliest earthquakes

Rank

Name

Date

Location

Fatalities

Magnitude

Comments

1

"Shaanxi"

January 23, 1556

Shaanxi, China

820,000– 830,000 (est.)

8.0

Estimated death toll in Shaanxi, China.

2

"Tangshan"

July 28, 1976

Tangshan, China

242,419– 779,000

7.5

Estimated death toll as high as 779,000.

3

"Antioch"

May 21, 0525

Antioch, Turkey

250,000

8

Procopius (II.14.6), sources based on John of Ephesus.

4

"Gansu"

December 16, 1920

Ningxia–Gansu, China

235,502

7.8

Major fractures, landslides.

5

"Aleppo"

October 11, 1138

Aleppo, Syria

230,000

8.5

The figure of 230,000 dead is based on a historical conflation of this earthquake with earthquakes in November 1137 on the Jazira plain and the large seismic event of 30 September 1139 in the Azerbaijani city of Ganja. The first mention of a 230,000 death toll was by Ibn Taghribirdi in the fifteenth century.

6

"Indian Ocean"

December 26, 2004

Sumatra, Indonesia

230,000+

9.1

Deaths from earthquake and resulting tsunami.

7

"Haiti"

January 12, 2010

Haiti

222,570 (Haitian sources)50,000-92,000 (non-Haitian sources)

7.0

Estimate June 2010.

8

"Great Kantō"

September 1, 1923

Kantō region, Japan

142,000

7.9

An earthquake which struck the Kantō plain on the Japanese main island of Honshū at 11:58 on the morning of September 1, 1923. Varied accounts hold that the duration of the earthquake was between 4 and 10 minutes. The quake had an epicenter deep beneath Izu Ōshima Island in Sagami Bay. It devastated Tokyo, the port city of Yokohama, surrounding prefectures of Chiba, Kanagawa, and Shizuoka, and caused widespread damage throughout the Kantō region.[9] The power and intensity of the earthquake is easy to underestimate, but the 1923 earthquake managed to move the 93-ton Great Buddha statue at Kamakura. The statue slid forward almost two feet. Casualty estimates range from about 100,000 to 142,000 deaths, the latter figure including approximately 40,000 who went missing and were presumed dead.

9

"Ashgabat"

October 6, 1948

Ashgabat, Turkmenistan

110,000

7.3

 

10

"Genroku"

December 31, 1703

Edo, Japan

108,800+

8

This earthquake shook Edo and killed an estimated 2,300 people. The earthquake is thought to have been an interplate earthquake whose focal region extended from Sagami Bay to the tip of the Bōsō Peninsula as well as the area along the Sagami Trough in the open sea southeast of the Boso Peninsula. This earthquake then resulted in a tsunami which hit the coastal areas of the Boso Peninsula and Sagami Bay. This caused more than 6,500 deaths, particularly on the Boso Peninsula. The Habu Pond on Izu Ōshima collapsed and it rushed into the sea. The tsunami was reported to have caused more than 100,000 fatalities.

11

"Lisbon"

November 1, 1755

Lisbon, Portugal

10,000– 100,000

7.3

Includes several thousands of deaths in Morocco and Spain