Earthquakes in China

Eastern Sichuan provinceNear city of Chengdu

2:28 pm May 12, 2008

• 7.9 magnitude on the Richter scale

• Shook Beijing (930 mi N), Shanghai, Thailand, Vietnam, Pakistan.

• Affected 10 million people: killing 15, 000

• Lasted 2 min• Epicenter was only 6

miles deep

Richter Earthquake Magnitude Effects

Used to measure Earthquake Severity

Less than 3.5 Generally not felt, but recorded.

3.5-5.4 Often felt, but rarely causes damage.

Under 6.0 At most slight damage to well-designed buildings. Can cause major damage to poorly constructed buildings over small regions.

6.1-6.9 Can be destructive in areas up to about 100 kilometers across where people live.

7.0-7.9 Major earthquake. Can cause serious damage over larger areas.

8 or greater Great earthquake. Can cause serious damage in areas several hundred kilometers across.

Damage

• Eighty percent of the buildings collapsed• May be 50,000 people dead• At least six schools collapsed• Telephone and power networks were

destroyed• Roads were damaged/blocked• 5 million people homeless• Dams may be cracked

Landslides

Refugees, soldiers and rescue workers carry survivors out of the county town of Beichuan.

The landslide that buried much of the town is visible in the background.

Why was there a big earthquake here?

Faults in China

Plate tectonics

Plate tectonics

Why so many earthquakes?

Results of Plate tectonics

• northward collisional convergence (at about 50 mm/y) of the India tectonic plate against the Eurasian plate.

• begun about 55 million years ago• has uplifted the Asian highlands and the

Tibetan Plateau to an average elevation of over 16,000 feet - the highest and largest plateau on Earth

• India has pushed into Asia at least 1,200 kms

A folded, faults land

The strong folds control the flow of rivers

Sediments collect in rivers

Cities and villages often build on the rivers

Soft sediments shake more in earthquakesEarthquakes are more destructive

Scientist predict more serious earthquakes for the future.

Los Angeles computer earthquake

• Movie:

Why so strong?• Longmenshan Fault

– 155 miles long– 2 stages: slipped in two places– 1st – 7 m, 2nd 4 m

• Very hard land in the area• Waves travel far, and stay strong• Waves slow down in softer land

• Had at least seven major aftershocks -- measuring between 4.0 and 6.0 magnitudes

• Have been many serious earthquakes in China