Earthquakes and Landscapes

Objectives

• Describe how earthquakes are produced by fault movement and how their strength is measured

• Discuss the cause and behavior of tsunamis• Consider the types of damage that earthquakes

produce• Relate the spatial pattern of earthquakes to plate

tectonics• Introduce the landscapes and landforms that

bear the signature of fault movement and earthquakes

What Produces Earthquakes?

• Faults– A fracture in crustal

rock where one side is displaced with respect to the other side

Earthquakes• Stress is applied to a body

of rock• Rocks deform while

storing energy• Eventually stress becomes

greater than the strength of the rock and the rock breaks

• Energy is released in the form of seismic waves

• Seismic waves radiate in all directions

Earthquakes

• Focus– The location where

earthquakes originate

• Epicenter– The point directly above

the focus on the Earth’s surface

Measuring Earthquake Strength

• Magnitude– Measures the amount of

energy released

• Seismograph– Instrument used to

detect and record earth’s motion

Base anchored to the surface of the Earth and suspended weight records earth’s motion. © USGS

Measuring Earthquake Strength• Intensity– Measures the amount of shaking that has occurred– Determined by humans and property damage– The amount of shaking decreases with increasing

distance from the focus – attenuation– Amplification occurs when the amount of shaking

increases with distance because of loose sediment

Descriptive table of Modified Mercalli Intensity scale. © USGS

Tsunami

• Giant sea wave• Commonly referred to a

seismic sea wave• Produced by a sudden

displacement of ocean water

Earthquake Damage

• Damage not proportional to magnitude

• Damage proportional to population density

• Alaska (1964)– 9.2M resulted in 131 deaths

• Haiti (2010)– 7.0M resulted in 300,000

deaths

Earthquake Distribution• Majority of earthquake occur along plate boundaries• Greatest concentration along Circum-Pacific belt

Great Subduction Zone Earthquakes

9.0M+ and tsunami•Japan (2011)– 4th strongest quake– Tsunami reached almost

30m (100 ft.)•Strongest earthquakes occur along subduction zones– Alaska (1964)– Chile (1960)– Sumatra (2004)

Intraplate Earthquakes• Earthquakes that do

not occur along a plate boundary

• Can potentially cause more damage because buildings are not built to withstand shaking

Earthquakes and Landscapes

• Fault scarp– Exposed clifflike face

• Fault plane– Contact surface along

which blocks move on either side of a fault

• Fault trace– Lower edge of a fault

scarp