EARTHQUAKES

Chapter 15

Recent quakes (last 7 days)

http://earthquake.usgs.gov/earthquakes/recenteqsww/

LARGEST QUAKES SINCE 1900• Chile 1960 9.5• Alaska 1964 9.2• Alaska 1957 9.1• Sumatra 2004 9.1• Japan 2011 9.0• Chile 2010 8.8

MAJOR RECENT QUAKES

• China 7.9 5/12/08 87,000 • Sumatra 7.0 12/26/04 230,000• Haiti 7.0 1/12/10

316,000• Chile 8.8 2/27/10 810• Japan 9.0 3/11/11 28,000 +• Philippines 6.7 2/6/12 113

Michigan earthquakes

• Year Date Mag. City • 1877 Aug 17 3.2 Greenfield • 1938 Mar 13 3.8 Gibralter • 1938 Mar 14 ? Gibralter• 1947 Aug 10 4.7 Coldwater • 1977 Oct 26 2.7 L Superior • 1980 Apr 29 0.5 L Superior • 1982 Nov 26 2.5 Scotts • 1994 Sep 02 3.4 Central Lansing• 2001 Oct 23 2.9 Prairie L

What is an Earthquake?

• Vibration of earth from rapid release of energy

• Movement at focus

• above focus is the epicenter

Elastic rebound theory

Aftershocks

• “Readjustment” of the plate in it’s new position

• Due to Elastic rebound theory

• Bigger earthquakes= bigger aftershocks

Normal faulttensional stress

footwall

Hanging wall

Reverse (thrust) faultcompressional stress

footwall

Hanging wall

Strike slipshearing stress

San Andreas Fault

EARTHQUAKE WAVES

Measured by a seismograph

P waves

• Primary• travel fastest• travels through liquids and solids• compressional wave

– push/pull

S waves

• Secondary• travels only through solids• shearing wave

– back and forth motion

Surface waves

• Travel on surface• slow• similar to water

waves• Usually cause

most damage

GPS seismometer

Label layers

Seismic wavesS waves do NOT travel through liquids

• Mantle= P + S waves= solid

• Outer core= P waves only= liquid

• Inner core-= solid

Locating an epicenter

• use lag time between P and S waves to calculate the distance the epicenter was from the seismograph

• Doesn’t tell direction

INTENSITY OF QUAKE

• Depends on– energy released (magnitude)– distance from epicenter– rock type (soft=worse)– depth

SCALES

• Mercalli– Created in 1902 (before

seismographs)– measures damage– I- XII– Depends on population, building type

Coldwater, MI 1947

RICHTER SCALE

• Developed by Charles Richter (1935)

• Measures ground shaking- each step is 10x higher wave amplitude

• Each step is 32x more energy- logarithmic

• 4.5 compared to 6.5 energy=

Richter Scale (ML)

• Under 2 not felt by humans

• Designed for California shallow quakes

• Not accurate for large quakes

Moment- Magnitude Scale (Mw)• More accurate than Richter,

especially for large quakes

• Mw= Area of fault’s rupture X slippage X rock resistance

Where do quakes happen?

At plate boundaries (most of the time)

Quakes outline plate boundaries

Depth of quakes

PLATE BOUNDARIES

•Divergent–small–shallow–normal faults

PLATE BOUNDARIES

•CONVERGENT– Most major

quakes– reverse faults– Shallow

through deep

PLATE BOUNDARIES

• INTRAPLATE– asthenospher

e causes vertical movement?

– Ancient faults?

Earthquake hazards

• Structural damage– Most prevalent

• Tsunamis• Fires (electrical lines + gas lines)• landslides

Peru 2007

Pakistan 2005

Chile

• Feb. 27, 2010• 8.8 Mw• Depth 35 km• 486 deaths• Reverse fault• Moved Santiago 11 inches to the west

Alaskan school, Good Friday 1964

                            

Olympia WA, 1949