Science of Natural Disasters: Earthquakes! 6 April 2016 Rebecca Clotts Department of Geology, University of St Thomas 1
What is an earthquake? An episode of ground shaking Any earthquakes today? http://earthquake.usgs.gov/ 2
Causes of Earthquakes 1 Slip on a FAULT (fracture on which sliding occurs) Formation of a new fault 3
Causes of Earthquakes 2 Movement of magma in a volcano Explosion of a volcano 4
Causes of Earthquakes 3 Giant Landslide 5
Causes of Earthquakes 4 Extraterrestrial Impact Events 6 http://media.nasaexplores.com/01-074/earth_impact.gif
Causes of Earthquakes 5 Humans 7
Causes of Earthquakes 5A Humans: Dams Photo from U.S. Bureau of Reclamation 8
Causes of Earthquakes 5A Humans: Dams 9 Photo from Prospect Magazine
Causes of Earthquakes 5B Humans: Liquid Waste Injection 10
Causes of Earthquakes Image from USGS 11 5B) Humans: Liquid Waste Injection
Causes of Earthquakes 12 5B Humans: Liquid Waste Injection
Causes of Earthquakes 13 5B Humans: Liquid Waste Injection
Causes of Earthquakes 5C Humans: Coal Mining Photo from Earth Magazine Maps from Wikipedia 14
Causes of Earthquakes 5D Humans: Liquid Extraction 15
Causes of Earthquakes 5E Humans: Nuclear testing Figure from BBC News 16
Causes of Earthquakes 5E Humans: Nuclear testing 17
What causes faults? 18
Earth s Interior 19
The CRUST http://earthquake.usgs.gov/images/glossary/crust.jpg 20
The MANTLE 21
OUTER CORE Made of IRON and NICKLE Very dense (~11 g/cm 3 ) Liquid because of high temperature (4,700 C or >7,000 F) 22
INNER CORE Same composition as outer core, more dense (~13 g/cm3) Hotter temperatures SOLID due to intense pressure 23 http://www.firewyre.force9.co.uk/attheearthscore.jpg
Making Plate Tectonics Happen 24
What causes plates to move? Energy Source? Mantle Convection: Primordial heat & radioactive decay 25
Sea Floor Spreading 26
Lithospheric Plates 27
How do geologist identify lithospheric plates?
Where are the Earthquakes? 29
Rocks Break Rock Deformation! Earth s internal heat - Tectonics forces squeeze, stretch, bend, and break rock in the lithosphere
What happens? https://www.classzone.com/books/earth_science/terc/content/investigations/es1102/es1102page01.cfm
What happens? The Elastic Rebound Theory Stresses build, rock next to fault bends, until it suddenly breaks 32 http://earthquake.us s/animation.php?fla
Features of Earthquakes Epicenter Focus 33
Features of Faults Fault Scarp displacement of the ground surface 34 http://geosun.sjsu.edu/~sedlock/112/images/abe05.jpg
Features of Faults 35
Features of Faults Displacement the amount of slip on a fault Vertical OR horizontal 36 photograph by G. K. Gilbert
Where do earthquakes occur? 37
When an earthquake occurs Epicenter Movement on a fault releases energy that travels outward as waves Focus 38
When an earthquake occurs SEISMIC WAVES are produced 39
Seismic Waves: Body Waves https://www.classzone.com/books/earth_science/terc/content/visualizations/es1002/es1002page01.cfm?chapter_no=visualization 40
Seismic Waves: Surface Waves https://www.classzone.com/books/earth_science/terc/content/visualizations/es1002/es1002page01.cfm?chapter_no=visualization 41
Seismic Waves & Earth s Interior P waves S waves https://www.classzone.com/books/earth_science/terc/content/visualizations/es1009/es1009page01.cfm?chapter_no=visualization 42
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Seismic Waves - Ground Shaking 44
Seismic Waves Determine Magnitude Amount of energy released http://discovertsunamis.org/multimedia/autoformat/get_swf.php?videosite=hitec&videofile=earthquake_magnitude_calculator.swf&videotitle= 45
Seismic Waves - Magnitude 46
How large was the largest earthquake ever recorded? You are here 47
Earthquake Hazards 1) Ground behaviors 2) Secondary hazards Ground Shaking Ground Rupture Liquefaction Tsunami 48
Seismic Waves Locate Epicenter 49
Seismic Waves Locate Epicenter B A C 50
Earthquake Predictions Short Term 51
Earthquake Predictions Long Term 52
Earthquake Predictions Long Term 53
Earthquake Risk 54
New Madrid Earthquakes 16 Dec 1811 M = 7.5 23 Jan 1812 M = 7.3 7 Feb 1812 M = 7.5 Image from USGS 55
A 19th-century print of New Madrid earthquake chaos. (Granger Collection, NYC) The screams of the affrighted inhabitants running to and fro, not knowing where to go, or what to do the cries of the fowls and beasts of every species the cracking of trees falling...formed a scene truly horrible, wrote one resident; -Smithsonian magazine, 2011 56
CAUSE of the New Madrid Earthquakes 57
New Madrid Seismic Zone NOW 58
Earthquakes: What s going to happen? https://pubs.er.usgs.gov/publication/ofr20161035 Image from USGS 59
So then Earthquakes in Minnesota Seismicity Map - 1974 to 2016, from USGS 60
So then Earthquakes in Minnesota Epicenter Mo/day/yr Lat. Long. Felt area (km2) Intensity Mag Nearest Town 1 Long Prairie 1860-61 46.1 94.9 --- VI-VII 5 2 New Prague 12/16/1860 44.6 93.5 --- VI 4.7 3 St. Vincent 12/28/1880 49 97.2 --- II-IV 3.6 4 New Ulm 2/5-2/12/1881 44.3 94.5 v.local VI 3.0-4.0? 5 Red Lake 2/6/1917 47.9 95 --- V 3.8 6 Staples 9/3/1917 46.34 94.63 48000 VI-VII 4.3 7 Bowstring 12/23/1928 47.5 93.8 --- IV 3.8 8 Detroit Lakes 1/28/1939 46.9 96 8000 IV 3.9-3 9 Alexandria 2/15/1950 46.1 95.2 3000 V 3.6 10 Pipestone* 9/28/1964 44 96.4 --- --- 3.4 11 Morris* 7/9/1975 45.5 96.1 82000 VI 4.8-4.6 12 Milaca* 3/5/1979 45.85 93.75 --- --- 1 13 Evergreen* 4/16/1979 46.78 95.55 --- --- 3.1 14 Rush City* 5/14/1979 45.72 92.9 --- --- 0.1 15 Nisswa* 7/26/1979 46.5 94.33 v.local III 1 16 Cottage Grove 4/24/1981 44.84 92.93 v.local III-IV 3.6 17 Walker 9/27/1982 47.1 97.6 v.local II 2 18 Dumont* 6/4/1993 45.67 96.29 69500 V-VI 4.1 19 Granite Falls* 2/9/1994 44.86 95.56 11600 V 3.1 61
The Great Lakes Tectonic Zone 62
Earthquake Risk 63