Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Sebastião José de Carvalho e Melo, 1st Marquis of Pombal wikipedia , lookup
Surface wave inversion wikipedia , lookup
Ring of Fire wikipedia , lookup
Seismic retrofit wikipedia , lookup
Seismometer wikipedia , lookup
2009–18 Oklahoma earthquake swarms wikipedia , lookup
Earthquake prediction wikipedia , lookup
Orogenesis Lecture 15: EARTHQUAKES mountain building by tectonic forces due to the movement of crustal plates Æ Orogenic belts mainly form convergent plate boundaries Geog 1000 Introduction to Physical Geography Fall 2012 : Dr. Hester Jiskoot, University of Lethbridge MAJOR OROGENS OF THE WORLD TWO STRUCTURAL REGIONS Cordilleran Eurasian-Himalayan Alps (Alpine orogeny) 20-120 my BP THE CAUSES AND DISTRIBUTION OF EARTHQUAKES • Earthquakes are caused by tectonic activity • Tectonic activity (divergence/convergence/transverse motion) along plate boundaries cause fault zones • Most earthquakes located in narrow belts where oceanic plates subduct under continental plates Rocky Mountains (Laramide orogeny) 40-80 my BP Himalayas (Himalayan orogeny) 45-54 my BP Earthquakes occur along major fault zones in the crust Tectonic earthquake terms epicentre focus slip measurements 1 Seismic waves Earthquakes in subduction zone Earthquake motion occurs at different depths along subduction zones Think: coiled spring Think: rope Volcanism P waves (Compressional or primary waves) • travel at speeds of 1.5 to 8 km/s in the Earth's crust • shake the ground in the direction they are propagating S waves (Shear or secondary waves) • shake perpendicularly or transverse to the direction of propagation • travel at 60% to 70% of the speed of P waves. Crust destroyed 8 Oct 2005 Pakistan Earthquake Predicted P-wave travel times in minutes FIRST MEASUREMENT INSTRUMENT Seismoscope Between the heavy black lines is the P-wave shadow zone • Invented in China 132 AD • Wine jar with 2 m diameter • Balls held in dragons’ mouths: 8 dragons, 1 in each of the compass directions • Shaking released balls into toads’ mouths • First ball released indicated direction towards earthquake epicenter Chang Heng's seismoscope http://earthquake.usgs.gov/ MEASUREMENT INSTRUMENTS MEASUREMENT SCALES Seismograph 1902 Mercalli: intensity Æ I to XII Damage indicator 1935 Need ≥ 3 for epicentre location Seismometer Richter: amplitude-magnitude Æ 1.0 to >8.0 logarithmic Measure of seismograph amplitude 1993 Moment-magnitude Æ 1.0 to >8.0 logarithmic Measure of fault's length, depth and its slip Modern Digital Seismometer Æ 2 Richter magnitude scale diagram RICHTER MAGNITUDE EARTHQUAKE EFFECTS < 3.5 Generally not felt, but recorded. 3.5-5.4 Often felt, but rarely causes damage. < 6.0 At most slight damage to well-designed buildings, but major damage to poorly constructed buildings over small regions. 6.1-6.9 Can be destructive in areas < 100 km 7.0-7.9 Major earthquake. Can cause serious damage over larger areas. > 8.0 Great earthquake. Can cause serious damage in areas >100 km across. HOW OFTEN DO EARTHQUAKES OCCUR ? Earthquakes > M 8 are called ‘great earthquakes’ and occur about once every 15 years Average number of earthquakes per year along major faultzones at shallow depth (0-70 km) and with magnitude ≥ 5 Ten largest earthquakes since 1900 4 http://neic.usgs.gov/neis/density/eq_density.html 1 2 3 4 5 6 7 8 9 10 4 Chile Prince William Sound, Alaska Andreanof Islands, Aleutian Islands Kamchatka Off the Coast of Ecuador Rat Islands, Aleutian Islands India-China Border Kamchatka Banda Sea, Indonesia Kuril Islands Northeast Indian Ocean (off Sumatra) 1960 1964 1957 1952 1906 1965 1950 1923 1938 1963 2004 Magnitude (Richter) 9.5 9.2 9.1 9.0 8.8 8.7 8.6 8.5 8.5 8.5 9.0 3 EFFECTS OF EARTHQUAKES Damage on Fault trace Dependent on the following factors: 1) Intrinsic to the earthquake - its magnitude, type, location (epicenter) and depth (focus) 2) Local geological conditions - distance from the event, path of the seismic waves - bedrock type and degree of water saturation 3) Societal conditions reacting to the earthquake - quality of construction, preparedness, time of day Rising sewage tank due to liquefaction Comparison of two earthquakes in 1989 Earthquake induced landslides and rockslides Damage after the 1989 earthquake in Armenia Magnitude 7.1 Loma Prieta earthquake in leastpopulated area of the San Francisco peninsula. - population well prepared and well-engineered buildings - rush hour, but few cars on the roads: large opening game on TV - ~ 67 deaths. Magnitude 6.7 earthquake in war-torn Armenia (between Russia & Turkey) - epicenter much closer to major cities - poorly-engineered houses of un-reinforced concrete collapsed - night-time: everyone in the house in bed: unprepare - > 25 000 deaths. 4 12 Jan 2010: Haiti 7.0 magnitude earthquake 222,570 people killed 300,000 injured 1.3 million displaced Tsunami A large wave of a series of water waves caused by the displacement of a large volume of a body of water in oceans/seas/large lakes. Generated by disturbances above or below the water. ¾ At plate boundary between the Caribbean and North America plate. Disturbances include earthquakes, volcanic eruptions, underwater (nuclear) explosions, landslides, meteorite ocean impacts, etc. Large tsunamis most often caused by earthquakes. EARTHQUAKE THAT CAUSED THE 26 DEC 2005 TSUNAMI IMPACT OF DEC 26th TSUNAMI ON BANDA ACEH, SUMATRA 10 Jan 2003 29 Dec 2005 India plate moves NE at a rate of 6 cm/yr relative to the Burma plate. This megathrust earthquake made ~1200 km of plate boundary slip REDRAW WORLD COASTAL MAPS Average fault plane displacement was 15 m Sea floor overlying thrust fault uplifted by several meters IKONOS satellite images http://www.nature.com/news/2005/050103/full/050103-2.html Seismograph of 3 Jan 2008 earthquake 43 km S of Lethbridge Depth ~25 km Magnitude 3.5 ML Earthquakes <100km radius since 1985 Lethbridge 5 Earthquakes in the last day, weeks, years Red = 24 hours before 15 Oct 2012 15:00 local time WHY EARTQUAKES NEAR LETHBRIDGE? http://www.lithoprobe.ca/ http://www.iris.edu/seismon/ Reading for Monday Chapter 9 p. 323-331 Volcanism 6