Lecture 3: Earthquakes (PHYS 1015) PDF

Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes Dr Adrienne Brotodewo Pages 229-291 and Figures taken from Earth Science (2015) 14th Ed, Tarbuck, Lutgens & Tasa, Pearson Education Ltd Astronomy and the Universe (PHYS 1015) Lectur...

Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes Dr Adrienne Brotodewo Pages 229-291 and Figures taken from Earth Science (2015) 14th Ed, Tarbuck, Lutgens & Tasa, Pearson Education Ltd Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Lecture 3 Earthquakes Plate Tectonics Geophysics Earthquakes 2 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics The Earth’s Crust divided into tectonic plates Plates are composed of rocks of different density and origin The mechanism of plate tectonics explains the processes of rock formation 3 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics 4 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics What are the materials that form the plates? Crust Continental 35-40 km thick (over 70 kms in mountain regions) Upper crust felsic (granitic) rocks (Si-Al) Lower crust is more akin to basalt Average density of 2.7 g cm-3 Up to 4,600 million years old (Ma) Oceanic 7 kms thick Mafic (basalt) composition (Si-Mg) Density about 3.0 g cm-3 Maximum of 180 Ma 5 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics Movement of the Earth’s Plates Hotter, weaker Asthenosphere (Upper Mantle) provides flexibility for movement of solid plates of the Lithosphere 6 https://concord.org/newsletter/2021-spring/everything-happens-for-a-reason-developing-causal-mechanistic-reasoning-of-plate-tectonics/ Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics Movement of the Earth’s Plates 7 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics Plate boundaries All major interactions among plates occur along the boundaries Three types: Convergent (destructive) Divergent (constructive) Transform Fault (neither constructive or destructive) 8 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics Convergent Plate boundaries: Oceanic-Continental Plates collide, an ocean trench forms, then the lithosphere is subducted into the mantle Denser oceanic slab sinks into the asthenosphere Pockets of magma develop and rise Continental volcanic arcs form Examples include the Andes, Cascades, and the Sierra-Nevadan system 9 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics Convergent Plate boundaries: Oceanic-Oceanic Two oceanic slabs converge, one descends beneath the other Often form volcanoes on the ocean floor Volcanic island arcs form as volcanoes emerge from the sea Examples include Tonga, the Aleutian, and Mariana islands 10 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics Convergent Plate boundaries Under sea volcanic eruption near Tonga trench, 18 March 2009 11 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics Convergent Plate boundaries: Continent-Continent When subducting plates contain continental material, two continents collide Can produce new mountain ranges such as the Himalayas 12 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics Convergent Plate boundaries: Continent-Continent The present Antarctica is a continent formed by the collision of smaller ancient continents 13 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics Divergent Plate boundaries: Seafloor Spreading Two plates move apart Mantle material upwells to create new seafloor Oceanic ridges develop along well-developed boundaries Along ridges, seafloor spreading creates new seafloor 14 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics Divergent Plate boundaries: Seafloor Spreading Diver between divergent plates at Thingvellir, Iceland 15 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics Divergent Plate boundaries: Continental Rift Continental rifts form at spreading centres within a continent 16 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics Transform fault boundaries Plates slide past one another No new crust is created or destroyed Transform faults Most join two segments of a mid-ocean ridge Aid the movement of oceanic crustal material 17 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics 18 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics Evidence for Plate Tectonics Model Drilling into ocean-floor sediment Age of deepest sediments Thickness of ocean-floor sediments verifies seafloor spreading Earthquakes Associated with plate boundaries Measurement of depth enables modelling of plate subduction 19 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics Evidence for Plate Tectonics Model Hot spots Caused by rising plumes of mantle material Volcanoes can form over them (Hawaiian Island chain) Mantle plumes Some originate at great depth, perhaps at the mantle-core boundary Long-lived structures 20 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Plate Tectonics Measuring plate motion By using hot spot “tracks” Hawaiian Island – Emperor Seamount chain Using technology to directly measure the relative motion of plates Very Long Baseline Interferometry (VLBI) Global Positioning System (GPS) 21 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Geophysics Geophysics is the study of seismic waves as they travel through the Earth. A seismic wave is a vibration that moves through any part of the Earth. Two types of waves radiate out from any disturbance in the Earth: Surface Waves Body Waves 22 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Geophysics Surface Waves travel along the Earth’s Surface Body Waves travel through the Earth’s Interior Two types of Body Wave: P-wave (pressure or primary), longitudinal high velocity (4-7 km s-1) S-wave (shear or secondary), transverse low velocity (2-5 km s-1) 23 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Geophysics P-waves travel through rock (solids), gases, and liquids. Gaining speed with increased density. S-waves can move through rock (solids) but not through fluids Wave propagation depends on the rock’s elastic properties and density – travels faster with increases in density and inflexibility 24 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Geophysics Waves are: reflected by boundaries between layers of different elasticity and density refracted (bent) when they travel between layers of different inflexibility 25 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Earth’s layered internal structure Observation of seismic waves helped to unlock the internal structure of the Earth Mohorovicic (‘Moho’) discontinuity Velocity of seismic waves increases at 50 km depth Separates the Crust from the underlying Mantle 26 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Earth’s layered internal structure Shadow Zone Absence of P-waves from 105° to 140° around the globe from an earthquake Explained if Earth contained a core composed of materials unlike the overlying mantle (density change) Shadow Zone 27 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Earthquakes Seismology is the study of earthquakes Seismograph – instrument to detect and record earthquakes The data is captured as a seismogram, which is a graph of amplitude in real-time 28 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Earthquakes Earthquake mechanism first explained by H Reid Rocks “spring back” called elastic rebound Vibrations (earthquakes) occur as rock elastically returns to its original shape 29 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Earthquakes Vibration of the Earth produced by the rapid release of stored energy Associated with: movement along faults plate boundaries Explained by plate tectonics theory Global Earthquakes for 7 day period 16 Sep 2021 Source: United States Geological Survey (USGS), http://earthquake.usgs.gov/earthquakes/map/ 30 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Earthquakes Surface, P, and S-waves are all present with earthquakes Surface waves cause rolling like ocean waves P-waves cause compression damage S-waves cause the shaking motion, but only through rock 31 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Earthquakes Using the different arrival times of the P and S waves from at least three recording stations, seismologists can locate the: Focus is the origin of the earthquake from within the Earth Epicenter is the point on the surface of the Earth directly above the focus 32 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Earthquakes Magnitude is measured by the Richter Scale using: The difference between the arrival time of the P and S-wave; and the largest amplitude of the S-wave 33 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Earthquakes Japan 2011 Christchurch 2011 34 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Earthquakes Intensity is the degree of earthquake shaking at a given locale based on the amount of damage Measured by using the Modified Mercalli Intensity Scale The Haitian earthquake of 2010 was rated X Typical Maximum Magnitude Modified Mercalli Intensity Under 2.0 I 2.0 – 2.9 I – II 3.0 – 3.9 II – IV 4.0 – 4.9 IV – VI 5.0 – 5.9 VI – VIII X. Many well-built structures destroyed, collapsed, or 6.0 – 6.9 VII – X moderately to severely damaged. Most other structures Intense 7.0 – 7.9 VIII or higher destroyed, possibly shifted off foundation. Large 8.0 or higher IX or higher landslides. 35 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Physical Effects Primary: Collapse of infrastructure and buildings Secondary: Rupture of pipe work for sewer, gas, and water. Disconnection of electricity and communications systems. Tertiary: Long term change in topography (elevation), river and land architecture. 36 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Effects Ground shaking Building collapse Liquefaction Japan 2007 Haiti 2010 Photo: National Geographic/J Photo: US Geological Survey/Walter Mooney Landslides apan Coast Guard/Handout/Reuters Displacement Roads cut Bridge collapse Pipe rupture Japan 1995 (7.2) Guatemala 1976 (7.5) Photo: National Geographic/Karen Kasmauski Photo: National Geographic/Robert W. Madden 37 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Effects Floods Ruptured dams Broken levees Tsunami Japan 2011(8.9) Photo: National Geographic/ Kyodo/Reuters Seiches Fire Broken gas lines Power lines down Forests Buildings/infrastructure Fuel Storage Facilities Japan 2011(8.9) Photo: National Geographic/ Kyodo/Associated Press 38 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Impact Very common (over 1 million earthquakes per year (Mag 2+)) Cost US$20 million per day! Factors: High population density Construction codes Geology (near plate boundaries or active fault zones) Citizen awareness Early detection and warning systems Emergency coordination strategies Development and affluence of country 39 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Mitigation Prediction No accurate method, even after decades of research! Monitoring of active fault zones and plate margins Forecast generation (short and long term) Issue warnings (cluster of events at high magnitude) Engineering Building codes in seismic risk zones Fault pumping Increase in fluid within the fault zone to decrease friction 40 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Case Study: Japan 2011 Subducting oceanic plate (under the sea) Richter Scale: 8.9 Focus Depth: 29 km 41 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Case Study: Japan 2011 15,703 people killed, 4,647 missing, 5,314 injured, 130,927 displaced 332,395 buildings, 2,126 roads, 56 bridges and 26 railways destroyed or damaged The majority of casualties and damage occurred in Iwate, Miyagi and Fukushima from a Pacific-wide tsunami with a maximum runup height of 37.88 m at Miyako. The total economic loss in Japan AUD$424 billion Electricity, gas and water supplies, telecommunications and railway service disrupted and several reactors severely damaged at a nuclear power plant near Okuma. Several fires occurred in Chiba and Miyagi. 1,800 houses destroyed when a dam failed in Fukushima. Contributed to the Fukushima Nuclear Power Plant failure! (taken from USGS (http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0001xgp/#summary)) 42 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Case Study: Japan 2011 Horizontal displacement and subsidence observed. Landslides occurred in Miyagi. Liquefaction observed at Chiba, Odaiba, Tokyo and Urayasu. The tsunami destroyed or severely damaged many coastal towns in the Kuji-Minamisanriku- Nami area. Several people killed around the Pacific by the tsunami and buildings damaged as far away as the Galapagos Islands, Ecuador. Felt (VIII) at Fukushima, (VII) at Agui, Hiratsuka, Kiryu, Komae, Oyama, Sendai and Tsukuba and (VI) in much of eastern Honshu, including the Tokyo-Yokohama area, Japan. Seiches observed at Leikanger, Norway. Water fluctuations observed in a well in Newfoundland, Canada. The tsunami also caused some massive slabs of ice to calve from the Sulzberger Ice Shelf, Antarctica. (taken from USGS (http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0001xgp/#summary)) 43 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Case Study: Christchurch, New Zealand 2011 Continental Fault Zone near plate boundary Richter Scale: 6.1 Focus Depth: 5.9 km 44 Astronomy and the Universe (PHYS 1015) Lecture 3: Earthquakes (Pages 229-291) Case Study: Christchurch, New Zealand 2011 181 people killed and 1,500 injured 100,000 buildings destroyed or damaged Cost AUD$34 billion Mercalli VIII in the Christchurch-Lyttleton area. Landslides and liquefaction occurred in the area. Felt in much of Canterbury and as far as Invercargill and Palmerston North. (taken from USGS (http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usb0001igm/#summary)) 45