GNR 639 GNR 639 : Natural Disaster And Management Lesson 2 Earthquake Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Earthquake Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Earthquake is the result of a sudden release of energy (seismic waves) in the Earth's crust, caused by sudden breaking and movement of large sections (tectonic plates) of the earth's crust. Most earthquakes occur along the fault lines when the plates slide past each other or collide against each other. The seismicity of an area refers to the frequency, type and size of earthquakes experienced over a period of time. This movement of masses generate shock waves that may be powerful enough to • alter the surface of the Earth, thrusting up cliffs and opening great cracks in the ground and • cause great damage - collapse of buildings, man-made structures, broken power and gas lines and the consequent fire, landslides, snow avalanches, tsunamis and volcanic eruptions. Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management (Source courtesy: usgs) Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Earthquake frequency - High Magnitudes Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Types of earthquake Tectonic Earthquakes when rocks in the earth's crust break due to geological forces created by movement of tectonic plates. Volcanic Earthquakes occur in conjunction with volcanic activity. Explosive Earthquakes result from the explosion of nuclear and chemical devices. Collapse Earthquakes are small earthquakes in underground caverns and mines. Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Tectonic earthquakes Continental plates converge, diverge or grind past each other (transform fault). Earthquakes are caused by a sudden release of stress along faults in the crust. Due to continuous motion of tectonic plates, stress builds in the rock on both sides of a fault. Most of them happen where tectonic plates meet and glide against each other due to the frictional stress of the movement exceeds the strength of the rocks, causing a failure at a fault line. Violent displacement of the Earth's crust follows, leading to a release of elastic strain energy. Fault or fault plane = the surface where when two blocks of the earth suddenly slip past one another Source courtesy: southaustralia Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Geological faults San Andrea’s fault California; Displacement of beds Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Epicenter is the point on the Earth's surface directly above the point where the fault begins to rupture. It is the area of greatest damage. However, in larger events, the length of the fault rupture is much longer, and damage can be spread across the rupture zone. Hypocenter (also know as focus) is the point within the earth where an earthquake rupture starts. The epicenter is the point directly above it at the surface of the Earth. Seismic waves propagate spherically out from the hypocentre. Source courtesy: scwcweb.cwb.gov.tw Seismic waves - an elastic wave by an earthquake or other means. Seismic waves: P (primary) waves , S (secondary) waves and surface waves, which arrive at seismic recording stations one after another. Both P and S waves penetrate the interior of the Earth while surface waves do not, hence, they are body waves. Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management P waves – Compressional, longitudinal waves. Travel at 1.5-8 km/sec in the Earth's crust and first to arrive at seismic stations They shake the ground in the direction they are propagating. Travel through the Earth's core S waves - shear waves slower than P waves, 2 nd to arrive at seismic stations. Shake the ground perpendicular to the direction in which they are propagating & do not travel through liquid (ie. water, molten rock, the Earth's outer core) Source courtesy: colarado.edu Surface waves (Love & Rayleigh) – travels only on earth’ surface. moves ups and down like ocean waves. Slowest of all (Source courtesy:ndma.gv.pk) Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Human induced seismicity Induced seismicity is a minor low magnitude earthquakes and tremors that are caused by human activity that alters the stresses and strains on the Earth's crust. Source courtesy: en.wikipedia.org Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Reservoir - induced seismic activity appears to occur on dams with heights more than 100 m. The extra water pressure created by large reservoirs is the most accepted explanation for the seismic activity. World Commission on Dams, Reservoir-Induced Seismicity (RIS) is related to the extra water pressure created in the micro-cracks and fissures in the ground . Hydraulic fracturing has a low risk for inducing earthquakes that can be felt by people. Underground injection of wastewater produced by hydraulic fracturing and other energy technologies has a higher risk of causing such earthquakes. Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Artificial lakes Creation of deep artificial lake ( high Water column) alters in-situ stress along an existing fault . Weight of the water column significantly change the stress on the underlying fault and increase the effective stress through the increased pore water pressure. This stress change can lead to sudden movement resulting in an earthquake Mining Large scale Voids alter the balance of forces in the rock, causing rock bursts. These voids may collapse producing seismic waves and also reactivate existing faults causing minor earthquakes . Collapse of Natural cavern sinkholes/ natural cavern produce an identical local seismic event. Waste disposal wells Injection of liquids (high-saline water) into waste disposal (salt water disposal (SWD) wells, is practiced in disposing of produced water from oil and natural gas wells. This activity result in increasing the subsurface pore pressure, trigger movement along faults. Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Extraction of fossil fuels / groundwater The changes in crustal stress patterns caused by the large scale extraction of groundwater as well fossil fuels has been shown to trigger earthquakes. Geothermal energy Enhanced geothermal systems (EGS), involves pumping fluids at pressure to enhance or create permeability through the use of hydraulic fracturing techniques. Hot dry rock (HDR) actively creates geothermal resources through hydraulic stimulation. Induced seismicity events are reported from the Geysers geothermal field has been strongly correlated with injection data Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Network of seismometers is used to calculate the magnitude Seismometer is an instrument for measures seismic and source of an earthquake in three dimensions: waves that are propagating vibrations that carry energy from the source of an earthquake outward in Magnitude : the size of the earthquake all directions. They travel through the interior of the Depth : how deep the earthquake was Earth and can be measured with sensitive detectors Location : where the earthquake occurred called seismographs . Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Seismograph of earthquake & Nuclear explosion shock waves Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Richter magnitude scale assigns a magnitude number to quantify the energy released by an earthquake. It is a base- 10 logarithmic scale, which defines magnitude as the logarithm of the ratio of the amplitude of the seismic waves to an arbitrary, minor amplitude. Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Modified Mercalli scale ranks intensity of earthquakes from (barely felt) to 12 (total destruction) Earthquake depth range: • shallow - 0 and 70 km , ( result of the sudden release of strain energy built up over time in rock by brittle fracture and frictional slip over planar surfaces ) • intermediate 70 - 300 km • deep 300 - 700 km (Subducted lithosphere subject to the pressure and temperature regime at depths greater than 300 km should not exhibit brittle behavior, but should rather respond to (Source courtesy: oliphantearth.com) stress by plastic deformation) Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Prof. R. Nagarajan, CSRE , IIT Bombay
GNR 639 GNR 639 : Natural Disaster And Management Prof. R. Nagarajan, CSRE , IIT Bombay
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