Transcript Slide 1
Table of contents First man induced Earthquake Theory Dam! Injecting fluids Extraction Mining Other factors First man-induced Earthquake Nikola Tesla Accidental earthquake created in study of ground resonance with a mechanical vibrator. <<The rhythmical vibrations pass through the Earth with almost no loss of energy. It becomes possible to convey mechanical effects to the greatest terrestrial distances and produce all kinds of unique effects. The invention could be used with destructive effect in war>> Tesla’s Controlled Earthquakes July 11, 1935 issue of the New York American � Theoretically speaking So far, most of the induced earthquakes have been accidental ones. Artificial seismicity will commonly be induced as we create some mass and pressure changes on the crust. These events usually happen in already highly stressed faulted areas. Anthropogenic factors are only postponing what would happen at some point anyway Coulomb stress changes (∆CSF) law ∆ CSF = ∆ fault shear + fric. coef. * (∆ Pore pressure+ ∆ Normal stress) where with increasing CSF, the risk of failure increases M>5 Induced Earthquakes. __________________________________________ Dam / Reservoir DP or Hydrocarbon Field Magnitude Seismicity Induced Earthquakes ____________________________________________________________ ____________________________________ Gazli field, EIS 7.3 low horizontal midplate Uzbekistan Koyna, RIS 6.5 low horizontal midplate India Coalinga field, EIS 6.5 high horizontal plate boundary USA Kremastaa, RIS 6.3 high vertical back arc extension Greece Hsinfengkiang, RIS 6.1 low horizontal midplate China Kettleman field, EIS 6.1 high horizontal plate boundary USA Montebello field, EIS 5.9 high horizontal plate boundary USA Oroville, RIS 5.9 low vertical Sierra Nevada foothills USA USA Kariba, RIS Zambia/Zimbabwee Marathona, RIS Greece Aswana, RIS Egypt Eucumbene, RIS Australia Hoover, RIS USA Denver, IIS USA Caviaga, EIS Italy Lake County, IIS USA Monteynard, RIS France El Reno, EIS USA Snipe Lake, EIS Canada 5.8 low vertical midplate 5.7 high n.a plate boundary 5.5 low vertical midplate 5.5 low n.a midplate 5.5 low vertical Colorado plateau 5.5 low vertical Colorado plateau 5.5 low horizontal midplate 5.3 low horizontal midplate 5.3 low vertical Alps foothills 5.2 low horizontal midplate 5.1 low horizontal midplate Water Dam Most common factor concerning induced seismicity (one third of world artificial occurences) Higher density of H2O compared to air increase the weight stress and the porosity pressure on the crust supporting reservoir. We usually can see a direct correlation between the filling of the water and the CSF value Risk varying depending on the reservoir emplacement and the fault plane orientation At home... Manic 5 142 km3 which represents 142 000 000 000 metric tons Dam! What a disaster 33 sure cases of reservoir-induced seismicity or M>4 (7 of them were over 5.5) Most know event is the Koyna Reservoir (India) earthquake in 1967. M=6.3 Over 200 fatalities and more than 1500 injured. Heated debates on the responsibility of the Zipingpu reservoir in the 2008 Sichuan earthquake. Over 68000 fatalities and has been felt all over China. Combined gravitational loading and pore pressure diffusion leaded to a ∆CSF of 0.1 Mpa in the upper 10km beneath the reservoir. During the initial impoundment, notable number of earthquakes (M 3.5) In general… ∆CSF will increase as the dam is filled This may significantly shorten the time before earthquake occurrence. Sometimes add up the stress that would take hundred years too accumulate by shear or normal stress. Seismicity may occur while the dam is filling or after. The potential hypocenter (of a fault) will tend to move towards the dam (has to be accounted when the dam is built) To avoid any risk, try not to build close to fault systems Extraction seismicity Extraction of oil, gaz and geothermal energy may lead to compaction by underground crust subsidence (result in seismicity). Some faults are usually slipping aseismically due to crust fluids. Extraction of these fluids may conduct to a lock up of the slipping (no moving anymore due to friction). The fault would then accumulate the stress until it bursts into an earthquake. We recorded worldwide over 24 oil fields associated with seismicity of M>3 Some believe the three earthquakes (m7) in Uzbekistan (1976-1980) (more than a thousand fatalities)could have been induced by the gas extraction installations. (injections and extraction) Injection-induced seismicity Fluids are sometimes injected into the ground using it as a waste disposal or as an artificial fluid tank (oil or gas). Such injections increase the pore pressure and usually lead to a decrease in the fault’s effective normal stress In 1961, army decided to dispose of toxic waste from napalm production: 165 million gallons pumped 12000 foot deep into the rockies in denver. They had to stop the operation when seismicity went out of control. The periods and amounts of injected waste coincided with the frequency and magnitude of the quakes Risks of contamination Seismicity induced by Mining and Quarrying UNDERGROUND MINING Underground mining will tend to remove an important supporting mass. It will lead in an increase of the pressure and stresses on the column and rock structure left behind. Can result in failure of the walls, ceiling or floor and on movement along pre-existing fault or even new faulting SURFACE MINING Will remove an important mass from the crust which may result in a spring up motion of the layers at depths. The waste rock will add a weight load on the waste area depending on the fault attitude and how we dig, numerous scenarios can occur, the two of them can even sometimes counteract so the earthquake occurrence will be delayed. Other earthquake inducing factors The tallest buildings: Cities are really heavy. We are adding some significant weight on the city ground Some geologists (2005) claimed that the second tallest building of the world, the Taipei 101 (Tawain), with a weight of 700 000 metric tons, was inducing seismicity on a long dormant fault. Some earthquakes were triggered Underground Nuclear Testing. Strong shockwaves can add energy to the fault system. However, for high scale induced seismicity, a wave shock is often less effective than mass or pressure changes. H.A.A.R.P. (High Frequency Active Auroral Research Program) shooting a billion watt electromagnetic beam into the ionosphere which would reflect back the waves toward the crust. If you build up resonance, you can add lots of energy to some rock layers. Hopefully, Lex Luthor won’t put his nasty hands on this.