quakes :0

quakes :0

1. CHARACTERISTICS

   • seismic waves
     • body
       • primary
         • compressional waves. moves in a straight line path, shakes the ground back and forth
       • secondary
         • shear wave. shakes ground up and down perpendicular to the direction of wave. particles oscillate about in their equilibrium position
     • surface
       • love
         • horizontal shifting of ground
       • rayleigh
         • involve both up-down and side-to-side motion. most destructive
   • epicenter
     • point in suface vertically above focus
   • focus
     • point inside the Earth where the earthquake originated

2. MEASUREMENT

   • magnitiude
     • 1. quantitative 2. Richter scale 3. 0 - 9+ 4. Accurate 5. Energy released 6. Seismogram
   • intensity
     • 1. qualitative 2. Mercalli scale 3. I - XII 4. abstract 5. degree of destruction 6. description

3. TYPES

   • tectonic
     • collision zone
       • Sikkim Earthquake (aka Himalayan earthquake) 2011 -Indian and Eurasian plate -epicentre: Mangan and Sakyong areas (over 50 km from the Sikkim-Nepal border) -magnitude: 6.9 -intensity: III - VII
     • subduction zone
       • Tohoku Earthquake 2011 -subducting Pacific plate and N American plate (Japan trench) -epicentre: off shore, 130km away from Sedai city -magnitude: 9.0 -intensity: V - VII
       • ^image is to show the relative position of the areas. (esp if you're like me who spent 20minute trying to figure out why san andreas and japan trench involve the same plate -_-)
     • diverging
       • Mozambique Earthquake 2006 -African and Somalia plate (southern end of East african rift) -epicentre: Machaze district in southern Manica province -magnitude: 7.5 -intensity: II - V
     • transform fault
       • originates in the transform fault, or in parallel strike slip faults, probably when a frictional resistance  in the fault system is overcome and the plate suddenly moves.
       • San Francisco Earthquake 1906 - Pacific and N American plate (San Andreas fault) - epicentre: off shore (about 2km away from city), near Mussel Rock -magnitude: 7.8 (other values proposed 7.7-8.25) -intensity: VII to IX
   • intra plate
     • occurs in the interior of a tectonic plate. very rare. 
     • Virginia Earthquake 2011 -N American plate - epicentre: Louisa County -magnitude: 5.8 -intensity: VII
   • volcanic
     • Krakatoa Earthquake, 1883. - in the Duch East Indies - eruption of Krakatoa + several eruption of its caldera = destruction of much of the island and surrounding archipelago 
     • volcano-tectonic earthquake
       • produced by stress changes in rock due to the injection or withdrawal of magma
     • long period earthquake
       • produced by the injection of magma into surrounding rock

4. EFFECTS

   • tsunami
     • Indian Ocean tsunami 2004 -Indian plate subducting under Burma plate -epicentre: 250km SE of the Indonesian city of Banda Aceh -magnitude: 9.0 -slammed into the coastline of 11 Indian Ocean countries, snatching people out to sea, drowning others in their homes or on beaches, and demolishing property from Africa to Thailand.
   • landslide
     • seismic shaking
       • passage of the earthquake waves through the rock and soil produces a complex set of accelerations that effectively act to change the gravitational load on the slope. 
       • El Salvador earthquake 1982 - Cocos Plate is subducting beneath the Caribbean Plate  -epicentre: Pacific Ocean about 60 km southeast of San Salvador -magnitude: 7.2 -causing damage to thousands of traditionally built houses and triggering hundreds of landslides, which were the main causes of fatalities.    
     • liquefaction
       • Christchuch Earthquake 2011
   • fire
     • secondary effect. -power lines may be knocked down + natural gas lines rupture = fireeeeeeeee -broken water lines broken, no water to put fire out.
     • San Francisco Earthquake 1906 -[refer to "transform fault"] -Devastating fires broke out lasted for several days due to the lack of water to control them -As a result, about 3,000 people died and over 80% of San Francisco was destroyed and intensified the loss of nearby cities (e.g. Fort Bragg and Santa Rosa)
   • destruction of property
     • duhh....  depends on severity of earthquake, standard of economic development, population density and distribution

5. MANAGEMENT

   • quakes :0 LDC and DC
   • prediction
     • location
       • plate boundaries correlated with seismic belts
       • HOWEVER, inter plate? New Madrid earthquake 1811-1812 -middle of N American plate -related to ancient, deep seated fault structures that gets reactivated from time to time ∴ difficult to predict
     • time
       • long term
         • paleoseismology
           • study of prehistoric earthquakes to determine recurrence intervals of major ones
           • Parkfield, Cali is situated along the San Andreas fault.  -seismologist discovered that this fault consistently produced magnitude 6.0 earthquake about every 22 years.  -so following 1996 earthquake, the predicted year was 1993. HOWEVER, the it struck in 2004.∴ successful to a limited extent
         • seismic gaps
           • segment of an active fault known to produce significant earthquakes that has not slipped in an unusually long period of time compared with other segments among the same structure
           • San Francisco, Loma Prieta, and Parkfield seismic gaps -low density of earthquakes in these gaps, the fault is often said to be locked long these areas and thus strain must be building -predict a future large event -allows areas to prep themselves
       • short term
         • dilatancy theory
           • when a rock is stressed, it begins to expand, this is caused by micro-fractures in the rock opening up and becoming larger. precursors:
           • 1) ground uplift and tilting - measurements taken in the vicinity of active faults sometimes show that prior to an earthquake, the ground is uplifted or tilted due to the swelling of rocks caused by the strain building on the fault -tiltmeters are used -Nigata, Japan, earthquake 1964 revealed that there had been an uplift just prior to the earthquake 
           • 2) foreshocks -felt most of the time -prior to 1975 eathquake in China, numerous foreshocks led to successful prediction of an earthquake and evacuation of the city of Haicheng  -magnitude 7.3 earthquake that occurred destroyed half of the city of about 100mil inhabitants, but resulted in only a few hundred deaths, because of successful evacuation  -HOWEVER, warnings were also issued in a province near HK, but no earthquake followed even after a month.
           • 3) creeping fault segments -lots of fault creep occurs = small chance of big earthquake -little amounts of fault creep = big chance of big earthquake -build up strain -Tohoku, Japan earthquake 2011 [refer to "subduction zone"]   >might explain the unusually large quake
           • 4) water levels in wells -as rocks become strained close to a fault, ground water pressure changes-Haicheng, China earthquake 1975 >changes in ground water levels
           • 5) emission of radon gas -deformation resulting from strain may force the radon out and lead to emission of the gas that shows up in well water -Kobe, Japan earthquake 1995   >significant increase in radon content in well water in the month prior to the earthquake.   >after the earthquake, emission reduced rapidly
           • 7) changes in the electrical resistivity of rocks - rocks are poor conductors of electricity, while water is a more efficient conductor - if micro cracks develop, groundwater is forced into the cracks, this may cause the electrical resistivity to decrease
           • 8) unusual radio waves - Loma Prieta earthquake 1989
         • seismic monitering
           • place aeiamometers along faults -when the ground shakes, seismometers convert the motion into an electrical signal, which is recorded and saved
         • satellites & GPS
           • better accuracy 
       • control
         • earthquakes have been known to be induced by human interaction with the Earth, hence future earthquake control may be possible
         • human induced earthquake: - construction of the Hoover Dam in Nevada, blocking the Colorado River to produce Lake Mead -earthquakes of magnitude 5.0 and 4.0 occurred 
   • mitigation
     • event
       • 1) Earthquake resistant design 2) building codes 3) concrete and steel construction 4) bridges 5) utilities all need to be proper and strong
     • vulnerability
       • 1) prediction and warning -allow people to evacuate the danger area before the earthquake
       • 2) hazard zone mapping -it is done based on a number of factors such as location of active plate margins, presence of geological structures
       • 3) land use planning - based on hazard zone mapping -restricts new development in hazardous areas, enforces aseismic buildings designs for new development and provides emergency evacuation plans
       • 4) community preparedness -public must be well aware about the type of hazards and how to face it -must also be trained and educated a in first aid, search and rescue operations and fire fighting techniques
     • loss
       • 1) aid -financial -rescue and search teams -medical personnel and support -basic needs -post-traumatic stress, rehabilitation and rebuilding
       • 2) insurance
   • response
     • -search and rescue - immediate relief - reconstruction, rehabilitation, recovery and long term redevelopment

Images and files in the map