1. Ground shaking intensity is defined as the severity of ground motion, i.e. displacement, during an earthquake and is assessed using the Modified Mercalli Intensity Scale (MMI). This scale is a good indicator on the effects and earthquake has on the environment and its population. It is based on three features:
People’s perception
Building performance
Changes in the natural environment
The MMI is often associated to Peak Ground Acceleration (PGA), which is used to quantify the severity of ground shaking as shown in Table 1.
The intensity of an earthquake is a qualitative measure of the shaking at a location and it usually depends on:
The Magnitude of an earthquake
Distance from the fault
Local Geology
These will all affect the way in which seismic waves will propagate through the ground and therefore will be responsible for all the subsequent event which will occur as a result of the earthquake.
Subsidence is a result of earthquake shaking. As the ground shakes, unconsolidated sediments lose their bearing strengths and the ground “shifts” downwards relative to sea level and this resulted in liquefaction and landslides and flooding. Subsidence can also occur as a result of downward displacement on one side of a fault which may sometimes affect large areas of land.
The 4th of September 2010 Darfield event generated a magnitude 7.1 earthquake with a MMI of 9. This earthquake resulted in extensive liquefaction and differential subsidence which was located close to major streams and rivers around Christchurch.
The 22nd of February 2011 Christchurch City event created a magnitude 6.3 earthquake with a MMI of 9. This earthquake occurred within 10 kilometres of the city at a shallow depth of 5 kilometres. This cau...
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...l change and liquefaction in the Avon-Heathcote Estuary. Report No. U11/13, Christchruch: Environment Canterbury Regional Council, 2011.
Quigley, M. Van Dissen, R., Villamor, P., Litchfield, N., Barrell, D., Furlong, K., Stahl, T., Duffy, B., Bilderback, E,. Noble, D., Townsend, D., Begg, J., Jongens, R., Ries, W., Claridge, J., Klahn, A., Mackenzie, H., Smith, A., Hornblow, S., Nicol, R. “Surface rupture of the Greendale Fault during the Mw 7.1 Darfield (Canterbury) earthquake, New Zealand: Initial Findings.” Bulletin of the New Zealand Society for Earthquake Engineering 43:4 (2010): 236-242.
SC Cox, HK Rutter , A Sims , M Manga , JJ Weir , T Ezzy , PA White , TW Horton & D Scott (2012). “Hydrological effects of the Mw 7.1 Darfield (Canterbury) earthquake, 4 September 2010, New Zealand.” New Zealand Journal of Geology and Geophysics 55:3 (September 2012): 231-247.
Earthquakes are best described as a shaking or vibration of the ground caused by breaking of rock. Sometimes they are very strong and other times you would hardly notice them. This shaking occurs when stress that builds up in the crust is suddenly released as the crust breaks free and/or slides against the other pieces of crust. Earthquakes may also be thought of as the breaking of a popsicle stick by applying pressure to both ends at the same time. Should you try this experiment , you will feel the pressure build up as you apply more force until the stick snaps. When the stick snaps you will feel an instant of pain at your fingers as the stress reduces and energy waves move throughout the stick. When the earth's crust is placed under similar types of stress, binding as the stress builds, it will also snap and release the energy into the surrounding rocks, 'ooch'. Thinking about earthquakes will become more clear if you try another experiment.
Earthquakes are a natural part of the Earth’s evolution. Scientific evidence leads many geologists to believe that all of the land on Earth was at one point in time connected. Because of plate tectonic movements or earthquakes, continental drift occurred separating the one massive piece of land in to the seven major continents today. Further evidence supports this theory, starting with the Mid-Atlantic ridge, a large mass of plate tectonics, which are increasing the size of the Atlantic Ocean while shrinking the Pacific. Some scientists believe that the major plate moveme...
The west coast of the islands is on the edge of a continental shelf created by ancient volcanic movement (Broadhead 5) .This volcanic activity is due to plate tectonic movement which also created the numerous amounts of earthquakes on the island. Compared to the rest of British Columbia, Haida Gwaii has the most earthquake activity (Broadhead 5), the last of which being in a magnitude of 7.7 on t...
The science of the natural disaster has baffled many, but from studying the San Francisco earthquake, scientists have made a number of important discoveries and they have a better understanding of earthquakes. At 5:12 on a fateful April morning in 1906, the mammoth Pacific and North American plates sheared at an incredible twenty-one feet along the San Andreas fault, surpassing the annual average of two inches (“San Francisco Earthquake of 1906”)(“The Great 1906 Earthquake and Fires”). The shearing caused a loud rumble in the Californian city of San Francisco. A few seconds later, the destructive earthquake occurred. The ground shifted at almost five feet per second, and the shaking could be felt all the way from southern Oregon to southern Los Angeles to central Nevada (“Quick”)(“The Great 1906 San Francisco Earthquake”). Moreover, the earthquake could be recorded on a seismograph in Capetown, South Africa, an astounding 10,236 miles away from San Francisco (“San Francisco ea...
Earthquakes have been recorded throughout history for thousands of years. Even before seismographs in early times, there are records and accounts of mysterious ground shaking. Earthquakes occur when rocks break along an underground fault (UPSeis, 2007). This, in return, causes vibrations through the earth which causes ground shaking. The magnitude of the shaking varies depending on how great the movement along the fault is; the greater the movement, the bigger the earthquake. Some earthquakes are huge and cause significant damage, while others are small and cause little or no damage what-so-ever. Earthquakes are unpredictable, and can happen at any time. It is uncertain where an earthquake will strike, but there is a greater risk of an earthquake for areas lying on or near a fault. No one is ever prepared for an earthquake, so the people affected must face a sometimes terrifying reality and can be scarred for life. One country in particular that has been severely affected from an earthquake is Italy. Over a century ago Messina, a city located in Sicily, was to face one of the most devastating natural events of the century.
Healy, J. H., Rubey, W. W., Griggs, D. T., & Raleigh, C. B. (1968, September). The Denver Earthquakes. Science, 161(3848), 1301-1310. Retrieved from JSTOR database.
benchmark for the future, and integrated investigation into the effects of earthquakes in the U.S.
The Physical and Human Factors Which Affect the Location and the Impact of the Earthquake Hazard
Mr. Adams describes the San Francisco earthquake as his most profound human suffering experience because the horror of shaking floors, parts of his mom’s house collapse to the floor, and got a broken nose from stumbling into a brick wall (Ansel Adams & The 1906 Earthquake 2008). Earthquakes are part of natural disasters of the earth and normally caused by shaking ground and rapid movement of one block of rock slipping past another a long fractures in the earth crust called faults. Faults that are usually locked excluding abrupt movements, which slippage creates an earthquake (Lutgens, F. & Tarbuck, E.
Soil liquefaction describes a phenomenon whereby a saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid. The phenomenon is most often observed in saturated, loose (low density), sandy soils. This is because the loose sand has a tendency to compress when a load is applied; dense sands by contrast tend to expand in volume. If the soil is saturated by water, then water fills the gaps between soil grains. In response to the soil compressing, this water increases in pressure and attempts to flow out from the soil to zones of low pressure (usually upward towards the ground surface). However, if the loading is rapidly applied and large enough, or is repeated many times (e.g. earthquake shaking, storm wave loading) such that it does not flow out in time before the next cycle of load is applied, the water pressures may build to an extent where they exceed the contact stresses between the grains of soil that keep them in contact with each other. These contacts between grains are the means by which the weight from buildings and overlying soil layers are transferred from the ground surface to layers of soil or rock at greater depths. This loss of soil structure causes it to lose all of its strength. According to the
Geologists today define an earthquake as the shaking and the trembling of the earth’s surface, known as the ground. Earthquakes are caused by the sudden release of energy, usually as a result of faulting which involves displacements of rocks along fraction. All of this energy has been building up for a long period of time and then suddenly just blows.
January 12, 2010 became the moment of tragedy for the population of Haiti: an earthquake of terrible force stroke the small island, killing and injuring thousands of people. The earthquake turned into a devastating power, destroying everything in the epicenter and miles beyond. It was the most powerful earthquake in Haiti in more than 100 years. Now, several months after the tragic event, Haitian authorities still work to restore the economic and social stability in the region. Earthquakes are difficult to predict the Haiti earthquake did not have any warning signs or foreshocks. It was equally unexpected and powerful. The aftershocks that followed confirmed the complexity of the natural processes that usually occur during earthquakes.
Earthquake is the earth tremor that results from the sudden release of the pent-up energy in the earth’s crust. This released energy creates the seismic waves that determine the frequency, type and size of the earthquakes. Any earthquakes whose magnitude is bellow 5 on the Richter scale is considered weak, while the earthquakes whose magnitude is above 7on the Richter scale is considered potentially dangerous. The largest earthquake ever register in the history of man is the earthquake in Japan in 2011 which had a magnitude of 9.0 on the Mercalli scale(Seeram, pars. 4-5). While most earthquakes are causes by seismic events on the earth’s crust, these can be accelerated by natural events, or the activities of the human beings. For example, when the geological faults lines rapture, pressure is created in the earth’s crust forcing its way out thereby causing a break or sliding along the fault line. Volcanic activities are also known to cause earthquakes and so are nuclear test, bombs and landslides. The hypocenter is the initial point from which the raptures occur, while the epicenters is the ground directly above the hypocenter (Zacharias,, sec. A)
Earthquakes belong to the class of most disastrous natural hazards. They result in unexpected and tremendous earth movements. These movements results from dissemination of an enormous amount of intense energy in form of seismic waves which are detected by use of seismograms. The impact of earthquakes leaves behind several landmarks including: destruction of property, extensive disruption of services like sewer and water lines, loss of life, and causes instability in both economic and social components of the affected nation (Webcache 2).
The 1989 Newcastle earthquake happened in Newcastle, New South Wales on Thursday, 28 December at 10:28am. It was one of the most damaging earthquake that hit Newcastle ever yet. The shock measured 5.6 on the Richter magnitude scale and was one of Australia's most severe natural disasters ever. An earthquake is the moment of an unexpected discharge of energy in the Earth's crust that produces seismic waves. It was very powerful that the earthquake was widespread across NSW. It was stated that the quake continued for numerous seconds and it sounded like loud explosion. Everyone was muddled on what was happening so some of them walked off out of the building, stunned and confused on what was going on. Little did they know it was an earthquake