Get Full Essay Get access to this section to get all help you need with your essay and educational issues. A natural hazard is a naturally occuring physical event which poses a threat and negatively impacts people and the environment.
Shaking, Landslides, Liquefaction, and Tsunamis Direct Shaking Hazards and Human-Made Structures Most earthquake-related deaths are caused by the collapse of structures and the construction practices play a tremendous role Earthquake and its effect the death toll of an earthquake.
In southern Italy in more thanpeople perished in an earthquake that struck the region. Almost half of the people living in the region of Messina were killed due to the easily collapsible structures that dominated the villages of the region.
A larger earthquake that struck San Francisco three years earlier had killed fewer people about because building construction practices were different type predominantly wood. Building practices can make all the difference in earthquakes, even a moderate rupture beneath a city with structures unprepared for shaking can produce tens of thousands of casualties.
Although probably the most important, direct shaking effects are not the only hazard associated with earthquakes, other effects such as landslides, liquefaction, and tsunamis have also played important part in destruction produced by earthquakes. Geologic Effects on Shaking When we discussed earthquake intensity we discussed some of the basic factors that affect the amplitude and duration of shaking produced by an earthquake earthquake size, distance from fault, site and regional geology, etc.
The level of damage done to a structure depends on the amplitude and the duration of shaking. The amplitudes are largest close to large earthquakes and the duration generally increases with the size of the earthquake larger quakes shake longer because they rupture larger areas. Regional geology can affect the level and duration of shaking but more important are local site conditions.
Although the process can be complicated for strong shaking, generally shaking in soft sediments is larger and longer than when compared with the shaking experienced at a "hard rock" site.
Preparing Structures for Shaking The first step in preparing structures for shaking is to understand how buildings respond to ground motions- this is the field of study for earthquake and structural engineers.
The inertia of the building it wants to stay at rest can cause shearing of the structure which can concentrate stresses on the weak walls or joints in the structure resulting in failure or perhaps total collapse. The type of shaking and the frequency of shaking depends on the structure.
Tall buildings tend to amplify the motions of longer period motions when compared with small buildings. Each structure has a resonance frequency that is characteristic of the building.
Predicting the precise behavior of buildings is complicated, a rule of thumb is that the period of resonance is about equal to 0. Thus Macelwane Hall resonates at about 0. Taller buildings also tend to shake longer than short buildings, which can make them relatively more susceptible to damage.
Fortunately many tall buildings are constructed to withstand strong winds and some precautions have been taken to reduce their tendency to shake. And they can be made resistant to earthquake vibrations. The worst possible structure for earthquake regions is the unreinforced masonry which is common in the St.
Estimating Hazards Preparing structures either new or old for earthquakes is expensive and the level of investment is a social and political decision.
The choice of building design is a compromise between appearance, function, structure, strength, and of course, cost. Standards are instituted through the establishment of Building Codes, which regulate the design and construction of buildings. Most of our building codes are designed to protect first the building occupants, and second the building integrity.
Building codes are usually drafted to meet the demands of the expected shaking in a given region that are summarized by seismologists and earthquake engineers in hazards maps.
Hazard maps are constructed by examining The earthquake history of the region to estimate the probability of an earthquake The expected shaking intensity produced by the earthquake often expressed as a peak acceleration The frequency of the shaking, the distance from the fault The regional geology and site conditions to estimate the maximum level of shaking expected during the lifetime of a building.
Constructing accurate hazard maps is a challenge and remains the focus of much Geoscience research. For the Midwest you may want to check out the WWW site of a large multidisciplinary effort to help prepare the eastern US for the low-probability, but high consequence earthquake hazards check out the Mid-America Earthquake Center.
Either approach can be expensive so we cannot build all our structures to withstand the largest possible earthquake. We must make compromises and accept some risk this is not unlike the risks that we accept every day, driving on a freeway, flying in an airplane, living in flood-prone regions, tornado "alley", hurricane-prone regions, etc.
We need different levels of resistance for different classes of structures. Critical structures such as hospitals, power, water-treatment, and chemical plants, dams, etc.
These structure require the largest investment of resources to insure that they can provide services following an earthquake. Since we know that sites with soft, water-saturated foundations are prone to damage, we should resist the temptation to build on those sits and we should certainly not put critical structures on such sites, and avoid building on these sites at all if possible.
We can take a number of steps to strengthen buildings including using steel frame construction, adequately securing the structure to the ground through a solid foundation, incorporating shear walls and or cross-bracing into the structure, or more sophisticated approaches such as using rubber or steel pads to isolate the structure from the shaking.
We have talked above seismic waves and how they vibrate the ground which can lead directly to the collapse of structures. There are other, secondary effects that are caused by earthquakes, most often a result of strong shaking.The objective of earthquake engineering is to foresee the impact of earthquakes on buildings and other structures and to design such structures to minimize the risk of damage.
Existing structures can be modified by seismic retrofitting to improve their resistance to earthquakes.
Earthquake environmental effects are the effects caused by an earthquake, including surface faulting, tsunamis, soil liquefactions, ground resonance, landslides and ground failure, either directly linked to the earthquake source or provoked by the ground shaking.
On the April 25th, , Nepal was struck with Rechter Scale destructive Earthquake at mid-day. On the other hand, on 11th of June, people were killed while were severely injured. When we discussed earthquake intensity we discussed some of the basic factors that affect the amplitude and duration of shaking produced by an earthquake (earthquake size, distance from fault, site and regional geology, etc.) and as you are aware, the shaking caused by seismic waves can cause damage buildings or cause buildings to collapse.
In its most general sense, the word earthquake is used to describe any seismic event — whether natural or caused by humans — that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults, This effect is called site or local amplification.
When we discussed earthquake intensity we discussed some of the basic factors that affect the amplitude and duration of shaking produced by an earthquake (earthquake size, distance from fault, site and regional geology, etc.) and as you are aware, the shaking caused by seismic waves can cause damage buildings or cause buildings to collapse. An earthquake is an oscillatory motion of the earth surface originated by the propagation of elastic waves caused by rock rupture at various depths. The effect is similar to that of an explosion which takes place at several kilometers in the subso. Earthquake environmental effects are the effects caused by an earthquake, including surface faulting, tsunamis, soil liquefactions, ground resonance, landslides and ground failure, either directly linked to the earthquake source or provoked by the ground shaking.
Causes and Effects of Earthquakes. Earthquake refers to the sudden violent movement of the earth’s crust. It creates seismic waves. It often causes great destruction. Its causes and effects are mentioned below. Causes of Earthquakes. The important causes of the earthquake are.