ISBN (PDF) This project aimed to revise historic earthquake measurements to more accurately reflect their true. caused by a hypothetical magnitude earthquake along the San Andreas Fault in southern . National Strong-Motion Project (NSMP). . (April ), at http:// caite.info Modified. An earthquake occurs when Earth's surface shakes because of the release of seismic energy following the rapid movement of large blocks of the crust along a .
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strike without warning and many of the Earth's earthquake zones coincide with areas of high population Seismology is the study of earthquakes and seismic waves. The seismograph .. The project is supported by. NERC and a customer . PDF | 35+ minutes read | Earthquake is one of the most devastating 15+ million members; + million publications; k+ research projects. All About Earthquakes: The Science Behind Earthquakes. What is an earthquake ? An earthquake is what happens when two blocks of the earth suddenly slip.
The actual faulting associated with an earthquake may be complex, and it is often not clear whether in a particular earthquake the total energy issues from a single fault plane. According to the beliefs of many peoples, earthquakes originate in mountains. When designing projects in earthquake-prone areas, it is imperative to ensure that the utility systems resist damage due to earthquake shaking. If you have any, please provide feedback. Building standards in some parts of the world are based on the required performance of a particular building in a future earthquake event. In areas of Africa where the concept of mana is particularly strong, many believe that the dead in the underworld are the causes of earthquakes, though in the upper Nile basin of The….
Roughnesses along the fault are referred to as asperities, and places where the rupture slows or stops are said to be fault barriers. Fault rupture starts at the earthquake focus, a spot that in many cases is close to 5—15 km under the surface.
The rupture propagates in one or both directions over the fault plane until stopped or slowed at a barrier. Sometimes, instead of being stopped at the barrier, the fault rupture recommences on the far side; at other times the stresses in the rocks break the barrier, and the rupture continues. Earthquakes have different properties depending on the type of fault slip that causes them as shown in the figure.
The lower wall of an inclined fault is called the footwall. Lying over the footwall is the hanging wall. When rock masses slip past each other parallel to the strike, the movement is known as strike-slip faulting. Movement parallel to the dip is called dip-slip faulting. Strike-slip faults are right lateral or left lateral, depending on whether the block on the opposite side of the fault from an observer has moved to the right or left. All known faults are assumed to have been the seat of one or more earthquakes in the past, though tectonic movements along faults are often slow, and most geologically ancient faults are now aseismic that is, they no longer cause earthquakes.
The actual faulting associated with an earthquake may be complex, and it is often not clear whether in a particular earthquake the total energy issues from a single fault plane. Observed geologic faults sometimes show relative displacements on the order of hundreds of kilometres over geologic time , whereas the sudden slip offsets that produce seismic waves may range from only several centimetres to tens of metres.
In the Tangshan earthquake , for example, a surface strike-slip of about one metre was observed along the causative fault east of Beijing , and in the Taiwan earthquake the Chelung-pu fault slipped up to eight metres vertically. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind.
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Written By: Bruce A. See Article History. Read More on This Topic. Earthquake or seismic forces, unlike wind forces, are generally confined to relatively small areas, primarily along the…. Page 1 of 7.
Next page Volcanism. Learn More in these related Britannica articles: When abrupt movements of the edges of these plates occur, the energy released propagates…. No natural event is as destructive over so large an area in so short a time as an earthquake. Throughout the centuries earthquakes have been responsible not only for millions of deaths but also for tremendous damage to property and the….
Many large dams have been built in the seismically active regions of the world, including Japan, the western United States, New Zealand, the Himalayas, and the Middle East.
In the Tokachi earthquake damaged 93 dams in Honshu, the main Japanese island; all…. According to the beliefs of many peoples, earthquakes originate in mountains. In areas of Africa where the concept of mana is particularly strong, many believe that the dead in the underworld are the causes of earthquakes, though in the upper Nile basin of The….
Several since have been devastating, including one in in what is now Bihar state that killed more than 10, people. In another tremor the Bhuj earthquake , farther from the mountains, in Gujarat state, was less powerful but…. More About Earthquake 83 references found in Britannica articles Assorted References aftershocks In aftershock association with volcanic eruptions In volcano infrasonic waves In infrasonics In infrasonics internal structure of Earth In Earth exploration: Seismic refraction methods In Earth exploration: Conclusions about the deep Earth prediction and control In seismograph In geology: Earthquake prediction and control soil liquefaction In soil liquefaction caused by dams In Asia: Water resources View More.
Help us improve this article! Contact our editors with your feedback. Edit Mode. Similarly, it is necessary to determine to what extent these regulations take into consideration the earthquake hazard in the region, and whether they provide sufficient protection. To do this, engage the local engineering community, especially those serving with the local government, in discussions.
Similarly, it is necessary to understand when these standards were last revised, and how often revisions occur. Earthquake information and engineering developments are rapid, and standards that have not been revised for more than five years may not meet requirements for project design.
In such cases, more stringent design standards may have to be followed. Many provisions in the building standards, if implemented, are intended to ensure that structures can adequately resist seismic forces during earthquakes.
Building standards in some parts of the world are based on the required performance of a particular building in a future earthquake event.
It should be understood however, that the costs will increase substantially for higher performance levels. Hence, if such standards are in use in the project area, it is essential to understand and consider the performance required for each building in the project, and to set the building-performance goal needed for each.
According to the building standards in some countries, the design will be influenced by how important the building is depending upon the functional use of the building, the hazardous consequences of its failure, its post-earthquake functional needs, historical value, occupancy or economic importance.
An Importance Factor say 1. This however, is still an indirect approach. More direct and better approaches are also available for important facilities see Design Considerations. If the local building codes do not reflect the seismicity of the area, consider adopting and complying with building standards from other regions sharing similar geological conditions and earthquake hazards.
In many countries, seismic hazard is not considered in building standards either because these are rare events or because the earthquake history is incomplete. However, it should be remembered that rare events can happen within the lifespan of the building and result in large losses. More Information: Even though the area under consideration falls in medium hazard according to the information that is currently available, it is important to understand the geology of the project site.
This is one of the first steps in the design process and determines whether the project site is likely to be affected by ground failure or other site-hazards during a future earthquake. Maps showing landslide hazard, liquefaction potential defined below , shaking amplification due to soft soil, and active fault zones may be available with the local emergency management officials or may be a part of a seismic microzonation study report.
The foundation is the lowest part of a building which interacts with the soil and transmits the load of the structure to the soil below.
Before a foundation type is decided, it is necessary to understand the characteristics of the soil at the site of construction. This is done by soil investigations which should be conducted by a geotechnical engineer who will test the soil at the site and will prepare a report that indicates physical properties of the soil, its bearing capacity, chemical composition, its liquefaction see below potential, the stability of natural slopes and other considerations for design.
The soil properties can vary from place to place and from layer to layer, even within the proposed project. It is thus very important for projects to undertake these tests, as buildings based on unfavorable soils can experience excessive ground motion or be subjected to the effects of liquefaction and ground failure.
The results of the soil studies and their analysis will be used by structural designers to design the foundations and structural elements required for earthquake resistance of the buildings.
Site Hazards: Make sure to select sites with minimal site hazards if possible. Ensure that the proposed project is not built on or in close proximity to active earthquake faults. The project site should not be exposed to falling rocks and landslides from nearby mountains.
The presence of large rocks that may have fallen from nearby mountains several years back is a good indication that there is a rockfall hazard. Knowing the height of the water table in the soil helps us determine its liquefaction potential, the viability of sub-soil floors and housing of critical utilities in such areas. In most earthquakes, building collapses cause the majority of deaths and injuries.
Building standards help to ensure safety of constructions. It is important for the technical personnel involved in building-projects in medium earthquake prone areas to understand all provisions in the building standards, and also why these are necessary to design and build earthquake resistant structures. They must understand the demands induced during earthquake shaking in the various building components and design measures to counter them so that loss of life and damage to property can be limited.
Sound technical advice is essential to ensure project structures can resist multiple hazards. For project structures to have adequate earthquake resistance, the technical personnel involved must also have relevant experience and expertise in conceptualizing, designing and constructing earthquake resistant structures.
Designing and building large structures is always a challenge, and that challenge is even greater when they are built in earthquake-prone areas. Earthquake engineering requires additional technical skills than ordinary structural engineering. All projects in areas of high and medium earthquake hazard should engage the services of technical personnel with knowledge and experience in constructing earthquake resistant structures. It is also important that the team contain geologists who specialize in applying geology to engineering projects, commonly called engineering geologists, in order to better understand current geological processes, the earthquake potential and threat of secondary geologic hazards.
It will be useful to contact local or international experts that have prior experience working in the project area to understand how they sought to reduce earthquake risk in past projects. These experts may be in private consulting practice, in the government, or in universities. Read More: Utilities such as power supply, water supply, and sanitation are critical for the continuous functioning of any building in the project.
In a strong earthquake, off-site utilities can be disrupted and may remain so for a few days.
It is important to ensure that adequate on-site backup is available, and that each critical utility system has been built earthquake resistant. When designing projects in earthquake-prone areas, it is imperative to ensure that the utility systems resist damage due to earthquake shaking. Earthquake shaking can damage electrical equipment, generators and water pumps; break pipelines; and disrupt utility services.
Utility services are interdependent, and damage to one can affect other services as well. Examples include: It is important to understand the criticality of each facility and to address all possible vulnerabilities in the design stage itself, so that the facility can limit disruption due to damage, to one or more of the utility services.
Consider the effects of earthquake forces on the components that form the utility services. Ensure that adequate steps are implemented to limit damage to these critical services by taking steps such as anchoring, bracing and adding flexible connectors. It is also important to estimate how long it would take to repair or reestablish damaged lifeline utilities and to consider the extent to which emergency supplies can meet local needs.
Reconnaissance following earthquakes in a number of countries indicates significant economic losses are the result of damage to architectural elements such as windows, suspended ceilings and doors , equipment, contents, and building utility systems. Damage to these items in earthquakes can cause deaths, injuries, the building losing ability to function, and economic losses.
Any of these non-structural components or contents placed close to exits may block exits and impede evacuations following earthquakes. Thus, constructions in earthquake prone regions require adequate steps to limit damage to these elements in the design stages. The design standards will depend on the functions of the building structure and the nature of the equipment and utilities within the building. In most countries, non-structural components and the majority of the building contents are not covered by building standard provisions and remain vulnerable to earthquake damage.
Mitigation solutions for most of these components are available in various manuals published across the world a few examples below and can be incorporated in the construction and maintenance phases so that losses due to them are limited.
In addition to all the other recommendations, the design of each building in the project must incorporate emergency evacuation considerations in the planning stage.
For projects where buildings will have to remain functional following an earthquake such as hospitals or emergency operations centers , in addition to having the entire building - including structure, finishes and equipment - protected from earthquake damage and providing back-up for critical utilities, a clear emergency management plan should be drafted and practiced to prepare the staff for crisis mitigation. Other recommendations for Medium earthquake prone regions include a.
Understanding the earthquake history of the region b. The adequacy of local building regulations c. Understanding the site and soil conditions at the project area d.