Earthquake Hazard level: Low ?

In the area you have selected (Sierra Leone) earthquake hazard is classified as low according to the information that is currently available. This means that there is a 2% chance of potentially-damaging earthquake shaking in your project area in the next 50 years. Based on this information, the impact of earthquake should be considered in the project, in particular during design and construction. Project planning decisions, project design, and construction methods should take into account the level of earthquake hazard. Further detailed information should be obtained to adequately account for the level of hazard.

Recommendations

• EARTHQUAKE HISTORY AND HAZARD: Get information about major earthquakes and secondary hazards (fires, landslides, liquefaction, tsunami in coastal areas) that have affected the project area in the past and the effects these caused. Community memory and historical accounts of earthquakes can provide useful information to supplement scientific studies. Contact the governmental organisations (e.g. Ministry of Environment and Geological Survey/ Ministry of Earth Sciences) responsible for earthquake risk management in the project country to obtain more detailed information on the potential earthquake hazard. Remember that low hazard does not mean no hazard. More information
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  Even though the earthquake hazard is considered low in your location, it is important to understand the earthquake history of the place to acknowledge the possibility that an earthquake can affect the region again. In many countries, earthquake history can be obtained from written historical records. It may seem unlikely that a large earthquake would take place hundreds of kilometers away from a tectonic plate boundary in areas with low levels of strain on the crust from tectonic motion. But such earthquakes have happened in the past, and understanding the earthquake history of a place is important before determining a location for a project and initiating the design of the structures.

  Community memory and historical accounts of earthquakes can provide useful information to supplement scientific studies. Recording of earthquakes using scientific instruments began only around 1900. In many areas, centuries may pass between major earthquakes, meaning that instrumental records provide an incomplete picture of the hazard. Scientists who study earthquakes use other tools: they investigate faults where earthquakes occur, measure the slow movement of tectonic plates, and search for geologic traces left by ancient earthquakes.

  Earthquakes can cause secondary hazards that include fires, landslides, liquefaction (see definition below), floods (can be triggered by failing dams and embankments, glacial lake outbursts, or by landslide-blocked rivers) and tsunami in coastal areas. Obtain information on these hazards from the government agency responsible for emergency management. Maps may exist that describe the extent of tsunami inundation, liquefaction, or land-sliding. Historical records may also contain accounts of secondary hazard events triggered by past earthquakes. Learning about potential tsunami hazard is essential in coastal areas with high, medium or low earthquake risk. Liquefaction takes place when loosely packed, saturated sediments at or near the ground surface lose their strength in response to strong ground shaking, and flow like a thick fluid. This can result in major damage during earthquakes. (More details at http://www.usgs.gov/faq/categories/9829/3301).

  Earthquakes triggered or induced by human activity are not included in these hazard levels. Instances of 'induced seismicity' and its causes are recorded at http://inducedearthquakes.org/ .

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• LOCAL BUILDING REGULATIONS: Find out if the local building regulations provide for earthquake protection. To do this, engage the local engineering community, especially those serving with the local government or consult external experts. If regulations do include earthquake protection, comply with the regulations with respect to planning, design and construction, including typology of construction, and materials of appropriate quality suitable for use in areas of low seismic hazard. If they do not, consider adopting and complying with standards from other low earthquake hazard areas. More information
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  Building standards, often called building codes, provide the first line of defense against potential earthquake damage and help to ensure safety in buildings designed and constructed in conformance with the codes. It is important to find out if the local building regulations provide for earthquake protection in the project location. If they do, then comply with the regulating provisions with respect to planning, design and construction, including typology of construction and quality materials for use in areas of seismic hazard.

  Reviewing local building regulations is essential for setting the standards for planning, design and construction. Similarly, it is necessary to analyze if these regulations take into consideration the low earthquake hazard in the region and provide sufficient protection. This can be understood in discussions with the local engineering community, especially those serving with the local government. It is equally important to understand how often and when these standards were last revised. 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.

  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). 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: The Importance of Building Codes in Earthquake-Prone Communities: http://www.fema.gov/media-library-data/1410554614185-e0da148255b25cd17a5510a80b0d9f48/Building%20Code%20Fact%20Sheet%20Revised%20August%202014.pdf

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• INTERACTING HAZARDS: Determine whether the project site is likely to be affected by ground failure or other site hazards during an earthquake. Soil investigations should be conducted by a geotechnical engineer to determine physical properties of the soil including its liquefaction potential, the stability of natural slopes and other considerations for design. Select a project location with minimal site hazards if possible. Ensure that the proposed project is not built on or near active earthquake faults. More information
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  Even though the area under consideration falls in low 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.

  Liquefaction takes place when loosely packed, saturated sediments at or near the ground surface lose their strength in response to strong ground shaking, and flow like a thick fluid. This can result in major damage during earthquakes. (More details at http://www.usgs.gov/faq/categories/9829/3301).

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• TECHNICAL EXPERTISE: Even in low hazard regions, it is important that competent technical personnel are involved in the project design and implementation. It is important for the technical personnel involved in building projects in earthquake-prone areas to understand all provisions in the building standards, and why these are necessary to design and build earthquake resistant structures. The designs should be reviewed by a structural engineer with earthquake engineering experience, to ensure that the structure meets a basic, minimum level of earthquake resistant design for low hazard areas as prescribed in the building code. More information
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  Even in low hazard regions, it is important that competent technical personnel are involved in the project design and implementation. 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 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. The designs should be reviewed by a structural engineer with earthquake engineering experience, to ensure that the structure meets a basic, minimum level of earthquake resistant design for low hazard areas as prescribed in the building code.

  Read More: ● http://science.howstuffworks.com/engineering/structural/earthquake-resistant-buildings.htm ● http://www.exploratorium.edu/faultline/damage/building.html

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• INSURANCE: Consider purchasing earthquake insurance to cover potential losses to the project. While insurance does not prevent injuries or deaths, or save communities, it can reduce financial losses and enable a project or facility to recover from the effects of an earthquake and regain its function more quickly. More information
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  Consider purchasing earthquake insurance to cover potential losses on the project. Earthquake insurance may be available from the government or from private insurers. Insurance can help provide funds after an earthquake, to help in reconstruction and replacement of damaged buildings, contents or other project components. This can ultimately enable the project to recover from the effects of the earthquake and regain its function more quickly. However, it is important to note that insurance only provides coverage for financial losses, but cannot prevent damage, business interruption, injuries or deaths.

  More information:
  • Insurance against Losses from Natural Disasters in Developing Countries : https://www.researchgate.net/profile/Reinhard_Mechler/publication/265286458_Insurance_against_Losses_from_Natural_Disasters_in_De-veloping_Countries/links/54ac53150cf21c477139d8c3.pdf • Earthquake Insurance in Japan: http://www.giroj.or.jp/english/pdf/earthquake/Chapter2.pdf • Insurance-related instruments for disaster risk reduction - http://www.preventionweb.net/english/hyogo/gar/2011/en/bgdocs/Suarez&_Linnerooth-Bayer_2011.pdf

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