"A seismic hazard is the probability that an earthquake will occur in a given geographic area, within a given window of time, and with ground motion intensity exceeding a given threshold."
The distribution of earthquakes around the world and the risk they pose to people and infrastructure.
Plate Tectonics: Overview of the movement and interactions of tectonic plates, including types of plate boundaries and associated seismic activity.
Earthquake Waves and Seismic Energy: Explanation of how waves propagate through the Earth's interior during an earthquake, the types of waves generated, and how they are measured.
Seismic Monitoring: Overview of the various ways scientists measure and monitor earthquakes, including seismometers, GPS, and satellite systems.
Seismicity and Earthquake Sources: Overview of the various types of earthquake sources, including faults, volcanoes, and man-made causes.
Seismic Hazard and Risk: Explanation of the difference between seismic hazard and seismic risk, including factors that contribute to each, such as location, magnitude, and population density.
Ground Motion and Site Effects: Discussion of how the characteristics of the ground surface affect the amplification and attenuation of seismic waves.
Earthquake Prediction and Forecasting: Overview of the various methods used to predict and forecast earthquakes, including statistical models, simulation and computer modeling.
Seismic Retrofitting and Building Codes: Overview of building codes and retrofitting strategies for structures in earthquake-prone regions.
Earthquake Response and Mitigation: Explanation of the various steps taken to prepare for and respond to earthquakes, including emergency planning, evacuation, education, and public awareness.
Historical and Cultural Impacts of Earthquakes: Discussion of how earthquakes have impacted different cultures throughout history, as well as how they contribute to geological and ecological changes.
Earthquakes: These are sudden and violent movements of the Earth's crust caused by disturbances in the tectonic plates. Earthquakes can result in severe damage to infrastructure and lead to casualties.
Volcanic activity: Volcanic activity can lead to earthquakes, landslides, and Tsunamis. Volcanic eruptions can result in devastating ash falls that can affect the health of animals and humans.
Landslides: These are the rapid movement of soil and rock downhill caused by the destabilization of slopes, which can be caused by seismic activity. Massive landslides can be highly hazardous and destroy infrastructure such as bridges and buildings.
Tsunamis: This is a sequence of ocean waves with an extremely long wavelength caused by massive disturbances, such as earthquakes or landslides, beneath the ocean floor. Tsunamis can cause tremendous damage to coastal areas and infrastructure.
Seiches: A seiche is a standing wave in an enclosed or semi-enclosed body of water caused by seismic activity, such as earthquakes, wind, or tsunamis. Seiches can cause damage to ports and ships.
Sinkholes: Sinkholes are depressions or sudden collapses of the soil caused by the dissolution of soluble rocks such as limestone due to seismic activity. Sinkholes can result in structural damages to buildings and roads.
Crustal deformation: This is the bending, stretching, or warping of the Earth's crust caused by tectonic forces or the cooling and contraction of the Earth's mantle. Crustal deformation can cause infrastructures to crack and result in sinkholes.
Liquefaction: Earthquakes can cause liquefaction, which is the transformation of solid soil into a watery mushy state. This can lead to soil sinking, tilting buildings, breaking gas and water pipelines, and other forms of damage.
"With a hazard thus estimated, risk can be assessed and included in such areas as building codes for standard buildings, designing larger buildings and infrastructure projects, land use planning, and determining insurance rates."
"The seismic hazard studies also may generate two standard measures of anticipated ground motion, both confusingly abbreviated MCE; the simpler probabilistic Maximum Considered Earthquake (or Event), used in standard building codes, and the more detailed and deterministic Maximum Credible Earthquake incorporated in the design of larger buildings and civil infrastructure like dams or bridges."
"Calculations for determining seismic hazard were first formulated by C. Allin Cornell in 1968."
"The regional geology and seismology setting is first examined for sources and patterns of earthquake occurrence, both in depth and at the surface from seismometer records; secondly, the impacts from these sources are assessed relative to local geologic rock and soil types, slope angle, and groundwater conditions."
"Zones of similar potential earthquake shaking are thus determined and drawn on maps."
"The well-known San Andreas Fault is illustrated as a long narrow elliptical zone of greater potential motion, like many areas along continental margins associated with the Pacific ring of fire."
"Zones of higher seismicity in the continental interior may be the site for intraplate earthquakes and tend to be drawn as broad areas, based on historic records, like the 1812 New Madrid earthquake since specific causative faults are generally not identified as earthquake sources."
"Each zone is given properties associated with source potential: how many earthquakes per year, the maximum size of earthquakes (maximum magnitude), etc."
"Finally, the calculations require formulae that give the required hazard indicators for a given earthquake size and distance."
"For example, some districts prefer to use peak acceleration, others use peak velocity, and more sophisticated uses require response spectral ordinates."
"The computer program then integrates over all the zones and produces probability curves for the key ground motion parameter."
"The final result gives a 'chance' of exceeding a given value over a specified amount of time."
"Standard building codes for homeowners might be concerned with a 1 in 500 years chance."
"Nuclear plants look at the 10,000 year time frame."
"A longer-term seismic history can be obtained through paleoseismology."
"More elaborate variations on the theme also look at the soil conditions. Higher ground motions are likely to be experienced on a soft swamp compared to a hard rock site."
"The standard seismic hazard calculations become adjusted upwards when postulating characteristic earthquakes."
"Areas with high ground motion due to soil conditions are also often subject to soil failure due to liquefaction. Soil failure can also occur due to earthquake-induced landslides in steep terrain."
"Large area landsliding can also occur on rather gentle slopes as was seen in the Good Friday earthquake in Anchorage, Alaska, March 28, 1964."