WIKIPEDIA SEISMIC HAZARDAseismic hazardis the probability that anearthquakewill occur in a given geographic area, within a given window of time, and with ground motion intensity exceeding a given threshold.[1]With a hazard thus estimated,riskcan be assessed and included in such areas asbuilding codesfor standard buildings, designing larger buildings and infrastructure projects,land use planningand determining insurance rates. The seismic hazard studies also may generate two standard measures of anticipated ground motion, both confusingly abbreviated MCE; the simplerprobabilisticMaximum Considered Earthquake (or Event[2]), used in standard building codes, and the more detailed anddeterministicMaximum Credible Earthquake incorporated in the design of larger buildings and civil infrastructure like dams or bridges. It is important to clarify which MCE is being discussed.[3]

Surface motion map for a hypothetical earthquake on the northern portion of theHayward Fault Zoneand its presumed northern extension, theRodgers Creek Fault ZoneCalculations for determining seismic hazard were first formulated byC. Allin Cornellin 1968[4]and, depending on their level of importance and use, can be quite complex.[5]The regional geology and seismology setting is first examined for sources and patterns of earthquake occurrence, bothin depthand at theat the surfacefromseismometerrecords; 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 knownSan Andreas Faultis illustrated as a long narrow elliptical zone of greater potential motion, like many areas along continental margins associated with thePacific ring of fire. Zones of higher seismicity in the continental interior may be the site forintraplate earthquakes) and tend to be drawn as broad areas, based on historic records, like the1812 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 usepeak 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 you a'chance' of exceedinga given value over a specified amount of time. Standard building codes for homeowners might be concerned with a 1 in 500 years chance, while nuclear plants look at the 10,000 year time frame. A longer-term seismic history can be obtained throughpaleoseismology. The results may be in the form of a groundresponse spectrumfor use inseismic analysis.More elaborate variations on the theme also look at the soil conditions.[6]If you build on a soft swamp, you are likely to experience many times the ground motions than your neighbour on solid rock. The standard seismic hazard calculations become adjusted upwards if you are postulatingcharacteristic 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-inducedlandslidesin steep terrain. Large area landsliding can also