An important parameter in the calculation of

seismic hazard 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. With a hazard thus estimated, risk can be assessed and includ ...

, maximum magnitude (expressed as

Moment magnitude scale The moment magnitude scale (MMS; denoted explicitly with or Mw, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. It was defined in a 1979 pape ...

) is also one of the more contentious. The choice of the value can greatly influence the final outcome of the results, yet this is most likely a size of

earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

that has not yet occurred in the region under study. Freqmag

The seismic hazard calculation involves a double integration (

integral In mathematics Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented i ...

) over the region, combined with the expected number (earthquake frequency) of earthquakes, from the smallest to the largest. The integration must close at the maximum magnitude. The figure shows a typical 'earthquake frequency' plot for a given region. This is a typical plot for

continent A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven ...

al interiors. The circles represent actual earthquake data. Note that the dataset is complete for small magnitudes, but becomes erratic for the larger. At about M5, there are no records, simply because the historical record is usually too short. In some cases paleoseismology can fill some of the gap, but this is rare for continental regions. The last part of the curve, perhaps the most important part, can be filled in by inference. This would come from studying similar geology throughout the world (using analogs to extend time), or by a study of

fault mechanics Fault mechanics is a field of study that investigates the behavior of geologic faults. Behind every good earthquake is some weak rock. Whether the rock remains weak becomes an important point in determining the potential for bigger earthquakes. ...

. For example, large-scale studies have been conducted for Stable Continental Regions (SCR's), which are defined "as regions of continental crust that have not experienced any major tectonism, magmatism, basement metamorphism or anorogenic intrusion since the early Cretaceous, and no rifting or major extension or transtension since the Paleogene." Finally there is the common question of what is the maximum magnitude for the whole world. Unfortunately, it cannot really be answered, since this earthquake has most likely not happened in the historical record, and we cannot search beyond the earth for analogs. Answers can again be inferred using the finite size of the world's plates (plate tectonics), and the possible limits of the various magnitude scales. The specific value, however, is not directly relevant to most people, since, except for

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explo ...

s, the local shaking effects come to a maximum at about M8, and greater earthquakes simply extend the rupture distance.

References

Seismology {{Seismology-stub