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How much shaking could one expect from an earthquake?

The amount of shaking from an earthquake depends on the size of the  earthquake, how close one is to the earthquake (also if it is deep or  shallow), what the surface conditions are at the surface (if one is on  solid rock, the shaking will be much less than if one were on a valley  of sediments, which could act like a bowl full of jelly), and the  competence of the structure one is in. For this reason, the modified  Mercalli scale was developed to measure the amount of shaking, It is  based on human perception and the amount of damage one may expect from a  certain amount of shaking—the figure below is an example of a typical  “shake map” put out by the USGS after a “felt” event. Also shown below  is the modified Mercalli scale, to give one an idea of how the scale  reflects different amounts of shaking. The figure is an example of a  magnitude 3.7 event at the Geysers Geothermal Field and the amount of  shaking observed, by distance. In general, the bigger the event, the  more shaking there is, if the distance is constant.  Note, however, that  the shaking is also dependent on the distance from the earthquake  event, as well as the amount of energy in the earthquake. In general,  the amount of shaking decreases as 1/distance from the event, regardless  of how big the event is.

An example of a typical “shake map” put out by the USGS after an “felt” event. At the bottom is the modified Mercalli scale to give one an idea of how the scale reflects different amounts of shaking. The figure is an example of a magnitude 3.7 at the Geysers geothermal field and the amount of shaking observed by distance.

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