It is a high level of activity that has since slowed and the norm is just an occasional earthquake. The 12-level intensity scale represents the effects of the shaking on people, manmade structures, and on the landscape by a number. Seismologists use the list to represent the severity of ground shaking in a community or part of a community by a number. A map showing intensities at individual locations may be contoured with isoseismal lines, to provide a representation of the broad variations of the shaking over the region surrounding the EQ source. An isoseismal map shows the different levels of intensity experienced in the affected area.
Seismic waves travel at different speeds in different types of rocks.
Passing from rock to soil, the waves slow down but get bigger. EQ intensity is a measure of the effects of ground shaking at a specific locality. By a seismographic network. Each seismic station in the network measures the movement of the ground at the site. The slip of block of rock over another in an EQ releases energy that makes the ground vibrate.