Earthquakes typically have

foreshocks before and after the quake
foreshocks before the quake and aftershocks after the quake
aftershocks before and after the quake
no shocks before the quake but foreshocks and aftershocks after the quake

measuring light intensity

light meters can be used to measure light intensity. the meter is held at the soil surface and pointed in the direction of the maximum light intensity, and then the meter is read.

errors can be made when measuring light intensity by accidentally shading the light meter. the reliability of the results can be checked by taking many samples.