The duration of shaking you feel from an earthquake depends in part on the distance you are from the epicenter of the earthquake. In short, the duration is different in different places. In order to study earthquakes, scientists deploy seismometers to measure ground motion. Seismograms are recordings of ground motion as a function of time and are the basic data which seismologists use to study the waves generated by earthquakes. These data are used to study the earthquakes themselves and to learn more about the structure of the Earth.
Seismologists generally describe earthquakes as local, regional, or teleseismic.
These terms refer to distance from the earthquake to the recording instrument. Local events occur within the immediate area less than 100km away. Regional events occur within 10 - 1400km away. Teleseismic events are those which occur at great distances, greater than 1400km away. Local and regional earthquakes are dominated by crustal waves, i.e., by waves which propagate through the crust.