Beginning in the 1960s, significant strides were made in the study of earthquakes and the Earth's structure with the deployment of the World-Wide Seismographic Station Network (WWSSN). This network consists of over 120 seismographs in 60 countries.

The seismographs were put in vaults or old mine shafts deep in the Earth in order to make sensitive recordings of seimic signals free from the "noise" created by cars and other environmental factors.

This "global observatory" illustrates the international nature of global seismology and the essential cooperation in data exchange needed to study earthquakes.

To better understand how and why earthquakes occur, we must understand the theory of Plate Tectonics.