Up until the early 20th century, seismologists had a mixed and warped picture of the distribution of earthquakes because their knowledge was restricted mostly to the earthquakes felt on the continents in which they resided.
As the 20th century advanced through technology, the efforts of a global seismograph network to locate earthquakes began to become a reality. This accomplishment has depended on the universal co-operation by seismologists of all global nations, during both war and peace in the exchanging of travel times of seismic waves. In 1990, there were approximately 3300 seismographic observatories participating in international data exchange.
Many seismographic stations from around the world each send readings of earthquakes or underground explosions by electronic communication means to The National Earthquake Information Centre (NEIC), in Golden, Colarado. These readings are used by the NEIC to compute rapidly the locations and magnitudes of earthquakes around the world. Readings also go to the International Seismological Centre in the United Kingdom, which prints permanent records of the world's seismicity in the form of catalogues listing the locations of earthquakes. These catalogues provide the basis for studies of the tectonic deformations of the Earth and for calculation of earthquake hazard in countires around the world.
Studies of the global earthquake distribution have provided crucial evidence on the present geodynamics and deformation of the whole Earth.