The spatial distribution of earthquakes

The term seismicity was probably used for the first time by Montessus de Ballore in 1906 to describe the distribution of earthquakes and their characteristics within a particular region. The most important aspects of seismicity are given by the geographic distribution of earthquakes' foci, their magnitude, their occurrence over time, their mechanisms, and the damage produced by them. Studies of seismicity are, then, based on seismic catalogs that include parameters such as the dates and times of occurrence, hypocenter coordinates, magnitudes and focal mechanisms of earthquakes and their correlation to regional geological and geophysical characteristics. Historical descriptions of earthquakes can be traced back to written records of old civilizations such as those of China and, for Europe, of Greece and Rome. Among the first universal catalogs of earthquakes were those published by J. Zahn in 1680 and by J. J. Moreira de Mendonca in 1758. Modern catalogs started about 1850 with the work of Perrey, Mallet, and Milne. Today global and regional catalogs are being compiled by various agencies, such as the ISC (International Seismological Centre, Newbury) and NEIC (National Earthquake Information Service, Denver) (Chapter 1). Among the first studies of seismicity were those of Montessus de Ballore between 1850 and 1923, Sieberg between 1923 and 1933, Gutenberg and Richter (1954) and Karnik (1969, 1971). Studies of seismicity are fundamental for understanding the seismotectonic and geodynamic conditions of a region and for the assessment of its seismic risk.