"Earthquake activity, or seismicity, is usually summarized in earthquake catalogs or shown graphically on maps. An earthquake catalog generally contains the time and location of earthquakes, together with auxiliary information such as damage and casualties, estimates of magnitude, etc. Because instrumental seismology was not developed until the end of the nineteenth century, earthquake catalogs for events before 1900 (with a few exceptions) are based on information gathered by human observers and thus are incomplete and subjective. These earthquake catalogs were usually compiled from existing literature and from surveys after the earthquakes." (W.H.K. Lee, in Encyclopedia of Physical Science and Technology (Third Edition), 2003).