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The publication of Edward S. Holden's catalog of Pacific coast earthquakes in 1898 represented the first systematic scientific inquiry into the seismic history of California and surrounding regions. This catalog, and its extension by McAdie (1907), formed the primary basis for the monumental catalog of Townley and Allen (1939) covering the years 1769-1928. These catalogs provide detailed descriptive accounts of virtually all the earthquakes that are now known from this period, and all subsequent analyses of seismicity up to the modern instrumental period build on these foundations.

Recent studies of preinstrumental seismicity have focused on quantification of the historical record. The catalog presented here relies heavily on the research of Tousson Toppozada and his associates (Toppozada and others, 1981; Toppozada and Parke, 1982), who developed extensive new information on seismic intensities from newspaper accounts and other original sources, and determined locations and magnitudes from the resulting isoseismal maps. In addition, several special studies of important events by other workers have contributed to the catalog.

The development of practical seismographic instrumentation around the turn of the 20th century led to the rapid growth of seismologic data, particularly for those events large enough to register at teleseismic distances on the early instruments. The publication of the Circulars of the Seismological Committee of the British Association for the Advancement of Science (1899-1912) and their continuation as the International Seismological Summary from 1913 on indicate a detection threshold of about M~~6 for the Western United States as early as 1898. Data from these and other sources enabled Gutenberg and Richter (1954) to systematically catalog seismicity from 1904 onward.

Modern seismographic instrumentation first installed in California in 1910 ushered in the era of earthquake observation at regional distances. The Bulletins of the Seismographic Stations of the University of California, Berkeley, from 1910 to the present form the principal source for events in northern California and adjoining areas. Routine epicentral determinations and magnitude assignments for earthquakes in the southern California region date from 1932 and are taken from the catalog of the Seismological Laboratory of the California Institute of Technology, Pasadena. Additional instrumental results come from various other sources, chiefly the U.S. Geological Survey and the University of Nevada, Reno.

The resulting catalog of major earthquakes in California, western Nevada, and northernmost Baja California from 1769 to 1989 (Table 6.1) contains 206 entries. This catalog omits several earthquakes listed in earlier catalogs where this or other recent studies have failed to corroborate previous interpretation as significant events or even, in some cases, their occurrence.