Solving the Mystery: The 21 October 1880 Portuguese Earthquake

Abstract

Online Material: Relevant accounts for intensity estimates of the 21 October 1880 Portuguese earthquake. Despite recent important contributions to the completeness of earthquake catalogs, there are still significant gaps in our knowledge about the preinstrumental seismicity of the Iberian Peninsula. This is true even for the second half of the nineteenth century, in spite of the vast increase in the number of scientific institutions and newspapers in these decades. In the last extensive revision of the Iberian earthquake catalog (Rodriguez de la Torre, 1990a,b), the number of known earthquakes occurring between 1851 and 1900 increased from 620 to 2066 as a result of the systematic search conducted by Rodriguez de la Torre mainly using Spanish sources. Relative to earlier earthquake catalogs, the new data enabled (Martinez Solares and Mezcua, 2002; Mezcua et al. , 2004) to present a very much improved catalog of the earthquakes that occurred in the Iberian Peninsula and its vicinity, with a new assessment of epicenters and magnitudes of the major events, through application of the Bakun and Wentworth (BW Bakun et al. , 2003). As Martinez Solares and Mezcua (2002) and Mezcua et al. (2004) pointed out, the B&W procedure was only applied to events for which there were enough intensity values. Although registered in this catalog, one major Iberian earthquake that is still waiting for epicenter and magnitude determinations is the 21 October 1880 (6:41 a.m.) earthquake. The event was unknown until 1990, when it was discovered by Fernando Rodriguez de la Torre (1990a) in Spanish and Portuguese nineteenth century newspapers. With this new information revealed, the 1880 earthquake was included in the catalog of Martinez …