The 1804 Dalías earthquake: ranking seismic sources with the Boxer and seismic scenario methods in SE Iberia

SE Iberia is a tectonically active area with an important history of destructive earthquakes. Some of these earthquakes have been associated with known active faults, but the seismic source of most of them remains unclear. The majority of these earthquakes happened long before instrumental record began, so we can only study them through paleoseismology and/or historical records. In some cases, due to current soil usage, paleoseismic studies are extremely difficult to perform and researchers can only rely on historical records. Such is the case of the 1804 Dalías earthquake.

In this communication our objective is double. First, we present a methodology which can be useful to constrain the seismic source of historical earthquakes for which only intensity data are available. And second, we apply this methodology to the 1804 Dalías earthquake in order to constrain its seismic source, which remains unclear up to this day. Our proposed methodology is a combination of Gasperini et al. (1999, 2010)’s and de Pro-Díaz et al. (2022)’s methods. Our methodology searches for the faults that are most plausible candidates for the earthquake rupture, then builds seismic scenarios for each candidate rupture and finally compares these scenarios with the observed intensity field in order to find the candidate with the best fit. Seismic scenarios are built using OpenQuake and ArcGIS software (although QGIS can be used as well). The candidate that generates the simulation which better resembles the observed intensity field is considered the best candidate and the one closest to the actual earthquake source.

For the 1804 Dalías earthquake, we consider different ruptures along the Loma del Viento Fault (LVF) and Llano del Águila Fault (LLAF) traces as candidate ruptures, including some combined ruptures along the two faults. Our results show that there are two almost equally best candidates: a full rupture of the whole inland extension of the LVF, and a combined rupture of this fault and the LLAF.