The researcher Davinia Moreno, a geochronologist at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), has participated in a paper published in the Journal of Structural Geology, in which a complete study of the recent activity of the Daroca Fault situated in the Iberian Chain and its potential to generate earthquakes of destructive magnitude is presented, which will help to improve the seismic hazard maps of Spain.

This multidisciplinary study, based on the integration of geomorphological, structural, paleoseismological, geochronological and geophysical data, has allowed data essential to the assessment of the seismic hazard associated to this fault to be obtained, especially on the magnitude of earthquakes and their frequency. “The dimensions of the structure mapped indicate that it could cause earthquakes of up to magnitude 7 on the Richter scale”, comments Moreno.

Thanks to the new geochronological data obtained using the technique of dating by Electronic Spin Resonance (ESR), it has been possible to show that this fault moves more slowly than had been thought and, therefore, it generates large earthquakes more often. “Fast-moving faults accumulate energy more quickly than slow ones and therefore give rise to earthquakes more frequently”, she explains.

Major earthquakes are associated to the sudden slippage of faults. Nevertheless, the official models of seismic hazard used in the seismic building codes in Spain still do not envisage active faults, due in large part to insufficient data for their proper characterization.

“There is an evident need to conduct investigations in the majority of the Quaternary faults of the Iberian Peninsula to unambiguously demonstrate their activity and assess their seismogenic potential”, affirms Francisco Gutiérrez, a researcher at the Universidad de Zaragoza who led the study.

Generally, earthquakes in Spain are perceived as a process of low risk compared with other geological processes such as floods and landslides. This is partly because the twentieth century has been a particularly tranquil period from the seismic point of view. Between 1900 and 2018 there were hardly any major earthquakes, and only 39 deaths were recorded, compared with the 1674 that took place in the nineteenth century.

Most recent seismic event

The results obtained from the excavation of a small trench in the Daroca Fault offer evidence of the most recent seismic event it generated, which happened about 2000 years ago according to the findings of radiocarbon dating.

The hypothesis is proposed that this earthquake could have been the cause of the destruction and later abandonment of Roman settlements in the area, such as the city of La Caridad, lying within the modern municipality of Caminreal (Teruel). This is the most important archaeological site of the Jiloca Valley and one of the most interesting in Roman Aragón, both because of its state of conservation and the amount, variety and interest of its material culture.

Reference

Francisco Gutiérrez, Domingo Carbonel, Jorge Sevil, Davinia Moreno, Rogelio Linares, Xavier Comas, Mario Zarroca, Carles Roqué & James P. McCalpin. Neotectonics and late Holocene paleoseismic evidence in the Plio-Quaternary Daroca Half-graben, Iberian Chain, NE Spain. Implications for fault source characterization. Journal of Structural Geology 131, (2020), 103933