Characterization of historical earthquakes through a study of landslides by lichenometry (Murcia, SE Iberia)

Abstract

Earthquakes with magnitudes greater than 4.5–5 induce massive rockfalls close to the fault rupture zone. Driven by seismic shaking, the blocks collapse through the hillslope, which yields a fresh surface that is unbeatable for new lichen colonization. The lichenometric technique involves dating lichens developed on the surfaces of rockfall blocks induced by earthquakes. This study is focused on Cejo de Cano (Lorca, Spain), which is an earthquake-prone landslide scarp, as shown after the 2011 Lorca shaking (Mw 5.2). After this event, the possibility that the rocky volume at the foot of its slope could have a seismic origin started to be considered. In this research, lichenometry is used to date lichens on rock surfaces and test a possible correlation with the cataloged historical earthquakes. This research is important because of the large number of rockfall earthquakes found at this site by applying lichenometry compared to other studies in the literature. This technique allows us to extend the regional seismic catalog because the oldest lichens are older than the documented catalog of historical earthquakes. An oriented rockfall pattern that correlates with the location of epicenters is observed. In addition, the parallel and oblique previous fracturing of Cejo de Cano makes this scarp a suitable place to test whether the fracturing direction of the scarp could control a greater volume of rockfalls. This research opens up a new field of study to evaluate this correlation in larger areas.