Enhanced palaeoseismic succession at the Concud Fault (Iberian Chain, Spain): new insights for seismic hazard assessment

Abstract

A new trench excavated at the southern sector of the Concud Fault provided evidence of three palaeoseismic events dated to ca. 21, 18 and 13–3 ka BP, respectively. The two youngest ones had not been detected in previous studies. The results extend the total recorded palaeoseismic succession for the fault: eleven events since ca. 74 ka BP to the present day, with an average recurrence period between 7.1 ± 3.5 and 8.0 ± 3.3 ka; total net accumulated slip of about 20.5 m, with average coseismic slip of 1.9 m. The displacement pattern shows alternating periods of fast slip (up to 0.53 mm/a) and slow slip (0.13 mm/a), resulting in average slip rate of 0.29 mm/a. Using this palaeoseismic information, as well as the potential magnitude previously attributed to the characteristic earthquake at the Concud Fault (M ≈ 6.5–6.6), a simple probabilistic seismic hazard analysis has been performed. The estimated probability of occurrence of the characteristic earthquake within the next 500-year period ranges from 2.3 to 26.1 %, according to distinct hypotheses on the elapsed time derived from the uncertainty about the age of the youngest event.