Episodic displacement on a sackung scarp in Benasque Valley (Central Spanish Pyrenees). Palaeoseismic record?

A sackung scarp has been investigated by trenching in the El Ubago glacial valley (centralSpanish Pyrenees). The scarp is located 18 km to the SW of the North Maladeta Fault, which was thesource of the Mw 5.3 Vielha earthquake of 1923. Three displacement events have been inferred based oncolluvial wedge stratigraphy and fault truncation. Event X at ca. 16.9 ka created the sackung. Events Yand Z have been constrained at 15-8.3 and 8.3-5.3 ka. The timing of event Y partially overlaps with thatof a faulting event recognised in a previously investigated sackung at about 2 km. A minimum verticalslip rate of 0.18 mm/yr has been calculated for the sackung. The spatial association of the sackungfeatures in this sector of the Pyrenees with the North Maladeta Fault and the millennial recurrence of theinferred displacement events (5.6 kyr) suggests that the kinematics of the studied sackung has beencontrolled by seismic activity. Demonstrating in future investigations that the sackung features in the areaconstitute archives of large paleoearthquake would be of great interest for seismic hazard assessments.They might help to improve the catalogue of paleoearthquakes and might provide information onearthquake recurrence intervals and the age of the MRE (most recent event).