Push-ups, fracture patterns, and palaeoseismology of the Leirubakki Fault, South Iceland

Field measurements and GPS mapping were conducted along the Leirubakki Fault, a 010°-trending right-lateral strike-slip fault located in the Holocene lava flows of the South Iceland Seismic Zone. Because of poor exposures south and north of the Holocene lava flow dissected by the fault, its length can only be traced for 7.5 km. The exposed surface rupture contains fractures that range in size over four orders of a magnitude, from the main fault, through fault segments (1000–2000 m long), fracture arrays (100–250 m long), to individual fractures (8–125 m long). Detailed measurements were made of 63 push-ups, located at junctions between individual fractures and between fracture arrays, and ranging in maximum height from 0.35 to 4.35 m. Using the push-ups, the maximum right-lateral displacement on the Leirubakki Fault is estimated at 2.67 m. Using empirical relationships established globally, it is concluded that for a maximum displacement of 2.67 m, the true rupture length of the Leirubakki Fault is around 50 km and that it gave rise to an earthquake of a moment magnitude 7.1.