The Longmen Shan Fault System is situated in the eastern border of the Tibetan Plateau and contains several faults. This earthquake ruptured at least two imbricate structures in Longmen Shan Fault System, i.e. the Beichuan Fault and the Guanxian–Anxian Fault. In the epicentral area, the average slip in Beichuan Fault was about 3.5 metres (11 ft) vertical, 3.5 metres (11 ft) horizontal-parallel to the fault, and 4.8 metres (16 ft) horizontal-perpendicular to the fault. In the area about 30 kilometres (19 mi) northeast of the epicenter, the surface slip on Beichuan Fault was almost purely dextral strike-slip up to about 3 metres (9.8 ft), while the average slip in Guanxian–Anxian Fault was about 2 metres (6 ft 7 in) vertical and 2.3 metres (7 ft 7 in) horizontal.
Try to answer this question if possible (otherwise reply "unanswerable"): What was the horizontal slippage in the Beichuan Fault at the epicenter?
3.5 metres