Published images and witness reports so far suggest this was a VERY abrupt high-G arrival with a large vertical decelleration component, to which the soft ground surface will have contributed adversly. I fear for the number and extent of survivor injuries here particulary spinal and major orthopedic injuries (Kegworth). Seat structure and orientation can only help so much in a high-G situation.
Minor point but I speculate that slide inflation-systems may have been damaged?
(500hr PPL/sailplanes, and medical doctor)