Shockwaves from impacts maybe?
Even if there is no seismic activity native to the planet, a large impact would send waves out just like an earthquake...
Wave-formed ripple result from the to-and-fro motion of waves and have a symmetrical profile.
Current ripple marks form in response to water or wind currents flowing in one direction and have asymmetric profiles.
The asymmetric profiles allow geologists to determine paleocurrent directions, in other words, which direction the wind or water was flowing from when the cross beds were deposited. This is possible due to the fact the longer side of the ripple always faces the upstream direction."
http://thisoldearth.net/Geology_Online-1_Subchapters.cfm?Chapter=5&Row=3