Many different moire patterns were reported on highly oriented pyrolytic graphite (HOPG) surfaces in scanning tunneling microscopy (STM) studies. Such observations were attributed to the dislocation of the top most graphene layers of the crystal with respect to the lower layers. So far, the corrugation height difference of a moire pattern observed by STM was reported to be independent of the tunnel junction bias regardless of the periodicity of the pattern. With the method we developed to generate moire patterns on HOPG surfaces quite easily and unharmfully to the crystals, we investigated a large number of different moire patterns. In this work we report on the apparent corrugation height variations of moire patterns, as a function of tunnel junction bias in STM images. We show that this change varies from moire pattern to moire pattern, and does not necessarily follow a continuous increase or decrease. We show strong experimental evidence that while several moire patterns may have structural origins; most of them have almost purely electronic character. (C) 2016 Elsevier Ltd. All rights reserved.