Maybe you could eventually explain what you meant here, then:
So why do earthquakes exist and what causes them?
There is a distinction between the occurrence of natural events which occurred before Adam's creation and those which occurred after Adam sinned.
The shifting of tectonic plates prior to the creation of Adam (here I am thinking of the various plates being arranged and put into place by God as a part of the pre-Adamic creation process) is not the result of Adam sinning, for Adam had yet to be created.
The shifting of tectonic plates after the fall were not due to God's creative purposes, for the creation of the earth had already been completed and was indeed "good", but rather, they were the result of the world being subjected to the devastating consequences of sin.
Global Consequences
As noted above there was an initial effect of sin that afflicted the newly created earth (e.g., thorns and thistles). It is scarcely realized, however, what a cataclysmic effect the Flood of Noah’s day had upon our planet. Subterranean “fountains” yielded vast and violent explosions of water. Combined therewith was an outpouring deluge from the “windows of heaven” (Genesis 7:11). Megatons of violent upthrusts of water and debris came from the bowels of the earth. Rain descended in unimaginable torrents for forty days and nights.
The composition of the ancient earth was radically affected. Global and continental temperature zones were altered, and varying pressure systems created an environment that facilitated hurricanes and tornados. Land mass arrangements became unsettled and earthquakes followed in their wake. The violent features of today’s earth have their ultimate origins in the catastrophic events of Genesis 6-8.
There is ample geologic and archaeological evidence of an ancient earth significantly different from today’s planet. Geologists testify to the early uniform climate of the earth as revealed by the fossil record—of both plants and animals (Rehwinkel, 1951, 1-54). Even skeptics concede that at a point in the ancient past the earth had a “mild and constant climate” and “the elements of that world were in perfect balance” (Jastrow, 1977, 69).