As used in the fifth sentence of the fourth paragraph, the word "essentially" means __

参考答案:

CC[试题分析]词义理解题。[详细解答]作者在提到圣安德里亚断层时用到了horizontal这个词，而用vertical来形容新马德里断层，而且，通过转折短语on the other hand，我们显然可以推断，essentially近义于basically，故答案为C。