In my Book of Mormon reading, I just read 3 Nephi 8. In this chapter, the earth shook at the time of Jesus’ crucifixion. The earth shaking at this time is also described in several verses in the New Testament.
I wonder, why did the earth shake? The earth shakes even today. Is there a reason? I do not know. Is it a fulfilling of prophecy? Scripture says that the Lord is not in the earthquake, but in the still small voice (1 Kings 19:11-12). This life is so temporary. Just have faith and repent.