Each Gospel writer chooses what to include and what not. There are many events that are only in one of the 4 Gospels. That doesn't discredit them, but rather indicates they were selective as author/historians. Every historian is selective; no one can include everything.
The sky turning dark is no big deal. Skies regularly turn dark for short periods of time. Heavy cloud cover for 3 hours. Heck, we have that today in my part of the country.
Earthquakes are also common in Jerusalem. It lies near a fault line. Josephus (
War VI. 299) tells of a quaking in the temple before the destruction and the Talmud tells of a quaking 40 years before the destruction of the temple.
So you want to talk about this event (the dead walking around) more. Sure. I told you I've done quite a bit of study in it. You say "Yet there is no historical account for this," but Matthew has a historical account of it, so we have 1 account, but no corroboration (sort of like Dr. Christine Ford: her account, but no corroboration, and yet people consider her a credible witness. Go figure.)
What did Matthew have to gain by making up such a story? Its ludicrous nature would make him a laughingstock, cause doubt to the rest of his Gospel, and possibly call into question his claims about the resurrection of Jesus. This, in my opinion, given a "criteria of embarrassment," speaks to the historicity of the event. Matthew lived in Jerusalem. He wouldn't dare manufacture such a thing if it were going to jeopardize the fledgling Christian movement, which it would if it were a ludicrous, wacko, sketchy story.
If we examine 8 normal kinds of tests to disprove a thing, possibly we can better evaluate Matthew's story.
ONE. The Intention Test. Can we responsibly look at Matthew's Gospel as his attempt at historiography? Luke claims to have written what actually happened (Lk. 1.1-4), and Matthew is close to Luke in genre. It seems that his historical intent would be similar to Luke's. His Gospel is written in a sober and responsible style, with accurate incidental details, obvious care in the telling of it, and some exactitude in his details. Generally speaking, you don't find outlandish flourishes and blatant mythologizing that is common in many other ancient writings.
Remember also that Christianity was born out of Judaism, known historically as careful preservers of sacred words. Given that Jesus's followers looked upon him as being even greater than a prophet, it seems very reasonable that they would have tried to preserve his words and actions reliably, as well as the events surrounding his life and especially his death.
There were plenty of controversies in the early church that could have been conveniently and efficiently resolved by the early Christian writers fictionalizing the account. This doesn't seem to have happened, or to have been on their minds. The continuance of these controversies demonstrates that Christians were interested in distinguishing between what happened during Jesus's lifetime and what was debated later in the churches.
TWO. The Ability Test. So what if they intended to write reliably historiography, were they able to do so? Can't we expect faulty memories, wishful thinking, theological insertions, and the development of legend?
In a culture where almost all teaching was by word of mouth and memory rather than by books, oral tradition placed a great emphasis on accurate memorization. They took care to memorize and pass such stories along accurately, especially of a person they truly considered to be the Son of God. The community would constantly be monitoring what was said and intervening to make corrections along the way to preserve the integrity of the message.
THREE. The Character Test. Is there anything in Matthew's writing to make us think he's a loony toon or a demented or hopelessly inaccurate source? We don't have much information to go on here, but neither do we have any reasonable evidence to suggest they were anything but people of integrity. After all, they are reporting on Jesus, who called them to as exacting a level of integrity as any religion ever known. The records we have say many of them were willing to die for what they were claiming. In terms of honesty, truthfulness, virtue and morality, these people had a track record that should be envied.
FOUR. The Consistency Test. There was obviously no collusion among the Gospel writers, especially about this episode. They were unarguably independent narrators of many of the same stories, but each Gospel also contains unique stories. There is no contradictory evidence against Matthew's account.
There is a logical fallacy called "Appeal to Ignorance." It mistakenly assumes that if a premise hasn’t been proved, it is therefore false. But that’s a fallacy of weak induction. We cannot conclude something is false just because it hasn’t been proved to be true.
FIVE. The Bias Test. Did Matthew have reason to skew the material? It's obvious the disciples weren't neutral observers, but it was part of their Christian worldview to show their love for Jesus by recording his life with integrity. Besides, they had nothing to gain from false reports except criticism, ostracism, and martyrdom. They certainly had nothing to win financially.
SIX. The Cover-Up Test. Might Matthew be covering up something that would be embarrassing to himself, the other disciples, or to Jesus? Just the opposite. Telling this story makes people look askew at his whole story. Telling this story is not in his self-interest. It's not even necessary to the Gospel. If it were left out, no one would know or care. It speaks to the truth of the account.
SEVEN. The Corroboration Test. We only have slight corroboration of this event in the Church Fathers, but there is at least some. It was considered historical, and not symbolic, by the Church Fathers.
EIGHT. The Adverse Witness Test. Were others present who would contradict or refute this story? There's no evidence of such. The early Christian movement was subjected to great persecutions, first from the Jews and later from the Romans. Critics were not shy about attacking the young faith system. We have no records of this event being contested.
Taken all together, I don't think it's likely that Matthew made up the story.
But were the disciples and the people of that time just gullible superstitionalists who would grab onto any nonsense and consider it real? Even a cursory reading of the Gospels shows that they weren't just fools:
* Andrew and Philip insisted on spending a whole day in conversation before they would buy into what John said about Jesus (Jn. 1.37-42).
* Nathanael was skeptical at first hearing (Jn. 1.46)
* The Jews demanded more than just a fit of prophetic rage (Jn. 2.18)
* The Jews questioned that he knew what he was talking about (Jn. 2.20)
* Nicodemus wouldn't just fall for his terminology but demanded explanation (Jn. 3.4)
And on and on it goes. Jesus was doubted, questioned, grilled, scorned, and ultimately rejected and killed. I wouldn't consider this to be a flighty and gullible response of the population.
In other words, as wacko as this event sounds, we have many plausible reasons to consider it to be historiography of an actual event.