Question: "Is Zechariah 14:4 a prophecy about the second coming of Christ?"
Answer: Zechariah 14:4 predicts, “On that day his feet will stand on the Mount of Olives, east of Jerusalem, and the Mount of Olives will be split in two from east to west, forming a great valley, with half of the Mount shall move north and half moving south.” “That day” is a reference to the Day of the Lord, and the One who stands on the mountain is the Lord Himself. So, yes, this passage predicts the second coming of Christ.
The opening of Zechariah 14 speaks of a future day when Jerusalem will be plundered by its enemies. Verse 2 prophesies that all nations will gather against Jerusalem and capture and ransack the city. Half of the citizens of Jerusalem will flee the devastation, but the other half will remain. This will be one half of the one third of the Jewish population still alive in Jerusalem after the Tribulation (13:8). Then, Zechariah says, the Lord Himself will go forth and engage these opponents in battle (14:3). Verse 4 speaks of the Messiah standing on the Mount of Olives, a hill near Jerusalem on the east. The mountain will split, creating an enormous valley. Since none of this has taken place yet, the prophecy points to a future time.
A parallel passage tells of the Battle of Armageddon (Revelation 19:11-21). Revelation 16:18-21 predicts horrible events at the end of the Tribulation when the seventh bowl is poured out:
“Then there came flashes of lightning, rumblings, peals of thunder and a severe earthquake. No earthquake like it has ever occurred since man has been on earth, so tremendous was the quake. The great city split into three parts, and the cities of the nations collapsed. . . . Every island fled away and the mountains could not be found. From the sky huge hailstones of about a hundred pounds each fell upon men. And they cursed God on account of the plague of hail, because the plague was so terrible.”
The earthquake in Revelation could very well speak of the event described in Zechariah when the Mount of Olives splits in two. Jesus the Messiah will cause an earthquake at His second coming that will serve as part of the destruction of God’s enemies. The outcome of this battle is never in doubt: Christ will be the victor, Israel’s enemies will be destroyed, and the beast (Antichrist) and false prophet will be thrown into the lake of fire (Revelation 19:11-21).