Tafsir of Az-Zalzala 99:2

Ibn Abbas stated that this means its dead. Al-Naqqash, Al-Zajjaj, and Mundhir ibn Sa’id said it means its treasures and its dead. It has also been narrated from Ibn Abbas—according to this view—that these treasures are distinct from the treasures that shall emerge during the days of the Dajjal, as indicated by the reports. This is because some shall emerge during his days and others at the second blast of the Horn. There is no impossibility in there being further treasures after the Dajjal, such that the earth brings them forth alongside what remained of the former.

It has been said that this occurs at the first blast of the Horn, and its "burdens" are the treasures within its interior, or both the treasures and the dead; the time is considered to be extended. It has also been said that it is possible the bringing forth of the dead is like that of the treasures at the first blast, and their resurrection is at the second blast, remaining upon the face of the earth between the two blasts—though you know that this contradicts what the texts indicate.

It has been said that the earth is shaken at the first blast, whereby it brings forth its treasures, and is shaken at the second, whereby it brings forth its dead; the time of the earthquake here is intended to encompass both times. Some have restricted the interpretation of "burdens" to treasures only, while intending the time of the second blast, stating that the earth brings forth its treasures on the Day of Resurrection so that those gathered may see them. Thus, the disobedient shall despair when they gaze upon them, having disobeyed Allah regarding them, only to leave them behind, as they shall avail them nothing. In the Hadith: "The earth shall cast forth its heart-pieces, like pillars of gold and silver. The murderer shall come and say, 'For this I killed.' The one who severed ties shall come and say, 'For this I severed my kinship.' The thief shall come and say, 'For this my hand was cut.' Then they shall leave it, taking nothing."

It has been said that this is so that the foreheads, flanks, and backs of those who hoarded them may be branded with them. Regardless, al-athqal (burdens) is the plural of thiql (with a vowel movement on the tha), which, according to the Qamus, refers to a traveler’s luggage and every precious, guarded thing; it is used here metaphorically for the latter. It is also possible that it is the plural of thiql (a noun with a quiescent second letter), meaning the weight of a pregnancy, by way of simile and metaphor as well, as Sharif al-Murtada stated in al-Durar. He indicated that it is not applied to what was mentioned except by way of metaphor.

Some have interpreted al-athqal here as "secrets," but this is far-fetched and contrary to the narrated traditions.

The explicit mention of "the earth" in place of a pronoun is to increase emphasis. It has been said it is to gesture toward the replacement of the earth with another earth, or because the earth's bringing forth is—in respect to some of its parts—a result of the earthquake, just as a carpet shakes off the dust and similar things contained within it. The waw (and) was chosen over the fa (then/consequently) to leave it to the listener's intuition, so it is said. Perhaps the apparent meaning is that the relationship of cause and effect was not intended, but rather that each of the mentioned events was stated without addressing whether one was caused by the other.