"The acta urbis. The sixth-century chronicler loannes Malalas, ..........., cites among his sources the names of four writers, all of whose works are lost, namely Pausanias (already discussed), Domninus, Timotheus, Theophilus. Our information concerning these writers is very scanty; according to the citations in Malalas, Domninus, and Pausanias each wrote a chronicle that was largely or primarily concerned with Antioch, while the others seem to have composed world-chronicles in which Antioch was mentioned. Malalas' citations sound as though he used these sources directly, but it is possible that he drew upon them only at second hand. Malalas also quotes the acta urbis (τα ακτα τηζ ρολεωζ, 443.20) as a source of his information concerning the earthquake of A.D. 528, and it is clear in any case that some of his information could well have come from local official records, though we are not sure precisely how the information would have reached him. We have not enough information to know whether there were acta urbis at Antioch for the whole of the Roman period, and we do not know know which kind of official records of local events might have been kept during the Seleucid period".
A more expansive examination of Malalas' sources is given by Peter van Nuffelen in his paper:
Malalas and the chronographic tradition
in L. Carrara, M. Meier, C. Radtki, eds., Die Weltchronik des Johannes Malalas – Quellenfragen, Stuttgart: Franz Steiner Verlag, 2017, 261-272
which is available on academia.edu here.