Let's consider 3 possibilities:
1. If Mark were first
I think this is the more difficult option, as Matthew's use of the word σεισμὸς would be unexpected. However, this needn't be conclusive evidence against the priority of Mark on its own.
As Mark Goodacre has observed:
[L]iterary style is a personal thing, and it is never surprising when
given writers choose not to use their source's literary
idiosyncrasies. It is unreasonable, therefore, to expect either
Matthew or Luke to have carried over every piece of Mark's literary
narration. As writers, we are all familiar with avoiding certain
terminology in the way we structure our prose. (The Synoptic Problem Four Views, pp. 129-130)
It may simply be that Matthew didn't like the word λαῖλαψ; it never does appear in his Gospel.
2. If Matthew were first
The word λαῖλαψ appears only twice in the entire New Testament--in these two passages in Mark & Luke (a variation of the word also appears in 2 Peter--see Strong's 2978 here). This certainly strengthens the case for a literary relationship between Mark & Luke--a rare word is used in exactly the same place.
On balance though I suggest the evidence from borrowed words comes down in favor of Matthean priority.
Eduard Zeller's study of this phenomenon suggested that for every example of a favorite word/phrase where it looks like Matthew is doing the borrowing from Mark, there are 2 examples going the other direction—that Mark is doing the borrowing.
Zeller's work on borrowed words didn't presuppose which Gospel was first, and concluded Mark borrowed from both Matthew & Luke. An excellent summary in English is in the Introduction to One Gospel from Two Mark's Use of Matthew and Luke.
This would mean that Matthew used an odd word--as noted in the OP, σεισμὸς, though grammatically permissible, is an unusual choice--and whoever came second chose to replace the odd σεισμὸς with the more clear λαῖλαψ.
3. If Greek Matthew is a translation
Shem Tob Matthew (a corrupted but potentially never-translated Hebrew copy of Matthew from the 14th century) is sometimes helpful in understanding the underlying Semitic thought behind the Gospels. If this document is a corrupted version of something originally written in Hebrew (as many who study it, most prominently George Howard, have suggested), then the word of interest in Matthew 8:24 is סער, a word used dozens of times in the OT to refer to a storm (see here)
If Matthew was originally composed in Hebrew, as Origen and other early church scholars attest, then, as user33515 already noted, it is the translator of Matthew who picked an odd word. This again could be because, as noted in the section on Markan Priority, the writer simply didn't like the word λαῖλαψ.
Or it could be that the translator was influenced by the Septuagint rendering of Isaiah 29:6...this observation goes a little more out on a limb, but I find it interesting that the word in Shem Tob Matthew (סער) is used in Isaiah 29:6. In Hebrew this passage refers to earthquake, storm, and tempest separately, as three distinct nouns (see here), but the Greek of the Septuagint just has a single noun. And what is that noun? None other than σεισμοῦ, a form of our friend σεισμός.
The Septuagint uses σεισμός in a relevant passage describing the Lord's power over the elements. If Matthew was translated from Hebrew to Greek, the translator clearly knew the Septuagint well. Greek Matthew may well have σεισμός because of what it conveys in the Septuagint.
Any of these options are possible. Because I believe on separate grounds that Matthew was written first and in Hebrew, the third possibility intrigues me the most. But on the evidence of this single passage I wouldn't rule out the other two explanations.