Ensuring death by Likho sounds like the simplest option.
I did think about the merits of amending it mechanically so that instead of just endlessly spewing shells at the same rate, it has to build up ammunition like the Zenith before blowing its load with the twist that it wouldn't just be one salvo, more a case of charge up for 1 minute (for instance) to get, say 30 seconds of bombardment. To incentivise use, this version of the Tremor would dish out the same number of shells but in half the time.
The idea would be to require active management to put it to best use, instead of just force fire somewhere and leave it. You would need to choose exactly when to let fly to best support your side. Multiple tremors could be timed to overlap to achieve the effect we see today, but at far higher cost in metal and the attention needed to time it right. However, with a shorter, but more intense bombardment, it could be used more proactively to quickly soften up a defensive position or army to be hit immediately by an assault force dispatched at the right time to land exactly as the barrage concludes.
It might add a bit more interaction to the artillery duel phase you often get in a large team game. On the other hand, it probably steps too much on the toes of the Merlin and perhaps there might be performance implications as well.
Would it be more interesting if, instead of just spamming explosive shells, it delivered a debuff barrage along with only nominal damage? Tank lacks a disarm platform, maybe tremor shells could gain that ability, tuned so that each individual shell is weak on disarm and it has a low disarm duration (no more than 2 secs) but with the barrage maintained a sizable area of porc (or an army that doesn't bother moving) could be silenced enabling a much more favourable environment for advancing heavy assualts (e.g Minotaur push). Yes, those heavy assaults would take some chip disarm damage fighting in the rain, but because they have fat HP pools, it'd take a long time for them to end up in the same state as their targets, by which time they should have won anyway (if not you clearly needed more TAAANKS!)
The barrage would hopefully however not have too much of an effect on a counter attack because mobile units would not be sitting around long enough to get disarmed in the bombardment, though low HP raiders might get muted in one hit.