I've always wondered if the melting of glaciers would move masses from one place to another and induce some tectonic moves. But the mass is most likely not significant enough; water/ice has a relatively low density after all.

It's more likely related to planetary positions and or solar cycle/activity, "recent studies suggest a notable statistical correlation between specific solar magnetic milestones and the shifting phases of the El Niño-Southern Oscillation"

Like in theory it doesn't make sense that el niño causes earthquakes, yet there seems to be more prominent ones during el niño however if both are related to sun cycle/activity it would make more sense (seeing how the moon affects earth as well)

The deep earth isn't all that well studied, so while we know a fair amount about plate tectonics, there could be hidden factors influencing that action in ways we can't anticipate from recorded history. Who's to say there aren't 1000 or 10k year cycles of earthquakes? Something novel could happen too, but our records don't let us set probabilities for 10k year natural disasters the way we can with 100 year tropical storms, floods, or earthquakes.

> Who's to say there aren't 1000 or 10k year cycles of earthquakes?

The Stratigraphy department of the International Union of Geological Sciences would be the obvious first port of call.

Follow that up with an off book chat with digital archivists for commercial oil and gas exploration geologists.

Does the stratigraphy department of the international union of geological sciences have such thorough knowledge that they can make predictions about this stuff on geologic timescales? Getting any kind of truth from commercial oil companies is expensive. To them, knowledge is a weapon, and they lie whenever it is advantageous to lie.

Or influence by the moon just as it pulls on oceans. Lot of liquid magma down there.

Or maybe some once in a rare incident involving coronal mass ejections somehow affecting the core of the planet. Could even be a delayed effect.

One of the More out there theories is that some earthquakes are caused by high energy cosmic particles going through the Earth.