Event chains
Anomaly Events
Colony Events
Early Story Events
Observation Events
Origin Events
Subterranean Civilization is a colony event chain that has a very small chance to trigger 2 or 3 years after any colony has been founded. It can only happen once per game. The event chain offers two mutually exclusive paths which both have eventual rewards and drawbacks. The hostile path can also be followed should peace fail.
Seismic Disturbances
There have been many reports of unexplainable seismic disturbances on [colony name]. Tremors can be felt across the [planet or moon], and many of our settlements have suffered damage. While investigating the earthquakes, our scientists discovered a vast network of subterranean caverns.
The deepest of these caverns are home to some kind of indigenous civilization, and they appear to be tunneling towards the surface! Ground vibrations from our settlements may have triggered this behavior, but we cannot be certain. There is no telling how these aliens will react when they spill out of their tunnels and encounter our colonists!
触发条件：
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平均发生时间（MTTH）：
30 months |
 We have to deal with the situation.
   Exterminate!
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Special Project Completed
 One of our probes burrowed through the ground and intercepted the tunneling aliens on [colony name]. After the startled alien workers calmed down, the probe was successful in establishing communications with their leaders.
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Special Project Completed
Our efforts to destroy the subterranean aliens on [colony name] have met with success! We managed to collapse several of their tunnels on top of their workers, and the caverns that housed their cities have been flooded with nerve gas. Casualty projections are close to 100%, and our security forces are confident they will be able to deal with any surviving stragglers.
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Famine
 We have been approached by a delegation from the subterranean aliens on [colony name]. It seems their empire has fallen on hard times recently, and they are facing the threat of a famine. They are pleading with us to provide whatever assistance we can.
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Subterranean Expansion
We have finished clearing out the nerve gas and the dead alien bodies from the tunnel network on [colony name]. It should now be safe for our colonists to move in. The primitive cities the aliens left behind will be demolished, of course, and replaced with our own advanced architecture.
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Subterranean Refugees
A large group of refugees from the underground alien empire on [colony name] recently streamed out of their tunnels onto the surface, chased by a small army. They are apparently part of some sort of religious minority, and claim to be fleeing persecution. If we let them join our colonists on the surface, it will no doubt anger the rulers of the empire they fled from. However, if we let the pursuing army take them back underground, they will likely face mass execution.
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Survivor Pocket
Our forces on [colony name] are still mapping the tunnel network below our colony. They have come upon a large city belonging to the subterranean aliens that managed to isolate itself from the rest of their underground empire before we flooded it with nerve gas. There are millions of frightened aliens in the city. Should our engineers collapse the cavern to finish the job?
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Gift
As a gift to celebrate the friendship between our two civilizations, a caravan from the subterranean aliens on [colony name] have brought a large quantity of gemstones to the surface. Stones such as these are apparently mined by their empire deep underground, as close to the [planet or moon]'s core as they dare to venture.
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Gold
Prospectors have ventured into some of the deeper tunnels that once belonged to the now dead subterranean aliens on [colony name]. They have finally discovered the long-rumored gold mines where it was believed the underground alien empire acquired its large reserve of precious metals!
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Xeno Anthropologists
Several xeno anthropologists from [capital name] have returned to the surface of [colony name] after spending a great deal of time living among the subterranean aliens native to that world. They have learned much about their ancient ways and customs, which will no doubt benefit our society research.
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Treasury
Scout units exploring the tunnel network on [colony name] have entered the royal palace in what was once the capital city of the underground alien empire. The corpse of what passed for their emperor is still perched on a massive throne in the main chamber. After using explosive charges to breach the palace treasury, our scouts found it filled with gold and strange alien art. The art will be shipped back to museums on [capital name], and the sale of the gold should provide a nice boost to our state budget.
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Earthquakes
There has been a wave of earthquakes on [colony name] recently, and buildings in several of our settlements have collapsed with many fatalities as a result. The subterranean alien empire is excavating a new cavern deep underground where they plan to build a new city, and this appears to be the source of the earthquakes.
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Earthquakes
 [colony name] has been racked by another wave of earthquakes recently. It seems that some of the deeper parts of the underground tunnel network has collapsed without the subterranean aliens to maintain it. Many of our settlements have suffered damage.
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Message Delivered
Trade with the subterranean aliens on [colony name] has dried up as of late, with their caravans showing up more and more seldom. Today we received a message from a representative of their military. They don't seem very pleased.
触发条件：
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平均发生时间（MTTH）：
20 days |
Let's see it.
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Subterranean Invasion!
The subterranean aliens on [colony name] have emerged on the surface! Large armies equipped with primitive yet lethal projectile weapons are spilling from the tunnels, and their vanguard has already begun an assault on our settlements.
Our security forces are responding, but we may need to send reinforcements!
触发条件：
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平均发生时间（MTTH）：
35 days |
To arms!
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Victory
Our forces have managed to drive the subterranean aliens on [colony name] back into their underground lairs, and they are contained for the moment. This is a temporary solution, however, and it is only a matter of time before they break out onto the surface again. We need to strike at them below ground, and our strategists have devised a new attack plan. It has been added to the Situation Log.
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Defeat
Our forces have been decimated on [colony name], and the subterranean aliens have taken full control over all of our settlements! They are using one of our own satellites to send a message to us.
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