Each time a fault fails, it tends to load up the faults around it with a little more stress.

Also, as the tectonic plates move, the faults tend to accumulate stress.

We don't have a reliable way to measure the stress in the ground, nor estimate how much stress is necessary to break the faults.

So we can calculate the changes in stress from the earthquakes and the tectonic plate movements, but not the absolute level of stress nor the time of the next earthquake.

We can sometimes compute when earthquakes have become more likely, however.