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So, we can apply 7 million pounds to this rock in this direction and three and a half million pounds of this direction. 
[Music] And that's enough to simulate the pressure that the rock exert, when you're about one or two 
kilometers deep. Most earthquakes are about five ten kilometres five to fifteen. So, we're not even we're not even squeezing the rock enough. But we're getting close. 
And so, what we do is we squeeze the rock together and then that set of cylinders moves one of the rock and rocks against the other one. So, we can imagine this is like the North American plate and then over here is the Pacific plate. If you're in California that would be the San Andreas Fault right here. 
It's not just slipping like a block it kind of slips more like a caterpillar. This block does not all slip at once part of it slips and then another part of it slips and then another part of it slips. So we need 16 sensors all the way down the length of the block to monitor when and where it was slipping. 
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