Like sea levels, the surface of the Earth also goes up and down with the tides, flexing the crust and stressing the faults inside.... “...[T]he moon, when it's pulling in the same direction that the fault is slipping, causes the fault to slip more – and faster,” said Nicholas van der Elst, a U.S. Geological Survey geophysicist... ... Like ocean tides, the strongest Earth tides occur when the sun and moon are aligned, and the weakest occur when they are 90 degrees apart. The same gravitational forces stretch and compress the Earth’s crust (though the rock moves less dramatically than...