Wednesday's big (7.5 on the Richter scale) earthquake off the coast of Indonesia near Jakarta sent seismic signals around the globe. When they reached the US Geological Survey's monitoring well near Christianburg, Va., they produced a noticeable fluctuation in water levels in the well.
As incredible as it seems, it's not unusual. The Christianburg well's sensitivity to major seismic events is well-known and long-watched by geologists and hydrologists. The well also shows regular rises and falls in response to the Earth's tidal movements. These are movements in the Earth's crust due to the gravitational pull of the sun and moon. They're the same forces that create ocean tides, except they're seen in the rock. And those movements cause the well water to rise and fall like water in a sponge.
This is a longer look at how the well's water level responds to the regular pulse of Earth tides. You can also see that water levels in the well are falling this summer.