Imagine you are holding a squishy foam ball. Now squeeze it! You just put the ball under strain, which means you changed its shape. Now, imagine you are as strong as a tectonic plate. This means that you can squish rock! A strainmeter measures how much the rocks are being squished or stretched.
In this picture, the colors show where tectonic plates are crashing together, pulling apart, or sliding past each other. Squeezing or stretching is happening the most is the red areas, and the least in the blue areas. The white areas are not being squeezed or stretched at all. Are you surprised how much the Earth is strained?
There are over 75 Borehole strainmeters and 6 Laser strainmeters being used in the EarthScope Plate Boundary Observatory to monitor Earth's strain.