text: Seismograms typically record motions in three cartesian axes ( x , y , and z ) , with the z axis perpendicular to the Earth 's surface and the x - and y - axes parallel to the surface .
simplified: Seisometers record motions in three cartesian axes ( x , y , and z ) , with the z axis perpendicular to the Earth 's surface and the x - and y - axes parallel to the surface .