Original: 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.