The study of earthquake waves, seismology dates back to attempts made by the Chinese almost 2,000 years ago to determine the direction from which these waves originated. Modern seismographs, instruments that record earthquake waves, are similar to the instruments used by the Chinese. Seismographs have a weight freely suspended from a support that is securely attached to bedrock ( Figure 8.7) When vibrations from an earthquake reach the instrument , the inertia of the weight keeps it relatively stationary while Earth and the support move . ( Inertia is the tendency of objects at rest to stay at rest and objects in motion to remain in motion )