The earthquake generated a seismic oscillation of the Earth's surface of up to , equivalent to the effect of the tidal forces caused by the Sun and Moon. The seismic waves of the earthquake were felt across the planet; as far away as the U.S. state of Oklahoma, where vertical movements of were recorded. By February 2005, the earthquake's effects were still detectable as a complex harmonic oscillation of the Earth's surface, which gradually diminished and merged with the incessant free oscillation of the Earth more than four months after the earthquake.