Earthquake in Chile causesd days to be longer, Austrian researchers find

On February 27, 2010, one of the strongest earthquakes of recent decades (magnitude 8.8) destroyed large parts of Chile's third-largest city Concepción and its surrounding area. At a central location, experts from the TU Vienna Institute of Geodesy and Geophysics have contributed to the important geodetic measurements that were carried out both before and after the earthquake. Highly precise geodetic measurements play an important role in geodesy (the measurement of Earth), in order to observe natural disasters and examine their causes. The measurements make it possible to determine with great accuracy the deformations in Earth's crust and the shifting of the tectonic plates. The GPS station in Concepción, which continued to operate without problems both during and after the earthquake, measured a shift of nearly 3 metres to the west. The movement vectors in this image indicate that the entire South American plate has not just "wandered over" to the west, but was instead "pulled apart."

"Observations using the radio telescope in Concepción will provide further important information on plate movement using the Very Long Baseline Interferometry (VLBI) process," speculates Dr Johannes Böhm, Head of the VLBI group at the Institute of Geodesy and Geophysics. Current VLBI analyses at the institute confirm the suspected shift of approximately 3 metres to the west and 0.65 metres to the south.

Effects on Earth's rotation: days are becoming longer

Experts suspect that the earthquake has also influenced Earth's rotation. The shift of mass within Earth's crust, caused by the earthquake, is affecting both the rotational speed of Earth and the direction of the axis of rotation, which contributes to polar motion. Using data about the magnitude of the earthquake and the deformations caused by it, the Institute of Geodesy and Geophysics is in the meantime determining the effects of the earthquake on Earth's rotation.

First results indicate that the rotational speed of Earth has become marginally slower and days have become longer by 0.3 microseconds. In the coming months, polar motion will deviate by approx. 2.6 milliarcseconds, which corresponds with 7 cm on Earth's surface, due to the earthquake in Chile. Dr Harald Schuh, Head of the Institute of Geodesy and Geophysics at TU Vienna and President of Commission 19 "Rotation of Earth" within the International Astronomical Union (IAU), confirms that "evidence that suggests a sudden shift of Earth's axis of rotation is not correct, according to these results."

Observations which were carried out using global navigation satellite systems, such as the American GPS or the Russian Glonass, or using the VLBI technique are currently being analysed to confirm the earthquake's effects on Earth's rotation. "This is not a simple task, as there are countless other factors that influence Earth's rotation besides the earthquake, such as strong winds or ocean tides," stresses Dr Tobias Nilsson, who is responsible for the corresponding work on the simulation model. Using modern geodetic measuring techniques, the geodesists' research will help improve the prediction of natural disasters and the possibilities of warning of these disasters shortly before they occur.