Observed relative velocity change for the station PATCX (blue line). Days in which local earthquakes with a magnitude greater than 5.5 occurred are indicated by vertical gray lines. Different effects are observed: 1 short-term decreases in seismic velocity due to local and regional earthquakes, 2 long-term increase in speed as recovery to the level before the Tocopilla earthquake (dashed orange line), 3 an annual periodic change in velocity due to the influence of temperature (compare with plotted temperature).

Changes of seismic velocities in the Earth's crust in Northern Chile

The seismic gap in Northern Chile is intensively monitored by the IPOC network operated by GFZ and cooperating institutions. We use the seismological data of this network to develop methods for possibly detecting temporal stress changes in the crust by means of changes in seismic velocities. Analyzing seismic noise has already been used in other regions for detecting seismic velocity changes in the Earth's crust successfully. Therefore cross- or auto-correlation functions are calculated over a certain period of time (e.g. one hour or day). These functions can be calculated over several years and analyzed for a phase shift of the seismic signals. This technique was applied to all seismic stations and most stations show a short-term velocity drop at the time of the Tocopilla earthquake on 14.11.2007. One station shows a velocity drop, which is restoring again in the course of several years. In addition to these long-term changes in seismic velocity, an annual and a daily change correlating well to temperature changes was observed at the same station. The reason for the velocity changes is unclear. It is supposed that a near salar amplifies the effects.

It was demonstrated that the seismic seismic noise can be successfully used in Northern Chile to measure changes of seismic velocity.

Prof. Dr. R. Kind (FU Berlin/GFZ)
T. Richter (FU Berlin/GFZ)

Details of project



DFG - German Research Foundation