In order to monitor the changes occurring to the CO2 reservoir at the Ketzin site (germany) with passive seismic methods, surface broadband 3-component stations around the injection siteare used. The objective of the study are: 1) locate the microseismicity induced by the injection rate change. 2) use the background noise to calculate empirical Green functions across the injection site, which may vary while the CO2 is stopped/injected.