MIIC: Monitoring and Imaging Based on Interferometric Concepts

Abstract

The capability of seismic interferometry to create virtual sources at receiver sites from records of ambient seismic noise is used for seismic monitoring and tomography of different targets. We present hardware developed specifically for the needs of seismic data acquisition in the context of monitoring and ambient noise tomography. Digitizers are capable of continuous recording and real time wireless data transmission in self organizing meshes to allow for robust telemetry in difficult circumstances such as cities or landslides that may cause the loss of stations. A software tool is described that implements required processing and analysis procedures for the interferometric processing. We have applied the novel 3D ambient noise surface wave tomography approach to the Issyk-Ata fault in Kyrgyzstan. It shows that seismic interferometry can successfully be used for structural investigations on length scales of only 100 m. The method uses 3D sensitivity kernels for a single-step inversion of phase velocity dispersion curves for subsurface S-wave velocity structure and incorporates topography. We recover lateral differences in sediment velocities and an offset of the bedrock depth across the fault. Applications of interferometric monitoring to the geological \(\mathrm{CO}_2\) storage test site in Ketzin (Germany) and to the Piton de la Fournaise volcano (La Reunion island) emphasize the value of this approach. At Ketzin site we identify variations of the subsurface velocities that are correlated with changes in the ground water level and mask potential signals from the reservoir depth. At Piton de la Fournaise volcano, seismic velocity changes are linked to volcanic processes as shown by comparison with surface displacement and seismicity that are typically used to characterize volcanic activity. We observe a clear distinction between phases of inflation prior to eruptions and deflation during periods of quiescence.