@article{StankiewiczWeberMohsenetal.2012, author = {Stankiewicz, Jacek and Weber, Michael H. and Mohsen, Ayman and Hofstetter, Rami}, title = {Dead Sea Basin imaged by ambient seismic noise tomography}, series = {Pure and applied geophysics}, volume = {169}, journal = {Pure and applied geophysics}, number = {4}, publisher = {Springer}, address = {Basel}, issn = {0033-4553}, doi = {10.1007/s00024-011-0350-y}, pages = {615 -- 623}, year = {2012}, abstract = {In the framework of the Dead Sea Integrated Research project (DESIRE), 59 seismological stations were deployed in the region of the Dead Sea Basin. Twenty of these stations recorded data of sufficiently high quality between May and September 2007 to be used for ambient seismic noise analysis. Empirical Green's functions are extracted from cross-correlations of long term recordings. These functions are dominated by Rayleigh waves, whose group velocities can be measured in the frequency range from 0.1 to 0.5 Hz. Analysis of positive and negative correlation lags of the Green's functions makes it possible to identify the direction of the source of the incoming energy. Signals with frequencies higher than 0.2 Hz originate from the Mediterranean Sea, while low frequencies arrive from the direction of the Red Sea. Travel times of the extracted Rayleigh waves were measured between station pairs for different frequencies, and tomographically inverted to provide independent velocity models. Four such 2D models were computed for a set of frequencies, all corresponding to different sampling depths, and thus together giving an indication of the velocity variations in 3D extending to a depth of 10 km. The results show low velocities in the Dead Sea Basin, consistent with previous studies suggesting up to 8 km of recent sedimentary infill in the Basin. The complex structure of the western margin of the Basin is also observed, with sedimentary infill present to depths not exceeding 5 km west of the southern part of the Dead Sea. The high velocities associated with the Lisan salt diapir are also observed down to a depth of similar to 5 km. The reliability of the results is confirmed by checkerboard recovery tests.}, language = {en} } @article{IllienSensSchoenfelderAndermannetal.2022, author = {Illien, Luc and Sens-Sch{\"o}nfelder, Christoph and Andermann, Christoff and Marc, Odin and Cook, Kristen L. and Adhikari, Lok Bijaya and Hovius, Niels}, title = {Seismic velocity recovery in the subsurface}, series = {Journal of geophysical research : Solid earth}, volume = {127}, journal = {Journal of geophysical research : Solid earth}, number = {2}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9313}, doi = {10.1029/2021JB023402}, pages = {18}, year = {2022}, abstract = {Shallow earthquakes frequently disturb the hydrological and mechanical state of the subsurface, with consequences for hazard and water management. Transient post-seismic hydrological behavior has been widely reported, suggesting that the recovery of material properties (relaxation) following ground shaking may impact groundwater fluctuations. However, the monitoring of seismic velocity variations associated with earthquake damage and hydrological variations are often done assuming that both effects are independent. In a field site prone to highly variable hydrological conditions, we disentangle the different forcing of the relative seismic velocity variations delta v retrieved from a small dense seismic array in Nepal in the aftermath of the 2015 M-w 7.8 Gorkha earthquake. We successfully model transient damage effects by introducing a universal relaxation function that contains a unique maximum relaxation timescale for the main shock and the aftershocks, independent of the ground shaking levels. Next, we remove the modeled velocity from the raw data and test whether the corresponding residuals agree with a background hydrological behavior we inferred from a previously calibrated groundwater model. The fitting of the delta v data with this model is improved when we introduce transient hydrological properties in the phase immediately following the main shock. This transient behavior, interpreted as an enhanced permeability in the shallow subsurface, lasts for similar to 6 months and is shorter than the damage relaxation (similar to 1 yr). Thus, we demonstrate the capability of seismic interferometry to deconvolve transient hydrological properties after earthquakes from non-linear mechanical recovery.}, language = {en} } @article{OverduinHaberlandRybergetal.2015, author = {Overduin, Pier Paul and Haberland, Christian and Ryberg, Trond and Kneier, Fabian and Jacobi, Tim and Grigoriev, Mikhail N. and Ohrnberger, Matthias}, title = {Submarine permafrost depth from ambient seismic noise}, series = {Geophysical research letters}, volume = {42}, journal = {Geophysical research letters}, number = {18}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0094-8276}, doi = {10.1002/2015GL065409}, pages = {7581 -- 7588}, year = {2015}, abstract = {Permafrost inundated since the last glacial maximum is degrading, potentially releasing trapped or stabilized greenhouse gases, but few observations of the depth of ice-bonded permafrost (IBP) below the seafloor exist for most of the arctic continental shelf. We use spectral ratios of the ambient vibration seismic wavefield, together with estimated shear wave velocity from the dispersion curves of surface waves, for estimating the thickness of the sediment overlying the IBP. Peaks in spectral ratios modeled for three-layered 1-D systems correspond with varying thickness of the unfrozen sediment. Seismic receivers were deployed on the seabed around Muostakh Island in the central Laptev Sea, Siberia. We derive depths of the IBP between 3.7 and 20.7m15\%, increasing with distance from the shoreline. Correspondence between expected permafrost distribution, modeled response, and observational data suggests that the method is promising for the determination of the thickness of unfrozen sediment.}, language = {en} }