@article{RamosMechieFeng2016,
  author    = {Ramos, C. and Mechie, James and Feng, M.},
  title     = {Shear wave velocity and Poisson's ratio models across the southern Chile convergent margin at 38{\^A}°15{\^a}€²S},
  series = {Geophysical journal international},
  volume    = {204},
  journal   = {Geophysical journal international},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0956-540X},
  doi       = {10.1093/gji/ggv541},
  pages     = {1620 -- 1635},
  year      = {2016},
  abstract  = {Using active and passive seismology data we derive a shear (S) wave velocity model and a Poisson's ratio (\&\#963;) model across the Chilean convergent margin along a profile at 38°15\&\#8242;S, where the Mw 9.5 Valdivia earthquake occurred in 1960. The derived S-wave velocity model was constructed using three independently obtained velocity models that were merged together. In the upper part of the profile (0-2 km depth), controlled source data from explosions were used to obtain an S-wave traveltime tomogram. For the middle part (2-20 km depth), data from a temporary seismology array were used to carry out a dispersion analysis. The resulting dispersion curves were used to obtain a 3-D S-wave velocity model. In the lower part (20-75 km depth, depending on the longitude), an already existent local earthquake tomographic image was merged with the other two sections. This final S-wave velocity model and already existent compressional (P) wave velocity models along the same transect allowed us to obtain a Poisson's ratio model. The results of this study show that the velocities and Poisson's ratios in the continental crust of this part of the Chilean convergent margin are in agreement with geological features inferred from other studies and can be explained in terms of normal rock types. There is no requirement to call on the existence of measurable amounts of present-day fluids, in terms of seismic velocities, above the plate interface in the continental crust of the Coastal Cordillera and the Central Valley in this part of the Chilean convergent margin. This is in agreement with a recent model of water being transported down and released from the subduction zone.},
  language  = {en}
}
@article{NooshiriSaulHeimannetal.2017,
  author    = {Nooshiri, Nima and Saul, Joachim and Heimann, Sebastian and Tilmann, Frederik and Dahm, Torsten},
  title     = {Revision of earthquake hypocentre locations in global bulletin data sets using source-specific station terms},
  series = {Geophysical journal international},
  volume    = {208},
  journal   = {Geophysical journal international},
  number    = {2},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0956-540X},
  doi       = {10.1093/gji/ggw405},
  pages     = {589 -- 602},
  year      = {2017},
  abstract  = {Global earthquake locations are often associated with very large systematic travel-time residuals even for clear arrivals, especially for regional and near-regional stations in subduction zones because of their strongly heterogeneous velocity structure. Travel-time corrections can drastically reduce travel-time residuals at regional stations and, in consequence, improve the relative location accuracy. We have extended the shrinking-box source-specific station terms technique to regional and teleseismic distances and adopted the algorithm for probabilistic, nonlinear, global-search location. We evaluated the potential of the method to compute precise relative hypocentre locations on a global scale. The method has been applied to two specific test regions using existing P- and pP-phase picks. The first data set consists of 3103 events along the Chilean margin and the second one comprises 1680 earthquakes in the Tonga-Fiji subduction zone. Pick data were obtained from the GEOFON earthquake bulletin, produced using data from all available, global station networks. A set of timing corrections varying as a function of source position was calculated for each seismic station. In this way, we could correct the systematic errors introduced into the locations by the inaccuracies in the assumed velocity structure without explicitly solving for a velocity model. Residual statistics show that the median absolute deviation of the travel-time residuals is reduced by 40-60 per cent at regional distances, where the velocity anomalies are strong. Moreover, the spread of the travel-time residuals decreased by similar to 20 per cent at teleseismic distances (>28 degrees). Furthermore, strong variations in initial residuals as a function of recording distance are smoothed out in the final residuals. The relocated catalogues exhibit less scattered locations in depth and sharper images of the seismicity associated with the subducting slabs. Comparison with a high-resolution local catalogue reveals that our relocation process significantly improves the hypocentre locations compared to standard locations.},
  language  = {en}
}
@article{NooshiriBeanDahmetal.2021,
  author    = {Nooshiri, Nima and Bean, Christopher J. and Dahm, Torsten and Grigoli, Francesco and Kristjansdottir, Sigriour and Obermann, Anne and Wiemer, Stefan},
  title     = {A multibranch, multitarget neural network for rapid point-source inversion in a microseismic environment},
  series = {Geophysical journal international},
  volume    = {229},
  journal   = {Geophysical journal international},
  number    = {2},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0956-540X},
  doi       = {10.1093/gji/ggab511},
  pages     = {999 -- 1016},
  year      = {2021},
  abstract  = {Despite advanced seismological techniques, automatic source characterization for microseismic earthquakes remains difficult and challenging since current inversion and modelling of high-frequency signals are complex and time consuming. For real-time applications such as induced seismicity monitoring, the application of standard methods is often not fast enough for true complete real-time information on seismic sources. In this paper, we present an alternative approach based on recent advances in deep learning for rapid source-parameter estimation of microseismic earthquakes. The seismic inversion is represented in compact form by two convolutional neural networks, with individual feature extraction, and a fully connected neural network, for feature aggregation, to simultaneously obtain full moment tensor and spatial location of microseismic sources. Specifically, a multibranch neural network algorithm is trained to encapsulate the information about the relationship between seismic waveforms and underlying point-source mechanisms and locations. The learning-based model allows rapid inversion (within a fraction of second) once input data are available. A key advantage of the algorithm is that it can be trained using synthetic seismic data only, so it is directly applicable to scenarios where there are insufficient real data for training. Moreover, we find that the method is robust with respect to perturbations such as observational noise and data incompleteness (missing stations). We apply the new approach on synthesized and example recorded small magnitude (M <= 1.6) earthquakes at the Hellisheioi geothermal field in the Hengill area, Iceland. For the examined events, the model achieves excellent performance and shows very good agreement with the inverted solutions determined through standard methodology. In this study, we seek to demonstrate that this approach is viable for microseismicity real-time estimation of source parameters and can be integrated into advanced decision-support tools for controlling induced seismicity.},
  language  = {en}
}
@article{HobigerCornouWatheletetal.2013,
  author    = {Hobiger, M. and Cornou, C. and Wathelet, M. and Di Giulio, G. and Knapmeyer-Endrun, B. and Renalier, F. and Bard, Pierre-Yves and Savvaidis, Alexandros and Hailemikael, S. and Le Bihan, N. and Ohrnberger, Matthias and Theodoulidis, N.},
  title     = {Ground structure imaging by inversions of Rayleigh wave ellipticity sensitivity analysis and application to European strong-motion sites},
  series = {Geophysical journal international},
  volume    = {192},
  journal   = {Geophysical journal international},
  number    = {1},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0956-540X},
  doi       = {10.1093/gji/ggs005},
  pages     = {207 -- 229},
  year      = {2013},
  abstract  = {The knowledge of the local soil structure is important for the assessment of seismic hazards. A widespread, but time-consuming technique to retrieve the parameters of the local underground is the drilling of boreholes. Another way to obtain the shear wave velocity profile at a given location is the inversion of surface wave dispersion curves. To ensure a good resolution for both superficial and deeper layers, the used dispersion curves need to cover a wide frequency range. This wide frequency range can be obtained using several arrays of seismic sensors or a single array comprising a large number of sensors. Consequently, these measurements are time-consuming. A simpler alternative is provided by the use of the ellipticity of Rayleigh waves. The frequency dependence of the ellipticity is tightly linked to the shear wave velocity profile. Furthermore, it can be measured using a single seismic sensor. As soil structures obtained by scaling of a given model exhibit the same ellipticity curve, any inversion of the ellipticity curve alone will be ambiguous. Therefore, additional measurements which fix the absolute value of the shear wave velocity profile at some points have to be included in the inversion process. Small-scale spatial autocorrelation measurements or MASW measurements can provide the needed data. Using a theoretical soil structure, we show which parts of the ellipticity curve have to be included in the inversion process to get a reliable result and which parts can be omitted. Furthermore, the use of autocorrelation or high-frequency dispersion curves will be highlighted. The resulting guidelines for inversions including ellipticity data are then applied to real data measurements collected at 14 different sites during the European NERIES project. It is found that the results are in good agreement with dispersion curve measurements. Furthermore, the method can help in identifying the mode of Rayleigh waves in dispersion curve measurements.},
  language  = {en}
}