@article{HammerFaehOhrnberger2017,
  author    = {Hammer, Conny and F{\"a}h, Donat and Ohrnberger, Matthias},
  title     = {Automatic detection of wet-snow avalanche seismic signals},
  series = {Natural hazards : journal of the International Society for the Prevention and Mitigation of Natural Hazards},
  volume    = {86},
  journal   = {Natural hazards : journal of the International Society for the Prevention and Mitigation of Natural Hazards},
  publisher = {Springer},
  address   = {New York},
  issn      = {0921-030X},
  doi       = {10.1007/s11069-016-2707-0},
  pages     = {601 -- 618},
  year      = {2017},
  abstract  = {Avalanche activity is an important factor when estimating the regional avalanche danger. Moreover, a complete and detailed picture of avalanche activity is needed to understand the processes that lead to natural avalanche release. Currently, information on avalanche activity is mainly obtained through visual observations. However, this involves large uncertainties in the number and release times, influencing the subsequent analysis. Therefore, alternative methods for the remote detection of snow avalanches in particular in non-observed areas are highly desirable. In this study, we use the excited ground vibration to identify avalanches automatically. The specific seismic signature of avalanches facilitates the objective detection by a recently developed classification procedure. A probabilistic description of the signals, called hidden Markov models, allows the robust identification of corresponding signals in the continuous data stream. The procedure is based upon learning a general background model from continuous seismic data. Then, a single reference waveform is used to update an event-specific classifier. Thus, a minimum amount of training data is required by constructing such a classifier on the fly. In this study, we processed five days of continuous data recorded in the Swiss Alps during the avalanche winter 1999. With the restriction of testing large wet-snow avalanches only, the presented approach achieved very convincing results. We successfully detect avalanches over a large volume and distance range. Ninety-two percentage of all detections (43 out of 47) could be confirmed as avalanche events; only four false alarms are reported. We see a clear dependence of recognition capability on run-out distance and source-receiver distance of the observed events: Avalanches are detectable up to a source-receiver distance of eight times the avalanche length. Implications for analyzing a more comprehensive data set (smaller events and different flow regimes) are discussed in detail.},
  language  = {en}
}
@article{LontsiGarciaJerezCamiloMolinaVillegasetal.2019,
  author    = {Lontsi, Agostiny Marrios and Garcia-Jerez, Antonio and Camilo Molina-Villegas, Juan and Jose Sanchez-Sesma, Francisco and Molkenthin, Christian and Ohrnberger, Matthias and Kr{\"u}ger, Frank and Wang, Rongjiang and Fah, Donat},
  title     = {A generalized theory for full microtremor horizontal-to-vertical [H/V(z,f)] spectral ratio interpretation in offshore and onshore environments},
  series = {Geophysical journal international},
  volume    = {218},
  journal   = {Geophysical journal international},
  number    = {2},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0956-540X},
  doi       = {10.1093/gji/ggz223},
  pages     = {1276 -- 1297},
  year      = {2019},
  abstract  = {Advances in the field of seismic interferometry have provided a basic theoretical interpretation to the full spectrum of the microtremor horizontal-to-vertical spectral ratio [H/V(f)]. The interpretation has been applied to ambient seismic noise data recorded both at the surface and at depth. The new algorithm, based on the diffuse wavefield assumption, has been used in inversion schemes to estimate seismic wave velocity profiles that are useful input information for engineering and exploration seismology both for earthquake hazard estimation and to characterize surficial sediments. However, until now, the developed algorithms are only suitable for on land environments with no offshore consideration. Here, the microtremor H/V(z, f) modelling is extended for applications to marine sedimentary environments for a 1-D layered medium. The layer propagator matrix formulation is used for the computation of the required Green's functions. Therefore, in the presence of a water layer on top, the propagator matrix for the uppermost layer is defined to account for the properties of the water column. As an application example we analyse eight simple canonical layered earth models. Frequencies ranging from 0.2 to 50 Hz are considered as they cover a broad wavelength interval and aid in practice to investigate subsurface structures in the depth range from a few meters to a few hundreds of meters. Results show a marginal variation of 8 per cent at most for the fundamental frequency when a water layer is present. The water layer leads to variations in H/V peak amplitude of up to 50 per cent atop the solid layers.},
  language  = {en}
}
@article{BommerAbrahamsonStrasseretal.2004,
  author    = {Bommer, Julian J. and Abrahamson, Norman A. and Strasser, F. O. and Pecker, Alain and Bard, Pierre-Yves and Bungum, Hilmar and Cotton, Fabrice and F{\"a}h, Donat and Sabetta, F. and Scherbaum, Frank and Studer, Jost},
  title     = {The challenge of defining upper bounds on earthquake ground motions},
  issn      = {0895-0695},
  year      = {2004},
  language  = {en}
}