TY  - JOUR
A1  - Hammer, Conny
A1  - Fäh, Donat
A1  - Ohrnberger, Matthias
T1  - Automatic detection of wet-snow avalanche seismic signals
JF  - Natural hazards : journal of the International Society for the Prevention and Mitigation of Natural Hazards
N2  - 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.
KW  - Snow avalanche recognition
KW  - Automatic detection
KW  - Avalanche forecasting
KW  - Hidden Markov model
Y1  - 2016
U6  - https://doi.org/10.1007/s11069-016-2707-0
SN  - 0921-030X
SN  - 1573-0840
VL  - 86
SP  - 601
EP  - 618
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Lontsi, Agostiny Marrios
A1  - Garcia-Jerez, Antonio
A1  - Camilo Molina-Villegas, Juan
A1  - Jose Sanchez-Sesma, Francisco
A1  - Molkenthin, Christian
A1  - Ohrnberger, Matthias
A1  - Krüger, Frank
A1  - Wang, Rongjiang
A1  - Fah, Donat
T1  - A generalized theory for full microtremor horizontal-to-vertical [H/V(z,f)] spectral ratio interpretation in offshore and onshore environments
JF  - Geophysical journal international
N2  - 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.
KW  - Numerical modelling
KW  - Earthquake hazards
KW  - Seismic interferometry
KW  - Site effects
KW  - Theoretical seismology
KW  - Wave propagation
Y1  - 2019
U6  - https://doi.org/10.1093/gji/ggz223
SN  - 0956-540X
SN  - 1365-246X
VL  - 218
IS  - 2
SP  - 1276
EP  - 1297
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Bommer, Julian J.
A1  - Abrahamson, Norman A.
A1  - Strasser, F. O.
A1  - Pecker, Alain
A1  - Bard, Pierre-Yves
A1  - Bungum, Hilmar
A1  - Cotton, Fabrice
A1  - Fäh, Donat
A1  - Sabetta, F.
A1  - Scherbaum, Frank
A1  - Studer, Jost
T1  - The challenge of defining upper bounds on earthquake ground motions
Y1  - 2004
SN  - 0895-0695
ER  -