Preprints
https://doi.org/10.5194/esurf-2022-10
https://doi.org/10.5194/esurf-2022-10
 
04 May 2022
04 May 2022
Status: this preprint is currently under review for the journal ESurf.

A template to obtain information on gravitational mass movements from the spectrograms of the seismic signals generated

Emma Suriñach1 and E. Leticia Flores-Márquez2 Emma Suriñach and E. Leticia Flores-Márquez
  • 1Department RISKNAT Avalanches Research Group- Institut Geomodels. Dpt. Dinàmica de la Terra i de l'Oceà. Facultat de Ciències de la Terra. c/ Martí i Franquès s/n, Universitat de Barcelona (UB). Barcelona 28008, Spain
  • 2Departamento de Geomagnetismo y Exploración. Instituto de Geofísica, UNAM, Circuito Instituto S/N, Coyoacán 04510, Mexico

Abstract. We present a template that helps in the classification of gravitational mass motions (snow avalanches, lahars and debris flows) by simply overlaying it graphically with the corresponding spectrogram of the generated seismic signal at the same scale. The template is created with different values of a parameter β'  that allows us to analytically reproduce the exponential form of the increase in amplitude of high frequencies in time of the SON (Signal Onset) section of the spectrogram when the mass movement descends a slope and approach a seismic sensor. This increasing shape is a consequence of the appearance of energy at high frequencies as the gravitational mass approaches the seismic sensor. We present a methodology that includes a link between the propagation properties of seismic waves and the results of the application of an image processing using the Hough transform to demonstrate that this shape is related to the speed of the avalanche and the characteristics of the terrain. Seismic data generated by lahars, debris flows, and avalanches are used for the study. Depending on the type of event, differences are obtained in the order of magnitude of the values of β'. The mean value of β'  for lahars is around 0.003 s-1, that for debris flows is an order of magnitude greater (0.017 s-1) and an order of magnitude less than that for avalanches (0.12 s-1). Furthermore, differences in β'  are observed within each type of event.

Once the appropriated value of β'  has been determined, the characteristics of the mass movement must be set according to expert judgement. This must be done for each site and for each type of gravitational mass movement. The application of the templates to the data of lahars and an avalanche recorded in two different places of its trajectory is presented as an example.  

Emma Suriñach and E. Leticia Flores-Márquez

Status: open (until 24 Jun 2022)

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Emma Suriñach and E. Leticia Flores-Márquez

Emma Suriñach and E. Leticia Flores-Márquez

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Short summary
A template that helps in the classification of gravitational mass movements (snow avalanches, lahars and debris flows) by simply overlaying it graphically with the corresponding spectrogram of the generated seismic signals is presented. The events must approach the seismic sensor. The template is created taking into account the propagation properties of seismic waves generated by the events. Examples are presented.