Seismic moment tensor and single force analysis of landslides in Switzerland and Greenland
Abstract
A seismic source can originate from a variety of phenomena, from mining and induced events to nuclear explosions, to natural processes such as earthquakes, volcanic activity, and landslides. A seismic moment tensor is a 3 × 3 symmetric matrix that characterizes the far-field seismic radiation from a source, and together with its uncertainties can be used to discriminate among sources, though it is not clear to what extent the moment tensor can describe the seismogenic source process of landslides. For the case of major landslides (with volume displacement in the order of 106{m}^3 or higher), their seismic radiation is typically modeled in terms of single-forces which describe the momentum exchanges between landslide mass and bedrock. The single-force analysis can thus be used to estimate the mass trajectory from the inverted force history. Here we apply the moment tensor and single-force methods to analyze two large landslides on 2017-06-17 near Nuugaatsiaq, Greenland, and on 2017-08-23 near Bondo, Switzerland. We estimate the moment tensor with a grid search over its six-dimensional space by generating synthetic waveforms at each grid point and then evaluating a misfit function between the observed and synthetic waveforms. Its uncertainty is described in terms of the variation in waveform misfit on the eigenvalue lune, a probability density function for moment tensor source type, and a confidence curve for the probability that the true moment tensor lies within the neighborhood of the best-fitting moment tensor. For the single-force analysis we follow an equivalent approach using observed seismograms and Green's functions to invert for the force history. In both analyses we use three-component seismic waveforms from all available regional broadband seismic stations, and compute Green's functions for a layered wavespeed model of the source region. We find that the Swiss event requires a source duration in the order of 10s of seconds, and the Greenland event can be analyzed as multiple episodes, with a moment tensor for each episode. The optimal moment tensor solutions for all events are towards negative isotropic, their probability density functions are localized in the negative isotropic region, and their moment magnitudes range between M w 4.5-5. The single-force analyses reveal complex force histories, and for the Greenland event associates the main episodes with different portions of the the landslide trajectory. These analyses allow us to gain insight into the landslide process including a lower bound of radiated energy, style of large-scale displacement, and mass trajectory.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S51D0367A
- Keywords:
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- 9805 Instruments useful in three or more fields;
- GENERAL OR MISCELLANEOUSDE: 9820 Techniques applicable in three or more fields;
- GENERAL OR MISCELLANEOUSDE: 1895 Instruments and techniques: monitoring;
- HYDROLOGYDE: 4315 Monitoring;
- forecasting;
- prediction;
- NATURAL HAZARDS