Built-up on top of ancient lake deposits, Mexico City experiences some of the largest seismic site effects worldwide. Besides the extreme amplification of seismic waves, duration of intense ground ...motion from large subduction earthquakes exceeds three minutes in the lake-bed zone of the basin, where hundreds of buildings collapsed or were seriously damaged during the magnitude 8.0 Michoacán earthquake in 1985. Different mechanisms contribute to the long lasting motions, such as the regional dispersion and multiple-scattering of the incoming wavefield from the coast, more than 300 km away the city. By means of high performance computational modeling we show that, despite the highly dissipative basin deposits, seismic energy can propagate long distances in the deep structure of the valley, promoting also a large elongation of motion. Our simulations reveal that the seismic response of the basin is dominated by surface-waves overtones, and that this mechanism increases the duration of ground motion by more than 170% and 290% of the incoming wavefield duration at 0.5 and 0.3 Hz, respectively, which are two frequencies with the largest observed amplification. This conclusion contradicts what has been previously stated from observational and modeling investigations, where the basin itself has been discarded as a preponderant factor promoting long and devastating shaking in Mexico City.
The wind mission Aeolus of the European Space Agency was a groundbreaking achievement for Earth observation. Between 2018 and 2023, the space-borne lidar instrument ALADIN onboard the Aeolus ...satellite measured atmospheric wind profiles with global coverage, which contributed to improving the accuracy of numerical weather prediction. The precision of the wind observations, however, declined over the course of the mission due to a progressive loss of the atmospheric backscatter signal. The analysis of the root cause was supported by the Pierre Auger Observatory in Argentina whose fluorescence detector registered the ultraviolet laser pulses emitted from the instrument in space, thereby offering an estimation of the laser energy at the exit of the instrument for several days in 2019, 2020, and 2021. The reconstruction of the laser beam not only allowed for an independent assessment of the Aeolus performance, but also helped to improve the accuracy in the determination of the laser beam’s ground track on single pulse level. The results presented in this paper set a precedent for the monitoring of space lasers by ground-based telescopes and open new possibilities for the calibration of cosmic-ray observatories.
Simulated Annealing for volcano muography Vesga-Ramírez, A.; Sanabria-Gómez, J.D.; Sierra-Porta, D. ...
Journal of South American earth sciences,
August 2021, 2021-08-00, Letnik:
109
Journal Article
Recenzirano
Muography or muon radiography is a non-invasive emerging image technology relying on high energy atmospheric muons, which complements other standard geophysical tools to understand the Earth’s ...subsurface.
This work discusses a geophysical inversion methodology for volcanic muography, based on the Simulated Annealing algorithm, using a semi-empirical model of the muon flux to reach the volcano topography and a framework for the energy loss of muons in rock.
The Metropolis-Simulated-Annealing algorithm starts from an “observed” muon flux and obtains the best associated inner density distribution function inside a syntetic model of the Cerro Machín Volcano (Tolima-Colombia). The estimated initial density model was obtained with GEOMODELER, adapted to the volcano topography. We improved this model by including rock densities from samples taken from the crater, the dome and the areas associated with fumaroles.
In this paper we determined the minimum muon energy (a function of the arrival direction) needed to cross the volcanic building, the emerging integrated flux of muons, and the density profile inside a model of Cerro Machin. The present inversion correctly reconstructed the density differences inside the Machín, within a 1% error concerning our initial simulation model, giving a remarkable density contrast between the volcanic duct, the encasing rock and the fumaroles area.
•Geophysical inversion methodology for volcanic muography based on the Simulated Annealing algorithm.•The inversion algorithm correctly reconstructed the density differences inside the Machin, within a 1% error concerning our initial simulation model.•We estimate the emerging integrated flux of muons and the density profile inside a model of Cerro Machin Volcano (Tolima, Colombia).
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