Browsing by Author "Campillo, Michel"

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    Clustering earthquake signals and background noises in continuous seismic data with unsupervised deep learning
    (Springer Nature, 2020) Seydoux, Léonard; Balestriero, Randall; Poli, Piero; de Hoop, Maarten; Campillo, Michel; Baraniuk, Richard
    The continuously growing amount of seismic data collected worldwide is outpacing our abilities for analysis, since to date, such datasets have been analyzed in a human-expert-intensive, supervised fashion. Moreover, analyses that are conducted can be strongly biased by the standard models employed by seismologists. In response to both of these challenges, we develop a new unsupervised machine learning framework for detecting and clustering seismic signals in continuous seismic records. Our approach combines a deep scattering network and a Gaussian mixture model to cluster seismic signal segments and detect novel structures. To illustrate the power of the framework, we analyze seismic data acquired during the June 2017 Nuugaatsiaq, Greenland landslide. We demonstrate the blind detection and recovery of the repeating precursory seismicity that was recorded before the main landslide rupture, which suggests that our approach could lead to more informative forecasting of the seismic activity in seismogenic areas.
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    Compositional heterogeneity near the base of the mantle transition zone beneath Hawaii
    (Springer Nature, 2018) Yu, Chunquan; Day, Elizabeth A.; de Hoop, Maarten V.; Campillo, Michel; Goes, Saskia; Blythe, Rachel A.; van der Hilst, Robert D.
    Global seismic discontinuities near 410 and 660 km depth in Earth’s mantle are expressions of solid-state phase transitions. These transitions modulate thermal and material fluxes across the mantle and variations in their depth are often attributed to temperature anomalies. Here we use novel seismic array analysis of SSwaves reflecting off the 410 and 660 below the Hawaiian hotspot. We find amplitude–distance trends in reflectivity that imply lateral variations in wavespeed and density contrasts across 660 for which thermodynamic modeling precludes a thermal origin. No such variations are found along the 410. The inferred 660 contrasts can be explained by mantle composition varying from average (pyrolitic) mantle beneath Hawaii to a mixture with more melt-depleted harzburgite southeast of the hotspot. Such compositional segregation was predicted, from petrological and numerical convection studies, to occur near hot deep mantle upwellings like the one often invoked to cause volcanic activity on Hawaii.
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    Mapping Mantle Transition Zone Discontinuities Beneath the Central Pacific With Array Processing ofﾠSSﾠPrecursors
    (Wiley, 2017) Yu, Chunquan; Day, Elizabeth A.; de Hoop, Maarten V.; Campillo, Michel; van der Hilst, Robert D.
    We image mantle transition zone (MTZ) discontinuities beneath the Central Pacific using ~120,000 broadband SS waveforms. With a wave packet‐based array processing technique (curvelet transform), we improve the signal‐to‐noise ratio of SS precursors and remove interfering phases, so that precursors can be identified and measured over a larger distance range. Removal of interfering phases reveals possible phase shifts in the underside reflection at the 660, that is, S660S, which if ignored could lead to biased discontinuity depth estimates. The combination of data quantity and improved quality allows improved imaging and uncertainty estimation. Time to depth conversions after corrections for bathymetry, crustal thickness, and tomographically inferred mantle heterogeneity show that the mean depths of 410 and 660 beneath the Central Pacific are 420 ± 3 km and 659 ± 4 km, respectively. The mean MTZ thickness (239 ± 2 km) is close to global estimates and suggests an adiabatic mantle temperature of ~1,400°C for the Central Pacific. Depth variations of the 410 and 660 appear to be relatively small, with peak‐to‐peak amplitudes of the order of 10–15 km. The 410 and 660 are weakly anticorrelated, and MTZ is thinner beneath Hawaii and to the north and east of the hotspot and thicker southwest of it. The relatively small discontinuity topography argues against the presence of large‐scale (more than 5° wide) thermal anomalies with excess temperatures over 200 K across the transition zone. The data used cannot exclude stronger thermal anomalies that are of more limited lateral extent or that are not continuous across the MTZ.