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Lallemand, Serge
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Lallemand, Serge
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- PublicationOpen AccessRelation between subduction megathrust earthquakes, trench sediment thickness and upper plate strain(2012)
; ; ; ; ; ;Heuret, A.; Dipartimento Scienze Geologiche, Università "Roma TRE", Rome, Italy ;Conrad, C. P.; Dept. Geology & Geophysics, Univ. Hawaii at Manoa, Honolulu, Hawaii, USA ;Funiciello, F.; Dipartimento Scienze Geologiche, Università "Roma TRE", Rome, Italy ;Lallemand, S.; Géosciences Montpellier, CNRS, Montpellier 2 University, France ;Sandri, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ; ; ; Giant earthquake (moment magnitude Mw >=8.5) forecasts for subduction zones have been empirically related to both tectonic stresses and geometrical irregularities along the subduction interface. Both of these controls have been suggested as able to tune the ability of rupture to propagate laterally and, in turn, exert an important control on giant earthquake generation. Here we test these hypotheses, and their combined influence, by compiling a dataset of trench fill thickness (a proxy for smoothing of subducting plate relief by sediment input into the subduction channel) and upper plate strain (a proxy for the tectonic stresses applied to the subduction interface) for 44 segments of the global subduction network. We statistically compare relationships between upper plate strain, trench sediment thickness and maximal earthquake magnitude. We find that the combination of both large trench fill (≥1 km) and neutral upper plate strain explains spatial patterns of giant earthquake occurrence to a statistically significant degree. In fact, the concert of these two factors is more highly correlated with giant earthquake occurrence than either factor on its own. Less frequent giant earthquakes of lower magnitude are also possible at subduction zones with thinner trench fill and compressive upper plate strain. Extensional upper plate strain and trench fill < 0.5 km appear to be unfavorable conditions, as giant earthquakes have not been observed in these geodynamical environments during the last 111 years.113 270 - PublicationRestrictedPhysical characteristics of subduction interface type seismogenic zones revisited(2011-01-19)
; ; ; ; ; ;Heuret, A.; Univ Roma Tre ;Lallemand, S.; Univ Montpellier ;Funiciello, F.; Univ Roma Tre ;Piromallo, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Faccenna, C.; Univ Roma Tre; ; ; ; Based on global earthquake catalogs, the hypocenters, nodal planes, and seismic moments of worldwide subduction plate interface earthquakes were extracted for the period between 1900 and 2007. Assuming that the seismogenic zone coincides with the distribution of 5.5 ≤ M < 7 earthquakes, the subduction interface seismogenic zones were mapped for 80% of the trench systems and characterized with geometrical and mechanical parameters. Using this database, correlations were isolated between significant parameters to identify cause-effect relationships. Empirical laws obtained in previous studies were revisited in light of this more complete, accurate, and uniform description of the subduction interface seismogenic zone. The seismogenic zone was usually found to end in a fore-arc mantle, rather than at a Moho depth. The subduction velocity was the first-order controlling parameter for variations in the physical characteristics of plate interfaces, determining both the geometry and mechanical behavior. As such, the fast subduction zones and cold slabs were associated with large and steep plate interfaces, which, in turn, had large seismic rates. The subduction velocity could not account for the potential earthquake magnitude diversity that was observed along the trenches. Events with Mw ≥ 8.5 preferentially occurred in the vicinity of slab edges, where the upper plate was continental and the back-arc strain was neutral. This observation was interpreted in terms of compressive normal stresses along the plate interface. Large lateral ruptures should be promoted in neutral subduction zones due to moderate compressive stresses along the plate interface that allow the rupture to propagate laterally.405 27 - PublicationOpen AccessMachine Learning can predict the timing and size of analog earthquakes(2019)
; ; ; ; ; ; ; ; ; ; ; ; ; Despite the growing spatio‐temporal density of geophysical observations at subduction zones, predicting the timing and size of future earthquakes remains a challenge. Here, we simulate multiple seismic cycles in a laboratory‐scale subduction zone. The model creates both partial and full margin ruptures, simulating magnitude Mw 6.2‐8.3 earthquakes with a coefficient of variation in recurrence intervals of 0.5, similar to real subduction zones. We show that the common procedure of estimating the next earthquake size from slip‐deficit is unreliable. On the contrary, Machine Learning predicts well the timing and size of laboratory earthquakes by reconstructing and properly interpreting the spatio‐temporally complex loading history of the system. These results promise substantial progress in real earthquake forecasting, as they suggest that the complex motion recorded by geodesists at subduction zones might be diagnostic of earthquake imminence.273 210 - PublicationRestrictedSubduction-triggered magmatic pulses: A new class of plumes?(2010-09-20)
; ; ; ; ; ; ;Faccenna, C.; Univ Roma TRE, Dip Sci Geol, Rome, Italy ;Becker, T. W.; Univ Calif Los Angeles, Dept Earth Sci, Los Angeles, CA USA ;Lallemand, S.; Univ Montpellier 2, CNRS, Lab Geosci Montpellier, F-34095 Montpellier 5, France ;Lagabrielle, Y.; Univ Montpellier 2, CNRS, Lab Geosci Montpellier, F-34095 Montpellier 5, France ;Funiciello, F.; Univ Roma TRE, Dip Sci Geol, Rome, Italy ;Piromallo, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; ; ; ; A variety of atypical plume-like structures and focused upwellings that are not rooted in the lower mantle have recently been discussed, and seismological imaging has shown ubiquitous small-scale convection in the uppermost mantle in regions such as the Mediterranean region, the western US, and around the western Pacific. We argue that the three-dimensional return flow and slab fragmentation associated with complex oceanic subduction trajectories within the upper mantle can generate focused upwellings and that these may play a significant role in regional tectonics. The testable surface expressions of this process are the outsidearc alkaline volcanism, topographic swell, and low-velocity seismic anomalies associated with partial melt. Using three-dimensional, simplified numerical subduction models, we show that focused upwellings can be generated both ahead of the slab in the back-arc region (though ~five times further inward from the trench than arc-volcanism) and around the lateral edges of the slab (in the order of 100 km away from slab edges). Vertical mass transport, and by inference the associated decompression melting, in these regions appears strongly correlated with the interplay between relative trench motion and subduction velocities. The upward flux of material from the depths is expected to be most pronounced during the first phase of slab descent into the upper mantle or during slab fragmentation. We discuss representative case histories from the Pacific and the Mediterranean where we find possible evidence for such slab-related volcanism.353 26