Slow slip source characterized by lithological and geometric heterogeneity

Slow slip events (SSEs) accommodate a significant proportion of tectonic plate motion at subduction zones, yet little is known about the faults that actually host them. The shallow depth (<2 km) of well-documented SSEs at the Hikurangi subduction zone offshore New Zealand offers a unique opportunity to link geophysical imaging of the subduction zone with direct access to incoming material that represents the megathrust fault rocks hosting slow slip. Two recent International Ocean Discovery Program Expeditions sampled this incoming material before it is entrained immediately down-dip along the shallow plate interface. Drilling results, tied to regional seismic reflection images, reveal heterogeneous lithologies with highly variable physical properties entering the SSE source region. These observations suggest that SSEs and associated slow earthquake phenomena are promoted by lithological, mechanical, and frictional heterogeneity within the fault zone, enhanced by geometric complexity associated with subduction of rough crust

Terres promises

Une quarantaine de contributions inédites composent cet ouvrage articulé autour de trois thématiques : l’histoire intérieure et extérieure des États-Unis, l’histoire des relations internationales, l’histoire contemporaine des Juifs. Sur l’Amérique du Nord (Canada et États-Unis), ce volume offre un panorama historique, de la colonisation au 11 septembre 2001. Il permet de comprendre la complexité des États-Unis actuels, à la fois dans leur relation au monde et dans les bouleversements qui touchent à leur identité au début du XXIe siècle, comme vient d’en témoigner l’élection de leur 44e président, Barack Obama. En ce qui concerne les relations internationales, outre une réflexion théorique, c’est le XXe siècle qui est interrogé, de la Seconde Guerre mondiale aux affrontements de la guerre froide et aux affaires européennes : ici encore, les sujets sont au cœur de l’actualité historiographique et politique. Enfin l’ouvrage propose, entre la Pologne et les États-Unis, entre la France et les rives de la Méditerranée, de nouveaux éclairages sur l’histoire contemporaine des Juifs : l’affaire Dreyfus, la “ francisation ” des élites à l’époque coloniale, les désillusions idéologiques, les épreuves du déracinement, de l’exil et du réenracinement dans une nouvelle patrie, et la tragédie de la Shoah. A ces trois parties s’ajoutent quelques réflexions sur les grands débats historiographiques récents. Au-delà, de leur variété, ces textes témoignent des leçons qu’André Kaspi n’a cessé de dispenser, dans le droit fil de la tradition universitaire et intellectuelle française : rigueur de la méthode et honnêteté exigeante, ampleur de la synthèse, clarté absolue de l’exposition pour une recherche historique résolument axée sur la compréhension du temps présent. Cet ouvrage se veut un hommage, en même temps qu’un signe d’amitié, adressé à l’historien par René Rémond - peu avant sa disparition -, par ses collègues et par ses élèves. Hommage d’abord à l’américaniste renommé, auteur infatigable et pédagogue inlassable, à la Sorbonne comme dans les médias; hommage au spécialiste des relations internationales, dans la lignée de ses maîtres, Pierre Renouvin et Jean-Baptiste Duroselle; hommage enfin à celui qui a fait œuvre pionnière en France dans le champ de l’histoire de la Shoah, dont il a introduit l’enseignement à l’Université.cours du Conseil scientifique de l’université Paris 1 Panthéon-Sorbonne

International ocean discovery program expedition 375 preliminary report: Hikurangi subduction margin coring and observatories unlocking the secrets of slow slip through drilling to sample and monitor the forearc and subducting plate

Slow slip events (SSEs) at the northern Hikurangi subduction margin, New Zealand, are among the best-documented shallow SSEs on Earth. International Ocean Discovery Program Expedition 375 was undertaken to investigate the processes and in situ conditions that underlie subduction zone SSEs at the northern Hikurangi Trough by (1) coring at four sites, including an active fault near the deformation front, the upper plate above the high-slip SSE sourc e region, and the incoming sedimentary succession in the Hikurangi Trough and atop the Tūranganui Knoll Seamount, and (2) installing borehole observatories in an active thrust near the deformation front and in the upper plate overlying the slow slip source region. Logging-while-drilling (LWD) data for this project were acquired as part of Expedition 372 (26 November 2017-4 January 2018; see th e Expedition 372 Preliminary Report for further details on the LWD acquisition program). Northern Hikurangi subduction margin SSEs recur every 1-2 years and thus provide an ideal opportunity to monitor deformation and associated changes in chemical and physical properties throughout the slow slip cycle. Sampling of material from the sedimentary section and oceanic basement of the subducting plate reveals the rock properties, composition, lithology, and structural character of material that is transported downdip into the SSE source region. A recent seafloor geodetic experiment raises the possibility that SSEs at northern Hikurangi may propagate all the way to the trench, indicating that the shallow thrust fault zone targeted during Expedition 375 may also lie in the SSE rupture area. Hence, sampling at this location provides insights into the composition, physical properties, and architecture of a shallow fault that may host slow slip. Expedition 375 (together with the Hikurangi subduction LWD component of Expedition 372) was designed to address three fundamental scientific objectives: (1) characterize the state and composition of the incoming plate and shallow plate boundary fault near the trench, which comprise the protolith and initial conditions for fault zone rock at greater depth and which may itself host shallow slow slip; (2) characterize material properties, thermal regime, and stress conditions in the upper plate above the core of the SSE source region; and (3) install observatories at an active thrust near the deformation front and in the upper plate above the SSE source to measure temporal variations in deformation, temperature, and fluid flow. The observatories will monitor volumetric strain (via pore pressure as a proxy) and the evolution of physical, hydrological, and chemical properties throughout the SSE cycle. Together, the coring, logging, and observatory data will test a suite of hypotheses about the fundamental mechanics and behavior of SSEs and their relationship to great earthquakes along the subduction interface

Slow slip source characterized by lithological and geometric heterogeneity

Slow slip events (SSEs) accommodate a significant proportion of tectonic plate motion at subduction zones, yet little is known about the faults that actually host them. The shallow depth (<2 km) of well-documented SSEs at the Hikurangi subduction zone offshore New Zealand offers a unique opportunity to link geophysical imaging of the subduction zone with direct access to incoming material that represents the megathrust fault rocks hosting slow slip. Two recent International Ocean Discovery Program Expeditions sampled this incoming material before it is entrained immediately down-dip along the shallow plate interface. Drilling results, tied to regional seismic reflection images, reveal heterogeneous lithologies with highly variable physical properties entering the SSE source region. These observations suggest that SSEs and associated slow earthquake phenomena are promoted by lithological, mechanical, and frictional heterogeneity within the fault zone, enhanced by geometric complexity associated with subduction of rough crust