Ongoing oroclinal bending in the Cascadia forearc and its relation to concave-outboard plate margin geometry

The concave-inboard (concave toward the overriding plate) geometry of most convergent margins is considered a natural consequence of the depression of the edge of a thin spherical cap, whereas concave-outboard margin segments commonly form around indenters on the subducting plate. At the Cascadia subduction zone, the apex of a > 500-km-long concave-outboard bend in the trench presently shows no obvious subduction of an indenter, but does coincide with the axis of an outboard-facing concavity in upper-plate rocks arched around the Olympic Peninsula in northwestern Washington State, USA. Here we synthesize paleomagnetic and structural data together with new analyses of Global Navigation Satellite System data to show that the upper plate at Cascadia has been folded from the Miocene to the present into an orocline with an axial trace that bisects the Olympic Peninsula. The processes that accommodate bending, which we suggest include (1) folding by flexural slip on the orocline limbs and (2) shortening, uplift, and escape within the core of the fold at the Olympic Mountains, have the combined result of relative motion of the forearc towards the arc at the core of the orocline, and sustained opposing rotations of the upper plate on the orocline limbs. We propose that oroclinal bending is promoted and maintained by along-strike variations in plate-boundary tractions resulting from the geometry of the plate interface at depth and suggest that these processes can contribute to the development of concave-outboard margins without the need for a subducting indenter

IODP workshop: Core-Log Seismic Investigation at Sea – Integrating legacy data to address outstanding research questions in the Nankai Trough Seismogenic Zone Experiment

The first International Ocean Discovery Program (IODP) Core-Log-Seismic Integration at Sea (CLSI@Sea) workshop, held in January–February 2018, brought together an international, multidisciplinary team of 14 early-career scientists and a group of scientific mentors specialized in subduction zone processes at the Nankai Trough, one of the Earth's most active plate-subduction zones located off the southwestern coast of Japan. The goal of the workshop was to leverage existing core, log, and seismic data previously acquired during the IODP's Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), to address the role of the deformation front of the Nankai accretionary prism in tsunamigenic earthquakes and slow slip in the shallow portion of the subduction interface. The CLSI@Sea workshop was organized onboard the D/V Chikyu concurrently with IODP Expedition 380, allowing workshop participants to interact with expedition scientists installing a long-term borehole monitoring system (LTBMS) at a site where the workshop's research was focused. Sedimentary cores from across the deformation front were brought onboard Chikyu, where they were made available for new description, sampling, and analysis. Logging data, drilling parameters, and seismic data were also available for investigation by workshop participants, who were granted access to Chikyu laboratory facilities and software to perform analyses at sea.Multi-thematic presentations facilitated knowledge transfer between the participants across field areas, and highlighted the value of multi-disciplinary collaboration that integrates processes across different spatiotemporal scales. The workshop resulted in the synthesis of existing geophysical, geologic, and geochemical data spanning IODP Sites C0006, C0007, C0011 and C0012 in the NanTroSEIZE area, the identification of key outstanding research questions in the field of shallow subduction zone seismogenesis, and fostered collaborative and individual research plans integrating new data analysis techniques and multidisciplinary approaches.</p

Low Coseismic Friction on the Tohoku-Oki Fault Determined from Temperature Measurements

The frictional resistance on a fault during slip controls earthquake dynamics. Friction dissipates heat during an earthquake; therefore, the fault temperature after an earthquake provides insight into the level of friction. The Japan Trench Fast Drilling Project (Integrated Ocean Drilling Program Expedition 343 and 343T) installed a borehole temperature observatory 16 months after the March 2011 moment magnitude 9.0 Tohoku-Oki earthquake across the fault where slip was ~50 meters near the trench. After 9 months of operation, the complete sensor string was recovered. A 0.31°C temperature anomaly at the plate boundary fault corresponds to 27 megajoules per square meter of dissipated energy during the earthquake. The resulting apparent friction coefficient of 0.08 is considerably smaller than static values for most rocks

Ongoing oroclinal bending in the Cascadia forearc and its relation to concave-outboard plate margin geometry

The concave-inboard (concave toward the overriding plate) geometry of most convergent margins is considered a natural consequence of the depression of the edge of a thin spherical cap, whereas concave-outboard margin segments commonly form around indenters on the subducting plate. At the Cascadia subduction zone, the apex of a &gt; 500-km-long concave-outboard bend in the trench presently shows no obvious subduction of an indenter, but does coincide with the axis of an outboard-facing concavity in upper-plate rocks arched around the Olympic Peninsula in northwestern Washington State, USA. Here we synthesize paleomagnetic and structural data together with new analyses of Global Navigation Satellite System data to show that the upper plate at Cascadia has been folded from the Miocene to the present into an orocline with an axial trace that bisects the Olympic Peninsula. The processes that accommodate bending, which we suggest include (1) folding by flexural slip on the orocline limbs and (2) shortening, uplift, and escape within the core of the fold at the Olympic Mountains, have the combined result of relative motion of the forearc towards the arc at the core of the orocline, and sustained opposing rotations of the upper plate on the orocline limbs. We propose that oroclinal bending is promoted and maintained by along-strike variations in plate-boundary tractions resulting from the geometry of the plate interface at depth and suggest that these processes can contribute to the development of concave-outboard margins without the need for a subducting indenter

Internal structure of the shallow plate boundary slip zone for the 2011 Tohoku-Oki Earthquake sampled during the Japan Trench Fast Drilling Project (JFAST)

The Mw=9 2011 Tohoku-oki earthquake ruptured to the Japan Trench, with largest coseismic slip (c. 50 m) unexpectedly occurring on the shallow part of the décollement. The JFAST Project, Integrated Ocean Drilling Program (IODP) Expedition 343/343T, successfully located and sampled the shallow part of the subduction thrust shear zone (Chester et al. 2013a,b). Temperature data from a downhole observatory confirm that a thin and weak clay rich layer, identified in logging-while-drilling data and core-sample observations, is the plate boundary fault that accommodated the large slip of the earthquake rupture, as well as most of the kilometres interplate motion at the drill site (Chester et al. 2013b; Fulton et al. 2013; Lin et al. 2013; Ujiie et al. 2013). The décollement separates folded and faulted frontal prism sediments in the overriding plate from incoming flat-lying sediments along the top of the subducting plate (Chester et al., 2013b). Observed stratigraphic discontinuities at the boundary and inside the recovered fault material (Chester et al. 2013a) suggest that it contains multiple slip surfaces, many of them probably not recovered. Core analysis shows that the décollement is localized upon a strongly deformed 5≤m thick layer of smectite-rich clay, likely derived from the Paleogene to middle Miocene Pacific Plate pelagic sediments. A pervasive scaly fabric, defined by polished lustrous surfaces, commonly striated, enclosing lenses of less fissile material (phacoids), which are self-similar at scales ranging from a few micrometers to centimeters, is distributed throughout the clay. The spacing of the surfaces increase from millimeter scale near the top of the recovered core to centimetre scale, toward the lower tectonic contact, reflecting a decrease in the magnitude of shear strain. In the upper highly sheared section, one extremely narrow discontinuity, crosscuts this fabric, truncating without deflection the foliations that are not parallel across the contact. While the scaly fabric is indicative of distributed shear across the recovered interval (~1 m) the sharp discontinuity, resulted from localized deformation and similar to those observed at coseismic slip rates in friction experiments, could record seismic slip although not necessarily that of the Tohoku-Oki earthquak

Inattention, hyperactivity, oppositional-defiant symptoms and school failure Desatenção, hiperatividade, sintomas de oposição e desafio e fracasso escolar

BACKGROUND: Attention-deficit hyperactivity disorder (ADHD) is associated with school failure. Inattention has been mainly implicated for this association. Oppositional-defiant disorder's (ODD) impact on academic performance remains controversial, because of the high comorbidity between ODD and ADHD. OBJECTIVE: To understand the role of inattention (IN), hyperactivity (H/I) and ODD in school failure. METHOD: Parents and teachers filled out SNAP-IV questionnaires for 241 / 6th grade students. The associations of the scores of oppositional-defiant (OP), H/I and IN symptoms with school year failure were calculated. RESULTS: IN was strongly correlated with school failure. H/I and OP were not associated with school failure, when controlled for IN. CONCLUSION: OP and H/I symptoms do not play an important role in school failure, when controlled for IN symptoms. Our study supports the cross-cultural role of IN as a major predictor of school failure.<br>Transtorno do déficit de atenção e hiperatividade (TDAH) está fortemente correlacionado a fracasso escolar. Desatenção (DA) parece ser primordialmente responsável por essa associação. A influência de transtorno desafiador de oposicão (TDO) sobre o desempenho acadêmico continua a ser controversa, principalmente devido à alta comorbidade entre TDO e TDAH. OBJETIVO: Entender melhor o papel da DA, hiperatividade/impulsividade (H/I) e sintomas opositivo-desafiadores (OP) no fracasso escolar. MÉTODO: Duzentos e quarenta e um estudantes da 6ª série foram avaliados com os questionários de Swanson, Nolan e Pelham (SNAP-IV), preenchidos pelos pais e professores. As associações entre as sub-escalas de OP, H/I e DA, com o número de notas "I" ("insuficiente") e com reprovação escolar foram calculadas. RESULTADOS: Sintomas OP não foram correlacionados com o número de notas "I", após o controle para a sua associação com H/I e DA. DA se associou com fracasso escolar. H/I não se correlacionou com fracasso escolar, uma vez controlada a sua associação com DA. CONCLUSÃO: OP e H/I não exercem papel importante no fracasso escolar, uma vez controladas as suas associações com DA. Esse estudo ressalta, em amostra brasileira, o papel transcultural da DA como ameaça ao bom desempenho escolar. A associação entre transtornos do aprendizado e sintomas de DA precisa ser mais extensamente investigada