Jason D. Chaytor

Bio: Jason D. Chaytor is an academic researcher from United States Geological Survey. The author has contributed to research in topics: Submarine landslide & Landslide. The author has an hindex of 23, co-authored 63 publications receiving 1869 citations. Previous affiliations of Jason D. Chaytor include University of New Hampshire & Woods Hole Oceanographic Institution.

Submarine Mass Movements and Their Consequences

Abstract: Submarine mass movements represent major offshore geohazards due to their destructive and tsunami-generation potential. This potential poses a threat to human life as well as to coastal, near shore and offshore engineering structures. Recent examples of catastrophic submarine landslide events that affected human populations (including tsunamis) are numerous; e.g., Nice airport in 1979 (Dan et al. 2007), Finneidfjord in 1996 (e.g., L’Heureux et al., this volume, Steiner et al., this volume), Papua-New Guinea in 1998 (Tappin et al. 2001), Stromboli in 2002 (Chiocci et al. 2008), and the 2006 and 2009 failures in the submarine cable network around Taiwan (Hsu et al. 2008). The Great East Japan Earthquake of March 2011 also generated submarine landslides that may have amplified effects of the devastating tsunami as shown in Fryer et al. (2004). Given that 30% of the World’s population lives within 60 km of the coast, the hazard posed by submarine landslides is expected to grow as global sea level rises. In addition, the deposits resulting from such processes provide-various types of constraints to offshore development (Shipp et al. 2004), and have significant implications for non-renewable energy resource exploration and production (Weimer and Shipp 2004; Beaubouef and Abreu 2010).

Late Holocene Rupture of the Northern San Andreas Fault and Possible Stress Linkage to the Cascadia Subduction Zone

Abstract: We relate the late Holocene northern San Andreas fault (NSAF) paleo- seismic history developed using marine sediment cores along the northern California continental margin to a similar dataset of cores collected along the Cascadia margin, including channels from Barclay Canyon off Vancouver Island to just north of Mon- terey Bay. Stratigraphic correlation and evidence of synchronous triggering imply earthquake origin, and both temporal records are compatible with onshore paleoseis- mic data. In order to make comparisons between the temporal earthquake records from the NSAF and Cascadia, we refine correlations of southern Cascadia great earth- quakes, including the land paleoseismic record. Along the NSAF during the last ∼2800 yr, 15 turbidites, including one likely from the great 1906 earthquake, establish an average repeat time of ∼200 yr, similar to the onshore value of ∼240 yr. The combined land and marine paleoseismic record from the southern Cascadia subduction zone includes a similar number of events during the same period. While the average recurrence interval for full-margin Cascadia events is ∼520 yr, the southern Cascadia margin has a repeat time of ∼220 yr, similar to that of the NSAF. Thirteen of the 15 NSAF events were preceded by Cascadia events by ∼0-80 yr, averaging 25-45 yr (as compared to ∼80-400 yr by which Cascadia events follow the NSAF). Based on the temporal association, we model the coseismic and cumulative post- seismic deformation from great Cascadia megathrust events and compute related stress changes along the NSAF in order to test the possibility that Cascadia earth- quakes triggered the penultimate, and perhaps other, NSAF events. The Coulomb fail- ure stress (CFS) resulting from viscous deformation related to a Cascadia earthquake over ∼60 yr does not contribute significantly to the total CFS on the NSAF. However, the coseismic deformation increases CFS on the northern San Andreas fault (NSAF )b y up to about 9 bars offshore of Point Delgada, most likely enough to trigger that fault to fail in north-to-south propagating ruptures.

Geologically current plate motions

Abstract: SUMMARY We describe best-fitting angular velocities and MORVEL, a new closure-enforced set of angular velocities for the geologically current motions of 25 tectonic plates that collectively occupy 97 per cent of Earth's surface. Seafloor spreading rates and fault azimuths are used to determine the motions of 19 plates bordered by mid-ocean ridges, including all the major plates. Six smaller plates with little or no connection to the mid-ocean ridges are linked to MORVEL with GPS station velocities and azimuthal data. By design, almost no kinematic information is exchanged between the geologically determined and geodetically constrained subsets of the global circuit—MORVEL thus averages motion over geological intervals for all the major plates. Plate geometry changes relative to NUVEL-1A include the incorporation of Nubia, Lwandle and Somalia plates for the former Africa plate, Capricorn, Australia and Macquarie plates for the former Australia plate, and Sur and South America plates for the former South America plate. MORVEL also includes Amur, Philippine Sea, Sundaland and Yangtze plates, making it more useful than NUVEL-1A for studies of deformation in Asia and the western Pacific. Seafloor spreading rates are estimated over the past 0.78 Myr for intermediate and fast spreading centres and since 3.16 Ma for slow and ultraslow spreading centres. Rates are adjusted downward by 0.6–2.6 mm yr−1 to compensate for the several kilometre width of magnetic reversal zones. Nearly all the NUVEL-1A angular velocities differ significantly from the MORVEL angular velocities. The many new data, revised plate geometries, and correction for outward displacement thus significantly modify our knowledge of geologically current plate motions. MORVEL indicates significantly slower 0.78-Myr-average motion across the Nazca–Antarctic and Nazca–Pacific boundaries than does NUVEL-1A, consistent with a progressive slowdown in the eastward component of Nazca plate motion since 3.16 Ma. It also indicates that motions across the Caribbean–North America and Caribbean–South America plate boundaries are twice as fast as given by NUVEL-1A. Summed, least-squares differences between angular velocities estimated from GPS and those for MORVEL, NUVEL-1 and NUVEL-1A are, respectively, 260 per cent larger for NUVEL-1 and 50 per cent larger for NUVEL-1A than for MORVEL, suggesting that MORVEL more accurately describes historically current plate motions. Significant differences between geological and GPS estimates of Nazca plate motion and Arabia–Eurasia and India–Eurasia motion are reduced but not eliminated when using MORVEL instead of NUVEL-1A, possibly indicating that changes have occurred in those plate motions since 3.16 Ma. The MORVEL and GPS estimates of Pacific–North America plate motion in western North America differ by only 2.6 ± 1.7 mm yr−1, ≈25 per cent smaller than for NUVEL-1A. The remaining difference for this plate pair, assuming there are no unrecognized systematic errors and no measurable change in Pacific–North America motion over the past 1–3 Myr, indicates deformation of one or more plates in the global circuit. Tests for closure of six three-plate circuits indicate that two, Pacific–Cocos–Nazca and Sur–Nubia–Antarctic, fail closure, with respective linear velocities of non-closure of 14 ± 5 and 3 ± 1 mm yr−1 (95 per cent confidence limits) at their triple junctions. We conclude that the rigid plate approximation continues to be tremendously useful, but—absent any unrecognized systematic errors—the plates deform measurably, possibly by thermal contraction and wide plate boundaries with deformation rates near or beneath the level of noise in plate kinematic data.

Subaqueous sediment density flows: Depositional processes and deposit types

Abstract: Submarine sediment density flows are one of the most important processes for moving sediment across our planet, yet they are extremely difficult to monitor directly. The speed of long run-out submarine density flows has been measured directly in just five locations worldwide and their sediment concentration has never been measured directly. The only record of most density flows is their sediment deposit. This article summarizes the processes by which density flows deposit sediment and proposes a new single classification for the resulting types of deposit. Colloidal properties of fine cohesive mud ensure that mud deposition is complex, and large volumes of mud can sometimes pond or drain-back for long distances into basinal lows. Deposition of ungraded mud (TE-3) most probably finally results from en masse consolidation in relatively thin and dense flows, although initial size sorting of mud indicates earlier stages of dilute and expanded flow. Graded mud (TE-2) and finely laminated mud (TE-1) most probably result from floc settling at lower mud concentrations. Grain-size breaks beneath mud intervals are commonplace, and record bypass of intermediate grain sizes due to colloidal mud behaviour. Planar-laminated (TD) and ripple cross-laminated (TC) non-cohesive silt or fine sand is deposited by dilute flow, and the external deposit shape is consistent with previous models of spatial decelerating (dissipative) dilute flow. A grain-size break beneath the ripple cross-laminated (TC) interval is common, and records a period of sediment reworking (sometimes into dunes) or bypass. Finely planar-laminated sand can be deposited by low-amplitude bed waves in dilute flow (TB-1), but it is most likely to be deposited mainly by high-concentration near-bed layers beneath high-density flows (TB-2). More widely spaced planar lamination (TB-3) occurs beneath massive clean sand (TA), and is also formed by high-density turbidity currents. High-density turbidite deposits (TA, TB-2 and TB-3) have a tabular shape consistent with hindered settling, and are typically overlain by a more extensive drape of low-density turbidite (TD and TC,). This core and drape shape suggests that events sometimes comprise two distinct flow components. Massive clean sand is less commonly deposited en masse by liquefied debris flow (DCS), in which case the clean sand is ungraded or has a patchy grain-size texture. Clean-sand debrites can extend for several tens of kilometres before pinching out abruptly. Up-current transitions suggest that clean-sand debris flows sometimes form via transformation from high-density turbidity currents. Cohesive debris flows can deposit three types of ungraded muddy sand that may contain clasts. Thick cohesive debrites tend to occur in more proximal settings and extend from an initial slope failure. Thinner and highly mobile low-strength cohesive debris flows produce extensive deposits restricted to distal areas. These low-strength debris flows may contain clasts and travel long distances (DM-2), or result from more local flow transformation due to turbulence damping by cohesive mud (DM-1). Mapping of individual flow deposits (beds) emphasizes how a single event can contain several flow types, with transformations between flow types. Flow transformation may be from dilute to dense flow, as well as from dense to dilute flow. Flow state, deposit type and flow transformation are strongly dependent on the volume fraction of cohesive fine mud within a flow. Recent field observations show significant deviations from previous widely cited models, and many hypotheses linking flow type to deposit type are poorly tested. There is much still to learn about these remarkable flows.

State of science: mental workload in ergonomics

Abstract: Mental workload (MWL) is one of the most widely used concepts in ergonomics and human factors and represents a topic of increasing importance. Since modern technology in many working environments imposes ever more cognitive demands upon operators while physical demands diminish, understanding how MWL impinges on performance is increasingly critical. Yet, MWL is also one of the most nebulous concepts, with numerous definitions and dimensions associated with it. Moreover, MWL research has had a tendency to focus on complex, often safety-critical systems (e.g. transport, process control). Here we provide a general overview of the current state of affairs regarding the understanding, measurement and application of MWL in the design of complex systems over the last three decades. We conclude by discussing contemporary challenges for applied research, such as the interaction between cognitive workload and physical workload, and the quantification of workload ‘redlines’ which specify when operators are approachi...