David Marsan

Bio: David Marsan is an academic researcher from University of Savoy. The author has contributed to research in topics: Aftershock & Induced seismicity. The author has an hindex of 33, co-authored 84 publications receiving 4120 citations. Previous affiliations of David Marsan include Pierre-and-Marie-Curie University.

Extending Earthquakes' Reach Through Cascading

Abstract: Earthquakes, whatever their size, can trigger other earthquakes. Mainshocks cause aftershocks to occur, which in turn activate their own local aftershock sequences, resulting in a cascade of triggering that extends the reach of the initial mainshock. A long-lasting difficulty is to determine which earthquakes are connected, either directly or indirectly. Here we show that this causal structure can be found probabilistically, with no a priori model nor parameterization. Large regional earthquakes are found to have a short direct influence in comparison to the overall aftershock sequence duration. Relative to these large mainshocks, small earthquakes collectively have a greater effect on triggering. Hence, cascade triggering is a key component in earthquake interactions.

Positive trend in the mean speed and deformation rate of Arctic sea ice, 1979–2007

Abstract: Using buoy data from the International Arctic Buoy Program, we found that the sea ice mean speed has substantially increased over the last 29 years (+17% per decade for winter and +85% for summer) A strong seasonal dependence of the mean speed is also revealed, with a maximum in October and a minimum in April The sea ice mean strain rate also increased significantly over the period (+51% per decade for winter and +52% for summer) We check that these increases in both sea ice mean speed and deformation rate are unlikely to be consequences of a stronger atmospheric forcing Instead, they suggest that sea ice kinematics play a fundamental role in the albedo feedback loop and sea ice decline: increasing deformation means stronger fracturing, hence more lead opening, and therefore a decreasing albedo This accelerates sea ice thinning in summer and delays refreezing in early winter, therefore decreasing the mechanical strength of the cover and allowing even more fracturing, larger drifting speed and deformation, and possibly a faster export of sea ice through the Fram Strait The September minimum sea ice extent of 2007 might be a good illustration of this interplay between sea ice deformation and sea ice shrinking, as we found that for both winter 2007 and summer 2007 exceptionally large deformation rates affected the Arctic sea ice cover

Multifractal Cascade Dynamics and Turbulent Intermittency

Abstract: Turbulent intermittency plays a fundamental role in fields ranging from combustion physics and chemical engineering to meteorology. There is a rather general agreement that multifractals are being very successful at quantifying this intermittency. However, we argue that cascade processes are the appropriate and necessary physical models to achieve dynamical modeling of turbulent intermittency. We first review some recent developments and point out new directions which overcome either completely or partially the limitations of current cascade models which are static, discrete in scale, acausal, purely phenomenological and lacking in universal features. We review the debate about universality classes for multifractal processes. Using both turbulent velocity and temperature data, we show that the latter are very well fitted by the (strong) universality, and that the recent (weak, log-Poisson) alternative is untenable for both strong and weak events. Using a continuous, space-time anisotropic framework, we th...

The long precursory phase of most large interplate earthquakes

Abstract: Many earthquakes are preceded by foreshocks. However, the mechanisms that generate foreshocks and the reason why they occur before some earthquakes and not others are unknown. Here we use seismic catalogues from the best instrumented areas of the North Pacific to analyse the foreshock sequences preceding all earthquakes there between 1999 and 2011, of magnitude larger than 6.5 and at depths shallower than 50 km. The data set comprises 31 earthquakes at plate boundaries, and 31 in plate interiors. We find that there is a remarkable contrast between the foreshock sequences of interplate compared with intraplate earthquakes. Most large earthquakes at plate interfaces in the North Pacific were preceded by accelerating seismic activity in the months to days leading up to the mainshock. In contrast, foreshocks are much less frequent in intraplate settings. We suggest that at plate boundaries, the interface between the two plates begins to slowly slip before the interface ruptures in a large earthquake. This relatively long precursory phase could help mitigate earthquake risk at plate boundaries.

Three-Dimensional Mapping of Dislocation Avalanches: Clustering and Space/Time Coupling

Abstract: There is growing evidence for the complex, intermittent, and heterogeneous character of plastic flow. Here we report a three-dimensional mapping of dislocation avalanches during creep deformation of an ice crystal, from a multiple-transducers acoustic emission analysis. Correlation analysis shows that dislocation avalanches are spatially clustered according to a fractal pattern and that the closer in time two avalanches are, the larger the probability is that they will be closer in space. Such a space/time coupling may contribute to the self-organization of the avalanches into a clustered pattern.

Precipitation downscaling under climate change: Recent developments to bridge the gap between dynamical models and the end user

Abstract: Precipitation downscaling improves the coarse resolution and poor representation of precipitation in global climate models and helps end users to assess the likely hydrological impacts of climate change. This paper integrates perspectives from meteorologists, climatologists, statisticians, and hydrologists to identify generic end user (in particular, impact modeler) needs and to discuss downscaling capabilities and gaps. End users need a reliable representation of precipitation intensities and temporal and spatial variability, as well as physical consistency, independent of region and season. In addition to presenting dynamical downscaling, we review perfect prognosis statistical downscaling, model output statistics, and weather generators, focusing on recent developments to improve the representation of space-time variability. Furthermore, evaluation techniques to assess downscaling skill are presented. Downscaling adds considerable value to projections from global climate models. Remaining gaps are uncertainties arising from sparse data; representation of extreme summer precipitation, subdaily precipitation, and full precipitation fields on fine scales; capturing changes in small-scale processes and their feedback on large scales; and errors inherited from the driving global climate model.

The Solar Wind as a Turbulence Laboratory

Abstract: In this review we will focus on a topic of fundamental importance for both plasma physics and astrophysics, namely the occurrence of large-amplitude low-frequency fluctuations of the fields that describe the plasma state. This subject will be treated within the context of the expanding solar wind and the most meaningful advances in this research field will be reported emphasizing the results obtained in the past decade or so. As a matter of fact, Ulysses’ high latitude observations and new numerical approaches to the problem, based on the dynamics of complex systems, brought new important insights which helped to better understand how turbulent fluctuations behave in the solar wind. In particular, numerical simulations within the realm of magnetohydrodynamic (MHD) turbulence theory unraveled what kind of physical mechanisms are at the basis of turbulence generation and energy transfer across the spectral domain of the fluctuations. In other words, the advances reached in these past years in the investigation of solar wind turbulence now offer a rather complete picture of the phenomenological aspect of the problem to be tentatively presented in a rather organic way.

More Evidence Linking Arctic Amplification to Extreme Weather in Mid-Latitudes

Abstract: [1] Arctic amplification (AA) – the observed enhanced warming in high northern latitudes relative to the northern hemisphere – is evident in lower-tropospheric temperatures and in 1000-to-500 hPa thicknesses. Daily fields of 500 hPa heights from the National Centers for Environmental Prediction Reanalysis are analyzed over N. America and the N. Atlantic to assess changes in north-south (Rossby) wave characteristics associated with AA and the relaxation of poleward thickness gradients. Two effects are identified that each contribute to a slower eastward progression of Rossby waves in the upper-level flow: 1) weakened zonal winds, and 2) increased wave amplitude. These effects are particularly evident in autumn and winter consistent with sea-ice loss, but are also apparent in summer, possibly related to earlier snow melt on high-latitude land. Slower progression of upper-level waves would cause associated weather patterns in mid-latitudes to be more persistent, which may lead to an increased probability of extreme weather events that result from prolonged conditions, such as drought, flooding, cold spells, and heat waves.