Slip distribution inversion by trans-dimensional Monte Carlo sampling: application to the 2009 L’Aquila Earthquake (Central Italy)

Non-uniform slip distribution on a fault plane from geodetic data is usually estimated in two steps. First, the geometric fault parameters are inferred by non -linear inversion assuming a uniform slip on a rectangular fault. A second analysis, based on linear inversion techniques, infers the slip distribution on an arbitrary subdivision of the fault plane into patches. Two main concerns arise. First, the fault geometry determined under the assumption of a uniform slip i s not guaranteed to properly represent the fault geometry for a spatially variable slip distribution. Moreover, an arbitrary fault subdivision into patches u nrelated to the observed data could bias the model resolution, introducing spurious features. In recent years, the availability of large coverage data, such as DInSAR images, improved mapping the coseismic displacements. The large amount of geodetic da ta from the area surrounding earthquake faults allows for improving the slip models and refining the knowledge of earthquake dynamics. Less attention has been given to the development of new inversion algorithms that can resolve the main concerns above. In particular, the question is whether the data themselves ca n constrain the slip model complexity, i.e., the unknown number and distribution of the fault patches needed to fit the observations. The reversible jump Mar kov chain Monte Carlo (RJMCMC) algorithm has been recently introduced in the geosciences to solve a variety of non linear inverse problems. RJMCMC combines a classical Markov chain Monte Carlo method with the ability to shift between models with a different number of unknowns. A posterior probability distribution of the num ber of unknowns is obtained at the end of the Markov chain, so that the model resolution is determined by the observed data. In this study, we apply a RJMCMC method to the Mw 6.3 L’Aquila earthquake that occurred on April 6th 2009 in Central Italy. Three DInSAR images, mapping the c oseismic displacement, are inverted to constrain not only the slip distribution but also the number of unknowns (i.e., the number of fault patches) and the ge ometry of non-rectangular patches

Two unusual silicoflagellate double skeletons

A study of silicoflagellate double skeletons revealed two unusual doublets that are illustrated and discussed here. One of these comprises two ten-sided Octactis skeletons that appear to form a doublet, but both in the same (apical) orientation. The other specimen is a double skeleton of Dictyocha that is slightly disarticulated, with a third, less robust skeleton in between. These unusual double skeletons suggest that there is much more to be learned about the formation of silicoflagellate skeletons and the reproductive processes in this protist grou

M-sequence geomagnetic polarity time scale (MHTC12) that steadies global spreading rates and incorporates astrochronology constraints

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): B06104, doi:10.1029/2012JB009260.Geomagnetic polarity time scales (GPTSs) have been constructed by interpolating between dated marine magnetic anomalies assuming uniformly varying spreading rates. A strategy to obtain an optimal GPTS is to minimize spreading rate fluctuations in many ridge systems; however, this has been possible only for a few spreading centers. We describe here a Monte Carlo sampling method that overcomes this limitation and improves GPTS accuracy by incorporating information on polarity chron durations estimated from astrochronology. The sampling generates a large ensemble of GPTSs that simultaneously agree with radiometric age constraints, minimize the global variation in spreading rates, and fit polarity chron durations estimated by astrochronology. A key feature is the inclusion and propagation of data uncertainties, which weigh how each piece of information affects the resulting time scale. The average of the sampled ensemble gives a reference GPTS, and the variance of the ensemble measures the time scale uncertainty. We apply the method to construct MHTC12, an improved version of the M-sequence GPTS (Late Jurassic-Early Cretaceous, ~160–120 Ma). This GPTS minimizes the variation in spreading rates in a global data set of magnetic lineations from the Western Pacific, North Atlantic, and Indian Ocean NW of Australia, and it also accounts for the duration of five polarity chrons established from astrochronology (CM0r through CM3r). This GPTS can be updated by repeating the Monte Carlo sampling with additional data that may become available in the future.A.M. and J.H. were supported by NSF grant OCE 09–26306, M.T. was supported by a Woods Hole Oceanographic Institution postdoctoral scholarship, and J.E.T.C. was supported by NSF grant OCE 09–60999.2012-12-3

The exploration of eastern Mediterranean deep hypersaline anoxic basins with MODUS: a significant example of technology spin-off from the Geostar Program

A significant example of technological spin-off from the GEOSTAR project is represented by the special-purpose instrumented module, based on the deep-sea ROV MODUS, which was developed in the framework of the EU-sponsored project BIODEEP. The goal to be achieved has been defined as the exploration, through real-time video images, measurements and accurate video-guided sampling, of the deep hypersaline anoxic basins of the eastern Mediterranean Sea at water depths well exceeding 3000 meters. Due to their peculiar characteristics, these basins are one of the most extreme environments on Earth and represent a site of utmost interest for their geochemical and microbial resources. The paper presents the strategies and the main results achieved during the two cruises carried out within the BIODEEP project

Evidence for a possible life-cycle association between Syracosphaera protrudens (heterococcolithophore) and Syracosphaera pulchra HOL pirus -type (holococcolithophore)

Abstract. An apparently unambiguous combination coccosphere from the Eastern Mediterranean (Aegean Sea, Greece) is documented involving Syracosphaera protrudens Okada & McIntyre, 1977 and Syracosphaera pulchra Lohmann, 1902 HOL pirus-type. This finding is difficult to interpret in terms of the current understanding of Syracosphaera taxonomy and adds evidence to the hypothesis of a distinctly complex Syracosphaera pulchra life cycle

Electrical anisotropy due to gas hydrate-filled fractures

In 2006, the Indian National Gas Hydrate Program Expedition 01, or NGHP-01, discovered gas hydrate as fill in near-vertical fractures in unconsolidated sediments at several drilling sites on the Indian continental margins. These gas hydrate-filled fractures were identified on logging-while-drilling resistivity images. The gas hydrate-filled fracture intervals coincide with high measured resistivity at the NGHP-01 sites. High measured resistivity translates into high hydrate saturations via Archie's equation; however, these high saturations contradict lower gas hydrate saturations determined from pressure core and chlorinity measurements. Also, in intervals with near-vertical gas hydrate-filled fractures, there is considerable separation between phase shift and attenuation resistivity logs, with 2-MHz resistivity measurements being significantly higher than 400-kHz resistivity measurements. We modeled the sensitivity of the propagation resistivity measurements in the gas hydrate-filled fracture intervals at NGHP-01 Sites 5 and 10. Near-vertical hydrate-filled fractures can cause the abnormally high resistivity measurements in vertical holes due to electrical anisotropy. The model suggests the gas hydrate saturations in situ are usually significantly lower than those calculated from Archie's equation. In addition, these modeled gas hydrate saturations generally agree with the lower gas hydrate saturations obtained from pressure core and chlorinity measurements at NGHP-01 Sites 5 and 10

Particle fluxes in the deep Eastern Mediterranean basins: the role of ocean vertical velocities

This paper analyzes the relationship between deep sedimentary fluxes and ocean current vertical velocities in an offshore area of the Ionian Sea, the deepest basin of the Eastern Mediterranean Sea. Sediment trap data are collected at 500 m and 2800 m depth in two successive moorings covering the period September 1999–May 2001. A tight coupling is observed between the upper and deep traps and the estimated particle sinking rates are more than 200 m day−1. The current vertical velocity field is computed from a 1/16°×1/16° Ocean General Circulation Model simulation and from the wind stress curl. Current vertical velocities are larger and more variable than Ekman vertical velocities, yet the general patterns are alike. Current vertical velocities are generally smaller than 1 m day−1: we therefore exclude a direct effect of downward velocities in determining high sedimentation rates. However we find that upward velocities in the subsurface layers of the water column are positively correlated with deep particle fluxes. We thus hypothesize that upwelling would produce an increase in upper ocean nutrient levels – thus stimulating primary production and grazing – a few weeks before an enhanced vertical flux is found in the sediment traps. High particle sedimentation rates may be attained by means of rapidly sinking fecal pellets produced by gelatinous macro-zooplankton. Other sedimentation mechanisms, such as dust deposition, are also considered in explaining large pulses of deep particle fluxes. The fast sinking rates estimated in this study might be an evidence of the efficiency of the biological pump in sequestering organic carbon from the surface layers of the deep Eastern Mediterranean basins

Cooperative Localization Enhancement through GNSS Raw Data in Vehicular Networks

The evolution and integration of communication networks and positioning technologies are evolving at a fast pace in the framework of vehicular systems. The mutual dependency of such two capabilities can enable several new cooperative paradigms, whose adoption is however slowed down by the lack of suitable open protocols, especially related to the positioning and navigation domain. In light of this, the paper introduces a novel vehicular message type, namely the Cooperative Enhancement Message (CEM), and an associated open protocol to enable the sharing of Global Navigation Satellite Systems (GNSS) raw measurements among connected vehicles. The proposed CEM aims at extending existent approaches such as Cooperative Awareness Messages (CAM) and Collective Perception Messages (CPM) by complementing their paradigms with a cooperative enhancement of the localization accuracy, precision, and integrity proposed by state-of-the-art solutions. Besides the definition of CEMs and a related protocol, a validation of the approach is proposed through a novel simulation framework. A preliminary analysis of the network performance is presented in the case where CEM and CAM transmissions coexist and are concurrently used to support cooperative vehicle applications