ALBERT

Description: In plain sight: the Chesapeake Bay crater ejecta blanket Solid Earth Discussions, 4, 363-428, 2012 Author(s): D. L. Griscom The discovery nearly two decades ago of a 90 km-diameter impact crater below the lower Chesapeake Bay has gone unnoted by the general public because to date all published literature on the subject has described it as "buried". To the contrary, evidence is presented here that the so-called "upland deposits" that blanket ∼5000 km 2 of the U.S. Middle-Atlantic Coastal Plain (M-ACP) display morphologic, lithologic, and stratigraphic features consistent with their being ejecta from the 35.4 Ma Chesapeake Bay Impact Structure (CBIS) and absolutely inconsistent with the prevailing belief that they are of fluvial origin. Specifically supporting impact origin are the facts that (i) a 95 %-pure iron ore endemic to the upland deposits of southern Maryland, eastern Virginia, and the District of Columbia has previously been proven to be impactoclastic in origin, (ii) this iron ore welds together a small percentage of well-rounded quartzite pebbles and cobbles of the upland deposits into brittle sheets interpretable as "spall plates" created in the interference-zone of the CBIS impact, (iii) the predominantly non-welded upland gravels have long ago been shown to be size sorted with an extreme crater-centric gradient far too large to have been the work of rivers, but well explained as atmospheric size-sorted interference-zone ejecta, (iv) new evidence is provided here that ~60 % of the non-welded quartzite pebbles and cobbles of the (lower lying) gravel member of the upland deposits display planar fractures attributable to interference-zone tensile waves, (v) the (overlying) loam member of the upland deposits is attributable to base-surge-type deposition, (vi) several exotic clasts found in a debris flow topographically below the upland deposits can only be explained as jetting-phase crater ejecta, and (vii) an allogenic granite boulder found among the upland deposits is deduced to have been launched into space and sculpted by hypervelocity air friction during reentry. An idealized calculation of the CBIS ejecta-blanket elevation profile minutes after the impact was carried out founded on well established rules for explosion and impact-generated craters. This profile is shown here to match the volume of the upland deposits ≥170 km from the crater center. Closer to the crater, much of the "postdicted" ejecta blanket has clearly been removed by erosion. Nevertheless the Shirley and fossil-free Bacons Castle Formations, located between the upland deposits and the CBIS interior and veneering the present day surface with units ∼10–20 m deep, are respectively identified as curtain- and excavation-phase ejecta. The neritic-fossil-bearing Calvert Formation external to the crater is deduced to be of Eocene age (as opposed to early Miocene as currently believed), preserved by the armoring effects of the overlying CBIS ejecta composed of the (distal) upland deposits and the (proximal) Bacons Castle Formation. The lithofacies of the in-crater Calvert Formation can only have resulted from inward mass wasting of the postdicted ejecta blanket, vestiges of which (i.e. the Bacons Castle and Shirley Formations) still overlap the crater rim and sag into its interior, consistent with this expectation. Because there appear to be a total of ∼10 000 km 2 of CBIS ejecta lying on the present-day surface, future research should center the stratigraphic, lithologic, and petrologic properties of these ejecta versus both radial distance from the crater center (to identify ejecta from different ejection stages) and circumferentially at fixed radial distances (to detect possible anisotropies relating the impact angle and direction of approach of the impactor). The geological units described here may comprise the best preserved, and certainly the most accessible, ejecta blanket of a major crater on the Earth's surface and therefore promise to be a boon to the field of impact geology. As a corollary, a major revision of the current stratigraphic column of the M-ACP will be necessary.

Description: Effects of fire on ash thickness in a Lithuanian grassland and short-term spatio-temporal changes Solid Earth Discussions, 4, 1545-1584, 2012 Author(s): P. Pereira, A. Cerdà, X. Úbeda, J. Mataix-Solera, D. Martin, A. Jordán, and M. Burguet Ash thickness is a key variable in the protection of soil against erosion agents after planned and unplanned fires. Thicker ash provides better protection against raindrop impact and reduces the runoff response by retaining water and promoting water infiltration although little is known about the distribution and the evolution of the ash layer after the fires. Ash thickness measurements were conducted along two transects (flat and sloping areas) following a a grid experimental design. Both transects extended from the burned area into an adjacent unburned area. We analysed ash thickness evolution according to time and fire severity. In order to interpolate data with accuracy and identify the techniques with the least bias, several interpolation methods were tested in the grid plot. Overall, the fire had a low severity. The fire significantly reduced the ground cover, especially on sloping areas owing to the higher fire severity and/or less biomass previous to the fire. Ash thickness depends on fire severity and is thin where fire severity was higher and thicker in lower fire severity sites. The ash thickness decreased with time after the fire. Between 4 and 16 days after the fire, ash was transported by wind. The major reduction took place between 16 and 34 days after the fire as a result of rainfall, and was more efficient where fire severity was higher. Between 34 and 45 days after the fire no significant differences in ash thickness were identified among ash colours and only traces of the ash layer remained. The omni-directional experimental variograms shown that variable structure did not change importantly with the time, however, the most accurate interpolation methods were different highlighting the slight different patterns of ash thickness distribution with the time. The ash spatial variability increased with the time, particularly on the slope, as a result of water erosion.

Description: Application of soil quality indices to assess the status of agricultural soils irrigated with treated wastewaters Solid Earth Discussions, 4, 1485-1509, 2012 Author(s): A. Morugán-Coronado, V. Arcenegui, F. García-Orenes, J. Mataix-Solera, and J. Mataix-Beneyto The supply of water is limited in some parts of the Mediterranean region, such as southeastern Spain. The use of treated wastewater for the irrigation of agricultural soils is an alternative to using better-quality water, especially in semi-arid regions. On the other hand, this practice can modify some soil properties, change their relationships, the equilibrium reached and influence soil quality. In this work two soil quality indices were used to evaluate the effects of irrigation with treated wastewater in soils. The indices were developed studying different soil properties in undisturbed soils in SE Spain, and the relationships between soil parameters were established using multiple linear regressions. This study was carried out in three areas of Alicante Province (SE Spain) irrigated with wastewater, including four study sites. The results showed slight changes in some soil properties as a consequence of irrigation with wastewater, the obtained levels not being dangerous for agricultural soils, and in some cases they could be considered as positive from an agronomical point of view. In one of the study sites, and as a consequence of the low quality wastewater used, a relevant increase in soil organic matter content was observed, as well as modifications in most of the soil properties. The application of soil quality indices indicated that all the soils of study sites are in a state of disequilibrium regarding the relationships between properties independent of the type of water used. However, there were no relevant differences in the soil quality indices between soils irrigated with wastewater with respect to their control sites for all except one of the sites, which corresponds to the site where low quality wastewater was used.

Description: Influence of a component of solar irradiance on radon signals at 1 km depth, Gran Sasso, Italy Solid Earth Discussions, 4, 1511-1544, 2012 Author(s): G. Steinitz, O. Piatibratova, and N. Charit-Yaari Exploratory monitoring of radon is conducted at one location at the deep underground Gran Sasso National Laboratory (LNGS). Measurements (15-min resolution) are performed over a time span of ca. 600 days in the air of the surrounding calcareous country rock. Utilizing both alpha and gamma-ray detectors systematic and recurring radon signals are recorded. Two primary signal types are determined: (a) non-periodic Multi-Day (MD) signals lasting 2–10 days, and (b) Daily Radon (DR) signals – which are of a periodic nature exhibiting a primary 24-h cycle. The local ancillary environmental conditions ( P , T ) seem not to affect radon in air monitored at the site. Long term patterns of day-time measurements are different from the pattern of night-time measurements indicating a day-night modulation of gamma radiation from radon in air. The phenomenology of the MD and DR signals is similar to situations encountered at other locations where radon is monitored with a high time resolution in geogas at upper crustal levels. In accordance with recent field and experimental results it is suggested that a components of solar irradiance is affecting the radiation from radon in air, and this influence is further modulated by the diurnal rotation of Earth. The occurrence of these radon signals in the 1 km deep low radiation underground geological environment of LNGS provides new information on the time variation of the local radiation environment. The observations and results place the LNGS facility as a high priority location for performing advanced investigations of these geophysical phenomena, due to its location and its infrastructure.

Description: Seismic imaging of sandbox experiments – laboratory hardware setup and first reflection seismic sections Solid Earth Discussions, 4, 1317-1344, 2012 Author(s): C. M. Krawczyk, M.-L. Buddensiek, O. Oncken, and N. Kukowski With the study and technical development introduced here, we combine analogue sandbox simulation techniques with seismic physical modelling of sandbox models. For that purpose, we designed and developed a new mini-seismic facility for laboratory use, comprising a seismic tank, a PC-driven control unit, a positioning system, and piezo-electric transducers used here the first time in an array mode. To assess the possibilities and limits of seismic imaging of small-scale structures in sandbox models, different geometry setups were tested in the first experiments that also tested the proper functioning of the device and studied the seismo-elastic properties of the granular media used. Simple two-layer models of different materials and layer thicknesses as well as a more complex model comprising channels and shear zones were tested using different acquisition geometries and signal properties. We suggest using well sorted and well rounded grains with little surface roughness (glass beads). Source receiver-offsets less than 14 cm for imaging structures as small as 2.0–1.5 mm size have proven feasible. This is the best compromise between wide beam and high energy output, and being applicable with a consistent waveform. Resolution of the interfaces of layers of granular materials depends on the interface preparation rather than on the material itself. Flat grading of interfaces and powder coverage yields the clearest interface reflections. Finally, sandbox seismic sections provide images of very good quality showing constant thickness layers as well as predefined channel structures and fault traces from shear zones. Since these can be regarded in sandbox models as zones of decompaction, they behave as reflectors and can be imaged. The multiple-offset surveying introduced here improves the quality with respect to S/N-ratio and source signature even more; the maximum depth penetration in glass bead layers thereby amounts to 5 cm. Thus, the presented mini-seismic device is already able to resolve structures within simple models of saturated porous media, so that multiple-offset seismic imaging of shallow sandbox models, that are structurally evolving, is generally feasible.

Description: The link between great earthquakes and the subduction of oceanic fracture zones Solid Earth Discussions, 4, 1229-1280, 2012 Author(s): R. D. Müller and T. C. W. Landgrebe Giant subduction earthquakes are known to occur in areas not previously identified as prone to high seismic risk. This highlights the need to better identify subduction zone segments potentially dominated by relatively long (up to 1000 yr and more) recurrence times of giant earthquakes. We construct a model for the geometry of subduction coupling zones and combine it with global geophysical data sets to demonstrate that the occurrence of great (magnitude ≥ 8) subduction earthquakes is strongly biased towards regions associated with intersections of oceanic fracture zones and subduction zones. We use a computational recommendation technology, a type of information filtering system technique widely used in searching, sorting, classifying, and filtering very large, statistically skewed data sets on the internet, to demonstrate a robust association and rule out a random effect. Fracture zone-subduction zone intersection regions, representing only 25% of the global subduction coupling zone, are linked with 13 of the 15 largest (magnitude ( M w ≥ 8.6) and half of the 50 largest, magnitude ≥ 8.4) earthquakes. In contrast, subducting volcanic ridges and chains are only biased towards smaller earthquakes (magnitude 〈 8). The associations captured by our statistical analysis can be conceptually related to physical differences between subducting fracture zones and volcanic chains/ridges. Fracture zones are characterized by laterally continuous, uplifted ridges that represent normal ocean crust with a high degree of structural integrity, causing strong, persistent coupling in the subduction interface. Smaller volcanic ridges and chains, not have a relatively fragile heterogeneous internal structure and are separated from the underlying ocean crust by a detachment interface, resulting in weak coupling and relatively small earthquakes, explaining the observed dichotomy.

Description: Regional wave propagation using the discontinuous Galerkin method Solid Earth Discussions, 4, 1129-1164, 2012 Author(s): S. Wenk, C. Pelties, H. Igel, and M. Käser We present an application of the discontinuous Galerkin (DG) method to regional wave propagation. The method makes use of unstructured tetrahedral meshes, combined with a time integration scheme solving the arbitrary high-order derivative (ADER) Riemann problem. The ADER-DG method is high-order accurate in space and time, beneficial for reliable simulations of high-frequency wavefields over long propagation distances. Due to the ease with which tetrahedral grids can be adapted to complex geometries, undulating topography of the Earth's surface and interior interfaces can be readily implemented in the computational domain. The ADER-DG method is benchmarked for the accurate radiation of elastic waves excited by an explosive and a shear dislocation source. We compare real data measurements with synthetics of the 2009 L'Aquila event (central Italy). We take advantage of the geometrical flexibility of the approach to generate a European model composed of the 3-D EPcrust model, combined with the depth-dependent ak135 velocity model in the upper-mantle. The results confirm the applicability of the ADER-DG method for regional scale earthquake simulations, which provides an alternative to existing methodologies.

Description: Organic carbon stocks in Mediterranean soil types under different land uses (Southern Spain) Solid Earth Discussions, 4, 1095-1128, 2012 Author(s): M. Muñoz-Rojas, A. Jordán, L. M. Zavala, D. De la Rosa, S. K. Abd-Elmabod, and M. Anaya-Romero Soil C sequestration through changes in land use and management is one of the sustainable and long-term strategies to mitigate climate change. This research explores and quantifies the role of soil and land use as determinants of the ability of soils to store C along Mediterranean systems. Detailed studies of soil organic C (SOC) dynamics are necessary in order to identify factors determining fluctuations and intensity of changes. In this study, SOC contents from different soil and land use types have been investigated in Andalusia (S Spain). We have used soil information from different databases, as well as land use digital maps, climate databases and digital elevation models. The average SOC content for each soil control section (0–25, 25–50 and 50–75 cm) was determined and SOC stocks were calculated for each combination of soil and land use type, using soil and land cover maps. The total organic C stock in soils of Andalusia is 415 Tg for the upper 75 cm, with average values ranging from 15.9 Mg C ha −1 (Solonchaks under "arable land") to 107.6 Mg C ha −1 (Fluvisols from "wetlands"). Up to 55% of SOC accumulates in the top 25 cm of soil (229.7 Tg). This research constitutes a preliminary assessment for modelling SOC stock under scenarios of land use and climate change.

Description: Dynamics of interplate domain in subduction zones: influence of rheological parameters and subducting plate age Solid Earth Discussions, 4, 943-992, 2012 Author(s): D. Arcay The properties of the subduction interplate domain are likely to affect not only the seismogenic potential of the subduction area but also the overall subduction process, as it influences its viability. Numerical simulations are performed to model the long-term equilibrium state of the subduction interplate when the diving lithosphere interacts with both the overriding plate and the surrounding convective mantle. The thermomechanical model combines a non-Newtonian viscous rheology and a pseudo-brittle rheology. Rock strength here depends on depth, temperature and stress, for both oceanic crust and mantle rocks. I study the evolution through time of, on one hand, the kinematic decoupling depth, z dec and, on the other hand, of the brittle-ductile transition (BDT) depth, z BDT , simulated along the subduction interplate. The results reveal that z BDT mainly depends on the friction coefficient characterising the interplate channel and on the viscosity at the lithosphere-asthenosphere boundary. The influence of the weak material activation energy is of second order but not negligible. z BDT becomes dependent on the ductile strength increase with depth (activation volume) if the BDT occurs at the interplate deocupling depth. Regarding the interplate decoupling depth, it is basically a function of (1) mantle viscosity at asthenospheric wedge tip, (2) difference in mantle and interplate activation anergy, and (3) activation volume. Specific conditions yielding z BDT = z dec are discussed. I then present how the subducting lithosphere age affects the brittle-ductile transition depth and the kinematic decoupling depth in this model. Simulations show that a rheological model in which the respective activation energies of mantle and interplate material are too close impedes strain localization during incipient subduction of a young (20 Myr old) and soft lithosphere under a thick upper plate. Finally, both the BDT depth and the decoupling depth are a function of the subducting plate age, but are not influenced in the same fashion: cool and old subducting plates deepen the BDT but shallow the interplate decoupling depth. Even if BDT and kinematic decoupling are instrinsically related to different mechanisms of deformation, this work shows that they are able to interact closely.

Description: A critical discussion of the electromagnetic radiation (EMR) method to determine stress orientations within the crust Solid Earth Discussions, 4, 993-1024, 2012 Author(s): M. Krumbholz, M. Bock, S. Burchardt, U. Kelka, and A. Vollbrecht In recent years, the ElectroMagnetic Radiation (EMR) method has been used to detect faults and to determine main horizontal stress directions from variations in intensities and directional properties of electromagnetic emissions, which are assumed to be generated during micro-cracking. Based on a large data set taken from an area of about 250 000 km 2 in Northern Germany, Denmark, and Southern Sweden with repeated measurements at one location during a time span of about 1.5 yr, the method was systematically tested. Reproducible observations of temporary changes in the signal patterns, as well as a strongly concentric spatial pattern of the main directions of the magnetic component of the EMR point to VLF transmitters as the main source and hence raise serious concerns about the applicability of the method to determine recent crustal stresses. We conclude that the EMR method, at its current stage of development, does not allow determination of the main horizontal stress directions.

Description: Insight into collision zone dynamics from topography: numerical modelling results and observations Solid Earth Discussions, 4, 889-917, 2012 Author(s): A. D. Bottrill, J. van Hunen, and M. B. Allen Dynamic models of subduction and continental collision are used to predict dynamic topography changes on the overriding plate. The modelling results show a distinct evolution of topography on the overriding plate, during subduction, continental collision and slab break-off. A prominent topographic feature is a temporary (few Myrs) deepening in the area of the back arc-basin after initial collision. This collisional mantle dynamic basin (CMDB) is caused by slab steepening drawing material away from the base of the overriding plate. Also during this initial collision phase, surface uplift is predicted on the overriding plate between the suture zone and the CMDB, due to the subduction of buoyant continental material and its isostatic compensation. After slab detachment, redistribution of stresses and underplating of the overriding plate causes the uplift to spread further into the overriding plate. This topographic evolution fits the stratigraphy found on the overriding plate of the Arabia-Eurasia collision zone in Iran and south east Turkey. The sedimentary record from the overriding plate contains Upper Oligocene-Lower Miocene marine carbonates deposited between terrestrial clastic sedimentary rocks, in units such as the Qom Formation and its lateral equivalents. This stratigraphy shows that during the Late Oligocene-Early Miocene the surface of the overriding plate sank below sea level before rising back above sea level, without major compressional deformation recorded in the same area. This uplift and subsidence pattern correlates well with our modelled topography changes.

Description: Three-dimensional thermal structure of subduction zones: effects of obliquity and curvature Solid Earth Discussions, 4, 919-941, 2012 Author(s): A. K. Bengtson and P. E. van Keken Quantifying the precise thermal structure of subduction zones is essential for understanding the nature of metamorphic dehydration reactions, arc volcanism, and intermediate depth seismicity. High resolution two-dimensional (2-D) models have shown that the rheology of the mantle wedge plays a critical role and establishes strong temperature gradients in the slab. The influence of three-dimensional (3-D) subduction zone geometry on thermal structure is however not yet well characterized. A common assumption for 2-D models is that the cross-section is taken normal to the strike of the trench with a corresponding velocity reduction in the case of oblique subduction, rather than taken parallel to velocity. A comparison between a full 3-D Cartesian model with oblique subduction and selected 2-D cross-sections demonstrates that the trench-normal cross-section provides a better reproduction of the slab thermal structure than the velocity-parallel cross-section. An exception is found in the case of strongly curved subduction, such as in the Marianas, where strong 3-D flow in the mantle wedge is generated. In this case it is shown that the full 3-D model should be evaluated for an accurate prediction of the slab thermal structure.

Description: Subduction to the lower mantle – a comparison between geodynamic and tomographic models Solid Earth Discussions, 4, 851-887, 2012 Author(s): B. Steinberger, T. H. Torsvik, and T. W. Becker It is generally believed that subduction of lithospheric slabs is a major contribution to thermal heterogeneity in Earth's entire mantle and provides a main driving force for mantle flow. Mantle structure can, on the one hand, be inferred from plate tectonic models of subduction history and geodynamic models of mantle flow. On the other hand, seismic tomography models provide important information on mantle heterogeneity. Yet, the two kinds of models are only similar on the largest (1000s of km) scales and are quite different in their detailed structure. Here, we provide a quantitative assessment how good a fit can be currently achieved with a simple viscous flow geodynamic model. The discrepancy between geodynamic and tomography models can indicate where further model refinement could possibly yield an improved fit. Our geodynamical model is based on 300 Myr of subduction history inferred from a global plate reconstruction. Density anomalies are inserted into the upper mantle beneath subduction zones, and flow and advection of these anomalies is calculated with a spherical harmonic code for a radial viscosity structure constrained by mineral physics and surface observations. Model viscosities in the upper mantle beneath the lithosphere are ~10 20 Pas, and viscosity increases to ~10 23 Pas in the lower mantle above D". Comparison with tomography models is assessed in terms of correlation, both overall and as a function of depth and spherical harmonic degree. We find that, compared to previous geodynamic and tomography models, correlation is improved significantly, presumably because of improvements in both plate reconstructions and mantle flow computation. However, high correlation is still limited to lowest spherical harmonic degrees. An important ingredient to achieve high correlation – in particular at spherical harmonic degree two – is a basal chemical layer. Subduction shapes this layer into two rather stable hot but chemically dense "piles", corresponding to the Pacific and African Large Low Shear Velocity Provinces. Visual comparison along cross sections indicates that sinking speeds in the geodynamic model are somewhat too fast, and should be 2±0.8 cm yr −1 to achieve a better fit.

Description: Segmentation of the Izu-Bonin and Mariana plates based on the analysis of the Benioff seismicity distribution and regional tomography results Solid Earth Discussions, 4, 823-850, 2012 Author(s): K. Jaxybulatov, I. Koulakov, and N. L. Dobretsov We present a new model of P- and S-velocity anomalies in the mantle down to 1300 km depth beneath the Izu-Bonin and Mariana (IBM) arcs. This model is derived based on tomographic inversion of global travel time data from the revised ISC catalogue. The results of inversion are thoroughly verified using a series of different tests. The obtained model is generally consistent with previous studies of different authors. We also present the distribution of relocated deep events projected to the vertical surface along the IBM arc. Unexpectedly, the seismicity form elongated vertical clusters instead of horizontal zones indicating phase transitions in the slab. We propose that these vertical seismicity zones mark zones of intense deformation and boundaries between semi-autonomous segments of the subducting plate. The P- and S-seismic tomography models consistently display the slab as prominent high-velocity anomalies coinciding with the distribution of deep seismicity. Based on joint consideration of the tomography results and the seismicity distribution we propose a scenario of the subduction evolution in the IBM zone during the recent time. We can distinguish at least four segments which subduct differently. The northernmost segment of the Izu-Bonin arc has the gentlest angle of dipping which is explained by backward displacement of the trench. In the second segment, the trench stayed at the same location, and we observe the accumulation of the slab material in the transition zone and its further descending to the lower mantle. In third segment, the trench is moving forward that causes steepening of the slab. Finally, for the Mariana segment, despite the backward displacement of the arc, the subducting slab is nearly vertical. We propose that it might be due to the high density of the slab which is responsible for turning any inclined subduction to the vertical position. Between the Izu-Bonin and Mariana arcs we clearly observe a gap which is traced down to about 400 km depth.

Description: Triplicated P-wave measurements for waveform tomography of the mantle transition zone Solid Earth Discussions, 4, 783-821, 2012 Author(s): S. C. Stähler, K. Sigloch, and T. Nissen-Meyer Triplicated body waves sample the mantle transition zone more extensively than any other wave type, and interact strongly with the discontinuities at 410 km and 660 km. Since the seismograms bear a strong imprint of these geodynamically interesting features, it is highly desirable to invert them for structure of the transition zone. This has rarely been attemped, due to the mismatch between the complex and bandlimited data and the (ray-theoretical) modeling methods. Here we present a data processing and modeling strategy to harness such broadband seismograms for finite-frequency tomography. We include triplicated P-waves (epicentral distance range between 14 and 30°) across their entire broadband frequency range, for both deep and shallow sources. We show that it is possible to predict the complex sequence of arrivals in these seismograms, but only after a careful effort to estimate source time functions and other source parameters from data, variables that strongly influence the waveforms. Modeled and observed waveforms then yield decent cross-correlation fits, from which we measure finite-frequency traveltime anomalies. We discuss two such data sets, for North America and Europe, and conclude that their signal quality and azimuthal coverage should be adequate for tomographic inversion. In order to compute sensitivity kernels at the pertinent high body-wave frequencies, we use fully numerical forward modelling of the seismic wavefield through a spherically symmetric earth.

Description: Using open sidewalls for modelling self-consistent lithosphere subduction dynamics Solid Earth Discussions, 4, 707-744, 2012 Author(s): M. Chertova, T. Geenen, A. van den Berg, and W. Spakman Subduction modelling in regional model domains, in 2-D or 3-D, is commonly done using closed, vertical boundaries. In this paper we investigate the merits of using open boundaries for 2-D modelling of lithosphere subduction but with implication for 3-D modelling. Open sidewalls allow for lateral in- and outflow consistent with the internal dynamics of the model and may simulate the real-mantle environment of subduction much better than closed boundaries, which induce return flows. Our experiments are focused on using open and closed (free-slip) sidewalls while comparing results for two model aspect ratios of 3:1 and 6:1. Slab buoyancy driven subduction with open boundaries immediately develops into strong rollback with high trench retreat velocities. Mantle asthenosphere flow forced by rollback is predominantly laminar and facilitated by the open boundaries. In contrast, free-slip sidewalls proof restrictive on subduction rollback evolution unless the lithosphere plates are allowed to move away from the sidewalls. This, however, initiates return flows pushing both plates toward the subduction zone speeding up subduction. Increasing the aspect ratio to 6:1 does not change the overall flow pattern when using open sidewalls. Again, in contrast, for free-slip boundaries, the slab evolution does change with respect to the 3:1 aspect ratio and does not resemble the 6:1 evolution obtained with open boundaries. We notice a general drop in the amplitude of mantle flow when changing to the 6:1 aspect ratio, which is caused by the increasing shear friction between mantle and lithosphere while the driving slab buoyancy is the same. Based on energy-dissipation arguments we applied a flow speed scaling to convert between flow fields of different model aspect ratios. This proved succesful for the open boundary model. We have also investigated the effect of far-field stress conditions in our open boundary models. Applying realistic normal stress conditions to the strong part of the overriding plate we show that "intra-plate" stresses control subduction dynamics resulting in slab roll-back, stationary or advancing subduction. We conclude that open boundaries are to be preferred for modelling subduction evolution (rollback, stationary or advancing). The relative independence of model aspect ratio avoids the need to place sidewalls at large distance and allows to focus all computational resources on a smaller modelling domain. Open boundaries simulate the natural subduction environment better and avoid the adverse effects (e.g. forced return flows) of free-slip boundaries.

Description: Up the down escalator: the exhumation of (ultra)-high pressure terranes during on-going subduction Solid Earth Discussions, 4, 745-781, 2012 Author(s): C. J. Warren The exhumation of high and ultra-high pressure rocks is ubiquitous in Phanerozoic orogens created during continental collisions, and is common in many ocean-ocean and ocean-continent subduction zone environments. Three different tectonic environments have previously been reported, which exhume deeply buried material by different mechanisms and at different rates. However it is becoming increasingly clear that no single mechanism dominates in any particular tectonic environment, and the mechanism may change in time and space within the same subduction zone. In order for buoyant continental crust to subduct, it must remain attached to a stronger and denser substrate, but in order to exhume, it must detach (and therefore at least locally weaken) and be initially buoyant. Denser oceanic crust subducts more readily than more buoyant continental crust but exhumation must be assisted by entrainment within more buoyant and weak material such as serpentinite or driven by the exhumation of structurally lower continental crustal material. Weakening mechanisms responsible for the detachment of crust at depth include strain, hydration, melting, grain size reduction and the development of foliation. These may act locally or may act on the bulk of the subducted material. Metamorphic reactions, metastability and the composition of the subducted crust all affect buoyancy and overall strength. Subduction zones change in style both in time and space, and exhumation mechanisms change to reflect the tectonic style and overall force regime within the subduction zone. Exhumation events may be transient and occur only once in a particular subduction zone or orogen, or may be more continuous or occur multiple times.

Description: Influence of a single lightning on the intensity of an air electric field and acoustic emission of near surface rocks Solid Earth Discussions, 4, 627-640, 2012 Author(s): S. E. Smirnov and Y. V. Marapulets The effect of a single lightning discharge on electric field intensity in the near ground atmosphere was investigated. The effect appeared as a sharp fall of electric field potential gradient from 80 V m −1 up to −21 V m −1 . The process of intensity recovery is described by flat capacitor model with characteristic time of recovery of 17 c. Simultaneously with electric field, the acoustic emission response in the near surface rocks on lightning discharge was registered in the frequency range of 6.5–11 kHz.

Description: Nature of orogenesis and volcanism in the Caucasus region based on results of regional tomography Solid Earth Discussions, 4, 641-662, 2012 Author(s): I. Koulakov, I. Zabelina, I. Amanatashvili, and V. Meskhia In the paper we discuss the problem of continental collision and related volcanism in the Caucasus and surrounding areas based on analysis of the upper mantle seismic structure in a recently derived model by Koulakov (2011). This model, which includes P- and S-velocity anomalies down to 1000 km depth, was obtained from tomographic inversion of worldwide travel time data from the catalogue of the International Seismological Center. It can be seen that the Caucasus region is squeezed between two continental plates, Arabian to the south and European to the north, which are displayed in the tomographic model as high-velocity bodies down to about 200–250 km depth. On the contrary, a very bright low-velocity anomaly beneath the collision area implies that the lithosphere in this zone is very thin, which is also supported by strong deformations indicating weak properties of the lithosphere. In the contact between stable continental and collision zones we observe a rather complex alternation of seismic anomalies having the shapes of sinking drops. We propose that the convergence process causes crustal thickening and transformation of the lower crust material into the dense eclogite. When achieving a critical mass, the dense eclogitic drops trigger detachment of the mantle lithosphere and its delamination. The observed high-velocity bodies in the upper mantle may indicate the parts of the descending mantle lithosphere which were detached from the edges of the continental lithosphere plates. Very thin or even absent mantle part of the lithosphere leads to the presence of hot asthenosphere just below the crust. The crustal shortening and eclogitization of the lower crustal layer leads to the dominantly felsic composition of the crust which is favorable for the upward heat transport from the mantle. This, and also the factor of frictional heating, may cause to the origin of volcanic centers in the Caucasus and surrounding collisional areas.

Description: Application of titanium-in-quartz thermobarometry to greenschist facies veins and recrystallized quartzites in the Hsüehshan range, Taiwan Solid Earth Discussions, 4, 663-706, 2012 Author(s): S. Kidder, J.-P. Avouac, and Y.-C. Chan The accuracy, reliability and best practices of Ti-in-quartz thermobarometry ("TitaniQ") in greenschist facies rocks have not been established. To address these issues we measured Ti concentrations in rutile-bearing samples of moderately deformed, partially recrystallized quartzite and vein quartz from Taiwan's Hsüehshan range. The spread of Ti concentrations of recrystallized grains in quartzite correlates with recrystallized grain size. Recrystallized quartz (grain size ~300 μm) that formed during early deformation within the biotite stability field shows a marked increase in intermediate Ti-concentration grains (~1–10 ppm) relative to detrital porphyroclasts (Ti ~0.1–200 ppm). Fine recrystallized quartz (~5% of the samples by area, grain size ~10–20 μm) has a further restricted Ti concentration peaking at 0.8–2 ppm. This trend suggests equilibration of Ti in recrystallized quartz with a matrix phase during deformation and cooling. Vein emplacement and quartzite recrystallization are independently shown to have occurred at 250–350 °C and 300–410 °C respectively, lithostatic pressure ~5 kbar, and hydrostatic fluid pressure. Estimates of the accuracy of TitaniQ at these conditions depend on whether lithostatic or fluid pressure is used in the TitaniQ calibration. Using lithostatic pressure, Ti concentrations predicted by the Thomas et al. (2010) TitaniQ calibration are within error of Ti concentrations measured by SIMS. If fluid pressure is used, predicted temperatures are ~30–40 °C too low. TitaniQ has potential to yield accurate PT information for vein emplacement and dynamic recrystallization of quartz at temperatures as low as ~250 °C, however clarification of the relevant pressure term and further tests in rutile-present rocks are warranted.

Description: Heat-flow and subsurface temperature history at the site of Saraya (eastern Senegal) Solid Earth Discussions, 4, 599-626, 2012 Author(s): F. Lucazeau and F. Rolandone New temperature measurements from eight boreholes in the West African Craton (WAC) reveal superficial perturbations down to 100 meters below the alteration zone. These perturbations are both related to a recent increase of the surface air temperature (SAT) and to the site effects caused by fluids circulations and/or the lower conduction in the alterites. The ground surface temperature (GST) inverted from the boreholes temperatures is stable in the past (1700–1940) and then dramatically increases in the most recent years (1.5 °C since 1950). This is consistent with the increase of the SAT recorded at two nearby meteorological stations (Tambacounda and Kedougou), and more generally in the Sahel with a coeval rainfall decrease. Site effects are superimposed to the climatic effect and interpreted by advective (circulation of fluids) or conductive (lower conductivity of laterite and of high-porosity sand) perturbations. We used a 1-D finite differences thermal model and a Monte-Carlo procedure to find the best estimates of these sites perturbations: all the eight boreholes temperatures logs can be interpreted with the same basal heat-flow and the same surface temperature history, but with some realistic changes of thermal conductivity and/or fluid velocity. The GST trend observed in Senegal can be confirmed by two previous boreholes measurements made in 1983 in other locations of West Africa, the first one in an arid zone of northern Mali and the second one in a subhumid zone in southern Mali. Finally, the background heat-flow is low (30 ± 1 m Wm −2 ), which makes this part of the WAC more similar with the observations in the southern part (33 ± 8 m Wm −2 ) rather than with those in the northern part and in the PanAfrican domains where the surface heat-flow is 15–20 m Wm −2 higher.

Description: Seismicity at the Rwenzori Mountains, East African Rift: earthquake distribution, magnitudes and source mechanisms Solid Earth Discussions, 4, 565-598, 2012 Author(s): M. Lindenfeld, G. Rümpker, A. Batte, and A. Schumann We have analysed the microseismic activity within the Rwenzori Mountains area in the western branch of the East African Rift. Seismogram recordings from a temporary array of up to 27 stations reveal approximately 800 events per month with local magnitudes ranging from –0.5 to 5.1. The earthquake distribution is highly heterogeneous. The majority of located events lie within faults zones to the East and West of the Rwenzoris with the highest seismic activity observed in the northeastern area, where the mountains are in contact with the rift shoulders. The hypocentral depth distribution exhibits a pronounced peak of seismic energy release at 15 km depth. The maximum extent of seismicity ranges from 20 to 32 km and correlates well with Moho depths that were derived from teleseismic receiver functions. We observe two general features: (i) beneath the rift shoulders seismicity extends from the surface down to ca. 30 km depth; (ii) beneath the rift valley seismicity is confined to depths greater than 10 km. From the observations there is no indication for a crustal root beneath the Rwenzori Mountains. The magnitude frequency distribution reveals a b-value of 1.1, which is consistent with the hypothesis that part of the seismicity is caused by magmatic processes within the crust. Fault plane solutions of 304 events were derived from P-polarities and SV/P amplitude ratios. More than 70 % of the source mechanisms exhibit pure or predominantly normal faulting. T-axis trends are highly uniform and oriented WNW-ESE, which is perpendicular to the rift axis and in good agreement with kinematic rift models. At the northernmost part of the region we observe a rotation of the T-axis trends to NEN-SWS, which may be indicative of a local perturbation of the regional stress field.

Description: Numerical models of trench migration in continental collision zones Solid Earth Discussions, 4, 429-458, 2012 Author(s): V. Magni, J. van Hunen, F. Funiciello, and C. Faccenna Continental collision is an intrinsic feature of plate tectonics. The closure of an oceanic basin leads to the onset of subduction of buoyant continental material, which slows down and eventually stops the subduction process. We perform a parametric study of the geometrical and rheological influence on subduction dynamics during the subduction of continental lithosphere. In 2-D numerical models of a free subduction system with temperature and stress-dependent rheology, the trench and the overriding plate move self-consistently as a function of the dynamics of the system (i.e. no external forces are imposed). This setup enables to study how continental subduction influences the trench migration. We found that in all models the trench starts to advance once the continent enters the subduction zone and continues to migrate until few million years after the ultimate slab detachment. Our results support the idea that the trench advancing is favoured and, in part provided by, the intrinsic force balance of continental collision. We suggest that the trench advance is first induced by the locking of the subduction zone and the subsequent steepening of the slab, and next by the sinking of the deepest oceanic part of the slab, during stretching and break-off of the slab. The amount of trench advancing ranges from 40 to 220 km and depends on the dip angle of the slab before the onset of collision.

Description: The strength and permeability of tuffisite-bearing andesite in volcanic conduits Solid Earth Discussions, 4, 459-473, 2012 Author(s): S. Kolzenburg, M. J. Heap, Y. Lavallée, J. K. Russell, P. G. Meredith, and D. B. Dingwell Tuffisites result from volcanically-induced subsurface fragmentation, transport and deposition, and are common in explosive volcanic environments. Their study provides direct insight to explosive volcanic processes operating within volcanic conduits. Here we report the influence of tuffisite veins on the fundamental physical properties of andesitic rocks. We find that: (1) strength is unaffected by the presence and/or orientation of tuffisites, (2) permeability doubles when tuffisites are oriented favorable (45 degrees to fluid flow), and (3) seismic wave velocities show a continuous increase with depth, independent of vein orientation. Although the influence of tuffisites on andesitic rock properties is modest, we emphasize that the material tested represents the post-eruptive state of tuffisite. Thus, these results delineate the upper boundary of strength and lower boundary of permeability and porosity. All evidence suggests that tuffisites become compacted and lithified on relatively short time scales, restoring the strength of the rock to their initial host rock values.

Description: Bromine monoxide/sulphur dioxide ratios in relation to volcanological observations at Mt. Etna 2006–2009 Solid Earth Discussions, 4, 475-505, 2012 Author(s): N. Bobrowski and G. Giuffrida Over a three year period, from 2006 to 2009, frequent scattered sun light DOAS measurements were conducted at Mt. Etna in a distance of around six kilometres downwind from the summit craters. During the same period and in addition to these measurements, volcanic observations were made by regularly visiting various parts of Mt. Etna. Results from these measurements and observations are presented and their relation is discussed. The focus of the investigation is the bromine monoxide/sulphur dioxide (BrO/SO 2 ) ratio, and its variability in relation to volcanic processes. That the halogen/sulphur ratio can serve as a precursor or indicator for the onset of eruptive activity was already proposed by earlier works (e.g. Noguchi and Kamiya, 1963; Menyailov, 1975; Pennisi and Cloarec, 1998; Aiuppa, 2002). However, there is still a limited understanding today because of the complexity with which halogens are released, depending on magma composition and degassing conditions. Our understanding of these processes is far from complete, for example of the rate and mechanism of bubble nucleation, growth and ascent in silicate melts (Carroll and Holloway, 1994), the halogen vapour-melt partitioning and the volatile diffusivity in the melt (Aiuppa et al., 2009). With this study we aim to add one more piece to the puzzle of what halogen/sulphur ratios might tell about volcanic activities. Our data set shows an increase of the BrO/SO 2 ratio several weeks prior to an eruption, followed by a decline before and during the initial phase of eruptive activities. Towards the end of activity or short afterwards, the ratio increases to baseline values again and remains more or less constant during quiet phases. To explain the observed evolution of the BrO/SO 2 ratio, a first empirical model is proposed. This model suggests that bromine, unlike chlorine and fluorine, is less soluble in the magmatic melt than sulphur. By using the DOAS method to determine SO 2 , we actually observe most of the emitted sulphur of Mt. Etna. Regarding bromine however, we are aware that by determining only the bromine monoxide (BrO) radical we might just observe a small or even a variable fraction of the total emitted bromine. Therefore we present first studies to justify the assumption that despite the disadvantage just mentioned, the BrO/SO 2 ratio can nevertheless serve as a new parameter to indicate the state of a volcano, when measurements are conducted under certain, but rather convenient conditions.

Description: Earth's rotation variations and earthquakes 2010–2011 Solid Earth Discussions, 4, 33-130, 2012 Author(s): L. Ostřihanský In contrast to unsuccessful searching (lasting over 150 years) for correlation of earthquakes with biweekly tides, the author found correlation of earthquakes with sidereal 13.66 days Earth's rotation variations expressed as length of a day (LOD) measured daily by International Earth's Rotation Service. After short mention about earthquakes M 8.8 Denali Fault Alaska 3 November 2002 triggered on LOD maximum and M 9.1 Great Sumatra earthquake 26 December 2004 triggered on LOD minimum and the full Moon, the main object of this paper are earthquakes of period 2010–June 2011: M 7.0 Haiti (12 January 2010 on LOD minimum, M 8.8 Maule Chile 12 February 2010 on LOD maximum, map constructed on the Indian plate revealing 6 earthquakes from 7 on LOD minimum in Sumatra and Andaman Sea region, M 7.1 New Zealand Christchurch 9 September 2010 on LOD minimum and M 6.3 Christchurch 21 February 2011 on LOD maximum, and M 9.1 Japan near coast of Honshu 11 March 2011 on LOD minimum. It was found that LOD minimums coincide with full or new Moon only twice in a year in solstices. To prove that determined coincidences of earthquakes and LOD extremes stated above are not accidental events, histograms were constructed of earthquake occurrences and their position on LOD graph deeply in the past, in some cases from the time the IERS (International Earth's Rotation Service) started to measure the Earth's rotation variations in 1962. Evaluations of histograms and the Schuster's test have proven that majority of earthquakes are triggered in both Earth's rotation deceleration and acceleration. Because during these coincidences evident movements of lithosphere occur, among others measured by GPS, it is concluded that Earth's rotation variations effectively contribute to the lithospheric plates movement. Retrospective overview of past earthquakes revealed that the Great Sumatra earthquake 26 December 2004 had its equivalent in the shape of LOD graph, full Moon position, and character of aftershocks 19 years earlier in difference only one day to 27 December 1985 earthquake, proving that not only sidereal 13.66 days variations but also that the 19 years Metons cycle is the period of the earthquakes occurrence. Histograms show the regular change of earthquake positions on branches of LOD graph and also the shape of histogram and number of earthquakes on LOD branches from the mid-ocean ridge can show which side of the ridge moves quicker.

Description: The lithosphere-asthenosphere boundary observed with USArray receiver functions Solid Earth Discussions, 4, 1-31, 2012 Author(s): P. Kumar, X. Yuan, R. Kind, and J. Mechie The dense deployment of seismic stations so far in the western half of the United States within the USArray project provides the opportunity to study in greater detail the structure of the lithosphere-asthenosphere system. We use the S receiver function technique for this purpose which has higher resolution than surface wave tomography, is sensitive to seismic discontinuities and has no problems with multiples like P receiver functions. Only two major discontinuities are observed in the entire area down to about 300 km depth. These are the crust-mantle boundary (Moho) and a negative boundary which we correlate with the lithosphere-asthenosphere boundary (LAB) since a low velocity zone is the classical definition of the seismic observation of the asthenosphere by Gutenberg (1926). Our S receiver function LAB is at a depth of 70–80 km in large parts of westernmost North America. East of the Rocky Mountains its depth is generally between 90 and 110 km. Regions with LAB depths down to about 140 km occur in a stretch from northern Texas over the Colorado Plateau to the Columbia Basalts. These observations agree well with tomography results in the westernmost USA and at the east coast. However, in the central cratonic part of the USA the tomography LAB is near 200 km depth. At this depth no discontinuity is seen in the S receiver functions. The negative signal near 100 km depth in the central part of the USA is interpreted by Yuan and Romanowicz (2010) or Lekic and Romanowicz (2011) as a recently discovered mid lithospheric discontinuity (MLD). A solution for the discrepancy between receiver function imaging and surface wave tomography is not yet obvious and requires more high resolution studies at other cratons before a general solution may be found. Our results agree well with petrophysical models of increased water content in the asthenosphere, which predict a sharp and shallow LAB also in continents (Mierdel et al., 2007).

Description: Geomagnetic jerks characterization via spectral analysis Solid Earth Discussions, 4, 131-172, 2012 Author(s): B. Duka, A. De Santis, M. Mandea, A. Isac, and E. Qamili In this study we have applied spectral techniques to analyze geomagnetic field time-series provided by observatories, and compared the results with those obtained from analogous analyses of synthetic data estimated from models. Then, an algorithm is here proposed to detect the geomagnetic jerks in time-series, mainly occurring in the Eastern component of the geomagnetic field. Applying such analysis to time-series generated from global models has allowed us to depict the most important space-time features of the geomagnetic jerks all over the globe, since the beginning of XXth century. Finally, the spherical harmonic power spectra of the third derivative of the main geomagnetic field has been computed from 1960 to 2002.5, bringing new insights to understanding the spatial evolution of these rapid changes of the geomagnetic field.

Description: New developments in the analysis of volcanic pyroclastic density currents through numerical simulations of multiphase flows Solid Earth Discussions, 4, 173-202, 2012 Author(s): S. Lepore and C. Scarpati A granular multiphase model has been used to evaluate the action of differently sized particles on the dynamics of fountains and associated pyroclastic density currents. The model takes into account the overall disequilibrium conditions between a gas phase and several solid phases, each characterized by its own physical properties. The dynamics of the granular flows has been simulated by adopting a Reynolds Average Navier-Stokes model for describing the turbulence effects. Numerical simulations have been carried out by using different values for the eruptive column temperature at the vent, solid particles frictional concentration, turbulent kinetic energy, and dissipation. The results obtained underline the importance of the multiphase nature of the model and characterize several disequilibrium effects. The low concentration (≤ 5 · 10 –4 ) sectors lie in the upper part of the granular flow, above the fountain, and above the pyroclastic current tail and body as thermal plumes. The high concentration sectors, on the contrary, form the fountain and remain along the ground of the granular flow. Hence, pyroclastic density currents are assimilated to granular flows constituted by a low concentration suspension flowing above a high concentration basal layer (boundary layer), from the proximal regions to the distal ones. Interactions among solid, differently sized particles in the boundary layer of the granular flow are controlled by collisions between particles, whereas particles dispersal in the suspension is determined by the dragging of the gas phase. The simulations describe well the dynamics of a tractive boundary layer leading to the formation of stratified facies during eruptions having a different magnitude.

Description: Possibility of titanium transportation within a mantle wedge: formation process of titanoclinohumite in Fujiwara dunite in Sanbagawa belt, Japan Solid Earth Discussions, 4, 203-239, 2012 Author(s): S. Ishimaru and S. Arai Titinoclinohumite-bearing dunites from Fujiwara, the Sanbagawa metamorphic belt of high-pressure type, Japan, were described to examine the possibility of Ti mobility during metasomatism within the mantle wedge. The Fujiwara dunite body and surrounding high-pressure Sanbagawa schists possibly form a subduction complex, and the dunites are a good analogue to the mantle wedge overlying the slab. The Fujiwara dunites are of deserpentinization origin; the deserpentinized olivine is high in Fo (up to 96) and low in NiO (0.2 to 0.3 wt %), and contains magnetite inclusions. Titanoclinohumites are associated with the deserpentinized olivine, as lamellar intergrowth or veinlets, up to 1 cm in width. Other metamorphic minerals include antigorite, brucite, chlorite, ilmenite, perovskite, Ti-rich ludwigite, and carbonates. The protolith of the Fujiwara dunite was partially serpentinized cumulative dunites from intra-plate magma, containing relatively low-Fo (85 to 86) olivines and TiO 2 -rich (up to 3 wt %) chromian spinels. The metamorphic olivines and titanoclinohumites contain micro-inclusions of methane (CH 4 ) with or without serpentine and brucite. The source of Ti for titanoclinohumite was possibly the Ti-rich chromian spinel, but Ti was mobile through hydrocarbon-rich fluids, which were activated during the metamorphism. The hydrocarbons, of which remnants are carbonates and methane micro-inclusions, were derived from carbonaceous materials or bitumen, possibly incorporated in the precursory serpentinized and brecciated peridotite (= the protolith for the Fujiwara dunites) before subduction. Ti can be mobile in the mantle wedge if hydrocarbons are available from the subducted slab.

Description: Global distribution of the lithosphere-asthenosphere boundary: a new look Solid Earth Discussions, 4, 279-313, 2012 Author(s): V. M. Hamza and F. P. Vieira New global maps of the depth to the boundary between the lithosphere and the asthenosphere are presented. The maps are based on updated global databases for heat flow and crustal structure. For continental regions the estimates of lithospheric thickness are based on determinations of subcrustal heat flow, after corrections for contributions of radiogenic heat in crustal layers. For oceanic regions the estimates of lithospheric thickness are based on the newly proposed finite half-space (FHS) model. Unlike the half-space cooling (HSC) and the Plate models the FHS model takes into account effects of buffered solidification at the lower boundary of the lithosphere and assumes that vertical domain for downward growth of boundary layer have an asymptotic limit. Results of numerical simulations reveal that theoretical values derived from FHS model provide vastly improved fits to observational data for heat flow and bathymetry than can be achieved with HSC and Plate models. Also, the data fits are valid for the entire age range of the oceanic lithosphere. Hence estimates of depths to lithosphere – asthenosphere boundary (LAB) based on FHS model, are believed to provide more reliable estimates than those reported in previous thermal models. The global maps of depths to LAB derived in the present work reveal several features in regional variations of lithosphere thicknesses that have not been identified in earlier studies. For example, regions of ocean floor with ages less than 55 Ma are characterized by relatively rapid thickening of the lithosphere. Also there is better resolution in mapping the transition from oceanic to continental lithosphere, as most of the latter ones are characterized by lithospheric thickness greater than 150 km. As expected the plate spreading centers in oceanic regions as well as areas of recent magmatic activity in continental regions are characterized by relatively thin lithosphere, with LAB depths of less than 50 km. On the other hand, the areas of continental collisions and Precambrian cratonic blocks and are found to have lithosphere thicknesses in excess of 250 km. Regional variations of lithosphere thickness in the interiors of continents are found to depend on the magnitude of subcrustal heat flux as well as the tectonic age of crustal blocks.

Description: High resolution reflection seismic profiling over the Tjellefonna fault in the Møre-Trøndelag Fault Complex, Norway Solid Earth Discussions, 4, 241-278, 2012 Author(s): E. Lundberg, C. Juhlin, and A. Nasuti The Møre-Trøndelag Fault Complex (MTFC) is one of the most prominent fault zones of Norway, both onshore and offshore. In spite of its importance, very little is known of the deeper structure of the individual fault segments comprising the fault complex. Most seismic lines have been recorded offshore or focused on deeper structures. This paper presents results from two reflection seismic profiles, located on each side of the Tingvollfjord, acquired over the Tjellefonna fault in the south-eastern part of the MTFC. Possible kilometer scale vertical offsets reflecting, large scale north-west dipping normal faulting separating the high topography to the south-east from lower topography to the north-west have been proposed for the Tjellefonna fault. In this study, however, the Tjellefonna fault is interpreted to dip approximately 50–60° towards the south-east to depths of at least 1.4 km. Travel-time modeling of reflections associated with the fault was used to establish the geometry of the fault structure at depth and detailed analysis of first P-wave arrivals in shot-gathers together with resistivity profiles were used to define the near surface geometry of the fault zone. A continuation of the structure on the north-eastern side of the Tingvollfjord is suggested by correlation of an in strike direction P-S converted reflection (generated by a fracture zone) seen on the reflection data from that side of the Tingvollfjord. The reflection seismic data correlate well with resistivity profiles and recently published near surface geophysical data. A highly reflective package forming a gentle antiform structure was also identified on both seismic profiles. The structure may be an important boundary within the gneissic basement rocks of the Western Gneiss Region. The Fold Hinge Line is parallel with the Tjellefonna fault trace while the topographic lineament diverges, following secondary fracture zones towards north-east.

Description: Upper Pliensbachian – Toarcian (Jurassic) palaeoenvironmental perturbations in a temporal and regional context: an extended 87 Sr/ 86 Sr, δ 13 C and δ 18 O belemnite isotope study from Bulgaria Solid Earth Discussions, 4, 315-361, 2012 Author(s): L. S. Metodiev, I. P. Savov, D. R. Gröcke, P. B. Wignall, R. J. Newton, P. V. Andreeva, and E. K. Koleva-Rekalova The Upper Pliensbachian–Toarcian (Jurassic) sedimentological, palaeontological and geochemical (belemnite 87 Sr/ 86 Sr, δ 13 C and δ 18 O) record is examined in two Eastern Tethyan (Bulgarian) locations. This interval contains the well-known Early Toarcian ocean anoxic event (T-OAE) and its manifestation and temporal context is examined in Bulgaria. Many of the features characteristic for the SW European sections were identified: collapse of carbonate platform productivity at the Pliensbachian/Toarcian boundary, the T-OAE (a short pulse of anoxic deposition in the Falciferum ammonite Zone), an Early Toarcian rapid warming event seen in the belemnite δ 18 O record that peaked around the Falciferum/Bifrons ammonite zonal boundary. The long-recognized positive δ 13 C excursion in the late Falciferum ammonite Zone is also seen but a precursor, sharp δ 13 C negative excursion seen around the Tenuicostatum/Falciferum ammonite zonal boundary in many organic carbon records is not evident in the belemnite data, a curious absence noted from other belemnite records. Subsequent fluctuations of the 87 Sr/ 86 Sr, δ 13 C and δ 18 O suggest there may be a further perturbation of the global isotopic systems. On the other hand, belemnite Sr isotope values from Bulgaria are in accord with those seen in Western Europe and hence its value for chronostratigraphy.

Description: Structural evolution of the VMS-hosting Kristineberg area, Sweden – constraints from structural analysis and 3-D-modelling Solid Earth Discussions, 4, 1281-1315, 2012 Author(s): P. Skyttä, T. Bauer, T. Hermansson, M. Dehghannejad, C. Juhlin, M. García, J. Hübert, and P. Weihed Structural mapping and 3-D-modelling with constraints from magnetotelluric (MT) and reflection seismic investigations have been used to provide a geological synthesis of the geometrically complex Kristineberg area in the western part of the Palaeoproterozoic Skellefte district. The results indicate that, like the south-eastern parts of the Skellefte district, the area was subjected to SSE-NNW transpressional deformation at around 1.87 Ga. The contrasting structural geometries between the Kristineberg and the central Skellefte district areas may be attributed to the termination and splaying of a major ESE-WNW-striking high-strain zone into several branches in the northern part of the Kristineberg area. The transpressional structural signature was preferentially developed within the southern of the two antiformal structures of the area, "the Southern antiform", which exposes the deepest cut through the crust and hosts all the economic volcanogenic massive sulphides (VMS) deposits of the area. Partitioning of the SSE-NNW transpression into N–S and E–W components led to formation of a characteristic "flat-steep-flat" geometry defining a highly non-cylindrical hinge of for the Southern antiform. Recognition of the transpressional structural signatures including the "flat-steep-flat" geometry and the distinct pattern of sub-horizontal E–W trending to moderately SW-plunging mineral lineations in the deeper crustal parts of the Kristineberg area is of significance for VMS exploration in both near mine and regional scales. The 3-D-model illustrating the outcomes of this study is available as a 3-D-PDF document through the publication website.

Description: Reprocessed height time series of GPS stations at tide gauges Solid Earth Discussions, 4, 1025-1067, 2012 Author(s): S. Rudenko, N. Schön, M. Uhlemann, and G. Gendt Precise weekly positions of 403 Global Positioning System (GPS) stations located worldwide are obtained by reprocessing GPS data of these stations at the time span from 4 January 1998 until 29 December 2007. The used processing algorithm and models as well as the solution and results obtained are presented. Vertical velocities of GPS stations having tracking history longer than 2.5 yr are computed and compared with the estimates from the colocated tide gauges and other GPS solutions. Examples of typical behavior of station height changes are given and interpreted. The derived time series and vertical motions of continuous GPS at tide gauges stations can be used for correcting tide gauge estimates of regional and global sea level changes.

Description: Causes of earthquakes and lithospheric plates movement Solid Earth Discussions, 4, 1411-1483, 2012 Author(s): L. Ostřihanský The goal of the paper was to verify triggering of earthquakes by the length of day variations, i.e. the sidereal 13.66 days Earth's rotation variations, in contrast with tidal biweekly 14.76 days variations (full and new Moon), which for hundred years of investigation give negative results. Earthquake triggering governed by sidereal variations caused by variable Moon's declination accelerates and decelerates the Earth's rotation. Profound Schuster's test proved that earthquakes are triggered both in Earth's deceleration and acceleration. For this investigation the most prominent earthquakes from 2010–2011 were used from Mid-Atlantic Ridge, Southeast Indian Ridge, Sumatra and Andaman Sea, Chile trench, Haiti and Honshu region including important older earthquakes of Sumatra 26 December 2004 and Denali Fault 3 November 2002. Dominant number of earthquake occurring in extremes of length of day variations initiated the calculation of forces acting in these time intervals. Calculated forces of tidal force acting on Earth's flattening and the westward drift are strong enough to trigger earthquakes and the movement of plates follows from GPS performed immediately after earthquakes on continents and from increased number of earthquakes of the side of the mid-ocean ridge belonging to the moving plate. Generally the Northern Hemisphere moves quicker westward than the Southern one. Earthquakes are repeated in 19 yr Metonic cycle. Repetitions caused by tidal force acting on Earth's fattening are exact in date. Repetitions caused by westward drift are delayed for several months.

Description: The boundary between the eastern and western domains of the Pyrenean Orogen: a Cenozoic triple junction zone in Iberia? Solid Earth Discussions, 4, 507-564, 2012 Author(s): S. Tavani The Cantabrian Transitional Area (CTA) is located in the eastern portion of the Cantabrian Mountain Range of the northern Spain. It represents the most important internal boundary within the Upper Cretaceous to Cenozoic E–W elongated Pyrenean Orogen. In the south-verging portion of this orogen, the CTA divides the western thick-skinned Cantabrian Domain, which accommodated for a limited portion of the total N–S oriented orogenic shortening, from the Pyrenean realm to the east, where the south-verging frontal structures are characterised by a marked thiN–Skin style of deformation, and significantly contributed to accommodate the total shortening. In the Cantabrian Transitional Area, Cenozoic syn-orogenic left-lateral, right-lateral and reverse dip-slip movements have occurred along different directions, postdating early-orogenic extensional structures. The latter indicate that the southern portion of the study area formed the eastern termination of the northward concave roughly E–W oriented proto Duero Foreland Basin. This basin was flanked to the north by the thick-skinned proto Cantabrian Belt, which included in its easternmost part the northern portion of the Cantabrian Transitional Area. Onset of right-lateral strike-slip tectonics along the WNW-ESE striking Ubiernal-Venatniella Fault System, which locates to the SW of the CTA and crosses the entire Cantabrian Belt and its formerly southern foreland basin, caused the dislocation of the belt-foredeep system. Contextually, thiN–Skinned structures belonging to the eastern domain of the Pyrenean Orogen laterally propagated and incorporated the eastern part of the proto Duero Foreland Basin. Coexistence of right-lateral and reverse movements to the west and to the east, respectively, determined the onset of an intrabelt compression at the boundary between the Cantabrian and Pyrenean domains, which was the ultimate act of the fusion of the two domains into a single orogen. Paradoxically, this fusion has basically occurred due to the penetration of the NW-SE-striking intraplate right-lateral transpressive system of the Iberian Chain into the Cantabrian Domain of the Pyrenean Orogen. Cenozoic right-lateral reactivation of the Ubierna Fault System, in fact, is part of a NW-SE striking intraplate strike-slip transpressive system, which to the south-east includes the Iberian Chain until the Mediterranean Sea and that, in the western termination of the Ubierna Fault System, branches off into three main splay faults, which are the Ventaniella and Leon faults, and the Duero frontal thrust. Taking into account the role of this Cenozoic transpressive system allows to drastically reduce the gap between plate kinematic reconstructions and geological evidences. This implies that, despite the limited amount of displacement, the Iberian Chain and the Ubierna-Ventaniella systems must be elevated to the rank of microplate boundary, which divided two sectors of the Iberian Plate. Accordingly, the intersection between this system and the Pyrenean Orogen, which occurs in the CTA, must be regarded as a triple junction zone.

Description: Strain localisation in mechanically Layered Rocks, insights from numerical modelling Solid Earth Discussions, 4, 1165-1204, 2012 Author(s): L. Le Pourhiet, B. Huet, P. Agard, L. Labrousse, L. Jolivet, and K. Yao Small scale deformation in stratified rocks displays a large diversity of micro-structures, from the microscopic scale to the scale of orogens. We have designed a series of fully dynamic numerical simulations aimed at assessing which parameters control this structural diversity and which underlying mechanisms lead to strain localisation. The influence of stratification orientation on the occurrence and mode of strain localisation is tested by varying the initial dip of inherited layering versus the large scale imposed simple shear. The detailed study of the models indicates that (1) the results are length-scale independent, (2) the new shear zones are always compatible with the kinematics imposed at the boundary (3) micro-structures formed encompass the full diversity of micro-structures observed in the field and chiefly depend on the direction of the initial anisotropy versus shear direction, (4) depending on the orientation of the anisotropy, the layers may deform along subtractive or additive shear bands, (5) the deformation in anisotropic media results in non-lithostatic pressure values that are on the order of the deviatoric stress in the strong layers and (6) the introduction of brittle rheology is necessary to form localised shear bands in the ductile regime.

Description: Ammonoid multi-extinction crises during the Late Pliensbachian – Toarcian and carbon cycle instabilities Solid Earth Discussions, 4, 1205-1228, 2012 Author(s): J. Guex, A. Bartolini, J. Spangenberg, J.-C. Vicente, and U. Schaltegger Five crises affecting ammonite evolution occurred during the Late Pliensbachian to Late Toarcian stages (Early Jurassic). The first two (Gibbosus and end-Spinatum zones) occurred during highly cold and regressive conditions which were followed by a global anoxic event generated during a supergreenhouse warm event (Levisoni subzone) concomitant with a worldwide transgressive event. The last two (Late Variabilis and Late Insigne zones) are related to regressive events. We present new carbon isotope data from Southern Peru that demonstrate that most of the major Toarcian crises affecting ammonite evolution can be correlated with the variations affecting the δ 13 C during that unstable period. The morphogenetic reactions of the ammonites during the five different upper Liassic critical episodes are analysed, showing how this group can be used as stress indicators.

Description: Thermal structure and intermediate-depth seismicity in the Tohoku-Hokkaido subduction zones Solid Earth Discussions, 4, 1069-1093, 2012 Author(s): P. E. van Keken, S. Kita, and J. Nakajima The cause of intermediate-depth (〉 40 km) seismicity in subduction zones is not well understood. The viability of proposed mechanisms, that include dehydration embrittlement, shear instabilities, and the presence of fluids in general, depends significantly on local conditions, including pressure, temperature and composition. The well-instrumented and well-studied subduction zone below Northern Japan (Tohoku and Hokkaido) provides an excellent testing ground to study the conditions under which intermediate-depth seismicity occurs. This study combines new high resolution finite elements models that predict the dynamics and thermal structure of the Japan subduction system with a high precision hypocenter data base. The upper plane of seismicity is principally contained in the crustal portion of the subducting slab and appears to thin and deepen within the crust at depths 〉 80 km. The disappearance of seismicity overlaps in most of the region with the predicted phase change of blueschist to hydrous eclogite, which forms a major dehydration front in the crust. The correlation between thermally predicted blueschist-out boundary and the disappearance of seismicity breaks down in the transition from the northern Japan to Kurile arc below western Hokkaido. Adjusted models, that take into account the seismically imaged modified upper mantle structure in this region, fail to adequately recover the correlation that is seen below Tohoku and eastern Hokkaido. We conclude that the thermal structure below Western Hokkaido is significantly affected by time-dependent, 3-D dynamics of the slab. This study generally supports the role of fluids in the generation of intermediate-depth seismicity.

Description: Mafic granulite xenoliths in the Chilka Lake suite, Eastern Ghats Belt, India: evidence of deep-subduction of residual oceanic crust Solid Earth Discussions, 4, 1379-1410, 2012 Author(s): S. Bhattacharya, A. K. Chaudhary, A. K. Saw, P. Das, and D. Chatterjee Granulite xenoliths preserve key geochemical and isotopic signatures of their mantle source regions. Mafic granulite and pyroxinite xenoliths within massif-type charnockitic rocks from the Eastern Ghats Belt have recently been reported by us. The mafic granulite xenoliths from the Chilka Lake granulite suite with abundant prograde biotite are geochemically akin to Oceanic Island Basalt (OIB). They can be distinguished from the hornblende-mafic granulite xenoliths with signatures of Arc-derived basalt occurring in the other suites of the Eastern Ghats Belt. These two groups of xenoliths in the Paleoproterozoic Eastern Ghats Province have quite distinct Nd-model ages- 1.9 Ga and 2.5 Ga respectively, which may be interpreted as their crustal residence ages. Strong positive Nb anomalies, indicating subducted oceanic crust in the source, LREE enrichment and strongly fractionated REE pattern are key geochemical signatures attesting to their origin as OIB-type magma. Also low Yb and Sc contents and high (La / Yb) N ratios can be attributed to melting in the presence of residual garnet and hence at great depths (〉 80 km). The variable enrichment in radiogenic 87 Sr, between 0.70052 and 0.71092 at 1.9 Ga and less radiogenic 143 Nd between ε-1.54 and 7.46 are similar to those of the OIBs compared to MORBs. As OIBs commonly contain some recycled oceanic crust in their sources, we suggest that the residue of the oceanic crust from a previous melting event (~ 2.5 Ga) that produced the Arc-derived basalts (protoliths of hornblende-mafic granulite xenoliths) could have subducted to great depths and mechanically mixed with the mantle peridotite. A subsequent re-melting event of this mixed source might have occurred at ca. 1.9 Ga as testified by the crustal residence ages of the biotite-mafic granulite xenoliths of the Chilka Lake granulite suite.

Description: Post-processing scheme for modeling the lithospheric magnetic field Solid Earth Discussions, 4, 1345-1378, 2012 Author(s): V. Lesur, M. Rother, F. Vervelidou, M. Hamoudi, and E. Thébault We investigated how the noise in satellite magnetic data affects magnetic lithospheric field models derived from these data in the special case where this noise is correlated along satellite orbit tracks. For this we describe the satellite data noise as a perturbation magnetic field scaled independently for each orbit, where the scaling factor has a specified variance. Under this assumption, we have been able to derive a model for errors in lithospheric models generated by the correlated satellite data noise. Unless the perturbation field is known, estimating the noise in the lithospheric field model is a non-linear inverse problem. We therefore proposed an iterative post-processing technique to estimate both the lithospheric field model and its associated noise model. The technique has been successfully applied to derive a lithospheric field model from CHAMP satellite data up to spherical harmonic 120. The model is in agreement with other existing models. The technique can be in principal extended for all kind of potential field data with "along track" correlated errors.

Description: New global maps of the depth to the boundary between the lithosphere and the asthenosphere are presented. The maps are based on updated global databases for heat flow and crustal structure. For continental regions the estimates of lithospheric thickness are based on determinations of subcrustal heat flow, after corrections for contributions of radiogenic heat in crustal layers. For oceanic regions the estimates of lithospheric thickness are based on the newly proposed finite half-space (FHS) model. Unlike the half-space cooling (HSC) and the Plate models the FHS model takes into account effects of buffered solidification at the lower boundary of the lithosphere and assumes that vertical domain for downward growth of boundary layer have an asymptotic limit. Results of numerical simulations reveal that theoretical values derived from FHS model provide vastly improved fits to observational data for heat flow and bathymetry than can be achieved with HSC and Plate models. Also, the data fits are valid for the entire age range of the oceanic lithosphere. Hence estimates of depths to lithosphere – asthenosphere boundary (LAB) based on FHS model, are believed to provide more reliable estimates than those reported in previous thermal models. The global maps of depths to LAB derived in the present work reveal several features in regional variations of lithosphere thicknesses that have not been identified in earlier studies. For example, regions of ocean floor with ages less than 55 Ma are characterized by relatively rapid thickening of the lithosphere. Also there is better resolution in mapping the transition from oceanic to continental lithosphere, as most of the latter ones are characterized by lithospheric thickness greater than 150 km. As expected the plate spreading centers in oceanic regions as well as areas of recent magmatic activity in continental regions are characterized by relatively thin lithosphere, with LAB depths of less than 50 km. On the other hand, the areas of continental collisions and Precambrian cratonic blocks and are found to have lithosphere thicknesses in excess of 250 km. Regional variations of lithosphere thickness in the interiors of continents are found to depend on the magnitude of subcrustal heat flux as well as the tectonic age of crustal blocks.

Description: Dynamic models of subduction and continental collision are used to predict dynamic topography changes on the overriding plate. The modelling results show a distinct evolution of topography on the overriding plate, during subduction, continental collision and slab break-off. A prominent topographic feature is a temporary (few Myrs) deepening in the area of the back arc-basin after initial collision. This collisional mantle dynamic basin (CMDB) is caused by slab steepening drawing material away from the base of the overriding plate. Also during this initial collision phase, surface uplift is predicted on the overriding plate between the suture zone and the CMDB, due to the subduction of buoyant continental material and its isostatic compensation. After slab detachment, redistribution of stresses and underplating of the overriding plate causes the uplift to spread further into the overriding plate. This topographic evolution fits the stratigraphy found on the overriding plate of the Arabia-Eurasia collision zone in Iran and south east Turkey. The sedimentary record from the overriding plate contains Upper Oligocene-Lower Miocene marine carbonates deposited between terrestrial clastic sedimentary rocks, in units such as the Qom Formation and its lateral equivalents. This stratigraphy shows that during the Late Oligocene-Early Miocene the surface of the overriding plate sank below sea level before rising back above sea level, without major compressional deformation recorded in the same area. This uplift and subsidence pattern correlates well with our modelled topography changes.

Description: In this study we have applied spectral techniques to analyze geomagnetic field time-series provided by observatories, and compared the results with those obtained from analogous analyses of synthetic data estimated from models. Then, an algorithm is here proposed to detect the geomagnetic jerks in time-series, mainly occurring in the Eastern component of the geomagnetic field. Applying such analysis to time-series generated from global models has allowed us to depict the most important space-time features of the geomagnetic jerks all over the globe, since the beginning of XXth century. Finally, the spherical harmonic power spectra of the third derivative of the main geomagnetic field has been computed from 1960 to 2002.5, bringing new insights to understanding the spatial evolution of these rapid changes of the geomagnetic field.

Description: Structural mapping and 3-D-modelling with constraints from magnetotelluric (MT) and reflection seismic investigations have been used to provide a geological synthesis of the geometrically complex Kristineberg area in the western part of the Palaeoproterozoic Skellefte district. The results indicate that, like the south-eastern parts of the Skellefte district, the area was subjected to SSE-NNW transpressional deformation at around 1.87 Ga. The contrasting structural geometries between the Kristineberg and the central Skellefte district areas may be attributed to the termination and splaying of a major ESE-WNW-striking high-strain zone into several branches in the northern part of the Kristineberg area. The transpressional structural signature was preferentially developed within the southern of the two antiformal structures of the area, "the Southern antiform", which exposes the deepest cut through the crust and hosts all the economic volcanogenic massive sulphides (VMS) deposits of the area. Partitioning of the SSE-NNW transpression into N–S and E–W components led to formation of a characteristic "flat-steep-flat" geometry defining a highly non-cylindrical hinge of for the Southern antiform. Recognition of the transpressional structural signatures including the "flat-steep-flat" geometry and the distinct pattern of sub-horizontal E–W trending to moderately SW-plunging mineral lineations in the deeper crustal parts of the Kristineberg area is of significance for VMS exploration in both near mine and regional scales. The 3-D-model illustrating the outcomes of this study is available as a 3-D-PDF document through the publication website.

Description: Giant subduction earthquakes are known to occur in areas not previously identified as prone to high seismic risk. This highlights the need to better identify subduction zone segments potentially dominated by relatively long (up to 1000 yr and more) recurrence times of giant earthquakes. We construct a model for the geometry of subduction coupling zones and combine it with global geophysical data sets to demonstrate that the occurrence of great (magnitude ≥ 8) subduction earthquakes is strongly biased towards regions associated with intersections of oceanic fracture zones and subduction zones. We use a computational recommendation technology, a type of information filtering system technique widely used in searching, sorting, classifying, and filtering very large, statistically skewed data sets on the internet, to demonstrate a robust association and rule out a random effect. Fracture zone-subduction zone intersection regions, representing only 25% of the global subduction coupling zone, are linked with 13 of the 15 largest (magnitude (Mw ≥ 8.6) and half of the 50 largest, magnitude ≥ 8.4) earthquakes. In contrast, subducting volcanic ridges and chains are only biased towards smaller earthquakes (magnitude 〈 8). The associations captured by our statistical analysis can be conceptually related to physical differences between subducting fracture zones and volcanic chains/ridges. Fracture zones are characterized by laterally continuous, uplifted ridges that represent normal ocean crust with a high degree of structural integrity, causing strong, persistent coupling in the subduction interface. Smaller volcanic ridges and chains, not have a relatively fragile heterogeneous internal structure and are separated from the underlying ocean crust by a detachment interface, resulting in weak coupling and relatively small earthquakes, explaining the observed dichotomy.

Description: With the study and technical development introduced here, we combine analogue sandbox simulation techniques with seismic physical modelling of sandbox models. For that purpose, we designed and developed a new mini-seismic facility for laboratory use, comprising a seismic tank, a PC-driven control unit, a positioning system, and piezo-electric transducers used here the first time in an array mode. To assess the possibilities and limits of seismic imaging of small-scale structures in sandbox models, different geometry setups were tested in the first experiments that also tested the proper functioning of the device and studied the seismo-elastic properties of the granular media used. Simple two-layer models of different materials and layer thicknesses as well as a more complex model comprising channels and shear zones were tested using different acquisition geometries and signal properties. We suggest using well sorted and well rounded grains with little surface roughness (glass beads). Source receiver-offsets less than 14 cm for imaging structures as small as 2.0–1.5 mm size have proven feasible. This is the best compromise between wide beam and high energy output, and being applicable with a consistent waveform. Resolution of the interfaces of layers of granular materials depends on the interface preparation rather than on the material itself. Flat grading of interfaces and powder coverage yields the clearest interface reflections. Finally, sandbox seismic sections provide images of very good quality showing constant thickness layers as well as predefined channel structures and fault traces from shear zones. Since these can be regarded in sandbox models as zones of decompaction, they behave as reflectors and can be imaged. The multiple-offset surveying introduced here improves the quality with respect to S/N-ratio and source signature even more; the maximum depth penetration in glass bead layers thereby amounts to 5 cm. Thus, the presented mini-seismic device is already able to resolve structures within simple models of saturated porous media, so that multiple-offset seismic imaging of shallow sandbox models, that are structurally evolving, is generally feasible.

Description: The goal of the paper was to verify triggering of earthquakes by the length of day variations, i.e. the sidereal 13.66 days Earth's rotation variations, in contrast with tidal biweekly 14.76 days variations (full and new Moon), which for hundred years of investigation give negative results. Earthquake triggering governed by sidereal variations caused by variable Moon's declination accelerates and decelerates the Earth's rotation. Profound Schuster's test proved that earthquakes are triggered both in Earth's deceleration and acceleration. For this investigation the most prominent earthquakes from 2010–2011 were used from Mid-Atlantic Ridge, Southeast Indian Ridge, Sumatra and Andaman Sea, Chile trench, Haiti and Honshu region including important older earthquakes of Sumatra 26 December 2004 and Denali Fault 3 November 2002. Dominant number of earthquake occurring in extremes of length of day variations initiated the calculation of forces acting in these time intervals. Calculated forces of tidal force acting on Earth's flattening and the westward drift are strong enough to trigger earthquakes and the movement of plates follows from GPS performed immediately after earthquakes on continents and from increased number of earthquakes of the side of the mid-ocean ridge belonging to the moving plate. Generally the Northern Hemisphere moves quicker westward than the Southern one. Earthquakes are repeated in 19 yr Metonic cycle. Repetitions caused by tidal force acting on Earth's fattening are exact in date. Repetitions caused by westward drift are delayed for several months.

Description: Granulite xenoliths preserve key geochemical and isotopic signatures of their mantle source regions. Mafic granulite and pyroxinite xenoliths within massif-type charnockitic rocks from the Eastern Ghats Belt have recently been reported by us. The mafic granulite xenoliths from the Chilka Lake granulite suite with abundant prograde biotite are geochemically akin to Oceanic Island Basalt (OIB). They can be distinguished from the hornblende-mafic granulite xenoliths with signatures of Arc-derived basalt occurring in the other suites of the Eastern Ghats Belt. These two groups of xenoliths in the Paleoproterozoic Eastern Ghats Province have quite distinct Nd-model ages- 1.9 Ga and 2.5 Ga respectively, which may be interpreted as their crustal residence ages. Strong positive Nb anomalies, indicating subducted oceanic crust in the source, LREE enrichment and strongly fractionated REE pattern are key geochemical signatures attesting to their origin as OIB-type magma. Also low Yb and Sc contents and high (La / Yb)N ratios can be attributed to melting in the presence of residual garnet and hence at great depths (〉 80 km). The variable enrichment in radiogenic 87Sr, between 0.70052 and 0.71092 at 1.9 Ga and less radiogenic 143Nd between ε-1.54 and 7.46 are similar to those of the OIBs compared to MORBs. As OIBs commonly contain some recycled oceanic crust in their sources, we suggest that the residue of the oceanic crust from a previous melting event (~ 2.5 Ga) that produced the Arc-derived basalts (protoliths of hornblende-mafic granulite xenoliths) could have subducted to great depths and mechanically mixed with the mantle peridotite. A subsequent re-melting event of this mixed source might have occurred at ca. 1.9 Ga as testified by the crustal residence ages of the biotite-mafic granulite xenoliths of the Chilka Lake granulite suite.

Description: The accuracy, reliability and best practices of Ti-in-quartz thermobarometry ("TitaniQ") in greenschist facies rocks have not been established. To address these issues we measured Ti concentrations in rutile-bearing samples of moderately deformed, partially recrystallized quartzite and vein quartz from Taiwan's Hsüehshan range. The spread of Ti concentrations of recrystallized grains in quartzite correlates with recrystallized grain size. Recrystallized quartz (grain size ~300 μm) that formed during early deformation within the biotite stability field shows a marked increase in intermediate Ti-concentration grains (~1–10 ppm) relative to detrital porphyroclasts (Ti ~0.1–200 ppm). Fine recrystallized quartz (~5% of the samples by area, grain size ~10–20 μm) has a further restricted Ti concentration peaking at 0.8–2 ppm. This trend suggests equilibration of Ti in recrystallized quartz with a matrix phase during deformation and cooling. Vein emplacement and quartzite recrystallization are independently shown to have occurred at 250–350 °C and 300–410 °C respectively, lithostatic pressure ~5 kbar, and hydrostatic fluid pressure. Estimates of the accuracy of TitaniQ at these conditions depend on whether lithostatic or fluid pressure is used in the TitaniQ calibration. Using lithostatic pressure, Ti concentrations predicted by the Thomas et al. (2010) TitaniQ calibration are within error of Ti concentrations measured by SIMS. If fluid pressure is used, predicted temperatures are ~30–40 °C too low. TitaniQ has potential to yield accurate PT information for vein emplacement and dynamic recrystallization of quartz at temperatures as low as ~250 °C, however clarification of the relevant pressure term and further tests in rutile-present rocks are warranted.

Description: Exploratory monitoring of radon is conducted at one location at the deep underground Gran Sasso National Laboratory (LNGS). Measurements (15-min resolution) are performed over a time span of ca. 600 days in the air of the surrounding calcareous country rock. Utilizing both alpha and gamma-ray detectors systematic and recurring radon signals are recorded. Two primary signal types are determined: (a) non-periodic Multi-Day (MD) signals lasting 2–10 days, and (b) Daily Radon (DR) signals – which are of a periodic nature exhibiting a primary 24-h cycle. The local ancillary environmental conditions (P, T) seem not to affect radon in air monitored at the site. Long term patterns of day-time measurements are different from the pattern of night-time measurements indicating a day-night modulation of gamma radiation from radon in air. The phenomenology of the MD and DR signals is similar to situations encountered at other locations where radon is monitored with a high time resolution in geogas at upper crustal levels. In accordance with recent field and experimental results it is suggested that a components of solar irradiance is affecting the radiation from radon in air, and this influence is further modulated by the diurnal rotation of Earth. The occurrence of these radon signals in the 1 km deep low radiation underground geological environment of LNGS provides new information on the time variation of the local radiation environment. The observations and results place the LNGS facility as a high priority location for performing advanced investigations of these geophysical phenomena, due to its location and its infrastructure.

Description: The supply of water is limited in some parts of the Mediterranean region, such as southeastern Spain. The use of treated wastewater for the irrigation of agricultural soils is an alternative to using better-quality water, especially in semi-arid regions. On the other hand, this practice can modify some soil properties, change their relationships, the equilibrium reached and influence soil quality. In this work two soil quality indices were used to evaluate the effects of irrigation with treated wastewater in soils. The indices were developed studying different soil properties in undisturbed soils in SE Spain, and the relationships between soil parameters were established using multiple linear regressions. This study was carried out in three areas of Alicante Province (SE Spain) irrigated with wastewater, including four study sites. The results showed slight changes in some soil properties as a consequence of irrigation with wastewater, the obtained levels not being dangerous for agricultural soils, and in some cases they could be considered as positive from an agronomical point of view. In one of the study sites, and as a consequence of the low quality wastewater used, a relevant increase in soil organic matter content was observed, as well as modifications in most of the soil properties. The application of soil quality indices indicated that all the soils of study sites are in a state of disequilibrium regarding the relationships between properties independent of the type of water used. However, there were no relevant differences in the soil quality indices between soils irrigated with wastewater with respect to their control sites for all except one of the sites, which corresponds to the site where low quality wastewater was used.

Description: Over a three year period, from 2006 to 2009, frequent scattered sun light DOAS measurements were conducted at Mt. Etna in a distance of around six kilometres downwind from the summit craters. During the same period and in addition to these measurements, volcanic observations were made by regularly visiting various parts of Mt. Etna. Results from these measurements and observations are presented and their relation is discussed. The focus of the investigation is the bromine monoxide/sulphur dioxide (BrO/SO2) ratio, and its variability in relation to volcanic processes. That the halogen/sulphur ratio can serve as a precursor or indicator for the onset of eruptive activity was already proposed by earlier works (e.g. Noguchi and Kamiya, 1963; Menyailov, 1975; Pennisi and Cloarec, 1998; Aiuppa, 2002). However, there is still a limited understanding today because of the complexity with which halogens are released, depending on magma composition and degassing conditions. Our understanding of these processes is far from complete, for example of the rate and mechanism of bubble nucleation, growth and ascent in silicate melts (Carroll and Holloway, 1994), the halogen vapour-melt partitioning and the volatile diffusivity in the melt (Aiuppa et al., 2009). With this study we aim to add one more piece to the puzzle of what halogen/sulphur ratios might tell about volcanic activities. Our data set shows an increase of the BrO/SO2 ratio several weeks prior to an eruption, followed by a decline before and during the initial phase of eruptive activities. Towards the end of activity or short afterwards, the ratio increases to baseline values again and remains more or less constant during quiet phases. To explain the observed evolution of the BrO/SO2 ratio, a first empirical model is proposed. This model suggests that bromine, unlike chlorine and fluorine, is less soluble in the magmatic melt than sulphur. By using the DOAS method to determine SO2, we actually observe most of the emitted sulphur of Mt. Etna. Regarding bromine however, we are aware that by determining only the bromine monoxide (BrO) radical we might just observe a small or even a variable fraction of the total emitted bromine. Therefore we present first studies to justify the assumption that despite the disadvantage just mentioned, the BrO/SO2 ratio can nevertheless serve as a new parameter to indicate the state of a volcano, when measurements are conducted under certain, but rather convenient conditions.

Description: The discovery nearly two decades ago of a 90 km-diameter impact crater below the lower Chesapeake Bay has gone unnoted by the general public because to date all published literature on the subject has described it as "buried". To the contrary, evidence is presented here that the so-called "upland deposits" that blanket ∼5000 km2 of the U.S. Middle-Atlantic Coastal Plain (M-ACP) display morphologic, lithologic, and stratigraphic features consistent with their being ejecta from the 35.4 Ma Chesapeake Bay Impact Structure (CBIS) and absolutely inconsistent with the prevailing belief that they are of fluvial origin. Specifically supporting impact origin are the facts that (i) a 95 %-pure iron ore endemic to the upland deposits of southern Maryland, eastern Virginia, and the District of Columbia has previously been proven to be impactoclastic in origin, (ii) this iron ore welds together a small percentage of well-rounded quartzite pebbles and cobbles of the upland deposits into brittle sheets interpretable as "spall plates" created in the interference-zone of the CBIS impact, (iii) the predominantly non-welded upland gravels have long ago been shown to be size sorted with an extreme crater-centric gradient far too large to have been the work of rivers, but well explained as atmospheric size-sorted interference-zone ejecta, (iv) new evidence is provided here that ~60 % of the non-welded quartzite pebbles and cobbles of the (lower lying) gravel member of the upland deposits display planar fractures attributable to interference-zone tensile waves, (v) the (overlying) loam member of the upland deposits is attributable to base-surge-type deposition, (vi) several exotic clasts found in a debris flow topographically below the upland deposits can only be explained as jetting-phase crater ejecta, and (vii) an allogenic granite boulder found among the upland deposits is deduced to have been launched into space and sculpted by hypervelocity air friction during reentry. An idealized calculation of the CBIS ejecta-blanket elevation profile minutes after the impact was carried out founded on well established rules for explosion and impact-generated craters. This profile is shown here to match the volume of the upland deposits ≥170 km from the crater center. Closer to the crater, much of the "postdicted" ejecta blanket has clearly been removed by erosion. Nevertheless the Shirley and fossil-free Bacons Castle Formations, located between the upland deposits and the CBIS interior and veneering the present day surface with units ∼10–20 m deep, are respectively identified as curtain- and excavation-phase ejecta. The neritic-fossil-bearing Calvert Formation external to the crater is deduced to be of Eocene age (as opposed to early Miocene as currently believed), preserved by the armoring effects of the overlying CBIS ejecta composed of the (distal) upland deposits and the (proximal) Bacons Castle Formation. The lithofacies of the in-crater Calvert Formation can only have resulted from inward mass wasting of the postdicted ejecta blanket, vestiges of which (i.e. the Bacons Castle and Shirley Formations) still overlap the crater rim and sag into its interior, consistent with this expectation. Because there appear to be a total of ∼10 000 km2 of CBIS ejecta lying on the present-day surface, future research should center the stratigraphic, lithologic, and petrologic properties of these ejecta versus both radial distance from the crater center (to identify ejecta from different ejection stages) and circumferentially at fixed radial distances (to detect possible anisotropies relating the impact angle and direction of approach of the impactor). The geological units described here may comprise the best preserved, and certainly the most accessible, ejecta blanket of a major crater on the Earth's surface and therefore promise to be a boon to the field of impact geology. As a corollary, a major revision of the current stratigraphic column of the M-ACP will be necessary.

Description: Precise weekly positions of 403 Global Positioning System (GPS) stations located worldwide are obtained by reprocessing GPS data of these stations at the time span from 4 January 1998 until 29 December 2007. The used processing algorithm and models as well as the solution and results obtained are presented. Vertical velocities of GPS stations having tracking history longer than 2.5 yr are computed and compared with the estimates from the colocated tide gauges and other GPS solutions. Examples of typical behavior of station height changes are given and interpreted. The derived time series and vertical motions of continuous GPS at tide gauges stations can be used for correcting tide gauge estimates of regional and global sea level changes.

Description: The dense deployment of seismic stations so far in the western half of the United States within the USArray project provides the opportunity to study in greater detail the structure of the lithosphere-asthenosphere system. We use the S receiver function technique for this purpose which has higher resolution than surface wave tomography, is sensitive to seismic discontinuities and has no problems with multiples like P receiver functions. Only two major discontinuities are observed in the entire area down to about 300 km depth. These are the crust-mantle boundary (Moho) and a negative boundary which we correlate with the lithosphere-asthenosphere boundary (LAB) since a low velocity zone is the classical definition of the seismic observation of the asthenosphere by Gutenberg (1926). Our S receiver function LAB is at a depth of 70–80 km in large parts of westernmost North America. East of the Rocky Mountains its depth is generally between 90 and 110 km. Regions with LAB depths down to about 140 km occur in a stretch from northern Texas over the Colorado Plateau to the Columbia Basalts. These observations agree well with tomography results in the westernmost USA and at the east coast. However, in the central cratonic part of the USA the tomography LAB is near 200 km depth. At this depth no discontinuity is seen in the S receiver functions. The negative signal near 100 km depth in the central part of the USA is interpreted by Yuan and Romanowicz (2010) or Lekic and Romanowicz (2011) as a recently discovered mid lithospheric discontinuity (MLD). A solution for the discrepancy between receiver function imaging and surface wave tomography is not yet obvious and requires more high resolution studies at other cratons before a general solution may be found. Our results agree well with petrophysical models of increased water content in the asthenosphere, which predict a sharp and shallow LAB also in continents (Mierdel et al., 2007).

Description: Ash thickness is a key variable in the protection of soil against erosion agents after planned and unplanned fires. Thicker ash provides better protection against raindrop impact and reduces the runoff response by retaining water and promoting water infiltration although little is known about the distribution and the evolution of the ash layer after the fires. Ash thickness measurements were conducted along two transects (flat and sloping areas) following a a grid experimental design. Both transects extended from the burned area into an adjacent unburned area. We analysed ash thickness evolution according to time and fire severity. In order to interpolate data with accuracy and identify the techniques with the least bias, several interpolation methods were tested in the grid plot. Overall, the fire had a low severity. The fire significantly reduced the ground cover, especially on sloping areas owing to the higher fire severity and/or less biomass previous to the fire. Ash thickness depends on fire severity and is thin where fire severity was higher and thicker in lower fire severity sites. The ash thickness decreased with time after the fire. Between 4 and 16 days after the fire, ash was transported by wind. The major reduction took place between 16 and 34 days after the fire as a result of rainfall, and was more efficient where fire severity was higher. Between 34 and 45 days after the fire no significant differences in ash thickness were identified among ash colours and only traces of the ash layer remained. The omni-directional experimental variograms shown that variable structure did not change importantly with the time, however, the most accurate interpolation methods were different highlighting the slight different patterns of ash thickness distribution with the time. The ash spatial variability increased with the time, particularly on the slope, as a result of water erosion.

Description: We investigated how the noise in satellite magnetic data affects magnetic lithospheric field models derived from these data in the special case where this noise is correlated along satellite orbit tracks. For this we describe the satellite data noise as a perturbation magnetic field scaled independently for each orbit, where the scaling factor has a specified variance. Under this assumption, we have been able to derive a model for errors in lithospheric models generated by the correlated satellite data noise. Unless the perturbation field is known, estimating the noise in the lithospheric field model is a non-linear inverse problem. We therefore proposed an iterative post-processing technique to estimate both the lithospheric field model and its associated noise model. The technique has been successfully applied to derive a lithospheric field model from CHAMP satellite data up to spherical harmonic 120. The model is in agreement with other existing models. The technique can be in principal extended for all kind of potential field data with "along track" correlated errors.

Description: Five crises affecting ammonite evolution occurred during the Late Pliensbachian to Late Toarcian stages (Early Jurassic). The first two (Gibbosus and end-Spinatum zones) occurred during highly cold and regressive conditions which were followed by a global anoxic event generated during a supergreenhouse warm event (Levisoni subzone) concomitant with a worldwide transgressive event. The last two (Late Variabilis and Late Insigne zones) are related to regressive events. We present new carbon isotope data from Southern Peru that demonstrate that most of the major Toarcian crises affecting ammonite evolution can be correlated with the variations affecting the δ13C during that unstable period. The morphogenetic reactions of the ammonites during the five different upper Liassic critical episodes are analysed, showing how this group can be used as stress indicators.

Description: Small scale deformation in stratified rocks displays a large diversity of micro-structures, from the microscopic scale to the scale of orogens. We have designed a series of fully dynamic numerical simulations aimed at assessing which parameters control this structural diversity and which underlying mechanisms lead to strain localisation. The influence of stratification orientation on the occurrence and mode of strain localisation is tested by varying the initial dip of inherited layering versus the large scale imposed simple shear. The detailed study of the models indicates that (1) the results are length-scale independent, (2) the new shear zones are always compatible with the kinematics imposed at the boundary (3) micro-structures formed encompass the full diversity of micro-structures observed in the field and chiefly depend on the direction of the initial anisotropy versus shear direction, (4) depending on the orientation of the anisotropy, the layers may deform along subtractive or additive shear bands, (5) the deformation in anisotropic media results in non-lithostatic pressure values that are on the order of the deviatoric stress in the strong layers and (6) the introduction of brittle rheology is necessary to form localised shear bands in the ductile regime.

Description: The cause of intermediate-depth (〉 40 km) seismicity in subduction zones is not well understood. The viability of proposed mechanisms, that include dehydration embrittlement, shear instabilities, and the presence of fluids in general, depends significantly on local conditions, including pressure, temperature and composition. The well-instrumented and well-studied subduction zone below Northern Japan (Tohoku and Hokkaido) provides an excellent testing ground to study the conditions under which intermediate-depth seismicity occurs. This study combines new high resolution finite elements models that predict the dynamics and thermal structure of the Japan subduction system with a high precision hypocenter data base. The upper plane of seismicity is principally contained in the crustal portion of the subducting slab and appears to thin and deepen within the crust at depths 〉 80 km. The disappearance of seismicity overlaps in most of the region with the predicted phase change of blueschist to hydrous eclogite, which forms a major dehydration front in the crust. The correlation between thermally predicted blueschist-out boundary and the disappearance of seismicity breaks down in the transition from the northern Japan to Kurile arc below western Hokkaido. Adjusted models, that take into account the seismically imaged modified upper mantle structure in this region, fail to adequately recover the correlation that is seen below Tohoku and eastern Hokkaido. We conclude that the thermal structure below Western Hokkaido is significantly affected by time-dependent, 3-D dynamics of the slab. This study generally supports the role of fluids in the generation of intermediate-depth seismicity.

Description: Quantifying the precise thermal structure of subduction zones is essential for understanding the nature of metamorphic dehydration reactions, arc volcanism, and intermediate depth seismicity. High resolution two-dimensional (2-D) models have shown that the rheology of the mantle wedge plays a critical role and establishes strong temperature gradients in the slab. The influence of three-dimensional (3-D) subduction zone geometry on thermal structure is however not yet well characterized. A common assumption for 2-D models is that the cross-section is taken normal to the strike of the trench with a corresponding velocity reduction in the case of oblique subduction, rather than taken parallel to velocity. A comparison between a full 3-D Cartesian model with oblique subduction and selected 2-D cross-sections demonstrates that the trench-normal cross-section provides a better reproduction of the slab thermal structure than the velocity-parallel cross-section. An exception is found in the case of strongly curved subduction, such as in the Marianas, where strong 3-D flow in the mantle wedge is generated. In this case it is shown that the full 3-D model should be evaluated for an accurate prediction of the slab thermal structure.

Description: The Møre-Trøndelag Fault Complex (MTFC) is one of the most prominent fault zones of Norway, both onshore and offshore. In spite of its importance, very little is known of the deeper structure of the individual fault segments comprising the fault complex. Most seismic lines have been recorded offshore or focused on deeper structures. This paper presents results from two reflection seismic profiles, located on each side of the Tingvollfjord, acquired over the Tjellefonna fault in the south-eastern part of the MTFC. Possible kilometer scale vertical offsets reflecting, large scale north-west dipping normal faulting separating the high topography to the south-east from lower topography to the north-west have been proposed for the Tjellefonna fault. In this study, however, the Tjellefonna fault is interpreted to dip approximately 50–60° towards the south-east to depths of at least 1.4 km. Travel-time modeling of reflections associated with the fault was used to establish the geometry of the fault structure at depth and detailed analysis of first P-wave arrivals in shot-gathers together with resistivity profiles were used to define the near surface geometry of the fault zone. A continuation of the structure on the north-eastern side of the Tingvollfjord is suggested by correlation of an in strike direction P-S converted reflection (generated by a fracture zone) seen on the reflection data from that side of the Tingvollfjord. The reflection seismic data correlate well with resistivity profiles and recently published near surface geophysical data. A highly reflective package forming a gentle antiform structure was also identified on both seismic profiles. The structure may be an important boundary within the gneissic basement rocks of the Western Gneiss Region. The Fold Hinge Line is parallel with the Tjellefonna fault trace while the topographic lineament diverges, following secondary fracture zones towards north-east.

Description: A granular multiphase model has been used to evaluate the action of differently sized particles on the dynamics of fountains and associated pyroclastic density currents. The model takes into account the overall disequilibrium conditions between a gas phase and several solid phases, each characterized by its own physical properties. The dynamics of the granular flows has been simulated by adopting a Reynolds Average Navier-Stokes model for describing the turbulence effects. Numerical simulations have been carried out by using different values for the eruptive column temperature at the vent, solid particles frictional concentration, turbulent kinetic energy, and dissipation. The results obtained underline the importance of the multiphase nature of the model and characterize several disequilibrium effects. The low concentration (≤ 5 · 10–4) sectors lie in the upper part of the granular flow, above the fountain, and above the pyroclastic current tail and body as thermal plumes. The high concentration sectors, on the contrary, form the fountain and remain along the ground of the granular flow. Hence, pyroclastic density currents are assimilated to granular flows constituted by a low concentration suspension flowing above a high concentration basal layer (boundary layer), from the proximal regions to the distal ones. Interactions among solid, differently sized particles in the boundary layer of the granular flow are controlled by collisions between particles, whereas particles dispersal in the suspension is determined by the dragging of the gas phase. The simulations describe well the dynamics of a tractive boundary layer leading to the formation of stratified facies during eruptions having a different magnitude.

Description: In contrast to unsuccessful searching (lasting over 150 years) for correlation of earthquakes with biweekly tides, the author found correlation of earthquakes with sidereal 13.66 days Earth's rotation variations expressed as length of a day (LOD) measured daily by International Earth's Rotation Service. After short mention about earthquakes M 8.8 Denali Fault Alaska 3 November 2002 triggered on LOD maximum and M 9.1 Great Sumatra earthquake 26 December 2004 triggered on LOD minimum and the full Moon, the main object of this paper are earthquakes of period 2010–June 2011: M 7.0 Haiti (12 January 2010 on LOD minimum, M 8.8 Maule Chile 12 February 2010 on LOD maximum, map constructed on the Indian plate revealing 6 earthquakes from 7 on LOD minimum in Sumatra and Andaman Sea region, M 7.1 New Zealand Christchurch 9 September 2010 on LOD minimum and M 6.3 Christchurch 21 February 2011 on LOD maximum, and M 9.1 Japan near coast of Honshu 11 March 2011 on LOD minimum. It was found that LOD minimums coincide with full or new Moon only twice in a year in solstices. To prove that determined coincidences of earthquakes and LOD extremes stated above are not accidental events, histograms were constructed of earthquake occurrences and their position on LOD graph deeply in the past, in some cases from the time the IERS (International Earth's Rotation Service) started to measure the Earth's rotation variations in 1962. Evaluations of histograms and the Schuster's test have proven that majority of earthquakes are triggered in both Earth's rotation deceleration and acceleration. Because during these coincidences evident movements of lithosphere occur, among others measured by GPS, it is concluded that Earth's rotation variations effectively contribute to the lithospheric plates movement. Retrospective overview of past earthquakes revealed that the Great Sumatra earthquake 26 December 2004 had its equivalent in the shape of LOD graph, full Moon position, and character of aftershocks 19 years earlier in difference only one day to 27 December 1985 earthquake, proving that not only sidereal 13.66 days variations but also that the 19 years Metons cycle is the period of the earthquakes occurrence. Histograms show the regular change of earthquake positions on branches of LOD graph and also the shape of histogram and number of earthquakes on LOD branches from the mid-ocean ridge can show which side of the ridge moves quicker.

Description: Titinoclinohumite-bearing dunites from Fujiwara, the Sanbagawa metamorphic belt of high-pressure type, Japan, were described to examine the possibility of Ti mobility during metasomatism within the mantle wedge. The Fujiwara dunite body and surrounding high-pressure Sanbagawa schists possibly form a subduction complex, and the dunites are a good analogue to the mantle wedge overlying the slab. The Fujiwara dunites are of deserpentinization origin; the deserpentinized olivine is high in Fo (up to 96) and low in NiO (0.2 to 0.3 wt %), and contains magnetite inclusions. Titanoclinohumites are associated with the deserpentinized olivine, as lamellar intergrowth or veinlets, up to 1 cm in width. Other metamorphic minerals include antigorite, brucite, chlorite, ilmenite, perovskite, Ti-rich ludwigite, and carbonates. The protolith of the Fujiwara dunite was partially serpentinized cumulative dunites from intra-plate magma, containing relatively low-Fo (85 to 86) olivines and TiO2-rich (up to 3 wt %) chromian spinels. The metamorphic olivines and titanoclinohumites contain micro-inclusions of methane (CH4) with or without serpentine and brucite. The source of Ti for titanoclinohumite was possibly the Ti-rich chromian spinel, but Ti was mobile through hydrocarbon-rich fluids, which were activated during the metamorphism. The hydrocarbons, of which remnants are carbonates and methane micro-inclusions, were derived from carbonaceous materials or bitumen, possibly incorporated in the precursory serpentinized and brecciated peridotite (= the protolith for the Fujiwara dunites) before subduction. Ti can be mobile in the mantle wedge if hydrocarbons are available from the subducted slab.

Description: We present an application of the discontinuous Galerkin (DG) method to regional wave propagation. The method makes use of unstructured tetrahedral meshes, combined with a time integration scheme solving the arbitrary high-order derivative (ADER) Riemann problem. The ADER-DG method is high-order accurate in space and time, beneficial for reliable simulations of high-frequency wavefields over long propagation distances. Due to the ease with which tetrahedral grids can be adapted to complex geometries, undulating topography of the Earth's surface and interior interfaces can be readily implemented in the computational domain. The ADER-DG method is benchmarked for the accurate radiation of elastic waves excited by an explosive and a shear dislocation source. We compare real data measurements with synthetics of the 2009 L'Aquila event (central Italy). We take advantage of the geometrical flexibility of the approach to generate a European model composed of the 3-D EPcrust model, combined with the depth-dependent ak135 velocity model in the upper-mantle. The results confirm the applicability of the ADER-DG method for regional scale earthquake simulations, which provides an alternative to existing methodologies.

Description: The properties of the subduction interplate domain are likely to affect not only the seismogenic potential of the subduction area but also the overall subduction process, as it influences its viability. Numerical simulations are performed to model the long-term equilibrium state of the subduction interplate when the diving lithosphere interacts with both the overriding plate and the surrounding convective mantle. The thermomechanical model combines a non-Newtonian viscous rheology and a pseudo-brittle rheology. Rock strength here depends on depth, temperature and stress, for both oceanic crust and mantle rocks. I study the evolution through time of, on one hand, the kinematic decoupling depth, zdec and, on the other hand, of the brittle-ductile transition (BDT) depth, zBDT, simulated along the subduction interplate. The results reveal that zBDT mainly depends on the friction coefficient characterising the interplate channel and on the viscosity at the lithosphere-asthenosphere boundary. The influence of the weak material activation energy is of second order but not negligible. zBDT becomes dependent on the ductile strength increase with depth (activation volume) if the BDT occurs at the interplate deocupling depth. Regarding the interplate decoupling depth, it is basically a function of (1) mantle viscosity at asthenospheric wedge tip, (2) difference in mantle and interplate activation anergy, and (3) activation volume. Specific conditions yielding zBDT = zdec are discussed. I then present how the subducting lithosphere age affects the brittle-ductile transition depth and the kinematic decoupling depth in this model. Simulations show that a rheological model in which the respective activation energies of mantle and interplate material are too close impedes strain localization during incipient subduction of a young (20 Myr old) and soft lithosphere under a thick upper plate. Finally, both the BDT depth and the decoupling depth are a function of the subducting plate age, but are not influenced in the same fashion: cool and old subducting plates deepen the BDT but shallow the interplate decoupling depth. Even if BDT and kinematic decoupling are instrinsically related to different mechanisms of deformation, this work shows that they are able to interact closely.

Description: We present a new model of P- and S-velocity anomalies in the mantle down to 1300 km depth beneath the Izu-Bonin and Mariana (IBM) arcs. This model is derived based on tomographic inversion of global travel time data from the revised ISC catalogue. The results of inversion are thoroughly verified using a series of different tests. The obtained model is generally consistent with previous studies of different authors. We also present the distribution of relocated deep events projected to the vertical surface along the IBM arc. Unexpectedly, the seismicity form elongated vertical clusters instead of horizontal zones indicating phase transitions in the slab. We propose that these vertical seismicity zones mark zones of intense deformation and boundaries between semi-autonomous segments of the subducting plate. The P- and S-seismic tomography models consistently display the slab as prominent high-velocity anomalies coinciding with the distribution of deep seismicity. Based on joint consideration of the tomography results and the seismicity distribution we propose a scenario of the subduction evolution in the IBM zone during the recent time. We can distinguish at least four segments which subduct differently. The northernmost segment of the Izu-Bonin arc has the gentlest angle of dipping which is explained by backward displacement of the trench. In the second segment, the trench stayed at the same location, and we observe the accumulation of the slab material in the transition zone and its further descending to the lower mantle. In third segment, the trench is moving forward that causes steepening of the slab. Finally, for the Mariana segment, despite the backward displacement of the arc, the subducting slab is nearly vertical. We propose that it might be due to the high density of the slab which is responsible for turning any inclined subduction to the vertical position. Between the Izu-Bonin and Mariana arcs we clearly observe a gap which is traced down to about 400 km depth.

Description: The exhumation of high and ultra-high pressure rocks is ubiquitous in Phanerozoic orogens created during continental collisions, and is common in many ocean-ocean and ocean-continent subduction zone environments. Three different tectonic environments have previously been reported, which exhume deeply buried material by different mechanisms and at different rates. However it is becoming increasingly clear that no single mechanism dominates in any particular tectonic environment, and the mechanism may change in time and space within the same subduction zone. In order for buoyant continental crust to subduct, it must remain attached to a stronger and denser substrate, but in order to exhume, it must detach (and therefore at least locally weaken) and be initially buoyant. Denser oceanic crust subducts more readily than more buoyant continental crust but exhumation must be assisted by entrainment within more buoyant and weak material such as serpentinite or driven by the exhumation of structurally lower continental crustal material. Weakening mechanisms responsible for the detachment of crust at depth include strain, hydration, melting, grain size reduction and the development of foliation. These may act locally or may act on the bulk of the subducted material. Metamorphic reactions, metastability and the composition of the subducted crust all affect buoyancy and overall strength. Subduction zones change in style both in time and space, and exhumation mechanisms change to reflect the tectonic style and overall force regime within the subduction zone. Exhumation events may be transient and occur only once in a particular subduction zone or orogen, or may be more continuous or occur multiple times.

Description: Soil C sequestration through changes in land use and management is one of the sustainable and long-term strategies to mitigate climate change. This research explores and quantifies the role of soil and land use as determinants of the ability of soils to store C along Mediterranean systems. Detailed studies of soil organic C (SOC) dynamics are necessary in order to identify factors determining fluctuations and intensity of changes. In this study, SOC contents from different soil and land use types have been investigated in Andalusia (S Spain). We have used soil information from different databases, as well as land use digital maps, climate databases and digital elevation models. The average SOC content for each soil control section (0–25, 25–50 and 50–75 cm) was determined and SOC stocks were calculated for each combination of soil and land use type, using soil and land cover maps. The total organic C stock in soils of Andalusia is 415 Tg for the upper 75 cm, with average values ranging from 15.9 Mg C ha−1 (Solonchaks under "arable land") to 107.6 Mg C ha−1 (Fluvisols from "wetlands"). Up to 55% of SOC accumulates in the top 25 cm of soil (229.7 Tg). This research constitutes a preliminary assessment for modelling SOC stock under scenarios of land use and climate change.

Description: In recent years, the ElectroMagnetic Radiation (EMR) method has been used to detect faults and to determine main horizontal stress directions from variations in intensities and directional properties of electromagnetic emissions, which are assumed to be generated during micro-cracking. Based on a large data set taken from an area of about 250 000 km2 in Northern Germany, Denmark, and Southern Sweden with repeated measurements at one location during a time span of about 1.5 yr, the method was systematically tested. Reproducible observations of temporary changes in the signal patterns, as well as a strongly concentric spatial pattern of the main directions of the magnetic component of the EMR point to VLF transmitters as the main source and hence raise serious concerns about the applicability of the method to determine recent crustal stresses. We conclude that the EMR method, at its current stage of development, does not allow determination of the main horizontal stress directions.

Description: It is generally believed that subduction of lithospheric slabs is a major contribution to thermal heterogeneity in Earth's entire mantle and provides a main driving force for mantle flow. Mantle structure can, on the one hand, be inferred from plate tectonic models of subduction history and geodynamic models of mantle flow. On the other hand, seismic tomography models provide important information on mantle heterogeneity. Yet, the two kinds of models are only similar on the largest (1000s of km) scales and are quite different in their detailed structure. Here, we provide a quantitative assessment how good a fit can be currently achieved with a simple viscous flow geodynamic model. The discrepancy between geodynamic and tomography models can indicate where further model refinement could possibly yield an improved fit. Our geodynamical model is based on 300 Myr of subduction history inferred from a global plate reconstruction. Density anomalies are inserted into the upper mantle beneath subduction zones, and flow and advection of these anomalies is calculated with a spherical harmonic code for a radial viscosity structure constrained by mineral physics and surface observations. Model viscosities in the upper mantle beneath the lithosphere are ~1020 Pas, and viscosity increases to ~1023 Pas in the lower mantle above D". Comparison with tomography models is assessed in terms of correlation, both overall and as a function of depth and spherical harmonic degree. We find that, compared to previous geodynamic and tomography models, correlation is improved significantly, presumably because of improvements in both plate reconstructions and mantle flow computation. However, high correlation is still limited to lowest spherical harmonic degrees. An important ingredient to achieve high correlation – in particular at spherical harmonic degree two – is a basal chemical layer. Subduction shapes this layer into two rather stable hot but chemically dense "piles", corresponding to the Pacific and African Large Low Shear Velocity Provinces. Visual comparison along cross sections indicates that sinking speeds in the geodynamic model are somewhat too fast, and should be 2±0.8 cm yr−1 to achieve a better fit.

Description: In the paper we discuss the problem of continental collision and related volcanism in the Caucasus and surrounding areas based on analysis of the upper mantle seismic structure in a recently derived model by Koulakov (2011). This model, which includes P- and S-velocity anomalies down to 1000 km depth, was obtained from tomographic inversion of worldwide travel time data from the catalogue of the International Seismological Center. It can be seen that the Caucasus region is squeezed between two continental plates, Arabian to the south and European to the north, which are displayed in the tomographic model as high-velocity bodies down to about 200–250 km depth. On the contrary, a very bright low-velocity anomaly beneath the collision area implies that the lithosphere in this zone is very thin, which is also supported by strong deformations indicating weak properties of the lithosphere. In the contact between stable continental and collision zones we observe a rather complex alternation of seismic anomalies having the shapes of sinking drops. We propose that the convergence process causes crustal thickening and transformation of the lower crust material into the dense eclogite. When achieving a critical mass, the dense eclogitic drops trigger detachment of the mantle lithosphere and its delamination. The observed high-velocity bodies in the upper mantle may indicate the parts of the descending mantle lithosphere which were detached from the edges of the continental lithosphere plates. Very thin or even absent mantle part of the lithosphere leads to the presence of hot asthenosphere just below the crust. The crustal shortening and eclogitization of the lower crustal layer leads to the dominantly felsic composition of the crust which is favorable for the upward heat transport from the mantle. This, and also the factor of frictional heating, may cause to the origin of volcanic centers in the Caucasus and surrounding collisional areas.

Description: We have analysed the microseismic activity within the Rwenzori Mountains area in the western branch of the East African Rift. Seismogram recordings from a temporary array of up to 27 stations reveal approximately 800 events per month with local magnitudes ranging from –0.5 to 5.1. The earthquake distribution is highly heterogeneous. The majority of located events lie within faults zones to the East and West of the Rwenzoris with the highest seismic activity observed in the northeastern area, where the mountains are in contact with the rift shoulders. The hypocentral depth distribution exhibits a pronounced peak of seismic energy release at 15 km depth. The maximum extent of seismicity ranges from 20 to 32 km and correlates well with Moho depths that were derived from teleseismic receiver functions. We observe two general features: (i) beneath the rift shoulders seismicity extends from the surface down to ca. 30 km depth; (ii) beneath the rift valley seismicity is confined to depths greater than 10 km. From the observations there is no indication for a crustal root beneath the Rwenzori Mountains. The magnitude frequency distribution reveals a b-value of 1.1, which is consistent with the hypothesis that part of the seismicity is caused by magmatic processes within the crust. Fault plane solutions of 304 events were derived from P-polarities and SV/P amplitude ratios. More than 70 % of the source mechanisms exhibit pure or predominantly normal faulting. T-axis trends are highly uniform and oriented WNW-ESE, which is perpendicular to the rift axis and in good agreement with kinematic rift models. At the northernmost part of the region we observe a rotation of the T-axis trends to NEN-SWS, which may be indicative of a local perturbation of the regional stress field.

Description: Triplicated body waves sample the mantle transition zone more extensively than any other wave type, and interact strongly with the discontinuities at 410 km and 660 km. Since the seismograms bear a strong imprint of these geodynamically interesting features, it is highly desirable to invert them for structure of the transition zone. This has rarely been attemped, due to the mismatch between the complex and bandlimited data and the (ray-theoretical) modeling methods. Here we present a data processing and modeling strategy to harness such broadband seismograms for finite-frequency tomography. We include triplicated P-waves (epicentral distance range between 14 and 30°) across their entire broadband frequency range, for both deep and shallow sources. We show that it is possible to predict the complex sequence of arrivals in these seismograms, but only after a careful effort to estimate source time functions and other source parameters from data, variables that strongly influence the waveforms. Modeled and observed waveforms then yield decent cross-correlation fits, from which we measure finite-frequency traveltime anomalies. We discuss two such data sets, for North America and Europe, and conclude that their signal quality and azimuthal coverage should be adequate for tomographic inversion. In order to compute sensitivity kernels at the pertinent high body-wave frequencies, we use fully numerical forward modelling of the seismic wavefield through a spherically symmetric earth.

Description: Subduction modelling in regional model domains, in 2-D or 3-D, is commonly done using closed, vertical boundaries. In this paper we investigate the merits of using open boundaries for 2-D modelling of lithosphere subduction but with implication for 3-D modelling. Open sidewalls allow for lateral in- and outflow consistent with the internal dynamics of the model and may simulate the real-mantle environment of subduction much better than closed boundaries, which induce return flows. Our experiments are focused on using open and closed (free-slip) sidewalls while comparing results for two model aspect ratios of 3:1 and 6:1. Slab buoyancy driven subduction with open boundaries immediately develops into strong rollback with high trench retreat velocities. Mantle asthenosphere flow forced by rollback is predominantly laminar and facilitated by the open boundaries. In contrast, free-slip sidewalls proof restrictive on subduction rollback evolution unless the lithosphere plates are allowed to move away from the sidewalls. This, however, initiates return flows pushing both plates toward the subduction zone speeding up subduction. Increasing the aspect ratio to 6:1 does not change the overall flow pattern when using open sidewalls. Again, in contrast, for free-slip boundaries, the slab evolution does change with respect to the 3:1 aspect ratio and does not resemble the 6:1 evolution obtained with open boundaries. We notice a general drop in the amplitude of mantle flow when changing to the 6:1 aspect ratio, which is caused by the increasing shear friction between mantle and lithosphere while the driving slab buoyancy is the same. Based on energy-dissipation arguments we applied a flow speed scaling to convert between flow fields of different model aspect ratios. This proved succesful for the open boundary model. We have also investigated the effect of far-field stress conditions in our open boundary models. Applying realistic normal stress conditions to the strong part of the overriding plate we show that "intra-plate" stresses control subduction dynamics resulting in slab roll-back, stationary or advancing subduction. We conclude that open boundaries are to be preferred for modelling subduction evolution (rollback, stationary or advancing). The relative independence of model aspect ratio avoids the need to place sidewalls at large distance and allows to focus all computational resources on a smaller modelling domain. Open boundaries simulate the natural subduction environment better and avoid the adverse effects (e.g. forced return flows) of free-slip boundaries.

Description: The effect of a single lightning discharge on electric field intensity in the near ground atmosphere was investigated. The effect appeared as a sharp fall of electric field potential gradient from 80 V m−1 up to −21 V m−1. The process of intensity recovery is described by flat capacitor model with characteristic time of recovery of 17 c. Simultaneously with electric field, the acoustic emission response in the near surface rocks on lightning discharge was registered in the frequency range of 6.5–11 kHz.

Description: New temperature measurements from eight boreholes in the West African Craton (WAC) reveal superficial perturbations down to 100 meters below the alteration zone. These perturbations are both related to a recent increase of the surface air temperature (SAT) and to the site effects caused by fluids circulations and/or the lower conduction in the alterites. The ground surface temperature (GST) inverted from the boreholes temperatures is stable in the past (1700–1940) and then dramatically increases in the most recent years (1.5 °C since 1950). This is consistent with the increase of the SAT recorded at two nearby meteorological stations (Tambacounda and Kedougou), and more generally in the Sahel with a coeval rainfall decrease. Site effects are superimposed to the climatic effect and interpreted by advective (circulation of fluids) or conductive (lower conductivity of laterite and of high-porosity sand) perturbations. We used a 1-D finite differences thermal model and a Monte-Carlo procedure to find the best estimates of these sites perturbations: all the eight boreholes temperatures logs can be interpreted with the same basal heat-flow and the same surface temperature history, but with some realistic changes of thermal conductivity and/or fluid velocity. The GST trend observed in Senegal can be confirmed by two previous boreholes measurements made in 1983 in other locations of West Africa, the first one in an arid zone of northern Mali and the second one in a subhumid zone in southern Mali. Finally, the background heat-flow is low (30 ± 1 m Wm−2), which makes this part of the WAC more similar with the observations in the southern part (33 ± 8 m Wm−2) rather than with those in the northern part and in the PanAfrican domains where the surface heat-flow is 15–20 m Wm−2 higher.

Description: The Cantabrian Transitional Area (CTA) is located in the eastern portion of the Cantabrian Mountain Range of the northern Spain. It represents the most important internal boundary within the Upper Cretaceous to Cenozoic E–W elongated Pyrenean Orogen. In the south-verging portion of this orogen, the CTA divides the western thick-skinned Cantabrian Domain, which accommodated for a limited portion of the total N–S oriented orogenic shortening, from the Pyrenean realm to the east, where the south-verging frontal structures are characterised by a marked thiN–Skin style of deformation, and significantly contributed to accommodate the total shortening. In the Cantabrian Transitional Area, Cenozoic syn-orogenic left-lateral, right-lateral and reverse dip-slip movements have occurred along different directions, postdating early-orogenic extensional structures. The latter indicate that the southern portion of the study area formed the eastern termination of the northward concave roughly E–W oriented proto Duero Foreland Basin. This basin was flanked to the north by the thick-skinned proto Cantabrian Belt, which included in its easternmost part the northern portion of the Cantabrian Transitional Area. Onset of right-lateral strike-slip tectonics along the WNW-ESE striking Ubiernal-Venatniella Fault System, which locates to the SW of the CTA and crosses the entire Cantabrian Belt and its formerly southern foreland basin, caused the dislocation of the belt-foredeep system. Contextually, thiN–Skinned structures belonging to the eastern domain of the Pyrenean Orogen laterally propagated and incorporated the eastern part of the proto Duero Foreland Basin. Coexistence of right-lateral and reverse movements to the west and to the east, respectively, determined the onset of an intrabelt compression at the boundary between the Cantabrian and Pyrenean domains, which was the ultimate act of the fusion of the two domains into a single orogen. Paradoxically, this fusion has basically occurred due to the penetration of the NW-SE-striking intraplate right-lateral transpressive system of the Iberian Chain into the Cantabrian Domain of the Pyrenean Orogen. Cenozoic right-lateral reactivation of the Ubierna Fault System, in fact, is part of a NW-SE striking intraplate strike-slip transpressive system, which to the south-east includes the Iberian Chain until the Mediterranean Sea and that, in the western termination of the Ubierna Fault System, branches off into three main splay faults, which are the Ventaniella and Leon faults, and the Duero frontal thrust. Taking into account the role of this Cenozoic transpressive system allows to drastically reduce the gap between plate kinematic reconstructions and geological evidences. This implies that, despite the limited amount of displacement, the Iberian Chain and the Ubierna-Ventaniella systems must be elevated to the rank of microplate boundary, which divided two sectors of the Iberian Plate. Accordingly, the intersection between this system and the Pyrenean Orogen, which occurs in the CTA, must be regarded as a triple junction zone.

Description: Tuffisites result from volcanically-induced subsurface fragmentation, transport and deposition, and are common in explosive volcanic environments. Their study provides direct insight to explosive volcanic processes operating within volcanic conduits. Here we report the influence of tuffisite veins on the fundamental physical properties of andesitic rocks. We find that: (1) strength is unaffected by the presence and/or orientation of tuffisites, (2) permeability doubles when tuffisites are oriented favorable (45 degrees to fluid flow), and (3) seismic wave velocities show a continuous increase with depth, independent of vein orientation. Although the influence of tuffisites on andesitic rock properties is modest, we emphasize that the material tested represents the post-eruptive state of tuffisite. Thus, these results delineate the upper boundary of strength and lower boundary of permeability and porosity. All evidence suggests that tuffisites become compacted and lithified on relatively short time scales, restoring the strength of the rock to their initial host rock values.

Description: Continental collision is an intrinsic feature of plate tectonics. The closure of an oceanic basin leads to the onset of subduction of buoyant continental material, which slows down and eventually stops the subduction process. We perform a parametric study of the geometrical and rheological influence on subduction dynamics during the subduction of continental lithosphere. In 2-D numerical models of a free subduction system with temperature and stress-dependent rheology, the trench and the overriding plate move self-consistently as a function of the dynamics of the system (i.e. no external forces are imposed). This setup enables to study how continental subduction influences the trench migration. We found that in all models the trench starts to advance once the continent enters the subduction zone and continues to migrate until few million years after the ultimate slab detachment. Our results support the idea that the trench advancing is favoured and, in part provided by, the intrinsic force balance of continental collision. We suggest that the trench advance is first induced by the locking of the subduction zone and the subsequent steepening of the slab, and next by the sinking of the deepest oceanic part of the slab, during stretching and break-off of the slab. The amount of trench advancing ranges from 40 to 220 km and depends on the dip angle of the slab before the onset of collision.

Description: The Upper Pliensbachian–Toarcian (Jurassic) sedimentological, palaeontological and geochemical (belemnite 87Sr/86Sr, δ13C and δ18O) record is examined in two Eastern Tethyan (Bulgarian) locations. This interval contains the well-known Early Toarcian ocean anoxic event (T-OAE) and its manifestation and temporal context is examined in Bulgaria. Many of the features characteristic for the SW European sections were identified: collapse of carbonate platform productivity at the Pliensbachian/Toarcian boundary, the T-OAE (a short pulse of anoxic deposition in the Falciferum ammonite Zone), an Early Toarcian rapid warming event seen in the belemnite δ18O record that peaked around the Falciferum/Bifrons ammonite zonal boundary. The long-recognized positive δ13C excursion in the late Falciferum ammonite Zone is also seen but a precursor, sharp δ13C negative excursion seen around the Tenuicostatum/Falciferum ammonite zonal boundary in many organic carbon records is not evident in the belemnite data, a curious absence noted from other belemnite records. Subsequent fluctuations of the 87Sr/86Sr, δ13C and δ18O suggest there may be a further perturbation of the global isotopic systems. On the other hand, belemnite Sr isotope values from Bulgaria are in accord with those seen in Western Europe and hence its value for chronostratigraphy.