Age estimation of the deposition of the cretaceous Upper Sandstones and a later remagnetization event,from Hirna area,SE Ethiopia

Outcrops of the Cretaceous Upper sandstone formation some 375 km to the East of Addis Ababa on the motor Highway to Harar was paleomagnetically investigated. About seventy core samples were collected at various stratigraphic levels from 250–300 meters thick sedimentary formation. After standard sample preparations in the laboratory the resulting specimens were subjected to routine paleomagnetic demagnetization protocol. In the first steps of demagnetizations process the recent and viscous magnetizations were removed by heating until a temperature of level of 300 °C. Further demagnetization of the samples resulted in the isolation of the final magnetization with stable line segments that is directed towards the origin, which is interpreted as Characteristic Remanent Magnetization (ChRM). Rock – magnetic experiments have identified goethite (αFeOOH), hematite (αFe₂O₃), detritial hematite, and magnetite as the magnetic mineral phases carrying the remanence. The ChRM identified resulted in an average value of (D_s = 0.5°, I_s = ?0.7°, α₉₅ = 4.3°, N = 34) for the red sandstones while an average value of (D_s = 335.8°, I_s = ?31.8°, α₉₅ = 4.7°, N = 14) for the limestone intercalations. The former ChRM in the red sandstone is determined to be secondary while the latter ChRM is known to be primary. Comparison of these directional results and their pole equivalents with the African plate Apparent Polar Wander Path curve established by Besse and Courtillot (2003) give ages of between 115–130 Million years for the limestone intercalation and ages of 30 million years for red sandstone unit. These are interpreted respectively as estimates of the age of deposition and a later remagnetization respectively.     

Correlations between electrical and elastic properties of solid–liquid composites with interfacial energy-controlled equilibrium microstructures

Electrical conductivity and seismic velocity are studied for plausible pore geometries in the Earth's interior for reliable quantitative analysis of experimental data such as seismic tomography and magnetotelluric explorations. Electrical conductivity of a two-phase system with equilibrium, interfacial energy-controlled phase geometry is calculated for the dihedral angles θ = 40°–100° that are typical for rock–aqueous fluid and θ = 20°–60° for rock–melt systems of lower crust and upper mantle for the case of tetrakaidecahedral grains. Electrical conductivity vs. seismic velocity correlations are acquired by combining of the simulated electrical conductivities with the seismic velocity calculated with the help of equilibrium geometry model Takei [Takei, Y., Effect of pore geometry on V_P/V_S: From equilibrium geometry to crack. J. Geophys. Res. 107 (2002): 10.1029/2001JB000522.] for the same pore geometries. The results show that electrical conductivity gradually decreases reaching zero when seismic velocities reach seismic velocities of intact rock for rock–melt systems, while for rock–aqueous fluid systems with θ ≥ 60° conductivity drops to zero at velocities up to 10% smaller. This can explain the seeming discrepancy of the low seismic velocity region, attributed to the high fluid fraction, and the low electrical conductivity of the same region, which is sometimes faced at collocated electromagnetic and seismic experiments.     

Whistlers observed at low-latitude ground-based VLF facility in Fiji

The propagation features of nighttime whistlers to low-latitude station, Suva (−18.2°, 178.3°, geomag. lat. −22.1°, geomag. long. 253.5°, L=1.15), Fiji, from preliminary observations made during the period from September 2003–2005, are reported. The observations of ELF–VLF signals commenced in September 2003 using the VLF set-up of World Wide Lightning Location Network at our station. The whistlers were observed during the severe magnetic storm of 20–22 November 2003 and moderate magnetic storm of 17–19 July 2005. A whistler with dispersion D=12.7 s^1/2 occurred on 22 November at 00:11 h LT. On 20 July at 01:00 h LT, a short whistler with dispersion D=20.9 s^1/2 and two whistler events having two-component whistlers with D=15.8, 16.7 s^1/2 and 16.7, 17.3 s^1/2 were observed. Non-ducted pro-longitudinal mode of the whistler propagation supported by negative latitudinal electron density gradients in the ionosphere that are enhanced by magnetic storms, seems most likely mode of propagation for the whistlers with dispersion of 12.7–17.3 s^1/2 to this low-latitude station.     

The equivalent dose of different grain size quartz fractions from lakeshore sediments in the arid region of north China

Equivalent dose (D_e) values were measured by using medium aliquots of different grain size quartz fractions of five lakeshore sediments from the arid region of north China. There are two different relationships between D_e values and grain sizes of these five samples. The first relationship is that the D_e values obtained from various grain sizes are in agreement within 1 delta errors. The second relationship is that D_e values are similar to each other for fractions between 125 and 300 μm, while the D_e value of the 63–90 μm fraction is 40～55% smaller than others. For example, the D_e values obtained for sample #3 are 20.15 ± 1.19 Gy, 19.80 ± 0.83 Gy and 20.93 ± 1.06 Gy for fractions of 90–125, 125–150 and 250–300 μm respectively, but are 10.79 ± 0.84 Gy for the 63–90 μm fraction. The second relationship can't be interpreted by previous studies of both dosimetry and heterogeneous bleaching. It is deduced for sample #2, #3 and #6 that fine particles (<90 μm) intruded after the dominant sedimentation. Comparison of OSL ages from different grain size fractions of sample #2 with a radiocarbon age from the same lithologic layer supports that fractions coarser than 125 μm yield more reliable burial ages, while the fraction finer than 90 μm yields underestimated ages for some lakeshore sediments from this arid region.     

Paleomagnetism of the Late Cretaceous ignimbrite from the Okhotsk-Chukotka Volcanic Belt,Kolyma-Omolon Composite Terrane: Tectonic implications

New Late Cretaceous paleomagnetic results from the Okhotsk-Chukotka Volcanic Belt in the Kolyma-Omolon Composite Terrane yield stable and consistent remanent directions. The Late Cretaceous (86–81 Ma) ignimbrites from the Kholchan and Ola suites were sampled at 19 sites in the Magadan area (60.4° N, 151.0° E). We isolated the characteristic paleomagnetic directions from 16 sampled sites using an alternating field demagnetization procedure. The primary nature of these directions is ascertained by dual polarities and positive fold tests. A tilt-corrected mean direction (D = 42.8°, I = 84.7°, k = 46.0, α₉₅ = 10.0°) yields a paleomagnetic pole of 66.7° N, 168.5° E (A₉₅ = 18.8°) which appears almost identical to the 90–67 Ma pole reported from the Lake El’gygytgyn area of the Okhotsk-Chukotka Volcanic Belt (Chukotka Terrane). This consistency suggests that the Kolyma-Omolon Composite Terrane and Chukotka Terrane has acted as a single tectonic unit since 80 Ma without any significant internal deformation. Accordingly, we calculate a combined 80 Ma characteristic paleomagnetic pole (Long. = 164.7° E, Lat. = 68.0°, A₉₅ = 10.9°, N = 12) for the Kolyma-Omolon-Chukotka Block which falls 16.5–17.5° south of the same age poles from Europe and East Asia. We ascribe this discrepancy in pole positions to tectonic activity in the area and infer a southward displacement of 1640 ± 1380 km for the Kolyma-Omolon-Chukotka Block with respect to the North American and Eurasian blocks since 80 Ma; more than 260 km of it is attributed to tectonic displacement in the Arctic Ocean due to the opening of the Canadian Basin.     

Importance of reversible attachment in predicting E. coli transport in saturated aquifers from column experiments

Drinking water wells indiscriminatingly placed adjacent to fecal contaminated surface water represents a significant but difficult to quantify health risk. Here we seek to understand mechanisms that limit the contamination extent by scaling up bacterial transport results from the laboratory to the field in a well constrained setting. Three pulses of Escherichia coli originating during the early monsoon from a freshly excavated pond receiving latrine effluent in Bangladesh were monitored in 6 wells and modeled with a two-dimensional (2-D) flow and transport model conditioned with measured hydraulic heads. The modeling was performed assuming three different modes of interaction of E. coli with aquifer sands: (1) irreversible attachment only (best-fit k_i = 7.6 day⁻¹); (2) reversible attachment only (k_a = 10.5 and k_d = 0.2 day⁻¹); and (3) a combination of reversible and irreversible modes of attachment (k_a = 60, k_d = 7.6, k_i = 5.2 day⁻¹). Only the third approach adequately reproduced the observed temporal and spatial distribution of E. coli, including a 4-log₁₀ lateral removal distance of ∼9 m. In saturated column experiments, carried out using aquifer sand from the field site, a combination of reversible and irreversible attachment was also required to reproduce the observed breakthrough curves and E. coli retention profiles within the laboratory columns. Applying the laboratory-measured kinetic parameters to the 2-D calibrated flow model of the field site underestimates the observed 4-log₁₀ lateral removal distance by less than a factor of two. This is promising for predicting field scale transport from laboratory experiments.     

The modified Reynolds equation for non-wetting fluid flow through a rough-walled rock fracture

The no-slip boundary condition has usually been assumed to hold for the Reynolds equations (local cubic law) for fluid flow through rough-walled fractures. However, its validity for non-wetting fluid flow, such as prevails in fractured oil reservoirs, has been questioned. A series of experiments with a rough-walled fracture with mean aperture of 760 μm finds a higher flow rate for non-wetting fluid than wetting fluid. A modified Reynolds equation with a slip boundary condition is derived for non-wetting fluid flow through rough-walled fractures. Comparison of the modified Reynolds equation predictions with experimental results confirms that slip was a plausible explanation for a higher flow rate. The amount by which the flow rate for non-wetting fluids exceeds that for wetting fluids is found to depend highly on, and increase with, the degree to which the flowing fluid was non-wetted to thin immobile films on the surfaces. Numerical studies using the modified Reynolds equation indicate that the flow rate of non-wetting fluid became higher than that of wetting fluid as the roughness of the fracture increases. As the aperture becomes smaller, the flow rate ratio of non-wetting fluid to wetting fluid becomes large, leading to the endpoint relative permeability for the non-wetting fluid to exceed 1. The experimental and numerical studies clearly show that as the aperture of the fracture became less than a few hundred microns, the modified Reynolds equation with slip boundary conditions provides a better model for flow of a non-wetting fluid through rough-walled fractures.     

Hybrid foundation for offshore wind turbines: Environmental and seismic loading

A hybrid foundation for offshore wind turbines (OWT) is studied, combining a monopile of diameter d and length L with a lightweight circular footing of diameter D. The footing is composed of steel plates and stiffeners forming compartments, backfilled to increase the vertical load. A special pile–footing connection is outlined, allowing transfer of lateral loads and moments, but not of vertical loads. The efficiency of the hybrid foundation is explored through 3D finite element modelling. Hybrid foundations of L=15 m are comparatively assessed to an L=30 m reference monopile. A detailed comparison is performed focusing on a 3.5 MW OWT. While the moment capacity of the monopile is larger, the hybrid foundation exhibits stiffer response, outperforming the monopile in the operational loading range. Under cyclic loading, the hybrid foundation experiences less stiffness degradation and rotation accumulation. Besides installation, the cost savings depend on the design of the footing and buckling can be crucial. The rubble fill is shown to provide lateral restraint to the stiffeners, being beneficial for buckling prevention. Although seismic shaking is not critical in terms of capacity, it may lead to substantial accumulation of rotation and settlement. Combined with cyclic environmental loading, the latter may challenge the serviceability of the OWT, potentially leading to a reduction of its service life. To derive insights on the effect of seismic loading, two scenarios are investigated: (a) seismic loading; and (b) combined environmental and seismic loading. In the first case, even a D=15 m hybrid foundation may outperform the reference monopile. This is not the case for combined environmental and seismic loading, where a D=20 m hybrid system would be required to outperform the reference monopile.     

Paleomagnetic dating of Phanerozoic kimberlites in Siberia

Diamond bearing kimberlite pipes are exposed across the north-central part of the Siberian platform. Three main time intervals are considered to be the age of emplacement: the Devonian–Early Carboniferous, Triassic, and Cretaceous. However, isotopic age data from of the pipes are scattered and provide a very broad age interval for the magmatic activity. New paleomagnetic poles from four kimberlite pipes (Eastern Udachnaya, Western Udachnaya, International and Obnazhennaya) are obtained to estimate their paleomagnetic age. The mean primary magnetization directions for the pipes are as follows: D = 4.3°, I = − 44.5° (k = 29.4, α₉₅ = 7.4°, N = 14); D = 340.5°, I = − 65.6° (k = 12.9, α₉₅ = 19.4°, N = 6); D = 291.1°, I = − 78.1° (k = 27.5, α₉₅ = 14.9°, N = 5); and D = 306.7°, I = − 82.6° (k = 38.4, α₉₅ = 5.8°, N = 17), respectively. On the basis of a comparison with the Siberian apparent polar wander path (APWP) we estimate the age of kimberlite magmatism, assuming primary magnetizations in these rocks. The paleomagnetic ages are as follows: 428 ± 13 Ma for Eastern Udachnaya; 251 ± 30 Ma for International pipe; and 168 ± 11 Ma for Obnazhennaya pipe. The Western Udachnaya pipe was remagnetized and no clear paleomagnetic age could be determined. The ages of magmatic activity span the Early Silurian to Middle Late Jurassic. Early Silurian magmatism could be associated with the formation of the Viluy rift. Middle to Late Jurassic magmatic activity is most likely related to subduction related to the accretion of surrounding terranes to Siberia.     

Evapotranspiration in the Pampean Region using field measurements and satellite data

Evapotranspiration (LE) is an important factor for monitoring crops, water requirements, and water consumption at local and regional scale. In this paper, we applied the semi-empirical model to estimate the daily latent heat flux (LE_d = Rn_d + A − B(Ts − Ta)). LE_d has been estimated using satellite images (Thematic Mapper sensor) and a local dataset (incoming and outgoing short- and long-wave radiation) measured during three years. We first estimated the daily net Radiation (Rn_d) from a linear equation derived from the instantaneous net Radiation (Rn_d = CRn_i + D). Subsequently, coefficients A and B have been estimated for two different cover vegetations (pasture and soybean). For each vegetation cover, an error analysis combining Rn_d, A, B, and surface and air temperatures has been calculated. Results showed that Rn_d had good performance (nonbias and low RMSE). LE_d errors for pasture and soybean were ±28 W m⁻² and ±40 W m⁻² respectively.     

Isotopic fractionation of zinc in tektites

Tektites are terrestrial natural glasses produced during a hypervelocity impact of an extraterrestrial projectile onto the Earth's surface. The similarity between the chemical and isotopic compositions of tektites and terrestrial upper continental crust implies that the tektites formed by fusion of such target rock. Tektites are among the driest rocks on Earth. Although volatilization at high temperature may have caused this extreme dryness, the exact mechanism of the water loss and the behavior of other volatile species during tektite formation are still debated. Volatilization can fractionate isotopes, therefore, comparing the isotope composition of volatile elements in tektites with that of their source rocks may help to understand the physical conditions during tektite formation.For this study, we have measured the Zn isotopic composition of 20 tektites from four different strewn fields. Almost all samples are enriched in heavy isotopes of Zn compared to the upper continental crust. On average, the different groups of tektites are isotopically distinct (listed from the isotopically lightest to the heaviest): Muong-Nong type indochinites (δ^66/64Zn = 0.61 ± 0.30‰); North American bediasites (δ^66/64Zn = 1.61 ± 0.49‰); Ivory Coast tektites (δ^66/64Zn = 1.66 ± 0.18‰); the Australasian tektites (others than the Muong Nong-type indochinites) (δ^66/64Zn = 1.84 ± 0.42‰); and Central European moldavites (δ^66/64Zn = 2.04 ± 0.19‰). These results are contrasted with a narrow range of δ^66/64Zn = 0–0.7‰ for a diverse spectrum of upper continental crust materials.The elemental abundance of Zn is negatively correlated with δ^66/64Zn, which may reflect that isotopic fractionation occurred by evaporation during the heating event upon tektite formation. Simple Rayleigh distillation predicts isotopic fractionations much larger than what is actually observed, therefore, such a model cannot account for the observed Zn isotope fractionation in tektites. We have developed a more realistic model of evaporation of Zn from a molten sphere: during its hypervelocity trajectory, the molten surface of the tektite will be entrained by viscous coupling with air that will then induce a velocity field inside the molten sphere. This velocity field induces significant radial chemical mixing within the tektite that accelerates the evaporation process. Our model, albeit parameter dependent, shows that both the isotopic composition and the chemical abundances measured in tektites can be produced by evaporation in a diffusion-limited regime.     

Analysis of aftershock sequences in South and Southeastern Spain

A probabilistic modeling is used to analyze the spatio-temporal behavior of eleven aftershock sequences occurred in South and Southeastern Spain. This study focuses on the analysis of two seismicity parameters: the b-value of the frequency-magnitude distribution, and the p-value, explaining the temporal decay rate of aftershocks. The estimated b values range between 0.77 ± 0.05 and 1.18 ± 0.10 close to the typical b-values of the aftershock frequency-magnitude relationship b ≈ 1.0. The estimated p-values range between 0.75 ± 0.03 and 1.43 ± 0.10 showing broad regimes of the temporal decay of aftershocks. The modified Bath’s law used to analyze the energy partitioning, suggests that a large fraction of the accumulated energy is released in the mainshock and relatively small fraction of energy is released during aftershock sequence, for example 80% of the total energy is released during the Mula 1999 mainshock, 88% during Bullas 2002 mainshock and 87% during La Paca 2005 mainshock. The fractal dimension D₂ is estimated using the correlation integral, and then used to derive the slip ratio, as the ratio of the slip occurred on primary fault segment to the total slip. For example, we obtained a slip ratio equal to 71% for the Mula 1999 aftershock sequence, 61% for the Bullas 2002 event, 58% for the La Paca 2005 aftershock, 50% for the Lorca 2011 sequence and 63% for the sequence triggered by the Gador 2002 mainshock.Finally, the correlations between the fractal dimension, the b-value and the p-value is analyzed, and the Aki’s relation D = 3b/c is discussed as well.     

Empirical relationship between leaf wax n-alkane δD and altitude in the Wuyi,Shennongjia and Tianshan Mountains,China: Implications for paleoaltimetry

Estimating past elevation not only provides evidence for vertical movements of the Earth's lithosphere, but also increases our understanding of interactions between tectonics, relief and climate in geological history. Development of biomarker hydrogen isotope-based paleoaltimetry techniques that can be applied to a wide range of sample types is therefore of continuing importance. Here we present leaf wax-derived n-alkane δD (δD_wax) values along three soil altitudinal transects, at different latitudes, in the Wuyi, Shennongjia and Tianshan Mountains in China, to investigate δD_wax gradients and the apparent fractionation between leaf wax and precipitation (ε_wax-p).We find that soil δD_wax track altitudinal variations of precipitation δD along the three transects that span variable environment conditions and vertical vegetation spectra. An empirical δD_wax-altitude relation is therefore established in which the average δD_wax lapse rate of ? 2.27 ± 0.38‰/100 m is suitable for predicting relative paleoelevation change (relative uplift). The application of this empirical gradient is restricted to phases in the mountain uplift stage when the atmospheric circulation had not distinctly changed and to when the climate was not arid. An empirical δD_wax–latitude–altitude formula is also calculated: δD_wax = 3.483LAT ? 0.0227ALT ? 261.5, which gives the preliminary spatial distribution pattern of δD_wax in modern China.Mean value of ε_wax-p in the extreme humid Wuyi Mountains is quite negative (? 154‰), compared to the humid Shennongjia (? 129‰) and the arid (but with abundant summer precipitation) Tianshan Mountains (? 130‰), which suggests aridity or water availability in the growing season is the primary factor controlling soil/sediment ε_wax-p. Along the Tianshan transects, values of ε_wax-p are speculated to be constant with altitude; while along the Wuyi and Shennongjia transects, ε_wax-p are also constant at the low-mid altitudes, but become slightly more negative at high altitudes which could be attributed to overestimates of precipitation δD or the vegetation shift to grass/conifer.Additionally, a reversal of altitude effect in the vertical variation of δD_wax was found in the alpine zone of the Tianshan Mountains, which might be caused by atmospheric circulation change with altitude. This implies that the paleo-circulation pattern and its changes should also be evaluated when stable isotope-based paleoaltimetry is applied.     

Coda-Q and its lapse time dependence analysis in the interaction zone of the Dinarides,the Alps and the Pannonian basin

The single backscattering model was used to estimate total attenuation of coda waves (Q_c) of local earthquakes recorded on eight seismological stations in the complex area of the western continental Croatia. We estimated Q₀ and n, parameters of the frequency dependent coda-Q using the relation Q_c = Q₀fⁿ. Lapse time dependence of these parameters was studied using a constant 30 s long time window that was slid along the coda of seismograms. Obtained Q_c were distributed into classes according to their lapse time, t_L. For t_L = 20–50 s we estimated Q₀ = 45–184 and n = 0.49–0.94, and for t_L = 60–100 s we obtained Q₀ = 119–316 and n = 0.37–0.82. There is a tendency of decrease of parameter n with increasing Q₀, and vice versa. The rates of change of both Q₀ and n seem to decrease for lapse times larger than 50–80 s, indicating an alteration in rock properties controlling coda attenuation at depths of about 100–160 km. A very good correlation was found between the frequency dependence parameter n and the Moho depths for lapse times of 50, 60 and 70 s.     

Persistent organic pollutants and stable isotopes in pinnipeds from King George Island,Antarctica

In the present work, fat, skin, liver and muscle samples from Leptonychotes weddellii (Weddell seal, n = 2 individuals), Lobodon carcinophagus (crabeater seal, n = 2), Arctocephalus gazella (Antarctic fur seal, n = 3) and Mirounga leonina (southern elephant seal, n = 1) were collected from King George Island, Antarctica, and analysed for POPs (PCBs, organochlorine pesticides and PBDEs) and stable isotopes (δ¹³C and δ¹⁵N in all tissues but fat). PBDEs could be found in only one sample (L. weddellii fat). Generally, PCBs (from 74 to 523 ng g⁻¹ lw), DDTs (from 14 to 168 ng g⁻¹ lw) and chlordanes (from 9 to 78 ng g⁻¹ lw) were the prevailing compounds. Results showed a clear stratification in accordance with ecological data. Nonetheless, stable isotope analyses provide a deeper insight into fluctuations due to migrations and nutritional stress. Correlation between δ¹⁵N and pollutants suggests, to some degree, a considerable ability to metabolize and/or excrete the majority of them.     

Remote sensing based water quality monitoring in Chivero and Manyame lakes of Zimbabwe

Lakes Chivero and Manyame are amongst Zimbabwe’s most polluted inland water bodies. MEdium Resolution Imaging Spectrometry level 1b full resolution imagery for 2011 and 2012 were used to derive chlorophyll-a (chl_a) and phycocyanin (blue-green algae) concentrations using a semi-empirical band ratio model; total suspended matter (TSM) concentrations were derived from the MERIS processor. In-situ measured chl_a was used to validate the remotely sensed values. Results indicate that remote sensing measurements are comparable with in situ measurements. A strong positive correlation (R² = 0.91; MAE = 2.75 mg/m³ (8.5%)) and p < 0.01 (highly significant)) between measured and modeled chl_a concentrations was obtained. Relationships between optically active water constituents were assessed. Measured chl_a correlated well with MERIS modeled phycocyanin (PC) concentration (R² = 0.9458; p < 0.01 (highly significant)) whilst chl_a and TSM gave (R² = 0.7344; p < 0.05 (significant)). Modeled TSM and PC concentrations manifested a good relationship with each other (R² = 9047; p < 0.001 (very highly significant)). We conclude that remote sensing data allow simultaneous retrieval of different water quality parameters as well as providing near real time and space results that can be used by water managers and policy makers to monitor water bodies.     

Laurentia crustal motion observed using TOPEX/POSEIDON radar altimetry over land

A new method to estimate the vertical crustal motion from satellite altimetry over land was developed. The method was tested around Hudson Bay, where the observed vertical motion is largely caused by the incomplete glacial isostatic adjustment (GIA) as a result of the Laurentide ice sheet deglaciation since the last glacial maximum (LGM). Decadal (1992–2003) TOPEX/POSEIDON radar altimetry data over land surfaces were used. The results presented here are improved compared to a previous study (Lee, H., Shum, C.K., Kuo, C.Y., Yi, Y., Braun, A., 2008. Application of TOPEX altimetry for solid Earth deformation studies. Terr. Atmos. Ocean. Sci. 19, 37–46. doi:10.3319/TAO.2008.19.1-2.37(SA).) which estimated vertical motion only over relatively flat land surfaces (standard deviation of the height variation <40 cm). In this study, we extended the concept of traditional 1-Hz (one-per-frame) radar altimeter ocean stackfiles to build 10-Hz (10-per-frame) land stackfiles over Hudson Bay land regions, and succeeded in obtaining vertical motion estimates over much rougher surfaces (standard deviation of the height variation <2 m). 90-m C-band Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) is used as a reference surface to select an optimal waveform retracker, to correct surface gradient errors, and to calculate land surface anomalies. Here, we developed an alternative retracker, called the modified threshold retracker, resulting in decadal vertical motion time series over a 1500 km by 1000 km region covering northern Ontario, northeastern Manitoba, and the Great Lakes region which is at the margin of the former Laurentide ice sheet. The average of the estimated uncertainties for the vertical motion is 2.9 mm/year which is comparable to 2.1 mm/year of recent GPS solutions. The estimated vertical motion is compared with other geodetic observations from GPS, tide gauge/altimetry, GRACE, and several GIA models. The data agree best with the laterally varying 3D GIA model, RF3S20 (β = 0.4) whereas the combination of land altimetry solution with other measurements match best with the models RF3S20 (β = 0.0) or RF3S20 (β = 0.2) in terms of mean and standard deviation of the differences. It is anticipated that this innovative technique could potentially be used to provide additional constraints for GIA model improvement, and be applied to other geodynamics studies.     

Formation of the Late Permian Panzhihua plutonic-hypabyssal-volcanic igneous complex: Implications for the genesis of Fe–Ti oxide deposits and A-type granites of SW China

The Late Permian (260 Ma) Emeishan large igneous province of SW China contains numerous magmatic Fe–Ti oxide deposits. The Fe–Ti oxide deposits occur in the lower parts of evolved layered gabbroic intrusions which are spatially and temporally associated with A-type granitic rocks. The 260 Ma Panzhihua layered gabbroic intrusion hosts one of the largest magmatic Fe–Ti oxide deposits in China and is coeval with a peralkaline A-type granitic pluton. The granite has intruded the overlying Emeishan flood basalts and fed at least one dyke which erupted onto the surface producing columnar jointed trachytes. The presence of syenodiorite between the layered gabbro and granite is evidence for compositional evolution from mafic to intermediate to felsic rocks. The syenodiorites have intermediate to felsic composition with SiO₂ = 61 to 65 wt.%, MgO = 0.27 to 0.6 wt.% and CaO = 1.0 to 2.5 wt.% as compared to the granite SiO₂ = 65 to 72 wt.%, MgO = 0.1 to 0.4 wt.%, CaO = < 1.0 wt.%. Primitive-mantle-normalized incompatible element plots show corresponding reciprocal patterns between the mafic and felsic rocks. The chondrite-normalized REE patterns show Eu anomalies changing from > 1(Eu/Eu? = 1.1 to 2.6) in the gabbroic intrusion, to < 1 in the syenodiorite (Eu/Eu? = 0.75 to 0.83), granites and trachytes (Eu/Eu? = 0.55–0.87). Previously published εNd_(T) values from clinopyroxenes (εNd_(T) = + 1.1 to + 3.2) of the gabbroic intrusion match the whole-rock values of the syenodiorite (εNd_(T) = + 2.1 to + 2.5), granite and trachyte (εNd_(T) = + 2.2 to + 2.9), suggesting that all rock types originated from the same mantle source. MELTS and trace element modeling confirm that all rock types can be generated by fractional crystallization of high-Ti Emeishan basalt. The jump in SiO₂ from the gabbro to the syenodiorite is attributed to the en masse crystallization of the Fe–Ti oxides. The geological and geochemical data indicate that fractional crystallization of a common parental magma produced the layered gabbroic intrusion and Fe–Ti oxide deposit, the syenodiorite, granites and trachyte of the Panzhihua region, which thus form a genetically related plutonic-hypabyssal-volcanic complex. Other granite–gabbro complexes in the region likely formed in a similar manner.     

Patterns of significant seismic quiescence on the Mexican Pacific coast

Many authors have proposed that the study of seismicity rates is an appropriate technique for evaluating how close a seismic gap may be to rupture. We designed an algorithm for identification of patterns of significant seismic quiescence by using the definition of seismic quiescence proposed by Schreider (1990). This algorithm shows the area of quiescence where an earthquake of great magnitude may probably occur. We have applied our algorithm to the earthquake catalog on the Mexican Pacific coast located between 14 and 21 degrees of North latitude and 94 and 106 degrees West longitude; with depths less than or equal to 60 km and magnitude greater than or equal to 4.3, which occurred from January, 1965 until December, 2014. We have found significant patterns of seismic quietude before the earthquakes of Oaxaca (November 1978, M_w = 7.8), Petatlán (March 1979, M_w = 7.6), Michoacán (September 1985, M_w = 8.0, and M_w = 7.6) and Colima (October 1995, M_w = 8.0). Fortunately, in this century earthquakes of great magnitude have not occurred in Mexico. However, we have identified well-defined seismic quiescences in the Guerrero seismic-gap, which are apparently correlated with the occurrence of silent earthquakes in 2002, 2006 and 2010 recently discovered by GPS technology.     

The use of Bayesian methods for fitting rating curves,with case studies

Using data from two very large watersheds and five smaller, this paper explores the use of Bayesian methods for fitting rating curves. Posterior distribution of rating-curve parameters were calculated using Markov Chain Monte Carlo (MCMC) methods, and 95% credible intervals were calculated for predicted discharges, given stage. Expected discharge was related to stage using a link function. For the five smaller watersheds, the assumptions were (a) that the distribution of discharge Q, given stage h, is Normal, with variance proportional to h; (b) that a log link function relates μ_Q, the mean of Q∣h, to a function of stage, of the form μ_Q = β(h + α)^λ. For the two large watersheds, however, a better fit was obtained by taking the distribution of Q to be log-Normal, and the link function as ln μ_Q = β₀ + β₁h. For the two large watersheds, priors for all three parameters were taken as uninformative; for the five smaller, the prior for parameter λ was taken as Normally distributed, N(2, 0.5). Acceptable ratings were obtained for all seven sites. It is argued that distributions of derived variables (such as annual maximum discharge) can be derived directly from (a) the posterior distribution of rating-curve parameters, and (b) the stage record, without recourse to additional assumptions. Estimates thus obtained for the T-year event will incorporate rating-curve uncertainty. It is argued that Bayesian methods are appropriate for rating-curve calculation because their inherent flexibility (a) allows the incorporation of prior information about the nature of a rating curve; (b) yields credible intervals for predicted discharges and quantities derived from them; (c) can be extended to allow for uncertainty in stage measurements.