Identification of precipitation zones within São Francisco River basin (Brazil) by global wavelet power spectra

Abstract

The definition of rainfall behaviour at the regional level is of great importance in planning policy for the rational use of water resources for both agricultural and urban uses. It allows the delimitation of areas of homogeneous rainfall features and shows the system dynamics in the area, so providing more comprehensive knowledge about the rainfall. Precipitation zones were identified within the São Francisco River basin, Northeast Brazil, by analysing the rainfall frequencies by means of global wavelet power spectra. Data from 200 raingauges were analysed and the results of the overall power spectra showed a high annual frequency throughout the basin; however, other frequencies are present with minor significance that represent changes in the rainfall regime. Although, the computed global wavelet power spectra presented an annual frequency, they showed peculiar patterns (denoted A and B) that could be used to characterize the region. Thus, three sub-regions with homogeneous rainfall patterns were identified as: Region A (south part of the basin) and Region B (north part of the basin), with frequency patterns A and B, respectively, and a Transition Zone in the central part that shows both frequency patterns.

Citation Santos, C.A.G. and Morais, B.S., 2013. Identification of precipitation zones within São Francisco River basin (Brazil) by global wavelet power spectra. Hydrological Sciences Journal, 58 (4), 789–796.     

In-Well Degassing of Monitoring Wells Completed in Gas-Charged Aquifers

Total dissolved gas pressure (P_TDG) measurements are useful to measure accurate in situ dissolved gas concentrations in groundwater, but challenged by in-well degassing. Although in-well degassing has been widely observed, its cause(s) are not clear. We investigated the mechanism(s) by which gas-charged groundwater in a recently pumped well becomes degassed. Vertical P_TDG and dissolved gas concentration profiles were monitored in the standing water column (SWC) of a groundwater well screened in a gas-charged aquifer for 7 days before and 15 days after pumping. Prior to pumping, P_TDG values remained relatively constant and below calculated bubbling pressure (P_BUB) at all depths. In contrast, significant increases in P_TDG were observed at all depths after pumping was initiated, as fresh groundwater with elevated in situ P_TDG values was pumped through the well screen. After pumping ceased, P_TDG values decreased to below P_BUB at all depths over the 15-day post-pumping period, indicating well degassing was active over this time frame. Vertical profiles of estimated dissolved gas concentrations before and after pumping provided insight into the mechanism(s) by which in-well degassing occurred in the SWC. During both monitoring periods, downward mixing of dominant atmospheric and/or tracer gases, and upwards mixing of dominant groundwater gases were observed in the SWC. The key mechanisms responsible for in-well degassing were (i) bubble exsolution when P_TDG exceeded P_BUB as gas-charged well water moves upwards in the SWC during recovery (i.e., hydraulic gradient driven convection), (ii) microadvection caused by the upward migration of bubbles under buoyancy, and (iii) long-term, thermally driven vertical convection.     

Stretch-free generalized normal moveout correction

The effective application of normal moveout correction processes mainly depends on four factors: the chosen traveltime approximation, the stretching associated with the given traveltime, crossing events and phase changes, the last two being inherent to the seismic data. In this context, we conduct a quantitative analysis on stretching considering a general traveltime expression depending on half-offset and midpoint coordinates. Through this analysis, we propose a mathematically proven procedure to eliminate stretching, which can be applied to any traveltime approximation. The proposed method is applied to synthetic and real data sets, considering different traveltime approximations and achieved complete elimination of stretching.     

The 9th of July 1998 Faial Island (Azores,North Atlantic) seismic sequence

The Faial earthquake (M _L 5.8) that occurred on the 9th of July, 1998, in the Azores region (north Atlantic), caused nine casualties and severe destruction affecting more than 5,000 people. The main shock was located at sea, 10 km NE of the Faial Island, and triggered a seismic sequence that lasted for several weeks and was characterized by an unusual high p-value of 1.40 for the modified Omori law. We present here the results of a joint inversion of hypocenters and 1D velocity model performed on the data collected by the permanent network complemented with a temporary network installed shortly after the occurrence of the main event. The 1D velocity model shows a heterogeneous upper crust, testified by the observed differences in site effects at the stations, while the middle crust from ∼2.5 to 8 km in depth is quite homogeneous. The Moho is located at a depth of about 12–13 km and the Vp/Vs ratio is found to be around 1.78. The events at depth are mainly concentrated in the middle-lower crust (8–12 km), while their spatial distribution shows a main cluster, visible after relocation, SSE trending. This direction of elongation is consistent with one of the fault planes (N151°E) of the centroid moment tensor (CMT) solution for the main shock. The same plane is the preferred main shock fault plane inferred after a Coulomb failure function analysis on the aftershock distribution. The main event relocation points to a focal depth shallower than 5 km. The aftershocks pattern shows that several fault systems were reactivated by the stress perturbation induced by the main shock. Besides the two main tectonic directions, trending WNW–ESE and NNW–SSE, observed in the tectonics of Faial, Pico, and S. Jorge, there is also evidence of a new tectonic direction trending WSW–ENE.     

Multi-scale approach using remote sensing images to characterize the iron deposit N1 influence areas in Carajás Mineral Province (Brazilian Amazon)

Mining activities cause a wide range of changes to the environment, substantially affecting both the physical and biological environmental sectors. In the Carajás Mineral Province, located in the Amazon rainforest, environmental regulations tend to be more rigorous, due to the fragility of the environment in which large iron deposits are found. The characterization of the impact of mining on environment considers: the type and extent of the impact, the physical chemistry differences and similarities of the mineral deposits, the deposit size, the adopted mining process, and the environment (both natural and economic) in which the mining process was developed. Remote sensing technology is utilized in this study, in particular, the use of ortho-aerial photograph, and optical and radar images with distinct spatial resolution. These permit the elaboration in synoptic maps, multi-scale and dynamic, of the changes wrought upon the environment: deforestation, removal of vegetation cover, topographic surface and landscape alteration, and slope instabilities among others. In this aspect, determining the extent of influence of the mining activity is directly tied to the characterization of its impact on various natural systems at the observed scale, and not by simply defining a predetermined Euclidean distance. The results showed that remote sensing technology, optical and radar images, proved to be efficient in the study of environmental information and the areas of influence on the semi-regional and local scales in the Amazon forest.     

Changes over a decade in fish assemblages exposed to both environmental and fishing constraints in the Sine Saloum estuary (Senegal)

To investigate the changes in the fish assemblage of the Sine Saloum estuary (Senegal) over a 10-year period, it was surveyed during a complete hydrological cycle (three principal hydro-climatic seasons) first in 1992 and then in 2002–2003. The sampling protocol for the two surveys was identical, using the same sampling technique, the same collection periods, and the same sampling stations.     

High-performance computing strategies for seismic-imaging software on the cluster and cloud-computing environments

Modern subsurface imaging techniques allow obtaining high-quality images but with high computational costs. Nonetheless, depending on the amount of data, their execution is limited by memory in the current generation's hardware. However, with the advancement of new hardware and cloud-based solutions, these problems are mitigated but still with the risk of work loss and instability. To mitigate the execution problems in memory-limited and fail-prone environments, we propose two high-performance computing techniques. The first is based on independent checkpointing alongside a fault-tolerant framework to store an execution state and recover from that state in case of failures. Besides, for memory-limited graphics processing units, we present a technique to reduce the amount of memory requirement that we call the hybrid strategy. The experiments showed that the independent checkpointing alongside the fault-tolerant framework is able to mitigate the performance penalty of node failures, with the independent checkpointing technique being more relevant when multiple nodes are terminated. Furthermore, the hybrid strategy technique has shown the possibility of execution of larger models that could make the graphics processing unit run out of memory otherwise. Finally, our implementation is scalable, allowing a significant improvement in performance when adding new nodes. In conclusion, our techniques can be used to deliver fast, high-fidelity subsurface imaging in unstable and memory-limited environments, such as the cloud.     

The Jolomba,Angola LL6 chondrite

Abstract— Accompanied by loud thunder at about 1.30 pm (local time) on 3 February 1974, a single stone weighing approx. 480 g was seen to fall and was recovered near the Jolomba village, Huambo District, Angola. The stone is strongly brecciated, has dark-greyish angular fragments within a lighter matrix and does not exhibit any chondritic textures. Jolomba consists of olivine (Fa 31), orthopyroxene (Fs 25), sodic plagioclase (An 11), sulphides (troilite), very scarce nickel-iron (Ni up to 56%), oxides (chromite and ilmenite) and apatite. Pervasive fracturing of silicates suggests that Jolomba suffered strong brecciation and partial recrystallization. Mineralogy and bulk chemical analysis indicate that Jolomba belongs to the LL group of chondrites (amphoterites). Uniform olivine and pyroxene composition, well-crystallized plagioclase and textural features in general indicate that Jolomba belongs to the petrologic type 6.