An overview on the seismicity of Cuba

The seismicity of Cuba is briefly presented together with a few fundamental neotectonic elements of the adjacent Caribbean region. The Cuban seismicity catalogue has been extended back to 1528 and it shows that the largest earthquakes occurred in 1766 and 1852 (I = IX MSK). Two types of seismicity (intraplate and interplate) can be distinguished in Cuba. Western and Eastern Seismotectonic Units correspond to intraplate type and the Southeastern Seismotectonic Unit to interplate type. Western Cuba is characterized by a low frequency of earthquake occurrence. Distribution of epicenters is not regular and the most important events mainly concentrate along two regional active fault system (Nortecubana and Surcubana). Due to the lack of seismic stations in this region, the characterization of seismicity is frequently done on the grounds of historical data available from 1693. The main seismogenic source for Cuba is the Bartlett-Cayman fault system, but inland there are other active structures. Some issues about historical and present day Cuban seismological research are also showed.     

Photoelectrons in the upper atmosphere: A formulation incorporating effects of transport

An efficient scheme is described for computation of photoelectron energy spectra. The method, similar to one used in radiative transfer theory, incorporates effects due to spatial and angular redistribution of electrons. These effects play a dominant role at heights above 400 km.     

A multimetric-index approach using fisheries data to assess fish assemblage structure in relation to salinity gradient in a tropical West African estuary

This study examines the effects of increasing salinity on fish assemblage structure in the Casamance Estuary, Senegal, using a series of indices. The study data were derived from commercial fishery surveys conducted between April and July 2005. Analysis of within-trophic-group diversity in the Casamance Estuary shows a significant drop in the diversity of apex predators in the upper, more saline reaches of the estuary. By contrast, primary consumers adapted well to salinity changes and exhibited higher taxonomic diversity in the upper reaches of the estuary than in the lower reaches. The findings also indicate decreases in average sizes of the landed species and the trophic levels among fish catches in the direction of the upper reaches. However, the catch per unit effort (CPUE) was globally higher in the upstream area of the estuary as compared with the downstream area. This increasing CPUE trend from the lower towards the upper reaches is attributed to (i) the high primary productivity in the upper Casamance Estuary; (ii) the increasing abundance of euryhaline fish species in an upstream direction; and (iii) ‘telescoping’ of the food chain through the presence of mostly herbivorous fishes in the upper reaches. Such a situation likely facilitated high fish production in the upstream area of the estuary, though multimetric indices indicated unfavourable living conditions for many fish taxa in this area.     

Classification of marine bioregions on the east coast of South Africa

Marine bioregional planning requires a meaningful classification and spatial delineation of the ocean environment using biological and physical characteristics. The relative inaccessibility of much of the ocean and the paucity of directly measured data spanning entire planning regions mean that surrogate data, such as satellite imagery, are frequently used to develop spatial classifications. However, due to a lack of appropriate biological data, these classifications often rely on abiotic variables, which act as surrogates for biodiversity. The aim of this study was to produce a fine-scale bioregional classification, using multivariate clustering, for the inshore and offshore marine environment off the east coast of South Africa, adjacent to the province of KwaZulu-Natal and out to the boundary of the exclusive economic zone (EEZ), 200 nautical miles offshore. We used remotely sensed data of sea surface temperature, chlorophyll a and turbidity, together with interpolated bathymetry and continental-slope data, as well as additional inshore data on sediments, seabed oxygen and bottom temperature. A multivariate k-means analysis was used to produce a fine-scale marine bioregionalisation, with three bioregions subdivided into 12 biozones. The offshore classification was primarily a pelagic bioregionalisation, whereas the inshore classification (on the continental shelf) was a coupled benthopelagic bioregionalisation, owing to the availability of benthic data for this area. The resulting classification was used as a base layer for a systematic conservation plan developed for the province, and provided the methods for subsequent planning conducted for the entire South African EEZ. Validation of the classification is currently being conducted in marine research programmes that are sampling benthic biota and habitats in a sampling design stratified according to the biozones delineated in this study.     

Seismotectonics of south-west Dominican Republic using recent data

The Dominican Republic has a high level of seismic activity, and a new seismic network has been installed to improve the detection of earthquakes. The network has been operated by Instituto Politécnico Loyola since 2012. It uses six new stations of its own, as well as 17 other stations publically available. In this study, we investigate in particular the south-west of the country where no seismic stations have been operating before. We find an area, SE of the Enriquillo Plantain Garden fault (responsible for the 2010 Haiti M7.0 earthquake), with a high seismic activity (M?=?2–4) compared to the surrounding area. This shallow seismicity (except two events around 40 km depth) is not seen in any global catalogs, and it does not seem to be associated with any known faults. However, the region has been under rapid recent uplift since margins between hills and valleys are filled with massive alluvial fans. We made 24 new fault plane solutions using P-polarities and S/P amplitude ratios. The solutions show mainly reverse mechanisms and the P-axis directions are mainly NNE oriented, which is in agreement with a published strain direction from GPS measurements. We conclude that the main cause of the seismicity in our study area is the push of the Beata Ridge against Enriquillo basin and the rest of the Gonave microplate, reflected in the mainly reverse focal mechanisms.     

Minimizing the impacts of contaminant intrusion in small water distribution networks through booster chlorination optimization

Contaminant intrusion in a water distribution network (DN) has three basic pre-conditions: source of contaminant (e.g., leaky sewer), a pathway (e.g., water main leaks), and a driving force (e.g., negative pressure). The impact of intrusion can be catastrophic if residual disinfectant (chlorine) is not present. To avoid microbiological water quality failure, higher levels of secondary chlorination doses can be a possible solution, but they can produce disinfectant by-products which lead to taste and odour complaints. This study presents a methodology to identify potential intrusion points in a DN and optimize booster chlorination based on trade-offs among microbiological risk, chemical risk and life-cycle cost for booster chlorination. A point-scoring scheme was developed to identify the potential intrusion points within a DN. It utilized factors such as pollutant source (e.g., sewer characteristics), pollution pathway (water main diameter, length, age, and surrounding soil properties, etc.), consequence of contamination (e.g., population, and land use), and operational factors (e.g., water pressure) integrated through a geographical information system using advanced ArcMap 10 operations. The contaminant intrusion was modelled for E. Coli O156: H7 (a microbiological indicator) using the EPANET-MSX programmer’s toolkit. The quantitative microbial risk assessment and chemical (human health) risk assessment frameworks were adapted to estimate risk potentials. Booster chlorination locations and dosages were selected using a multi-objective genetic algorithm. The methodology was illustrated through a case study on a portion of a municipal DN.     

Early warning system for rainfall-triggered landslides based on real-time probabilistic hazard assessment

Natural Hazards - A methodology to define rainfall-landslide thresholds, using a probabilistic model in which the accumulated rainfall at any time is treated as a random variable, is proposed. The...     

Observations of urban and suburban environments with global satellite scatterometer data

A global and consistent characterization of land use and land change in urban and suburban environments is crucial for many fundamental social and natural science studies and applications. Presented here is a dense sampling method (DSM) that uses satellite scatterometer data to delineate urban and intraurban areas at a posting scale of about 1 km. DSM results are analyzed together with information on population and housing censuses, with Landsat Enhanced Thematic Mapper Plus (ETM+) imagery, and with Defense Meteorological Satellite Program (DMSP) night-light data. The analyses include Dallas-Fort Worth and Phoenix in the United States, Bogotá in Colombia, Dhaka in Bangladesh, Guangzhou in China, and Quito in Ecuador. Results show that scatterometer signatures correspond to buildings and infrastructures in urban and suburban environments. City extents detected by scatterometer data are significantly smaller than city light extents, but not all urban areas are detectable by the current SeaWinds scatterometer on the QuikSCAT satellite. Core commercial and industrial areas with high buildings and large factories are identified as high-backscatter centers. Data from DSM backscatter and DMSP nighttime lights have a good correlation with population density. However, the correlation relations from the two satellite datasets are different for different cities indicating that they contain complementary information. Together with night-light and census data, DSM and satellite scatterometer data provide new observations to study global urban and suburban environments and their changes. Furthermore, the capability of DSM to identify hydrological channels on the Greenland ice sheet and ecological biomes in central Africa demonstrates that DSM can be used to observe persistent structures in natural environments at a km scale, providing contemporaneous data to study human impacts beyond urban and suburban areas.     

Communicating human health risks associated with disinfection by-products in drinking water supplies: a fuzzy-based approach

Chlorine used for the disinfection of water supplies can react with naturally occurring organic compounds and form potentially harmful disinfection by-products (DBPs). A risk index for two regulated groups of chlorinated DBPs—trihalomethanes (THMs) and haloacetic acids (HAAs), using fuzzy C-means (FCM) clustering algorithm and fuzzy rule-based modeling is proposed for risk communication. The proposed index evaluates the cancer and non-cancer risks individually for THMs and HAAs using the FCM algorithm. Subsequently, two different fuzzy rule-bases were used to evaluate the overall risk-index based on cancer and non-cancer risks. The overall risk-index will provide drinking water utilities with an effective communication tool for communicating aggregated water quality compliance. Simulated DBP occurrence data obtained from the City of Quebec, Canada, is used to demonstrate the application of this methodology.