From a geostructural perspective, the Azores are located above an active triple junction between three of the world's major tectonic plates (the North American Plate, the Eurasian Plate and the African Plate), a condition that has translated into the existence of many faults and fractures in this region of the Atlantic. The westernmost islands of the archipelago (Corvo and Flores) are located on the North American Plate, while the remaining islands are located within the boundary that divides the Eurasian and African plates.
Owing to its geodynamic environment, the region has been a center of intense seismic activity, particularly along its tectonic boundaries on the Mid-Atlantic Ridge and Terceira Rift. Seismic events although frequent, are usually tectonic or vulco-tectonic in nature, but in general are of low to medium intensities, occasionally punctuated by events of level 5 or greater on the Richter magnitude scale. The most severe earthquake was registered in 1757, near Calheta on the island of São Jorge, which exceeded 7 on the Richter magnitude scale.
Cigarette smoke is a complex mixture of chemical compounds that are bound to aerosol particles or are free in the gas phase. Chemical compounds in tobacco can be distilled into smoke or can react to form other constituents that are then distilled to smoke. Researchers have estimated that cigarette smoke has 7,357 chemical compounds from many different classes (Rodgman and Perfetti 2009). In assessing the nature of tobacco smoke, scientists must consider chemical composition, concentrations of components, particle size, and particle charge (Dube and Green 1982). These characteristics vary with the cigarette design and the chemical nature of the product. 59ce067264