Just over two years <a href=" http://www.astralroad.com/tag/book-marketing/ ">genericos viagra cialis levitra tc</a> Such events send waves rippling along the entire surface of the planet. At most well sites, these have little effect, but in a few cases they produce swarms of small tremors that are followed, months later, by larger, locally generated earthquakes. Van der Elst says that this type of seismic swarm might serve as a warning that an injection-well zone is on the verge of overloading its nearby faults, potentially producing a damaging earthquake.