National Geographic: Extreme ocean storms have ramped up in frequency over the past 30 years, according to new research based on small tremors. The faint tremors, called microseisms, are periodic movements of Earth’s surface that can last anywhere from 5 to 30 seconds. Unlike earthquakes, which are caused by movements of Earth’s tectonic plates, microseisms are created by the incessant beating of waves along the coasts. The phenomena are usually dismissed as background noise by scientists …