The United States Geological Survey, or USGS, monitors earthquakes and land movement over extended periods of time to update fault line maps. They primarily use GPS monitors that track differences in tectonic plate positions. Additional information is obtained from Geodetic satellites operated by NOAA, the National Oceanic and Atmospheric Administration.Continue Reading
A tectonic plate is a section of the Earth's crust that floats on top of the mantle, which is made up of molten rock. As one tectonic plate butts up against another, it creates pressure. The two plates create fault lines, which is where pressure is stored and eventually released in an earthquake.
One example is the Pacific Plate that pushes against the North American Plate, creating the San Andreas Fault. GPS monitors reaching from Southern California to the Canadian border keep track of the movement of that fault, as well as smaller faults. Sometimes after an earthquake event, scientists discover new faults and add them to the maps.
NOAH's Geodetic satellites help map undersea faults. One example is in a part of the Indian Ocean where three plates come together on the seafloor. The satellites monitor plate movement and can also advise of volcanic activity. The latter is caused by plates moving over pools of molten lava that are closer to the surface, also known as "hot spots."Learn more about Maps & Cartography