Even though it is impossible to prevent an earthquake or volcanic eruption from happening, millions of people live in regions around the world that are prone to these natural disasters. Therefore, scientists must learn more about earthquakes and volcanoes to predict where and when they will occur. Specialized devices to monitor movement in Earth's crust provide scientists with information about changes at plate boundaries and the activity of volcanoes.
By monitoring plate movement and volcanic activity around-the-clock, scientists have noticed that earthquakes and volcanoes often provide a few hints before they strike or erupt. Usually, changes to the level or shape of the ground occur. These changes are caused by stress building up in layers of rock caused as plates push against one another at a fault. It can also be caused as magma rises and fills a volcano's magma chamber. The change in volume caused by the magma can exert tremendous pressure upon the walls within the volcano resulting in a bulge. These surface changes are closely monitored so scientists can predict the location and magnitude of an earthquake or the extent to which a volcano may erupt.
Tilt Meters
Scientists use tilt meters to detect elevation changes of the land. Tilt meters work like a carpenter's level, where a bubble is placed in a tube of liquid. Any change in elevation on either side of the tube will move the bubble. The degree of tilt is recorded by how far the bubble moves. Tilt meters are usually placed near the edge of a fault or on the slope of a volcano.
Lasers
In order to detect very small surface movements, electronic distance measurements are made using lasers. A laser beam is aimed at a reflector placed some distance away, which reflects the beam back to the device. A computer calculates the distance by calculating the time it took for the laser to bounce back. Laser measurements are sensitive enough to detect land movements of just 1 mm (0.04 in.) over a distance of 1 km (0.6 mi)!
Satellites
One of the most effective ways of detecting surface changes is by remote sensing using satellites. Orbiting from such a high altitude, satellites are extremely useful tools for monitoring change because they are able to monitor Earth's surface on a wide scale.
Satellites equipped with imaging radar can detect changes in the elevation and tilt of the ground surface, and have mapped changes caused by earthquakes and volcanoes. Ground-based receivers of Global Positioning System (GPS) satellite navigation signals can monitor the direction in which plates move. This gives scientists, like Dr. Walter Smith, a more complete understanding of the mechanisms driving plate tectonics and the different interactions between plates.
Satellites can also be equipped with temperature sensors, which monitor Earth's surface temperature changes. Temperature increases detected in surface layers of rock near a volcano are usually the result of magma rising, a sign that a volcano is about to erupt. Volcanic activity can also be monitored using sensors that detect the release of ash and gas by volcanoes.
Seismographic Data
Because a large proportion of earthquakes and eruptions occur near faults, which are tectonic boundaries, it is important for geologists to determine where boundaries are located. Some are easy to see, like parts the San Andreas Fault on the west coast of North America or the Great Rift Valley in northeastern Africa. Others are buried under layers of rock, soil, and water, or are hidden by dense vegetation.
Seismographs can be used to detect these hidden boundaries by detecting and measuring the reflection of seismic waves. When seismic waves encounter boundaries, such as faults, they reflect. By locating areas where these reflections occur, scientists can map the depth and length of these boundaries.
Monitoring seismic activity can also reveal areas along faults that have very little seismic activity compared to other areas along the fault. One might think that an area around a fault that did not have much seismic activity would be safe. However, the absence of earthquakes can indicate that the plate boundaries are "stuck," and if they become "unstuck," they could unleash a powerful earthquake.
Undersea Mapping
Dr. Walter Smith's sea-floor mapping work also provides us with valuable knowledge about earthquakes and volcanoes. His maps help scientists predict potential locations for earthquakes, tsunamis, and undersea volcanic eruptions. Using Walter's maps, scientists can estimate the motion of plates and the potential magnitude of earthquakes in certain regions of the world by identifying the plate boundaries. They can also use his maps to identify the many volcanoes hidden beneath hundreds, and even thousands, of meters of water.
Creating maps of the ocean floor, studying the direction and speed in which plates move, and monitoring earthquakes and volcanoes are helping us better understand the dynamic nature of our world. The application of the knowledge we gain from these scientific studies is also helping to protect people and property around the world.