Faults A fault is a planar fracture in a rock in which the rock on one side of the fracture has moved with respect to the rock on the other side. A fault that runs along the border between two tectonic plates is called a transform fault. The two sides of a non-vertical fault are called the hanging wall and footwall.
Faults can be categorized into three groups based on the sense of slip: • Dip-slip faults: It is classified into two types: normal and reverse faults. A normal fault occurs when the crust is extended. The hanging wall moves downward , relative to the footwall. A reverse fault is the opposite of a normal fault — the hanging wall moves up relative to the footwall. TYPES:
• Strike-slip faults: The fault surface is usually near vertical and the footwall moves either left or right or laterally with very little vertical motion. Strike-slip faults with left-lateral motion are also known as sinistral faults . Those with right-lateral motion are also known as dextral faults . • Oblique-slip faults: it is a mix of dip-slip and strike-slip faults. The hanging wall moves down or up and right or left relative to the footwall.
• Listric fault: A listric fault is a type of normal fault in which fault plane is curved. The dip of the fault plane becomes shallower with depth. • Ring faults: Are faults that occur within collapsed volcanic calderas. Ring faults may be filled by ring dikes.
EARTHQUAKES An earthquake is a jolt of the area caused by the shock of the tectonic plates and the liberation of energy. Most of them are too weak to be felt by people, but others cause enormous damages, as the ground shakes and building collapse. Earthquakes often happen on the San Andreas fault, because the two plates of the fault slide in the same direction at different speeds.
WHAT CAN WE DO TO PROTECT PEOPLE FROM EARTHQUAKES?
Major earthquakes have caused enormous damages. The science can help us to reduce the number of kills in earthquakes.
One of the precautions is not to live near plate borders, but this is not always posible because some big cities grew up before people knew about the risk of the earthquakes.
Another precaution we can take is the careful design of buildings. This can help to withstand earthquakes without collapsing.
The last precaution can be the prediction of the earthquake, but this is too difficult for scientists.
VOLCANOES Volcanoes are produced by enormous releases of energy and they can cause massive disasters. It is an opening in a planet’s surface, which allows hot magma, ash and gases to escape from below the surface. When the magma rises to the surface becomes known as lava, and this explosion is called eruption.
A supervolcano is a type of volcano that produces the largest and most voluminous eruptions on the Eart. They are formed from huge collapsed craters, called calderas, with a magma chamber beneath. The supervolcanoes are so powerful and destructive that only one eruption could alter all life on the Earth. Scientists say that the last supervolcano eruption was in Sumatra, 74,000 years ago. SUPERVOLCANOES