Mark Ellis 13Bn
Geography
Earthquakes don’t kill people. Buildings do!
Tectonic folding, faulting and warping of rocks form major features of the earth’s surface such as mountain ranges and ocean basins. Earthquakes, volcanoes and tsunamis are hazards that result from these major geological processes. Earthquakes can be located on conservative, constructive and destructive plate margins. At a conservative margin the tectonic plates move past each other resulting in shear stresses. The motion occurs along a break in the crust known as a fault. At a constructive plate margin (along the ocean ridges) earthquakes are shallow and are a result of volcanic activity as magma is moving upwards, but these earthquakes pose no threat to people as they are submarine. On a destructive plate margin (where oceanic plate is being sub-ducted beneath a continental plate or where two oceanic plates collide in island arc zones) the compressional force causes crustal stresses and earthquakes can occur in medium and deep depths. These areas can pose a threat to people living near the coast near one of these margins. These earthquakes can also cause tsunamis. Also on a destructive margin, there can be continental crust colliding to produce mountain ranges. This is where shallow earthquakes can occur and pose a threat to people aswell as many people do live in the mountain ranges, for example in Iran, June 1990, strees was caused between the Arabian plate and Eurasian plate, these two plates created the Elburz mountains, and caused 35000 deaths and 100000 injuries. Areas of lateral crust movement in continental regions cause mainly shallow earthquakes, and example of this is the San Andreas fault in the USA. Although with all of this said some 15% of earthquakes occur in stable continental crust. These earthquakes are called intra-late earthquakes, and can be caused by stresses due to plate movement but also have other causes and this is why it is hard to predict them. Isostatic recoil can causes some stresses in crustal rocks that may reactivate ancient faults.
