Changes brought about by the earthquakes?
The earthquakes cause major changes in the crust and on the surface of the Earth. Important changes are as given below:
(1). Expansion of Earth’s Crust
(2). Contraction of Earth
(3). Disturbance of drainage system
(4). Mud Volcanoes
(5). Cultural Landscape
(8). Liquefaction, Subsidence, and Related Effects
(1). Expansion of Earth’s crust:
Earth’s crust is displaced as a result of the earthquake. Violent shaking of the crust causes the formation of cracks or faults planes, which bring changes below and above the surface of Earth. The displacement can be vertical or lateral in the shape of fault scarp, fault trace, or fault plane. When a fault is created, the result is visible at the surface in the form of fault scarp. It is the exposed cliff-like face of the fault plane, the surface of contact along, which blocks on either side of a fault move. The lower edge of the fault scarp is called a fault trace. A band of crushed rock pieces called fault breccia lie along the trace.
(2). Contraction of Earth:
An earthquake also causes the contraction of Earth because the ends of the joints come closer. The contraction of Earth causes collapses of river bridges along with the doubling, buckling, or bending of railway lines, and pipelines.
(3). Disturbance of drainage system:
As a result of the earthquake, the drainage system is disturbed because the expansion and construction affect the beds of water bodies below the Earth’s surface. Similarly, in some cases, fountains of water gush forth, whereas lakes are drained at some places. For example, in one of the earthquakes, the Lungarno Pacnotti in Pisa (Italy) dropped nine feet creating deep crevices on the road.
(4). Mud Volcanoes:
Sometimes an earthquake releases jets of water, which gather mud and sand at their mouths. Later on, the mud rises high and abrupt the shape of a cone which is called a mud volcano.
(5). Cultural Landscape:
An earthquake brings dramatic changes to the cultural landscape. It offsets linear features such as roads, hedges, pipelines, electricity towers, telephone lines, and poles besides devastating tall buildings and bridges.
The rupture of ground and shaking of unstable slopes cause land sliding. The slide land bulks can easily destroy buildings and paths in their way. They can also block the roads and railway tracks. Landsliding bulks can also take the hill top homes along with them as they tumble. Land sliding material can also block the streams and can dam the rivers, like in August 17 1959 Hebgen Lake (South western Montana).
Tsunami, which is popularly misconceived as ”Tidal Waves”. They are a devastating grave hazard to many parts of the world, particularly around the Pacific Ocean basin. These hazardous waves are caused by seafloor movement caused by seismic energy under the seawater. These waves can travel vast distances in a short period of time. Tsunami waves can travel by a velocity of 700 km/hr, comparable to some jet planes, and when a tsunami reaches shallow water in the sea, their height may reach up to a height of 27 meters (90 feet). The starting waves of the tsunami are very gentle and slow motion, but the later waves rise abruptly with a huge water mass and momentum. The tsunami waves bring enormous destruction to the buildings and infrastructures coming in their way.
(8). Liquefaction, Subsidence, and Related Effects:
Liquefaction and subsidence of the ground are other outcomes of earthquakes. These two phenomena are very common on an unconsolidated ground. When the loosely packed, water-logged sediments at or near the ground surface lose their strength in response to strong ground shaking, it is known as Liquefaction. Major damage during earthquakes occurs when liquefaction is under the buildings and infrastructures. While subsidence means the sudden sinkage of ground surface deep into the ground due to underground movement of the material. The underground movement of the material is most often caused by the removal of water, oil, natural gas, or mineral resources out of the ground by pumping, fracking, or mining activities.
Buildings have actually tipped over and sunk partway into liquefied soils, as in the 1964 Niigata earthquake in Japan. Underground gas tanks and septic tanks (yuck!) have been known to float to the surface through liquefied soils. All told, liquefaction and associated effects resulted in more than $20 billion damage in the 1995 Kobe earthquake, and similar levels of damage are possible in US port facilities during a large earthquake.
Earthquake cause another disaster in the form of fire. Ground rupture, liquefaction and subsidence may rupture gas and water pipelines. The rupture of gas and water mains can easily contribute to the ignition of fires and also hinder to control of the broken-out fire. For instance, during the 1994 Northridge earthquake, there were actually places where water was pouring down streets from broken water mains — and at the same spot and same time, fire was roaring out of ruptured gas mains! Shaking also contributes to starting fires, by knocking down power lines, spilling flammable liquids from storage containers, and tossing hot coals from barbeques and stoves. In the 1923 Kanto earthquake in Japan nearly 100,000 people died — over 70,000 of them due to fires that swept the area after the earthquake. And of course, most of the damage in San Francisco from the 1906 earthquake was caused by the subsequent fires.