Plate tectonics. The progress of the earth sciences and the advancement of technologies associated with the understanding of our planet during the 1940's and 50's have led geologists to develop a new way of looking at the world and how it works. This exhibit explains the history of our new understanding of the Earth and provides a brief overview of the theories behind it.
AVI version Animated gifs Last 750 million years: [1.04 MB] [506 KB] [261 KB] Last 750 million years in reverse: [1.04 MB] [506 KB] From 750 mya to the beginning of the Paleozoic: [294 KB] [166 KB] From 750 mya to the beginning of the Mesozoic: [532 KB] [284 KB] [156 KB] From the beginning of the Mesozoic to Recent: [301 KB] [163 KB] [96 KB] All animations built from maps used with the permission of C.R. Scotese, PALEOMAP Project. …………………………… There are a number of excellent sites dealing with the modern theory of plate tectonics. Here is a modest sample:
Finally, it seems appropriate to mention the Alfred Wegener Institute, the German national research center for polar and marine research, carrying on Wegener's tradition of interdisciplinary earth science. Sources:
|
http://www.ucmp.berkeley.edu/geology/tectonics.html
Shifting grounds: Is increasing seismic activity in north India a sign of worry?
The Himalayan region is the most active seismic regions in the world because it is at the edge or boundary of the Indian plate which is colliding with the stationary Eurasian plate.
DINESH C SHARMA | MAIL TODAY | NEW DELHI, MAY 5, 2013 | UPDATED 11:40 IST
Increasing seismic activity in north India a sign of worry?
This week, five earthquakes of mild or moderate intensity rocked parts of Jammu and Kashmir. Their magnitude ranged from 3.7 to 5.8.
Though the last one felt on Friday in Kishtwar was of magnitude 3.7, it caused more damage and was felt widely as it occurred at a shallow depth of five kilometers and in a relatively populated area.
All the rest were on the border of Jammu and Kashmir, and Himachal Pradesh. This seismic activity in the North India was preceded by quakes in Pakistan, Afghanistan and Iran in the recent weeks. Some of them were felt as far as the national capital.
While it is known that the Himalayan belt and North India are in the high seismicity zone, the question foremost in people's mind is - has seismicity in the region gone up?
"Yes, this perception is right to a great extent. We are currently in a 'seismically active window period' globally," pointed out Dr Rajender Kumar Chadha, chief scientist at the National Geophysical Research Institute (NGRI), Hyderabad.
An analysis of earthquakes in the past 110 years shows that while average occurrence of quakes in different seismic zones has not changed, there are seismically active periods lasting for 15 to 20 years during which the occurrence of large or great earthquakes increases.
"The first such period was 1905-1920 during which several quakes of magnitude 8 and above occurred. The second window was 1950-1965 - which saw the worst-ever quake of 9.5 magnitude in Chile. During both these windows the rate of smaller quakes also increased.
Third such period of high seismicity has begun with the 2004 Sumatra quake of 9.3 magnitude. Going by this theory, we will see quakes of magnitude 8.5 and above over the next four or five years. Whether these quakes will be in the Himalayas, Japan, Chile or Indonesia, nobody can predict just yet", Dr Chadha said.
However, other experts like American seismologist Roger Bilham believe that a great earthquake is long overdue in the Himalayan region. As per the plate tectonics theory, the Indian plate is moving in a North-North-East direction and is colliding with the Eurasian plate along the Himalayan mountain range.
This collision is responsible for the formation of faults such as Main Boundary Thrust and Main Central Thrust in and along the Himalayas. All big quakes in India and the region occur along these faults.
The Himalayan region is the most active seismic regions in the world because it is at the edge or boundary of the Indian plate which is colliding with the stationary Eurasian plate.
The plate motion, monitored through a GPS network along the boundary and elsewhere in the shield, shows the Indian plate moving at a speed of 5 centimetres a year. It is much faster than the speed of other tectonic plates.
Scientists also believe that the Northwards moving Indian plate is breaking away from the Australian plate, probably somewhere South of Sri Lanka in the Indian Ocean. This is the zone of diffused seismicity.
"It may take one million years or so for the Indian plate to break from the Australian plate, according to the current hypothesis", Dr Chadha said.
The increased frequency of quakes that we are seeing currently is an aftermath of the 2004 quake in Sumatra, which shook up the entire earth even causing it to wobble a bit from its axis.
In addition to quakes on the boundary, increased seismic activity in the Peninsular India is being witnessed. These are called intraplate quakes. For instance, several tremors of magnitude 2 and 3 have been recorded in Andhra Pradesh in a short span of time.
In the Koyna region in Maharashtra and Bhuj region in Gujarat, there is moderate rise in seismic activity. All such tremors, scientists point out, can be attributed to stresses building up due compressive forces arising out of the movement of the Indian plate.
In this scenario, the right thing to do would be to make buildings and cities safer and citizens more aware.
http://indiatoday.intoday.in/story/increasing-seismic-activity-north-india-sign-of-worry-india-today/1/269352.html