Acehtsunami

An example of a deep underwater explosion is the WAHOO test, which was carried out in 1958 as part of Operation Hardtack. The nuclear device was detonated at a depth of 500 feet (150 m) in deep water. There was little evidence of a fireball. The spray dome rose to a height of 900 feet (270 m). Gas from the bubble broke through the spray dome to form jets which shot out in all directions and reached heights of up to 1700 feet (520 m). The base surge at its maximum size was 2½ miles (4 km) in diameter and 1000 feet (300 m) high.

The heights of surface waves generated by deep underwater explosions are greater because more energy is delivered to the water. Deep underwater explosions are thus particularly able to damage coastal areas, because surface waves increase in height as they move over shallow water, and can flood the land beyond the shoreline. Many of the theories and concepts about these waves are similar to those that are applicable to other types of surface waves, in particular, tsunamis, and waves generated by the fall of a meteor.

If a deep underwater explosion occurs at a sufficient depth, the rising gas bubble can overexpand because the gas pressure falls below the pressure of the surrounding water. This causes the bubble to collapse, which causes a second shock wave and bubble expansion. This may be repeated, though there are unlikely to be more than three expansions. An example is the WIGWAM test, which was carried out in 1955. The nuclear device was detonated at a depth of 2000 feet (600 m)

You’re going about your normal daily routine when suddenly, something is not quite right. It may be frighteningly obvious, like watching your shelves emptied by a sudden and violent shaking that stops just as mysteriously as it began. It may be very subtle, perhaps just a slight queasy feeling and the gentle swaying of a hanging lamp. If you’re in a wide open space and in a good mood, it can even be fun — a free roller coaster ride that lasts a few seconds. Whatever the case, experiencing an earthquake tends to leave a lasting impression.

If you’ve lived in southern California for more than a year or two, it’s likely you’ve had an experience similar to one of those mentioned above. Maybe you’ve even had several. Certainly you’ve heard the news reports. Reporters talk at length about faults and aftershocks and magnitudes, and we grow accustomed to hearing these words, and even using them in conversation. But despite the ability of earthquakes to strike awe in all of us — amazed and a little fearful as we are of their power and unpredictable nature — many people never really come to understand the concepts behind them.

Before you launch into this module, which is designed to help you understand what earthquakes are all about, here’s a chance to test your knowledge of earthquakes in a fun way. In the activity below, you will take on the role of emergency response and, armed only with your knowledge of seismology, stage a rescue in Pinevale!

The enormity of the tragedy that scarred Orissa in the aftermath of the super cyclone is yet to be assessed. But a question arises: Is nature biased against poorer people and developing countries? Even a cursory analysis of the scale of natural disasters, whether floods, earthquakes or hurricanes, would show that economically developed countries have a much greater resilience to withstand calamities and suffer far lower loss of life.

In Orissa the human tragedy was clearly the handiwork of man. Orissa is a state rich in natural resources. Its people, among the poorest, can not be accused of over-consumption and greed. Policies of the state at the Central and state levels have ensured that much of these resources are utilised or underutilised. In India, this lack of development has been the result of 50 years of state control over the economy. As a result, there are no resources left to deal with calamities like the recent cyclone.

Even 10 days after the cyclone, no clear information had emerged about the scale of destruction. The communication system, which has almost been a handmaiden of the state in India, as is now clear, was totally inadequate. Instead of a wide range of technology, from local broadcasting stations, wireless, telephone and satellites, continuously informing the people of the impending disaster and advising them of precautions to be taken, the information barely flowed.

The Mid-Atlantic Ridge, a submerged mountain range, which extends from the Arctic Ocean to beyond the southern tip of Africa, is a divergent tectonic plate boundary. It is just one segment of the global mid-ocean ridge system that encircles the Earth. The rate of spreading along the Mid-Atlantic Ridge averages about 2.5 centimeters per year, or 25 km in a million years. The Mid-Atlantic Ridge separates the Eurasian Plate and the North American Plate in the North Atlantic, and separates the African Plate from the South American Plate in the South Atlantic.

1992 Erzincan Earthquake, Turkey

The 1755 Lisbon earthquake also known as the Great Lisbon Earthquake, took place on November 1, 1755, at just about 9:40 in the morning. The earthquake was followed by a tsunami and fires, which caused near-total damage of Lisbon in Portugal, and adjoining areas. Geologists today estimate the Lisbon earthquake approached magnitude 9 on the Richter scale, with an epicenter in the Atlantic Ocean about 200 km (120 mi) west-southwest of Cape St. Vincent. Estimates place the death toll in Lisbon alone between 10,000 and 100,000 people, making it one of the most harsh earthquakes in history.

The earthquake accentuated political tensions in Portugal and profoundly disrupted the country’s eighteenth-century colonial ambitions. The event was widely discussed and dwelt upon by European Enlightenment philosophers, and inspired main developments in theodicy and in the philosophy of the sublime. As the first earthquake studied scientifically for its effects over a large area, it led to the birth of modern seismology and earthquake engineering.