EARTH QUICK 

A man inspects the damage from the quake.

Earthquake epicenters occur mostly along tectonic plate boundaries, and especially on the Pacific Ring of Fire.

Global plate tectonic movement

An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in size from those that are so weak that they cannot be felt to those violent enough to toss people around and destroy whole cities. The seismicity, or seismic activity, of an area is the frequency, type and size of earthquakes experienced over a period of time. The word tremor is also used for non-earthquake seismic rumbling.

At the Earth's surface, earthquakes manifest themselves by shaking and displacing or disrupting the ground. When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides, and occasionally volcanic activity.

In its most general sense, the word earthquake is used to describe any seismic event — whether natural or caused by humans — that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults, but also by other events such as volcanic activity, landslides, mine blasts, and nuclear tests. An earthquake's point of initial rupture is called its focus or hypocenter. The epicenter is the point at ground level directly above the hypocenter.

.protection 

Protecting cities from earthquakes is still a grand challenge that needs addressing, as recent disasters in Nepal, Japan, Haiti, and Chile confirm. Although significant progress has been made in understanding seismic activity and developing building technology, we still don’t have a satisfactory way of protecting buildings on a large scale.

For new buildings, anti-seismic technology is today considered quite advanced and it is possible to build individual structures that can withstand the vast majority of recorded earthquakes. Devices such as isolation systems and dampers, which are designed to reduce the vibrations (and as a consequence the damage) of structures induced by earthquakes, are successfully employed in the design of new buildings.

But large numbers of buildings exist in earthquake zones that don’t have built-in protection, particularly in developing countries where replacing them or introducing stricter – and more expensive – building codes aren’t seen as an option. More than 130,000 houseswere destroyed by the earthquake in Nepal in April 2015.

What’s more, these technologies are rarely used for protecting existing buildings, as they generally require substantial alteration of the original structure. In the case of heritage buildings, critical facilities or urban housing especially in developing countries, traditional localised solutions might be impractical.

This means there is a need for alternative solutions that protect multiple existing buildings without altering them using a single device. At the University of Brighton, we have designed a novel vibrating barrier (ViBa) to reduce the vibrations of nearby structures caused by an earthquake’s ground waves. The device would be buried in the soil and detached from surrounding buildings, and should be able to absorb a significant portion of the dynamic energy arising from the ground motion with a consequent reduction of seismic response (between 40-80%).

In need of protection. Narendra Shrestha/EPA

The idea behind this is to look at buildings as an integral part of a city model, which also includes the soil underneath and the interaction between each element, rather than as independent structures. Each ViBa can be designed to protect one or more buildings from an earthquake but also it forms part of a network of devices placed at strategic locations in order to protect entire cities.

The ViBa itself is essentially a box containing a solid central mass held in place by springs. These allow the mass to move back and forth and absorb the vibrations created by seismic waves. The entire structure is connected to the foundations of buildings through the soil to absorb vibrations from them. The box’s position underground would depend on how deep the surrounding foundations went and could even be placed on the surface.

As the ViBa is designed to reduce all vibrations in the soil, it could also be used to insulate buildings against ground waves from human activities such as road traffic, high-speed trains, large machinery, rock drilling and blasting. In this way, the technology would be able to absorb a larger quantity of energy than traditional measures used to insulate railways such as trenches or buried sheet-pile walls.

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