Our Habitat looks this week at earthquakes – about which there has been some news in the media over the last two weeks. We begin with a look at what they are, how they occur, and how they are measured. Have questions or comments? E-mail williamsp@jamaicaobserver.com.

EARTHQUAKES – also called temblors, quakes, shakers or seismic activity – are phenomena resulting from the shaking, rolling or sudden shock of the earth’s surface.

Wikipedia online encyclopaedia describes it as “a sudden release of stored energy in the earth’s crust that creates seismic waves”.

The Southern Cross University (SCU) website notes that an earthquake occurs when rocks break under the stress of “constant movement and collision of the thin jigsaw-like tectonic plates found at the surface of the Earth”.

The breakage is called “faulting” and as such it may be said that earthquakes occur on faultlines in the earth’s crust. The breakage results in a release of energy as stored stress is suddenly converted to movement.

The vibrations produced are known as seismic waves, which “travel outwards in all directions at up to 14 kilometres per second”, the SCU website notes. While the waves distort the rock they pass through, the rock will return to its original shape afterward.

There exists, meanwhile, what is called the epicentre of the earthquake. It refers to that point on the earth’s surface that is located directly above the source or focus of the earthquake, which may be as deep as 700 kilometres.

Earthquakes do not occur deeper than this because rocks are no longer rigid at very high pressures and temperatures.

Smaller earthquakes occur more frequently, causing little or no damage. A very large earthquake may be succeeded by a series of smaller aftershocks while minor faulting occurs during an adjustment period that may last for several months.

Earthquakes may also cause tsunamis (giant ocean-waves). These waves are capable of travelling for miles across the ocean, while its impact may be felt for several hours after inception. The damage caused may be extensive, as was seen in south-east Asia in 2005.

Measuring earthquakes

The strength of earthquakes may be measured using the popular Richter scale. Earthquakes measuring below 2.0 on the Richter scale cannot be felt, even as those measuring 4.0, while felt, do not cause damage. Those measuring above 5.0 on the scale do cause damage. Earthquakes measuring 6.0 on the scale are regarded as strong while those measuring 7.0 are considered major and will do serious damage.

The Richter magnitude scale was developed in 1935 by Charles F Richter (1891-1989) of the California Institute of Technology. Richter, an American seismologist, was studying earthquakes in California at the time and needed a simple way to measure, comparatively, the size of earthquakes.

Sources: the Federal Emergency Managemnet Agency website www.fema.gov/kids/quake.htm, the Southern Cross University website, www.scu.edu.au, and wikipedia online encyclopedia.

More on earthquakes next week.

Our Habitat this week continues the series on sea birds that may be found at Yallahs Pond in St Thomas. The bird species that will be looked at this week are the Turkey Vulture and the Royal Tern.

The Turkey Vulture (cathartes aura)

Also referred to as the “John Crow” in Jamaica, the turkey vulture is a large bird with a red, bare-skinned face as well as long wings and tail. It grows up to between 64 and 81 centimetres and has a wingspan of between 170 and 178 centimetres.

It may weigh up to 2000 grams or 70.6 inches. Its body feathers are entirely blackish-brown. While both male and female appear similar, the female is a tad larger.

A quiet bird, the turkey vulture will, however, hiss at carcasses, roosts and nests, according to information from the web site www.birds.cornell.edu.

The bird uses its sense of smell to pinpoint the location of carrion (dead, rotting flesh). That section of the turkey vulture’s brain which processes smell is larger than that identified in other birds. Typically, it looks for food on its own.

It is able to sustain its stability and lift in the sky without flapping its wings by holding them (wings) up in a flight v-shape and teetering from side to side as it flies.

The turkey vulture, meanwhile, passes its feces on its legs and subsequently uses the water from the feces to cool itself down.

The Royal Tern (sterna maxima)

The Royal tern may be found only along ocean beaches, such as at Yallahs Pond in St Thomas. Growing to between 45 and 50 centimetres, this bird has a wingspan of between 125 and 135 centimetres and weighs up to 450 grams, or 15.89 ounces.

It makes its nest on the ground of low-lying islands. It thereafter passes its feces along the rim of the nest – some believe this is so the nest is protected from floods. After a number of weeks, the feces on the rim will harden.

Young birds of this specie will lave the nest only a day after hatching and get together in a group called a crèche. The crèche can comprise ages two to 35 days old. Of note is the fact that a pair of adult Royal Terns will feed only their own young, which they are able to identify, it is suggested, recognising the young’s call (http:www.birds.cornell.edu).

The Royal Tern feeds on a steady diet of fish and shrimp.

The bird also goes by the names Stern Royale in French, and Pagaza Real in Spanish.