Natural disasters:

Earthquake storms?

Earthquakes - a powerful word that sends shivers down one's spine and causes many to panic, especially those who have been unfortunate victims of this; one of the world's worst natural disasters. Millions of people around the world live in fear of earthquakes that cause such havoc and misery wherever they strike.

Even though our little island has not experienced a devastating earthquake as such, we have certainly been victims of the destructive monster an earthquake could trigger off - a tsunami. The entire world was aghast by the trail of death and destruction the tsunami left in December 2004, as a result of an earthquake which occurred in the sea off the Island of Sumatra. Now, even in our country, more attention is paid to earthquakes that occur in the Asian region, not just to monitor the threat of a tsunami, but also the possibility of an earthquake that could affect our country, directly. All this time we were very complacent about the dangers of earthquakes because our country was not located in the 'earthquake belt.' But now, seismologists and geologists say that new plates are forming in the region bringing our little island nation, more closer to an earthquake belt.

Since, many of you may not be aware of all the scientific details of earthquakes and what causes them, we'll briefly explain them to you, later (see Fast facts), but what we like to highlight today is yet another aspect of earthquakes - a relatively new theory that is still being researched into.

We like to enlighten you about something called earthquake storms - yes, sounds strange because we normally don't associate storms with earthquakes. But - the storms in this connection are not like the usual storms we are familiar with. So, let's check out as to what exactly an earthquake storms is.

It is a series of large earthquakes that take place along the same plate boundary, triggered off by one on the plate.

As we said before, an earthquake storm is a recently proposed theory that came about following certain observations made by experts in the field as far back as 1992.

We know by now that earthquakes are unpredictable and no matter how much sophisticated the monitoring equipment is, no one can predict the exact time an earthquake would strike. So, serious attempts are being made the world over to know more about these natural phenomena by studying earthquakes that have already struck. It was during such research into an earthquake that took place in 1992 in a town called Landers in California, that a scientist Dr. Rose Stein came up with a new theory. Three hours after the Landers earthquake another earthquake had struck at a place called Big Bear, which is 67 km away from Landers. Dr. Stein had been of the view that the earthquake at Big Bear was NOT an aftershock of the earthquake at Landers, but a separate earthquake triggered off by the one at Landers.

Stein believed that when an earthquake occurs the stress that has built up along the fault, is transferred, in part, along the fault line. Now you are bound to be confused as to what a fault is, so refer the 'Fast facts' for clarification. Accordingly, he theorised that it was this energy transfer that caused other quakes to occur, hours, days or months after the original earthquake.

Now, since this was something that was yet to be checked out, Stein and his team had used a computer model which they had already been working on to study the relationship between earthquakes. The data collected from the Landers/Big Bear quake had enabled them to create a model that could predict where the 'stress' from the Landers quake would have been transferred to. What do you think the result of the calculations on the computer model was? Just as they theorised; the stress would have been transferred along the fault line to - Big Bear.They had then plotted all the subsequent 'aftershocks' and discovered that virtually all of them had taken place within a high-risk area the team had labelled as the 'red zone.' Even though this did not directly prove the theory of an earthquake storm, scientists from around the world were strongly attracted by this new theory.

And, going by the available data on earthquakes, there was indeed one part of the world where this theory might just hold true. Where do you think it was? Turkey.

The cyclic behaviour of the North Anatolian Fault in northern Turkey had fascinated Professor Geoffrey King. So, he used Dr. Stein and his team's computer model to study this behaviour; earthquakes in this particular region moved from east to west with a period of quiet at the end before the cycle began again.King initially studied an earthquake that hit the city of Erizican in 1939. Then using available data and the computer model he discovered that a town called Tokat in the west was within the red or danger zone. And in 1942, Tokat was hit by a quake. The model seemed to be working because another town in the red zone, Adapazari was hit in 1967. It certainly seemed as if the stress was being transferred to the west. As the quakes were separated by years, not hours, the possibility of them being 'aftershocks' was ruled out.What's interesting is that King discovered the next possible point for an earthquake by using this method. It was a city called Izmit with a population of about 500,000 people. Even if the earthquake cannot be prevented, at least buildings could be improved and modified to withstand the quake and minimise damage and loss of lives. So, the remarkable news was made public via newspapers, science journals and other publications. But, unfortunately there wasn't enough time for action and also not enough of interest from the local community. And was King right? Yes, tragically. In August 1999, a massive energetic earthquake, lasting just 45 seconds, struck Izmit, killing over 25,000 people.Going by this theory and using the data from Izmit King plotted the next possible site. The result caused a great deal of concern because at the edge of the red zone lay Istanbul a city which is home to more than four million people. If the earthquake storm theory is right and King's predications are accurate, Istanbul is in grave danger.

Only time will tell whether this populace city will be hit by an earthquake or not.

More on earthquakes next week.

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Fast facts

What is an earthquake?

An earthquake is a shaking of the ground caused by the sudden breaking and movement of large sections (tectonic plates) of the Earth's rocky outermost crust. The edges of the tectonic plates are marked by faults (lines of weakness or fractures). Most earthquakes occur along the fault lines when the plates slide past each other or collide against each other, when pressure builds up beneath the Earth's crust.Sometimes tension can be built up for hundreds or thousands of years before it's released in a great quake.

The shifting masses send out shock waves that may be powerful enough to alter the surface of the Earth, thrusting up cliffs and opening great cracks in the ground, that cause great damage.

The collapse of buildings and other man-made structures, broken power and gas lines (and the consequent fire), landslides, snow avalanches, tsunamis (giant sea waves) and volcanic eruptions, are some of the after effects of earthquakes.

Earthquake-prone areas like San Francisco and Los Angeles continue to be at risk from a large quake.

What is an earthquake's epicentre?

It's the scientific name given to the location on the surface of the Earth that is above the focal point of an earthquake. From this point the waves of the earthquake radiate outward, like the ripples in a pond.The Hypocenter is the location below the Earth surface where the earthquake starts.

Fault or fault plane is the surface area where two blocks of the Earth suddenly slip past one another. one such place. The San Andreas Fault stretches about 650 miles (1,050 kilometres) along the California coast, from San Francisco in the north to the Mojave desert in the south. There are many such faults all over the world.

What is the Richter scale?

The Richter Scale (named after Charles F Richter) who developed it in 1935 is used to measure the magnitude of earthquakes. The scale, more formally known as the Richter magnitude test scale, ranges from 0 to over 8.0. It is a logarithmic scale, meaning each unit increase on the scale corresponds to an absolute increase by an order of magnitude, or factor of 10.

Earthquakes less than about 2 on the Richter scale are meaningless as they can barely even be measured, much less felt. An earthquake is not really newsworthy until it hits about 5. At magnitudes of 7.0 or 8.0 the damage can be catastrophic.

The magnitude of an earthquake (the amount of energy at its point of origin) is measured using a seismometer. The original Richter scale was based on a particular sort of seismometer.

Earthquakes cannot be measured very accurately using the Richter scale when the magnitude is above about 8.3, so a more modern measuring metric known as the seismic moment is commonly used.

How often do they occur?

Great earthquakes, with a magnitude of 8.0 or greater, happen about once a year. Smaller earthquakes happen hundreds or thousands of times a year. Some of these can barely be measured. An earthquake smaller than 3.0 on the Richter scale cannot be felt by most people. The largest earthquake ever recorded measured 9.5 on the Richter scale, and occurred in Chile, but caused damage as far away as Hawaii due to tsunamis. The 2004 tsunami was also caused by such an earthquake.

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The San Andreas Fault

* The average rate of motion across the San Andreas Fault Zone during the past three million years is 56 mm/yr (2 in/yr). This is about the same rate at which your fingernails grow. Assuming this rate continues, scientists project that Los Angeles and San Francisco will be adjacent to one another in approximately 15 million years.

* The San Andreas fault is NOT a single, continuous fault, but rather is actually a fault zone made up of many segments. Movement may occur along any of the many fault segments along the zone at any time. The San Andreas fault system is more than 1300 km (800 miles) long, and in some spots is as much as 16 km (10 miles) deep.

* The origin of the name of the San Andreas Fault is often cited as the San Andreas Lake. However, based on some 1895 and 1908 reports by geologist A.C. Lawson, who named the fault, the name was actually taken from the San Andreas Valley. He did not realise at the time that the fault ran almost the entire length of California!

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