27.10.2013 A matter of seconds
Scientists in Japan and elsewhere have developed earthquake
early warning systems. Where do we stand?
By Akseeb Jawed
What does preparedness for an earthquake actually mean? Can there be an effective earthquake warning system? Before we look into the questions let us first briefly see what is an earthquake and how does it come about?
According to definition, earthquakes are the result of shifting or movement of earth’s tectonic plates. Earthquakes occur when the frictional stress of gliding plate boundaries builds and causes rupture at a fault line. As a result, elastic strain energy is released and waves radiate, shaking the ground.
As we know, major earthquakes affect large areas of population either by generating tsunamis or leveling the entire cities. Comparatively speaking, minor earthquakes can also be induced or caused by human activities like extraction of minerals from the earth and the collapse of large buildings.
Scientists can predict where major earthquakes might happen in a general sense, but research does not yet allow forecasts for specific locations or accurate predictions of timing.
Approximately, two-thirds of the total area of Pakistan is on fault lines, putting the lives and property of more than 170 million people at risk. Now and then, experts have expressed concerns that neglecting the fault lines while making big structures in cities might be the cause of massive destruction.
Pakistan has been hit by some forty earthquakes to this day, some of them deadly. Recently, Pakistan was jolted by an intense earthquake of 7.7 magnitude. The epicenter of the earthquake was 69km north of Awaran district in Quetta and some 270km north of Karachi. The shocks were also felt in Turbat, Panjgur, Chaghai, Khuzdar, Gwadar, Quetta, Hub, Kharan, Jhal Magsi, Qalat, Sibi, Mastung, and Jafferabad, and even in Karachi.
Four major tectonic plates — Arabia, Eurasia, India, and Africa — and one smaller tectonic block — Anatolia — are the cause for tectonic activities in the Middle East and the adjacent regions.
In geological terms, the Aawran earthquake occurred due to oblique north-south to northeast-southwest strike-slip type motion at shallow crustal depths that is primarily accommodated on the Chaman faultline, with the earthquake potentially occurring on one of the southern-most strands of this fault system.
The Chaman faultline runs along Pakistan’s western frontier with Afghanistan from Kalat, in the northern Makran range, past Quetta and then on to Kabul, Afghanistan. A faultline also runs along the Makran coast and is believed to be of the same nature as the west coast faultline along the coast of Maharashtra, India.
We cannot totally escape from an earthquake but we can be a survivor if given a 60 seconds head start before an impending earthquake due to an early-warning system. How is it possible to issue a warning of the phenomenon that cannot even be predicted?
The statement of seismologist, Richard Allen, director of the Seismological Laboratory at the University of California, Berkeley, aptly resolves this paradox. Generally, when people talk about prediction, they’re talking about when an earthquake will occur — when rocks in a fault slip past each other. Most seismologists say we won’t be able to predict this for the foreseeable future. We’re predicting the shaking that comes from when the earthquake ruptures. So, basically, an earthquake has already started.
People think of an earthquake as being an instantaneous occurrence. It’s not. The energy that radiates out from an earthquake is what causes the shaking that people feel. P waves come first and S waves come next, as they carry most of the energy so they do most of the damage. The intensity of the shaking that’s carried by the S waves can be estimated, and that’s the basis for an early warning. Basically, the warning provides an advantage of sixty seconds which, in turn, also depends on the distance from the epicenter.
Earthquake early-warning system is designed to detect the first strong pulse coming from an earthquake, which carries information about its size. This shockwave travels faster than the slower waves that do most of the shaking damage during an earthquake. The farther you are from an earthquake’s epicenter, the more warning you get. Therefore, the governments in some of the earthquake-prone countries, like Japan, Mexico, and the State of California, institute early warning systems to alert the public to expect potentially hazardous shaking.
In 2007, Japan launched a comprehensive nationwide online earthquake early-warning system. It is considered as one of the most advanced systems as yet. It detects tremors, calculates an earthquake’s epicenter and sends out brief warnings from its 1,000-plus seismographs scattered throughout the country via mobile phones, radio, TV, and sirens. Area Mail Disaster Information Service disseminates earthquake early warnings issued by Japan Meteorological Agency.
The subscribers of the service receive the information via mobile phones either in the form of pop-up display or special emergency tone. In California, the scientists are in the early stages of developing the techniques and framework of earthquake early-warning system. They are following the lead of Japan in developing their warning system.
Although the early warning systems can only give warnings from seconds to one or two minutes before the powerful S-waves hit and shaking gets serious, it can mean the difference between life and death. It can be just enough time to take cover, drive a car to the side of the road, step back from getting on an elevator or stop medical surgery, turn off gas burners, or duck preparedness, move away from windows, etc, to reduce the risk of injury and minimize damage.
Experts say most of the major cities of Pakistan are located on the faultline, which also crosses the centre of Margalla Hills. Therefore, Pakistan Meteorological Department (PMD) should work on developing an effective earthquake warning system. Moreover, PMD should enhance the potentiality of the existing National Seismic and Tsunami Monitoring System that is responsible for disseminating earthquake information.
The writer is a researcher based in Islamabad