The Rim of Fire is making its presence keenly felt again with three devastating earthquakes and one tsunami, stretching from Samoa to Sumatra, in the space of three days from September 29 to October 1 2009.  As we watch the television coverage of the sufferings of these fragile areas of the world, hoping that our governments will do something to help alleviate the distress and perhaps dipping into our own depleted pockets, should we be worrying that this is just a warning of the death and destruction that could be coming soon to a Pacific population centre much nearer home?

Shaped like a 40,000 kilometre-long horseshoe, the zone known as the Pacific Rim of Fire stretches along the west coast of the Americas from Alaska in the north to Tierra del Fuego in the south and on towards Antarctica.  It resumes its course in New Zealand and travels northwards through the coastal nations of eastern Asia before arriving in far eastern Russia.

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It is a region renowned for volcanic eruptions, earthquakes and tsunamis, and it features 452 volcanoes, including the USA’s Mount St.Helens, Mexico’s Paricutin, Mount Pinatubo in the Philippines and Mount Fuji in Japan.

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Ninety percent of the world’s earthquakes occur in the Pacific Ring of Fire, as plates in the earth’s crust move and collide with each other.  Indonesia, site of the two most recent earthquakes on the island of Sumatra, sits in a perilous position between the Rim of Fire and the Alpide Belt, another area of heavy seismic activity extending from the island of Java and through the Himalayas to southern Europe and the Atlantic Ocean.

Earthquakes are especially terrifying because they occur without advance warning.  Unlike storms and floods there is no efficient way of predicting them, and they can cause massive casualties and property damage in heavily-populated areas such as Kobe in Japan, where the 1995 earthquake killed more than 5,000 people and caused damage costing over $300 billion, and the ‘great Tokyo fire’ caused by the Kanto earthquake of 1923. The December 26 2004 earthquake in the Indian Ocean off the coast of Sumatra triggered the devastating tsunami which killed approximately 230,000 people, mostly in Indonesia, Sri Lanka, Thailand and India.

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It had a magnitude of 9.3, the second largest earthquake ever recorded on a seismograph.  (The largest was a 9.5  magnitude in Valdivia, Chile in 1960.)  Fatalities caused by earthquakes depend less on their magnitude than on their location, since deep ocean earthquakes tens of thousands of kilometres from land will not cause the collapse of buildings and devastating fires, and resulting tsunamis will lose their force before reaching landfall.

California has its own very active earthquake zone, the San Andreas fault, and Washington state has the volcano Mount St. Helens which erupted in 1980.  So, should the USA be worried that the terrifying events in south east Asia will be coming to its own shores?  The USgovernment’s National Earthquake Hazards Reduction Program (NEHRP) began trying, from the 1970s onwards, to find geological methods of predicting the likely location and timing of earthquakes in order to reduce death and injury by giving advance warning.  However, the task proved more difficult than anticipated, and the NEHRP website now describes the program as playing a “lead role to plan and coordinate this national effort to mitigate earthquake losses by developing and applying earth science data and assessments essential for land-use planning, engineering design, and emergency preparedness decisions”.  They are also developing early warning systems that are triggered immediately a quake has started, thus giving people and businesses farther away from the epicentre a few minutes or even seconds to flee from danger, or to shut down or back up critical systems such as a nuclear power plant.  An interesting feature of the website is Lastest Earthquakes In The World which links to a US Geological Survey page showing the magnitude and location of earthquakes in the last seven days in the USA and the rest of the world.  The sobering fact is, major earthquakes cannot be predicted.

The prediction of volcanic eruptions is less problematic since it is always preceded by seismic activity, usually allowing some time for the issuing of warnings between the seismic event and the actual eruption.  Instruments are used to  measure changes in the behaviour of a volcano, the surrounding land and the escaping gases, which could signal that an eruption is about to happen.

Tsunamis can also be predicted, to a certain extent.  Tsunami warning systems have two elements:

The first element is a network of sensors to detect earthquakes which might trigger a tsunami.  Seismic waves travel at about 14,400 kilometres  per hour, whereas tsunamis travel more slowly, relatively speaking, at between 500 and 1,000 kilometres per hour. Thus a warning of a potential tsunami could be issued to a coastal population several hours before it is likely to arrive.  However, this will not be of much help if the undersea earthquake occurs very close to a coastal region, reducing the possible warning time to minutes instead of hours.  There have been reports that this was the case with the recent tsunami in Samoa and American Samoa

The second element is an effective communication system to issue the warnings when it is decided they are necessary.  Unfortunately, because there is no foolproof way of deciding which earthquakes will trigger tsunamis, it is likely that many warnings will turn out to be false alarms, thus reducing their effectiveness.  It also presupposes that the coastal population has some high ground on which to take refuge, which is regrettably not always the case for tiny Pacific islands.

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So, are the seismic events in Samoa and Sumatra an indication that something new and dangerous is happening in the Ring of Fire?  No.  They are only a reminder that the earth beneath our feet is not as stable as we think.  If we choose to live on the rim of the Pacific Ocean we need to be aware of the risks and accept that our chances of avoiding harm from volcanoes and tsunamis depend on the effectiveness of the monitoring systems and how prepared we are to heed any warnings that are issued.  As for earthquakes, the source of many evils, it seems we can only cross our fingers and hope for the best, or go live somewhere else.