News raced around the world last week of a 6.7 Richter Scale earthquake that hit Kos on the Aegean Sea. While we don’t get too many big ones of the kind that happened here, we are in a seismically active zone of the world.
You may well have a story to tell of how the earth moved while you were with the love of your life on a Kavas yacht – not just after a romantic dinner when you were alone together… Earthquakes happen all the time but you aren’t at a great risk of being killed by one.
A US news agency (NBC news) reported the event las week: “Two people were killed and at least 100 injured after a magnitude 6.7 earthquake rocked popular Greek and Turkish tourist destinations on the Aegean Sea early Friday, the U.S. Geological Survey and officials said. The earthquake sent tourists and locals running into the streets on the Greek island of Kos and the Turkish port city of Bodrum shortly after 1.30 a.m.”
There was a minor tsunami too. The Independent news website reported, “Authorities had given advance warning of a tsunami, and witnesses described a “swelling” of the sea after the earthquake. A seafront road and parts of the island’s main town were flooded, and the rising seawater pushed a boat onto the main road, causing several cars to slam into each other.”
At the end of the day, journalists love a good scare story. As writers we want to mess with your emotions and be remembered. The facts aren’t as worrying as some tabloid hack would have you believe.
The Richter Scale
The US Geological Survey website explains that the Richter Scale is a logarithmic progression. A magnitude 2 on the scale is 10 times greater than a magnitude 1. The site explains, “a magnitude 5.3 might be computed for a moderate earthquake, and a strong earthquake might be rated as magnitude 6.3.
Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; as an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.”
You may not notice a 4.2 magnitude earthquake yet a 6.7 will shake you about a lot.
Let’s look at some facts
According to the Earthquaketrack.com website, there have been eight earthquakes in the Aegean Sea region in the last month. Most of them have been knee tremblers at around 4.2 on the Richter Scale. The last magnitude 6 or above we had in the region was three years ago, and 16 years ago there were two in one year.
Japan is one of the wealthiest countries in the world, yet experiences a lot more earthquakes than we do here in Greece. The Factsanddetails.com
“In the last 75 years, the Japanese archipelago or areas immediately offshore have experienced five earthquakes measuring more than eight on the Richter scale; and 17 measuring more than seven on the Richter scale. It is unusual for a year to go by without three or four earthquakes measuring 6.0 or more.”
In Japan you will almost certainly feel an earthquake of the magnitude we had in Greece at least once a year while we see them far less often.
At the surface of the Earth, there are a number of ‘tectonic plates’ that float on the magma beneath us. Some get pushed up in a collision (the Himalayas are a classic example of this with Mount Everest growing in height by several centimetres a year) while others get pushed under another, as happens in the Pacific near Japan and close to us in Greece.
A 2003 paper explained (link), “The results of geological, satellite and earthquake data in the Aegean and surrounding regions show that the African plate is converging due north with respect to the Eurasian Plate, leading to subduction of a remnant ocean under the Aegean lithosphere.
The subduction rate is fast enough to produce a degree of roll-back at the Hellenic trench, leading to stretching of the overriding plate.” In short, the African tectonic plate is being pushed under the Eurasian Plate. When the plates move there is an earthquake.
Other research has shown there is a risk of tsunamis (‘tidal waves’) (link) : “The historic record shows that parts of both the Turkish and Greek coastlines were struck by destructive tsunamis (Yalciner et al., 2001, 2004). Most of the historic tsunamis have occurred along well known geologic fault zones and volcanoes.
However, there are numerous other areas that can generate destructive tsunamis in the Mediterranean region in the future.” Earthquake induced tsunamis occur when the sea bottom over the tectonic plate moves up or down, and forces the entire sea to move, as would happen when you lift your hand up in a basin of water. Again, in the last earthquake it was a relatively tiny amount – enough to push a boat across a road but not enough to swamp a port.
What this all means
In most cases, being at sea is the best place to be during an earthquake. You won’t feel it. If you see a one metre tsunami (a very big one that hasn’t occurred for many years in the region) you would be a little unamused but a one metre wave at sea, at the end of the day isn’t unusual.
All modern building codes in Greece ensure that buildings can withstand large tremors without causing fatalities. You may see cracks in modern buildings after the 6.7 quake that hit last week but they are the safer place to be. If you are in an older building (built before the 1970’s) then it may be an idea to get out.
The message is clear – you may well experience an earthquake here in Greece, but the risks of a major one based on recent historical data are low. While we could never say the ‘Big One’ will never hit (let’s face it, they have and will), the likelihood is that you won’t be here when it occurs. Geological time is measured in millennia – your time in Greece is measured in weeks!