Story URL: http://news.medill.northwestern.edu/chicago/news.aspx?id=211393
Story Retrieval Date: 9/18/2014 10:41:39 AM CST
You are vacationing on the beach far from home and the ocean suddenly recedes.
What do you do?
Earthquakes and tsunamis are hard to predict. Right now, the best way to reduce the number of deaths is education and adhering to strict building codes.
“Let’s think about the many tourists who were in Thailand and were victims of the tsunami,” said Emile Okal, seismologist from Northwestern University. “It turns out that very few Japanese tourists died because they noticed the anomalous behavior of the sea, which started by recessing away from the beach, and they went up to the top stories of the big hotels because they know about tsunamis.”
“There were also many Swedes who were in the hotels on the beach, and when they saw the sea recess, they said, ‘Hey, that’s funny. Let’s go and take a closer look.’ And they were completely washed away by the sea when it came back,” Okal said. “Why? Because these people were not educated to the dangers of tsunamis.”
Even people who don’t live in earthquake-tsunami danger zones need to be educated.
“All over the world, we need to educate people to these dangers because in this day and age, the Swedes are vacationing in Thailand, and if it isn’t vacation, your business can take you there,” Okal said.
Adherence to strict building codes also helps save lives.
“I’m reasonably optimistic that the enactment and the enforcement of building codes and fire codes in the United States can be counted on,” Okal said.
With the Loma Prieta (1989) and Northridge (1994) earthquakes in California, only about 65 people died during each earthquake. In contrast, during the Armenian earthquake of 1988, which was similar to the Loma Prieta earthquake in magnitude, 50,000 people died. During the Japanese earthquake in 1995, which was similar to the Northridge earthquake in magnitude, 5,000 people died, Okal said.
“And you have to ask the question, ‘Why?’” Okal said. “In Armenia, when they went through the rubble of the buildings, supposedly reinforced buildings, they couldn’t find the steel bars because they had been stolen. What was disastrous in Kobe, Japan, was that the city was engulfed in fires, and the expressways which were built essentially on viaducts all over town collapsed because they were poorly built.”
What can you do when there is a tsunami?
“It depends on the size of the event — it depends on many factors, but it’s a matter of a few minutes to maybe something like 20 minutes, typically, [before the sea rushes back in as a tsunami],” Okal said. “It is short, which means you don’t have time to do anything that would involve several steps in your action.”
Okal warns not to take a car because you will get stuck in a traffic jam. It is better to run or bike to a higher altitude, or take refuge in a tall building above the fifth floor if you are near a tsunami’s origin.
“If you are at a great distance, you have the luxury of time,” Okal said. “A tsunami propagates roughly at the speed of a jet plane in the Pacific. If you are in the far field, usually, the local civil defense people know what they’re doing, and you should follow their evacuation orders. In the far field, you can probably take a car.”
If you are close to the earthquake-tsunami, there is not much time to evacuate because we can’t predict earthquakes. But we do know how earthquakes and tsunamis occur.
“Earthquakes are created by a slippage in a fault [between tectonic plates],” said Harry Yeh, geoscientist at Oregon State University. “The Earth is moving; it’s not stationary. In some places, Earth is really dynamic. The tectonic plates are moving around and always making adjustments. Sometimes faults slip. Once a fault slips, that creates a disturbance and that creates the earthquake.”
“If the fault slippage happens under the ocean, that means the slippage creates a displacement of the seafloor,” Yeh said. “The seafloor displacement consequently creates a disturbance in the water, which means a displacement of the water surface, and that’s the origin of a tsunami.”
But scientists still can’t predict earthquake-tsunamis.
“We only have data for 80 or 90 years, so we simply cannot make accurate predictions for this geological event,” Yeh said. “If you’re going to try to make a prediction for tomorrow, a year later, that’s very difficult, but if you’re going to make a prediction for a 1,000-year span, it could be possible.”
“A prediction should be based on a scientific understanding, and right now we don’t understand these premonitory phenomena,” Okal said. "There have been a number of instances where earthquakes were preceded by phenomena that we think are probably related to their eventual occurrence, such as a flurry of small earthquakes before the major one, but you have no repetition of these precursors, which makes them unreliable.”
Even if scientists find a precursor, they would need one that gave the authorities enough time to move people out of harm’s way.
So right now, it all comes back to education.
“In the end, what you need to save are human lives, and the recurring theme everywhere is that the educated individual is going to fare better than the non-educated one,” Okal said.