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A quake that shifted the Earth

April 30, 2010

Concepcion: There was another tremor earlier today, Claudio tells us cheerfully, when we arrive in Concepcion after a long – although our most luxurious to date – bus ride from Puerto Montt.

Nick enjoys an empanada on our luxury bus

We were slightly nervous of coming to this auspicious city – where independence hero Bernardo O’Higgins declared a free Chilean republic in 1810 – because despite calls and internet enquiries, we’d failed to find anywhere to stay. The massive quake on 27 February destroyed what remained of the city’s old buildings – ie those that were standing after the 1929 and 1960 earthquakes – and the hostels with them. Many were flattened, closed down or are unsafe. The few standing places are fully booked and have hiked their prices.

So we were especially grateful when my dad’s friend Claudio (from their time working at Imperial College in London) met us from the bus and took us straight to a hostel that he’d kindly scouted out for us.

Much of the town was damaged by the quake, including heroic O’Higgins’ statue, even though Chile has very strict building regulations for the area, requiring constructions to resist quakes up to 9. The tsunamis were the bigger killers though, destroying entire villages.

The chemistry department at University of Concepcion was destroyed by a series of explosions caused by chemicals that leaked during the quake. The building burned for 30 hours and noisy repair work is still causing disruption.

The quake was not a complete surprise. Scientists had been predicting the ‘big one’ for some time. There’s a lot happening in the planet under Concepcion and the rest of the continent’s west coast. The Nazca oceanic plate is moving fast, 8cm per year, in a northeasterly direction and is subducted under the South American plate, which is moving very slowly in a westerly direction.

In 1835, after a large quake here (at the same time of year), Darwin stopped for a few weeks visiting Concepcion and nearby island port of Talcahuano, intrigued by the rock disturbances and visible destruction wrought by the quake. He writes:

“It came on suddenly, and lasted two minutes, but the time appeared much longer. There was no difficulty in standing upright, but the motion made me almost giddy: it was something like the movement of a vessel in a little cross-ripple, or still more like that felt by a person skating over thin ice, which bends under the weight of his body. A bad earthquake at once destroys our oldest associations: the earth, the very emblem of solidity, has moved beneath our feet like a thin crust over a fluid; – one second of time has created in the mind a strange idea of insecurity, which hours of reflection would not have produced.

The tides were very curiously affected. The great shock took place at the time of low water; and an old woman who was on the beach told me that the water flowed very quickly, but not in great waves, to high- water mark, and then as quickly returned to its proper level; this was also evident by the line of wet sand.

I landed at Talcahuano, and afterwards rode to Concepcion. Both towns presented the most awful yet interesting spectacle I ever beheld. The ruins were so mingled together, and the whole scene possessed so little the air of a habitable place, that it was scarcely possible to imagine its former condition. In Concepcion each house, or row of houses, stood by itself, a heap or line of ruins; but in Talcahuano, owing to the great wave, little more than one layer of bricks, tiles, and timber with here and there part of a wall left standing, could be distinguished. From this circumstance Concepcion, although not so completely desolated, was a more terrible, and if I may so call it, picturesque sight. The first shock was very sudden.

Not a house in Concepcion or Talcahuano was standing; seventy villages were destroyed; and a great wave had almost washed away the ruins of Talcahuano. During my walk round the island, I observed that numerous fragments of rock, which, from the marine productions adhering to them, must recently have been lying in deep water, had been cast up high on the beach; one of these was six feet long, three broad, and two thick.

The ground in many parts was fissured in north and south lines, perhaps caused by the yielding of the parallel and steep sides of this narrow island. Some of the fissures near the cliffs were a yard wide. The effect of the vibration on the hard primary slate, which composes the foundation of the island, was still more curious: the superficial parts of some narrow ridges were as completely shivered as if they had been blasted by gunpowder. This effect, which was rendered conspicuous by the fresh fractures and displaced soil, must be confined to near the surface, for otherwise there would not exist a block of solid rock throughout Chile; nor is this improbable, as it is known that the surface of a vibrating body is affected differently from the central part. It is, perhaps, owing to this same reason, that earthquakes do not cause quite such terrific havoc within deep mines as would be expected.”

Since Darwin’s visit, more than 150 years ago, there had been little movement in this highly pressurised zone. Which means, around 12 metres of built up friction force.

This was released a couple of months ago (on 27 February) in more than 100 large quakes, including a massive 8.8 on the Richter scale. Half an hour later, the first of three tsunamis hit the city. The second, followed 30 minutes later, and the third, weirdly, 3 hours later.

The quake moved Concepcion 3 metres westward, meaning that all the GPS readings for the country and as far as Buenos Aires are no wrong and need to be adjusted. Property lines for houses, title deeds, planning departments and so on are all out.

The army is still on the streets after being called in with water canons to control looting and unrest

Some 500 people died in the quake, blackouts lasted days and there was no drinking water in the city for three weeks. Looting and civil unrest led to scenes of chaos in this otherwise remarkably ordered nation.

The quake was to powerful that it shifted the very earth on its axis by 8 centimetres and thereby shortened the length of our days by 1.26 microseconds.

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