For 50 seconds on 17 August 1999, the ground in north-western Turkey shook violently.
It was a massive earthquake, with its epicentre in Izmit, that claimed more than 17,000 lives.
Six years later, experts warn the next quake will be much nearer to Istanbul. But the city is not even close to ready.
High in the hills overlooking the Bosphorus, scientists at the Kandilli Observatory have kept the print-out from that day - a dense waveform measuring 7.4 on the Richter scale.
These days the paper seismographs are only kept for back-up. The Turkish government has spent more than $1m (£575,000 or 855,000 euros) upgrading the station to digital technology. There are now four times more monitoring stations - mostly focused around the Sea of Marmara.
There is good reason for that.
"The ruptures in the fault are migrating westwards," Niyazi Turkelli explains, waving towards a map of Turkey on the wall with the active North Anatolian fault-line marked in red. The only section still unruptured is the one closest to Istanbul.
"The fault could break once or in several stages," Niyazi says. "If it ruptures once, then the expected magnitude will be 7.7, maybe 30km (19 miles) from Istanbul. It could be a disaster."
The World Bank released a $400m loan to the Turkish government last month to help prepare Istanbul for that eventuality. The money will be used to strengthen 40 hospitals and 600 schools.
"Reinforcing those buildings will make them safe zones in the event of an earthquake," the bank's country director, Andrew Vorkink explains. "People could go there for shelter."
The 1999 quake struck late at night. Thousands of people were crushed in their beds when their buildings collapsed. At the time, there was a public outcry that shoddy construction work had cost so many lives.
All building work is now subject to much more rigorous inspection. But very few contractors have been punished.
That August, Erdogan Koparal's wife and six-year-old daughter were enjoying a stay at their summer house just an hour's ferry ride from Istanbul.
"As soon as I saw the site that day I had no hope they'd survived," Erdogan remembers, his silver curls blown by the sea wind. "There was no space to hide."
Expert reports proved Erdogan's building was the wrong shape for an earthquake zone and showed that corrosive sea-sand was used in the cement.
A court found four men guilty of negligence, but their jail sentences were commuted to fines of just $35.
For Erdogan, that is no justice.
"No one has learned any lessons since 1999," he says. "Come and find me again after thousands die in Istanbul, and I'll tell you again what I'm telling you now."
Back in Istanbul and the 1970s district of Avcilar, local housing official Sedat Yanar is keen to prove otherwise.
This swampy suburb is one of the city's highest risk areas for an earthquake. So on a side-street building site, Sedat points out thick new concrete walls around a mesh of reinforcing metal.
"That's an earthquake curtain," he explains. "It makes the building more flexible."
But it is costly work - money few here have to spend.
"I'm confident the buildings done since 1999 are safe," Sedat Bey admits. "But only about 500 other blocks have been strengthened. Nothing's been done about the rest, and it has to be."
And it seems concerns about builders have not been entirely eradicated.
Contractor Hussein Apaydin is battling the mayor's office over one of his buildings, badly damaged in the last earthquake. Hussein insists it is structurally sound, but Sedat Yanar says sea-sand in the cement corroded the block's metal bars.
"Everyone here uses sea-sand. There's no law against it," Hussein protests when the men meet in the street. "Our suppliers vacuum it from the sea and it's fine if it's washed properly."
But Hussein admits he does not do that.
"If the government said you had to wash the sand, people would do it. But they don't."
In fact, using unwashed sea-sand to mix cement has been illegal in Turkey since 1999. Hussein Apaydin last built a block of flats here in 2002.
Over on the other side of the suburb, a group of men play a furious game of dominos in a coffee house thick with cheap cigarette smoke.
It is the heart of Avcilar's shanty region, home to more than 50,000 people who came to Istanbul looking for work. Their houses are called gecekondus, which means "put up overnight". They are utterly illegal - and nothing like quake-proof.
There are vast swathes of Istanbul just like it.
"Just building one storey costs $15,000. People here can't add the cost of an engineer to that," Dursun Bey says between sips of strong tea.
"There's talk of a quake of 7.6 or more - and none of our houses are earthquake-resistant."
"We've already experienced one earthquake, and we know the next time will be much worse," his son Hussein adds. "We are not comfortable with our buildings, but what can we do?"