Istanbul is home to up to 20 million people, many of them still haunted by memories of Turkey's major 1999 earthquake, when more than 17,000 people died, including 1,000 in their city. Istanbul has grown substantially since then, becoming a magnet for people attracted to its booming economy -- and oblivious to the active fault line running across its southern edge. That changed on February 6, when a 7.8-magnitude earthquake killed tens of thousands across Turkey and Syria, leaving cities in ruins. Since then, Istanbulites have requested more than 140,000 checks to test whether their building will crumble when the next big quake strikes Istanbul. IMAGES AND SOUNDBITES