san francisco's skyline is moving up. seven out of the 10 tallest buildings in s francisco were ilt in the last decade. because real estate in the city is limited, so it's tech companies like s es force expand they're building vertically. with eight fault lines cutting rough the bay area, some earthquake experts worry the buildings f tall could make the city more unsafe during a catastrophic quake. >> there are a number of credible studies that suggest that the collapse of a high rise building is not -- is possible. >> earthquake exper say big quake in the bay area will likely happen during our lifetime. that rattles the nerves of people like justin pratt. >> it's a sry concept. i mean, it doesn't necessarily keep me up at night, but it's something that's always in the back of your mind. >> it's happened before. the great quake of 19 kled more than 3 now, people and destroyed 28,000 buildings. this newly discovered footage of the devastation following the quake shows markets lining the arteries. >> it's a costly solution, there are unknowns. we don't rlly know precisely the probability of collapseor ne