[Alex Chadwick:] Once search-and-rescue efforts are under control in China, building experts are going to begin looking at the extent of structural damage. Stanford University's Ann Kiremidjian is a structural engineer. She helped assess damage years after China's 1976 huge earthquake that killed about 250,000 people. Ann Kiremidjian, when you look at the pictures and video of the collapsed buildings around Chengdu, I bet you see things that I don't notice.
[Professor Ann Kiremidjian:] Alex, what I have seen from the video clips is first of all a lot of concrete buildings, what we call concrete frames, and I would classify them as a non-ductile concrete frame. What that means is that there is very little steel reinforcement in the concrete and as a result, the concrete cannot resist displacement in the horizontal direction.
[Alex Chadwick:] It needs to have steel bars, I think that is called rebar. Yeah.
[Professor Ann Kiremidjian:] That is correct. Not enough rebar both in the vertical direction and in the horizontal direction. And in addition, you have to provide rebar going from the column to the beam at the joint to provide continuity and a way to transfer the forces from one member to the other.
[Alex Chadwick:] You inspected buildings after this last, huge, terrible earthquake more than 30 years ago. Did you make recommendations to the Chinese government then?
[Professor Ann Kiremidjian:] At the time, they didn't have earthquake-resistant codes in place. And since then, we've had numerous discussions, and the Chinese have had very strong programs to develop seismic codes, to develop seismic hazard maps. The seismic hazard maps similar to the ones that we have in the United States, are developed with the purpose to identify regions of frequent large earthquakes that can cause damage to buildings, the very first step in any earthquake-resistant design.
[Alex Chadwick:] And what about this region around Chengdu, the Sichuan province, is this prone to earthquakes?
[Professor Ann Kiremidjian:] Yes, all of China is in a highly seismic area. You would notice that there is a fault that runs along the plateau between the Himalayas and where Chengdu is. If you trace all the aftershocks, you can probably trace the fault line that has ruptured. To cause a magnitude 7.8 earthquake, you will need to rupture more than 100 kilometers of a fault, and it looks it is almost 200 kilometers of locations of aftershock which is likely to be the length of the rupture of the fault.
[Alex Chadwick:] Is there some way to measure the size of the earthquake and then overlay that on a map of the region and figure out, we have to look at every single building within a particular radius from the epicenter? I mean do you have to do that?
[Professor Ann Kiremidjian:] Oh, we do that all the time. In fact, what typically you would do is you would focus within the first 15 or 20 kilometers from the rupture zone. It's not just the epicenter, but it is the rupture zone, and the rupture can run about a couple of hundred kilometers, as it is in the case of China. So you are talking a lot of buildings. A single inspector or 10 or 20 inspectors cannot perform that task in a reasonable amount of time. What you have to do is recruit all the professional structural engineers to help with the inspection process.
[Alex Chadwick:] Ann, you're speaking to us from your home in Los Altos Hills, that's south of San Francisco. And it's two miles from the most notorious earthquake fault in North America, the San Andreas Fault.
[Professor Ann Kiremidjian:] Correct.
[Alex Chadwick:] Can you explain to me why a structural engineer would build a house there?
[Professor Ann Kiremidjian:] Yes, indeed. You have to take certain precautions. We have taken into consideration the fact that we are close to the fault. Can we do more? Yes, we can. There's always a balancing act between the economics, how much can you afford, and what you are willing to live with. It's a beautiful area, the weather is lovely, it's close to my work, that's where I live.
[Alex Chadwick:] Ann Kirmidjian teaches structural engineering at Stanford University. Professor, thank you.
[Ms. Kirmidjian:] You're welcome.
[Alex Chadwick:] NPR's DAY TO DAY continues.