What can we learn from the Chilean Earthquake?
What can we learn from the Chilean Earthquake?
We are just beginning the process of obtaining detailed information on the impacts of the Chilean Earthquake and we expect to learn many lessons that will be applicable to construction in the United States. We are particularly interested in what similarities we will find with the Pacific Northwest where we have our own version of the Chilean Earthquake waiting to happen on the Cascadia Subduction Zone (CSZ). Much like Chile, where the Nazca Plate is subducting below the South American Plate, in the Northwest we have the Jaun De Fuca Plate subducting below the North American Plate. These types of subduction zone earthquakes have unique characteristics including long duration and long period ground motions.
Reports on the ground motions from the Chilean earthquake are just starting to come out but preliminary reports indicate between 1 and 2 minutes of strong ground shaking with long period motion in the 1 to 2 second range. Most earthquakes that we experience in the United states have less than 30 seconds of strong ground motions and it is predicted that the large 9.2 on the Cascadia Subduction Zone will result in 3 to 4 minutes of strong shaking. We currently to do not address duration of the shaking directly in our structural design and this may need to change. The impacts of long period motions will be most observable in taller buildings, longer span bridges, and some dams. It is expected that the results of Chile will provide very valuable data to help us start to understand the impact of duration. It is also expected that it may take time to discover some of the damage in taller structures just like much of the moment frame damage from the 1994 Northridge Earthquake was not readily apparent. We understand how the long period ground motions impact our structures but they are not always fully considered in design.
We must collaborate with our Chilean counterparts to gather data from this great earthquake so we can learn and improve our own practices. It is incumbent upon all of us in the profession to do our part and advance our knowledge of how structures respond to earthquakes when we have a tragic event such as this one.
March 4th, 2010 at 9:20 pm
Hi Stacy,
I think the call to action and the wake up is most prescient. I wondered how the buildings in the San Francisco area would stand up to the same kind of sustained shaking. Would the new multi-storied condos still be standing or would the damage be so severe that it would render them uninhabitable? The call for collaboration is most urgent. Is it occurring? And what does our government do to help gather information? Great thought provoking post.
Stacey Maziarz
March 5th, 2010 at 4:44 pm
To my understanding, depending on the structural system and its configuration, the duration of the Earthquake could have a significant impact on both, low-rise or high-rise structures due to P-Delta effects. In the year 2005, professor Richard Fenwick from Canterbury University in New Zealand was going to conduct a study on the matter.I am not sure it came through or not.