Saturday, March 12, 2011

Disaster in Japan

Sendai Airport inundated by tsunami (Reuters photo)

My wife and I have been transfixed by the astonishing images broadcast in the aftermath of the massive 8.9 magnitude earthquake and tsunamis that struck northeastern Japan on Friday. The Sendai event was the largest earthquake to hit Japan in modern times. That fact alone is remarkable given the island nation’s long history of frequent and devastating temblors.

As I write this, no one knows for sure how many people lost their lives; the number of deaths directly attributable to the earthquake and tsunamis may eventually be numbered in the thousands. The scope of property and economic damage is more readily evident.

I have friends and family living in Japan. As soon as I heard about the disaster, I confirmed (via Facebook) that our former AIA-SWO colleagues Yasuyuki Yanigisawa, Nicolai Kruger, and their daughter Naomi are fine. I also called my father to learn if he heard from my uncle and cousins; they’re okay too.

It’s actually amazing that the toll in lives and buildings isn’t greater. There is no doubt that the damage could have been considerably worse were it not for the stringency of the Japanese building codes and the constant readiness of the populace. Japanese engineers routinely integrate extensive measures to minimize the risk of building collapse in an earthquake. These include extra bracing, base isolation pads, and embedded hydraulic shock absorbers. Contrast the vast devastation suffered last year during the 7.0 magnitude earthquake in Haiti. Buildings throughout the capital city of Port-au-Prince were significantly damaged or destroyed, and hundreds of thousands of people were killed.

There are marked differences between the United States and Japan when it comes to seismic design standards. In this country, the emphasis is upon preventing collapse, while in Japan—with its greater number of earthquakes—the goal is to prevent any major damage to buildings. If an earthquake equal in force to Sendai was to occur tomorrow off the Oregon coast, the destruction would be unimaginable. Better-designed buildings might not topple but their ongoing serviceability would be in question.

I previously documented a presentation by John Evans of Pillar Consulting Group regarding the threat posed by earthquakes to Oregon. He described how the Cascadia subduction zone—the boundary where the Juan de Fuca plate is sliding beneath the North American plate—can generate a huge quake, as much as magnitude 9.0. The last known Cascadia subduction event occurred in 1700. They’re estimated to occur every 300 to 500 years, so we’re coming due again. Friday’s earthquake in Japan was of the subduction variety.

The Wikipedia article about the Cascadia subduction zone reports that geologists believe the convergent plate boundary is more complex and volatile than previously thought. They predict a 37 percent chance of a M8.2+ event in the next 50 years, and a 10 to 15 percent chance that the entire Cascadia subduction will rupture with a M9+ event within the same time frame. Authorities have also determined the Pacific Northwest is not prepared for such a colossal quake. The tsunami produced could reach heights of 80 to 100 feet (24 to 30 m), much larger than those that devastated the communities along Honshu’s northeast coast.

Structure of the Cascadia Subduction Zone

The potential for seismic activity in our state is greater than most Oregonians grasp. To minimize the risk to life and property, it behooves us to understand the effect of earthquakes and the lateral forces they generate upon the vulnerable, older building stock in our communities, particularly those constructed of unreinforced masonry. If there is a silver lining to the tragedies in Japan and Haiti (and recently too in Chile and Sumatra) it is that the need for improvements to our buildings is heightened.

The watchwords going forward will be preparedness, response, recovery, and rebuilding. It’s not a question of whether a catastrophic earthquake will occur in the Northwest—such a disaster is inevitable. It is only a matter of when. There will be many lessons for architects and engineers to be learned from Japan’s experience. We will undoubtedly translate these lessons by enacting stricter building codes and implementing advanced design strategies for seismic resistance. To do otherwise would be irresponsible. After what has occurred in Japan, we must all surely realize we’re living on borrowed time.

Enhanced by Zemanta

No comments: