Nearly two months after the Tohoku earthquake, tsunami and subsequent nuclear accident, scholars came together Monday night for the first event in a two-part series about the disaster.
Panelists at the talk, entitled “Stanford Public Symposium: The Great Tohoku, Japan Disaster,” included Chair of Geophysics Gregory Beroza, Director of the Blume Earthquake Engineering Center Gregory Deierlein and Center of International Security and Cooperation (CISAC) Fellow Katherine Marvel. Pamela Matson, dean of the School of Earth Sciences, moderated the event.
The audience and speakers engaged in a panel-style conversation. In addition, Beroza, Deierlein and Marvel each gave a brief presentation on seismology, structural engineering and the nuclear disaster, respectively.
Beroza detailed the four-shock sequence comprising the disaster as well as the plate tectonics involved in an earthquake and its aftershocks.
“Unless you were in an airplane, you witnessed this earthquake,” he said. “In California, we moved a couple centimeters, about an inch…There was a 7.9 aftershock — probably the most obscure 7.9 earthquake ever.”
Beroza stressed the importance of “accurate hazard characterizations” in mitigating the risk of similar “nasty disasters” in the future.
“This is the first great earthquake to hit a developed country with modern infrastructure and cutting-edge earthquake science and earthquake know-how,” he said. “Lessons learned will be critical to improving the resilience of other regions, including California.”
Deierlein, meanwhile, spoke about the structural engineering of various buildings in Tokyo and Sendai, Japan hit by the quake. While some buildings were devastated, others — especially those that had been reinforced after previous shocks — were barely damaged.
“Some interesting anomalies come up,” he said. “High-frequency motion sometimes doesn’t have the damage that we think it might.”
He mentioned an April 7 aftershock of 7.4 magnitude intensity as an example of the constant damage-repair cycle that takes place in earthquake hotspots such as Japan or California.
“In Japan, as in the U.S., the challenge is to retrofit the structure so it survives the next quake,” he said. “It’s always a case of balancing our resources…Generally, our large reinforced buildings can survive tsunamis pretty well, even though they were only built to survive earthquakes.”
Marvel gave the final talk on the details of the subsequent nuclear accident.
“While there were explosions at the nuclear plant, there weren’t nuclear explosions,” she said. “As far as I can tell, the actual structural integrity of the buildings was not compromised by the earthquake or tsunami.”
Instead, Marvel explained that the tsunami knocked out the cooling system, which caused an accumulation of hydrogen gas and a “meltdown” of the nuclear fuel. The worst-case scenario would have been a combination of a total core meltdown as well as a containment failure. However, she stressed, “this is all speculative.”
Both Marvel and Matson emphasized the global humanitarian crisis as opposed to the scientific intricacies of the earthquake and tsunami.
“Japan is still facing a devastating humanitarian crisis as a result of the earthquake and tsunami, and I find it sad that much of the media has focused on the nuclear disaster,” Marvel said. “We shouldn’t let our cultural obsession with nuclear disasters overshadow the crisis.”
“For many of us, this cascade of disasters is past tense, but for millions of Japanese, it’s not over, and it’s not going to over for a while,” Matson said.
Part two of the symposium takes place tonight at 7 p.m. in Room 200 of the Hewlett Teaching Center.