02/01/2024
Many media journalists pose the question why the loss after yesterday's Japan earthquake of Mw7.5 is significantly lower than that Kahranmanmaras earthquake sequence of February the 6th earlier this year.
General discourse claims that this is mainly attributed to Japan's high levels of preparedness and the Early Warning Systems installed, giving some vital seconds for people to evacuate buildings and a few minutes to move to safer areas ahead of an incoming tsunami. In my opinion, this is valid; advanced seismic codes that are properly enforced, EWS mobile phone messages alerting the population, train signals and automatic shut down of critical hazardous facilities, along with a nation that is systematically trained to be resilient at a community and individual level are new generation practices and tools that can set a paradigm of a well-thought preparedness plan.
That been said, comparison with the recent Turkiye earthquake cannot directly be made: the Kahranmanmaras dual earthquakes of Mw7.5 and Mw7.8 happened within 8 hours onshore and close to major cities with high exposure of people and the building stock. There were regions where buildings (old, substandard as well as new ones) were exposed to two mainshocks with accelerations between 0.7-1.0g back-to-back. In contrast, yesterday's earthquake in Japan occurred offshore and on the West coast of the island whereas most major cities are located on the East coast about 200miles from the epicentre. The same applies to the 2011 Tohoku earthquake measuring Mw9.1, releasing energy of about 100 times higher than yesterday's event with the epicentre being 80miles offshore Sendai, that is, significantly closer.
Overall, yesterday's earthquake in Japan is an important case to study on how loss can be mitigated under 'expected conditions'. The challenge is to keep on learning from good practice and policies starting from Japan and the US, while devising ways to enhance resilience to our continuously growing megacities, focusing on regions where it is really hard to implement high-cost seismic design solutions and/or ensure quality control.
photo credit: Kyodo/Reuters retrieved from Skynewsuk.com
