RMS Study Highlights Challenges in Estimating Short-term Earthquake Risk
Newark, Calif. -
February 28, 2012 -
As the first anniversary of the M9.0 Tohoku, Japan Earthquake and Tsunami approaches, Risk Management Solutions (RMS) has released a study that highlights the challenges in estimating the changes in short-term earthquake risk due to this unprecedented event. The event generated the largest-ever number of ground motion recordings for a great earthquake (i.e., M≥8.0) and the highest measured tsunami waves in a well-prepared region (with run-up heights over 35 m above sea level). As of late February 2012, close to 15,900 people were confirmed dead and another 3,400 people are still missing. And nearly a year later, impacts of the M9.0 event on seismicity in the region continue to manifest.
Since the March 11, 2011 event, there has been some concern as to whether more damaging earthquakes can now be expected around Japan and how the event may have affected the timing of earthquakes on other seismic sources in the region. As part of the research that RMS is undertaking to re-characterize Japan’s seismic risk following the event, RMS explored the numerous models proposed for the event’s coseismic slip distribution, their uncertainties, and their potential implications for estimating static stress changes on Japan‘s seismic sources. Furthermore, elevated seismicity patterns since March 11, 2011 were analyzed to determine their influence on overall short-term seismic risk.
For the Tokyo region, RMS found that short-term earthquake risk due to “static stress changes”— redistribution of stress in the region post-Tohoku — remains relatively unchanged following last year’s event. However, occurrence rate changes cannot be resolved exclusively by analyzing static stress changes on known seismic sources. The presence of many unknown seismic sources makes this a limiting approach to understanding short-term changes in hazard — and risk.
"Considering both static stress changes and the patterns of post-event seismic activity, average annual loss estimates (AALs) can vary significantly," said Patricia Grossi, director of research at RMS. "In Tokyo, for example, AALs can potentially increase 70%, while in Miyagi, AALs can potentially decrease by 50%."
The ongoing seismicity in the wake of the 2011 Tohoku Earthquake and Tsunami suggests that there are lessons yet to be learned. In early 2012, Japan continues the long process of rebuilding viable communities. To better understand and mitigate Japan‘s earthquake risk into the future, continued research on the changing seismicity patterns in the Tohoku region, as well as explorations into fully probabilistic tsunami solutions, is necessary, and RMS will continue to closely monitor and examine research findings and events as they unfold.