Another fine report on the M6.8 (JMA6.9) earthquake that occurred on January 13 at 9:19 PM local time off the coast of Miyazaki Japan. The earthquake was within the area of the Nankai Trough where a large tsunami-genic earthquake is considered likely in the long-term and where a short-term operational earthquake forecasting system is in place. The earthquake of August 8, 2024, at M7.0 met the criteria for an advisory which, as you mentioned, was issued following this earlier event. Our research group conducted a survey of local governments in the Nankai region (which includes 707 municipal governments and 29 prefectures) to assess the level of planning for an advisory or warning (based on the occurrence of a M8.0 event in one of the Nankai Trough subregions) and discovered that approximately 85% of these jurisdictions have considered receipt of an alert (an advisory or warning) in their earthquake response plans. Based on comments from seismologists following the earlier M7 earthquake, the location of this earthquake was less likely to be followed by a much larger earthquake and that an event of similar or greater magnitude off the Izu Peninsula would be of far greater concern. If your readers would be interested in how local government in the Nankai region are likely to respond to a short-term operational earthquake forecast from the Japan Meteorological Agency, our paper is:
Goltz, James D., Katsuya Yamori, Kazuya Nakayachi, Hideyuki Shiroshita, Takashi Sugiyama, Yu Matsubara 2024. Operational Earthquake Forecasting in Japan: A Study of Municipal Government Planning for an Earthquake Advisory or Warning in the Nankai Region. Seismological Research Letters. 95(4): 2251-2265. doi: https://doi.org/10.1785/0220230304
Very readable report Kyle, thankyou. I find such as these of great interest, as I live on the Pacific plate edge in New Zealand where we have the Hikurangi trench fault and the Alpine fault to contend with. I am closer to the Alpine fault in the South Island and am very aware of the certain disaster lurking with this over-due, M8+ monster.
It is interesting to watch how the more active faults play out in Japan, and I admire, bordering on envy, how seriously the japanese authorities take and react to the threats posed by their section of the Pacific plate edge.
As a matter of discussion, how serious a threat of a further earthquake does there need to be before public warnings would be issued? 5%, 10%, 50%, 70%?
To many false alarms might lead to public ignoring the warnings and to few might lead to unnecessary deaths.
How do they make the call and still maintain credibility?
Hi Steve, it's definitely a tricky question - especially since the probability is actually probably well below 5%! Last August is actually the first time a megaquake advisory was issued, so this is still something that's being worked out.
The goal makes sense: to keep the public informed about scientific information bearing on risk. But whether the public can actually absorb that information in a way that is useful remains to be seen. After all, most people don't change their behavior when they travel between areas with different seismic risk profiles, so why should they change their behavior if there is a change in risk profile over time? (And what should that behavioral change look like, if anything?) The most effective way to manage seismic risk is to build for it - time-variable risk isn't really relevant in that case. So, definitely an interesting question.
The other comment here by Dr. James Goltz addresses how people at different governmental levels can manage and respond to advisories like this, so you might take a look at his paper.
Another fine report on the M6.8 (JMA6.9) earthquake that occurred on January 13 at 9:19 PM local time off the coast of Miyazaki Japan. The earthquake was within the area of the Nankai Trough where a large tsunami-genic earthquake is considered likely in the long-term and where a short-term operational earthquake forecasting system is in place. The earthquake of August 8, 2024, at M7.0 met the criteria for an advisory which, as you mentioned, was issued following this earlier event. Our research group conducted a survey of local governments in the Nankai region (which includes 707 municipal governments and 29 prefectures) to assess the level of planning for an advisory or warning (based on the occurrence of a M8.0 event in one of the Nankai Trough subregions) and discovered that approximately 85% of these jurisdictions have considered receipt of an alert (an advisory or warning) in their earthquake response plans. Based on comments from seismologists following the earlier M7 earthquake, the location of this earthquake was less likely to be followed by a much larger earthquake and that an event of similar or greater magnitude off the Izu Peninsula would be of far greater concern. If your readers would be interested in how local government in the Nankai region are likely to respond to a short-term operational earthquake forecast from the Japan Meteorological Agency, our paper is:
Goltz, James D., Katsuya Yamori, Kazuya Nakayachi, Hideyuki Shiroshita, Takashi Sugiyama, Yu Matsubara 2024. Operational Earthquake Forecasting in Japan: A Study of Municipal Government Planning for an Earthquake Advisory or Warning in the Nankai Region. Seismological Research Letters. 95(4): 2251-2265. doi: https://doi.org/10.1785/0220230304
Very readable report Kyle, thankyou. I find such as these of great interest, as I live on the Pacific plate edge in New Zealand where we have the Hikurangi trench fault and the Alpine fault to contend with. I am closer to the Alpine fault in the South Island and am very aware of the certain disaster lurking with this over-due, M8+ monster.
It is interesting to watch how the more active faults play out in Japan, and I admire, bordering on envy, how seriously the japanese authorities take and react to the threats posed by their section of the Pacific plate edge.
As a matter of discussion, how serious a threat of a further earthquake does there need to be before public warnings would be issued? 5%, 10%, 50%, 70%?
To many false alarms might lead to public ignoring the warnings and to few might lead to unnecessary deaths.
How do they make the call and still maintain credibility?
Hi Steve, it's definitely a tricky question - especially since the probability is actually probably well below 5%! Last August is actually the first time a megaquake advisory was issued, so this is still something that's being worked out.
The goal makes sense: to keep the public informed about scientific information bearing on risk. But whether the public can actually absorb that information in a way that is useful remains to be seen. After all, most people don't change their behavior when they travel between areas with different seismic risk profiles, so why should they change their behavior if there is a change in risk profile over time? (And what should that behavioral change look like, if anything?) The most effective way to manage seismic risk is to build for it - time-variable risk isn't really relevant in that case. So, definitely an interesting question.
The other comment here by Dr. James Goltz addresses how people at different governmental levels can manage and respond to advisories like this, so you might take a look at his paper.