Earthquake in Central Honshu!

This morning (my time) there was a large earthquake in central Honshu. Here is the USGS page for this earthquake. The earthquake hypocentral depth is shallow, giving rise to the likelihood of damage to infrastructure and people.
Here is a map of the region, showing the epicenter in orange, near Nangano. This earthquake occurred along the Itoigawa-Shizuoka Tectonic Line, a convergent plate boundary between the Eurasian/Amurian plate and the North America/Okhotsk plates. This earthquake is in the region where this fault zone flips vergence (in the south it dips to the southwest and to the north it dips to the northeast. This is where the Niigata-Kobe fold and thrust belt meets the mobile belt of the east margin of the Japan Sea.

This is the moment tensor, which is interesting in that it is not evidently parallel to the tectonic boundary of this region. The main tectonic boundary is complicated here and changes strike and also incorporates some strike slip faulting.

Here is an illustration showing the subduction zones and how they meet near Honshu. This image is from here.

This map shows the current tectonic configuration of this region, along with some inherited features from the tectonic past (e.g. green lines). This is from NUMO’s report: “Evaluating Site Suitability for a HLW Repository (Scientific Background and Practical Application of NUMO’s Siting Factors), NUMO-TR-04-04.”

Also from the NUMO report, this shows the Niigata-Kobe fold and thrust belt.

Here is the shaking intensity map as modeled using ground motion prediction equations (attenuation models).

Compare the above map with this one, which is generated by surveys from real people, not models.

Here is the attenuation plot, showing how the shaking intensity drops off with distance from the earthquake. Note how the real data (dots) match with the attenuation curve that was developed using seismicity in California, rather than the curve using central and eastern USA seismicity. Think about why you think this is.

Given the shallow depth for this earthquake, we can see that the PAGER estimate of damage is high.

2 thoughts on “Earthquake in Central Honshu!

Leave a Reply

Your email address will not be published. Required fields are marked *