A research group led by Associate Professor Aitaro Kato of the Earthquake Research Institute, the University of Tokyo found that the area of the foreshock that occurred in the 2016 Kumamoto earthquake expanded in the traveling and tilting directions of the fault plane.In addition to the change in force due to the foreshock, the slow slip (* 1) was transmitted to the rupture starting point of the mainshock, suggesting that the mainshock was promoted.
In the Kumamoto earthquake, a mainshock with a magnitude of 7.0 occurred on April 4.Two days before that, there was a magnitude 16 foreshock.The research group estimated a series of seismic activity with high accuracy and analyzed how the location of the earthquake changes over time.
According to it, it was found that after the foreshock occurred, the area where the earthquake occurred gradually expanded in the traveling direction and the dip direction of the fault, and headed toward the rupture starting point of the mainshock.At the crustal movement observation point near the foreshock, it was confirmed that the area where the earthquake occurred gradually moved from the foreshock to the mainshock.
Assuming that this phenomenon occurred on the fault plane of the foreshock, the situation is consistent with various other observational data.For this reason, the research group believes that the slip caused a force on the fault plane that caused the mainshock, causing the mainshock.
The phenomenon that the area of occurrence of the earthquake expands during the activity of the foreshock has been confirmed in the earthquake that occurs on the boundary between the ocean plate and the land plate, but a similar phenomenon has occurred in the inland active fault earthquake. Became clear.
* 1 Slow slip In seismological terms, a slip phenomenon that occurs at a crustal movement rate that is much slower than the slip of a plate due to a general earthquake.
