2023-06-28 00:50:33
An earthquake that observed a seismic intensity of 3 in Hokkaido at 8:00 am Phenomenon called “abnormal seismic area” (Meteorological forecaster Nichinao June 28, 2023)-Japan Weather Association tenki.jp
An earthquake with a seismic intensity of 3 observed in Hokkaido at 8:00 AM Phenomenon called “abnormal seismic area”
June 28, 2023 09:50
At around 8:39 am on the 28th, an earthquake of magnitude 6.2 occurred with its epicenter in the northern part of the Sea of Japan, and a maximum seismic intensity of 3 was observed in Hokkaido. This earthquake was very deep, about 480 km, and it is believed that a phenomenon called an “abnormal seismic zone” occurred in which stronger shaking was observed in a place away from the epicenter.
Outline of the earthquake
At around 8:39 am on the 28th, an earthquake with a maximum seismic intensity of 3 occurred in Hokkaido. The epicenter was in the northern part of the Sea of Japan (42.1 degrees north latitude, 134.4 degrees east longitude).
There is no tsunami from this earthquake.
Municipalities where seismic intensity 3 or more was observed
◆Hokkaido
Urahoro Town
The epicenter and the area where the shaking was observed are far apart. The depth of this earthquake was very deep, about 480 km, and it is believed that a phenomenon called an “abnormal seismic zone” occurred, in which stronger shaking was observed at a location far from the epicenter.
What is an anomalous seismic area?
In the case of a “deep earthquake” with a very deep epicenter like this time, there is almost no tremor near the epicenter directly above, and the tremor may be strong in places far away. This phenomenon is called an “abnormal seismic zone”.
Most earthquakes spread around the area directly above the epicenter, but in the case of an “abnormal seismic zone,” the distribution of seismic intensity differs greatly from these earthquakes. “Abnormality” is a phenomenon that occurs frequently depending on the conditions, and does not mean that there is an abnormality in the seismic activity itself.
The reason is that seismic waves propagate differently depending on the nature of the bedrock inside the earth.
Around Japan, the plates collide with each other, and the oceanic plate is subducting under the land plate. When an earthquake occurs deep in the subducted oceanic plate, there is a layer above that that easily attenuates seismic waves, so the tremors are smaller directly above the epicenter. On the other hand, seismic waves tend to propagate through the interior of the oceanic plate without being attenuated so much, so tremors are greater at locations far from the epicenter.
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