July 11, 2022
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* In the crust of the Noto region, Ishikawa prefecture, the number of earthquakes
is increasing since about 2018, the seismic activity became high since
December 2020, and it has become higher since about July 2021. In the series
of the seismic activity, from December 1, 2020 till July 8, 2022 at 09
o’clock (JST), there occurred 183 earthquakes with seismic intensity 1
or over: of these 30 earthquakes with seismic intensity 3 or over. The
largest is an M5.4 earthquake occurring on June 19, 2022, which caused
maximum seismic intensity 6 Lower observed in Ishikawa prefecture. In addition,
an M5.0 earthquake on September 16, 2021 caused maximum seismic intensity
5 Lower and an M5.0 earthquake on June 20, 2022 caused maximum seismic
intensity 5 Upper.
The series of the seismic activity still continues to be high showing no sign of decline at present.
* The series of the seismic activity occurs in the area about 15 km in
an E-W direction and about 15 km in an N-S direction. Especially the activity
is high in the northern and eastern parts, where the M5.1 earthquake on
September 16, 2021, the M5.4 earthquake on June 19, 2022 and the M5.0 earthquake
on June 20 occurred. In the eastern part, the number of earthquakes of
M3.0 or over has increased since about March 2022.
In the series of the seismic activity, several distributions of hypocenters dipping south-east appeared and the distribution is expanding from deep to shallow depth as time passes. The focal mechanism solutions of earthquakes show reverse fault types with compression axes in generally NW-SE direction and generally harmonious with the south-east dipping distribution of hypocenters.
* According to the GNSS observation, since about December 2020, the following
crustal deformation has been observed: the cumulative displacement of 1
cm over in the south-southeast direction and the uplift of 4 cm or so at
the Suzu observatory in Suzu City, Ishikawa prefecture and the cumulative
displacement of 1 cm over in the south-southwest direction at the Noto
observatory in Noto Town. Also, the crustal deformation of radial expansion
and uplift with the center being the seismic activity area is seen by adding
the data of the more GNSS observing stations in the surrounding area.
Note that no significant crustal deformation was observed accompanying the M5.4 earthquake on June 19, 2022.
* Accompanying the M5.4 earthquake on June 19, 2022, large accelerations were observed such as 606 gal (synthesis of 3 components) at the K-NET Shoin Observatory, Suzu City, Ishikawa prefecture.
* In the surrounding of the recent seismic activity area, no active seismic activity such as the recent one, in which the earthquakes of the same order scale occur consecutively for a long period, is known. On the other hand, such an active seismic activity has been sometimes observed in Japan. Matsushiro earthquake swarm beginning in 1965, and recently the seismic activity in the area extending from Aizu, Fukushima prefecture to Okitama region, Yamagata prefecture beginning in March 2011, and the seismic activity in the Kagoshima Bay beginning in December 2016. Of these a few continued for more than 1 year.
* In the surrounding area of the Noto Peninsula, there have been large scale earthquakes with damage. On March 25, 2007, there occurred "the 2007 Noto Hanto Earthquake" (M6.9) which caused maximum seismic intensity 6 Upper observed. Also, in 1993 there was an M6.6 earthquake in the north side of the recent seismic activity area. Besides the following earthquakes are known as the earthquakes accompanying damage in the vicinity of the recent seismic activity area: M6.6~7.0 earthquake in 1729 and M5.7 earthquake in 1896.
* It is known that active faults exist in the ocean bottom offshore north coast of the Noto Peninsula. These active faults are estimated to be generally with strikes in an NE-SW direction and reverse faults dipping southeast.
* Based on the situation of the seismic activity and the crustal deformation, the series of the seismic activity will continue for the time being and we should pay attention for a strong shaking.
Note: GNSS is a general name of satellite positioning system such as GPS.