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[SSS09-09] Characteristic distribution of JMA seismic intensity observed in the northeastern Kanto Plain
Keywords:seismic intensity, Kanto Plain, high frequency
In the earthquake that occurred in southern Ibaraki Prefecture at 17:40 on November 9, 2022, the seismic intensity at Shirosato-machi Ogachi observation point on Ibaraki Prefecture in northeastern Kanto Plain was larger than those surrounding observation points. At the inspection at Shirosato-machi Ogachi observation point after this earthquake, the observation environment has been normal. It is important for the seismic hazard to understand the distribution of seismic intensity of the earthquake that occurred in southern Ibaraki Prefecture including repeating earthquakes.
Firstly, we have compared the seismic intensity between the Shirosato-machi Ogachi point and those surrounding observation points using previous earthquakes. As a result, seismic intensity observed at Shirosato-machi Ogachi point has no significant difference compared with those of surrounding points. This result may show that the cause of observed large seismic intensity for the earthquake occurred on November 9, 2022 is caused by multiple factors such as source characteristics and propagation of this earthquake, and ground condition and structure in the northeastern Kanto Plain.
Then, in the earthquakes occurred in the boundary between the Philippine Sea Plate and the Eurasia Plate in the southern Ibaraki Prefecture, the distribution of the seismic intensity shows that the northern area of the epicenter has larger seismic intensity than the southern area. This result may be due to the source characteristics of these earthquakes.
In addition, at Shirosato-machi Ogachi point, maximum acceleration is about 700 cm/s2 in this earthquake. The horizontal component of the acceleration at Shirosato-machi Ogachi point have around 8 Hz of dominant frequency and several tens times larger amplitude than the vertical component. These features are also observed in the northern area of the epicenter of this earthquake.
Firstly, we have compared the seismic intensity between the Shirosato-machi Ogachi point and those surrounding observation points using previous earthquakes. As a result, seismic intensity observed at Shirosato-machi Ogachi point has no significant difference compared with those of surrounding points. This result may show that the cause of observed large seismic intensity for the earthquake occurred on November 9, 2022 is caused by multiple factors such as source characteristics and propagation of this earthquake, and ground condition and structure in the northeastern Kanto Plain.
Then, in the earthquakes occurred in the boundary between the Philippine Sea Plate and the Eurasia Plate in the southern Ibaraki Prefecture, the distribution of the seismic intensity shows that the northern area of the epicenter has larger seismic intensity than the southern area. This result may be due to the source characteristics of these earthquakes.
In addition, at Shirosato-machi Ogachi point, maximum acceleration is about 700 cm/s2 in this earthquake. The horizontal component of the acceleration at Shirosato-machi Ogachi point have around 8 Hz of dominant frequency and several tens times larger amplitude than the vertical component. These features are also observed in the northern area of the epicenter of this earthquake.