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Observed Strong Motions and Site Effects During the Jan. 1, 2024 Noto-Hanto Earthquake in Japan and Its Reproduction Based on a Priori Information

On January 1, 2024, the Noto-Hanto earthquake of Mw7.6 occurred a little offshore of the Noto Peninsula in Japan. The shaking caused devastating damage to wooden houses in rural cities and towns and local roads and expressways on the peninsula. The casualties were over 200, and the number of collapsed buildings could be over 10,000. The primary source of strong ground motions was the western side of the whole fault segment, which was extended bilaterally to SSW and NNE directions for about 70 to 80 km from the epicenter at the peninsula's tip. About 20 strong motion stations are operated by NIED and JMA within 60 km of the fault. The source was a south-dipping thrust fault, the activity of which forms the Noto Peninsula. The highest observed PGA was 2.7 g at one K-NET (NIED) site, ISK006 in Shiga Town, while the highest observed PGV was 1.5 m/s at ISK005 in Anamizu Town. We have visual evidence of the cyclic mobility phenomenon at ISK005, so the pore water pressure may play an important role at this site.

Before the earthquake, we performed the generalized inversion analysis (GIT) to separate source, path, and site terms from about 60,000 strong motion records in Japan for both the S-wave portion with the maximum duration of 15 seconds and the whole duration of motion. The resultant horizontal site amplification factor for the former is named sHSAF, while the latter is wHSAF. If we have no significant basin effects, their spectral shapes are quite similar, with some amplitude difference up to 2 times. If the sites are located inside sedimentary basins, a large discrepancy in amplitude in the smaller (0.1 ~1 Hz) frequency range can be seen because of the strong generation of the basin-induced surface waves. At 20 sites inside the Noto Peninsula, we cannot find such a site with a large contribution of the basin-induced surface waves, and therefore, we can use the 1D assumption to extract sHSAF or wHSAF from the observed data. We would like to show the validation exercise for our strong motion prediction technique based on GIT by using the observed strong motion data in the epicentral area of this earthquake.

Session: How Well Can We Predict Broadband Site-Specific Ground Motion and Its Spatial Variability So Far? - II

Type: Oral

Room: Kahtnu 1

Date: 5/1/2024

Presentation Time: 10:30 AM (local time)

Presenting Author: Hiroshi Kawase

Student Presenter: No

Additional Authors