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Noto Peninsula, Japan, Earthquake, January 1, 2024: Implications of Inconsistent Seismic Energy Estimates From Teleseismic and Strong Ground Motion Observations

Description: 

The excellent network of strong motion accelerographs on the Noto Penninsula enables comparison of the radiated seismic energy (E_S) from the earthquake of January 1, 2024, as observed locally and at teleseismic distances. At teleseismic distances, IRIS estimates that the radiated energy in the broadband frequency range was 2.32 e+15 J. Considering alternative fault geometries, the strong motion stations on the hanging wall yield estimates in the range 8.8-20.2 e+15 J, i.e about 4-9 times greater. These results can be compared with other earthquakes using the scaled energy (E_S/M₀), log scaled energy (θ), or apparent stress (τ_a=μE_S/M₀). For the Noto Penninsula earthquake, the teleseismic data imply τ_a=0.44 MPa, while local estimates give 1.6-3.8 MPa. Differences in the observed frequency bands are ruled out as a cause for the discrepancy between the teleseismic and local estimates. For perspective, the teleseismic study of Convers and Newman (2011) reports average values of θ for reverse, strike slip, and normal faulting that convert to values of τ_a of 0.7, 1.6, and 1.2 MPa, respectively.

The local - teleseismic discrepancy here may be typical of reverse faulting events, as the free surface boundary for the upper wedge allows it to move more than the rock below the fault. If this discrepancy is general, a teleseismic estimate of τ_a would not be reliable for local hazard estimates. Also, the average apparent stress in reverse faulting events may not be smaller than normal and strike-slip events. One might expect that some energy radiated into the wedge is reflected to teleseismic distances and contributes to the teleseismic estimate, but even if this is true, the large discrepancy remains. Perhaps that is because the fault not transparent while it ruptures. One possible mechanism is separation of the hanging wall from the foot wall, (e.g. Brune, 2001; Gabuchian et al., 2017). Non-linearity in the upper wedge, in the bedrock as well as in soils, would also absorb energy before it can be reflected to teleseismic distances.

Session: The 2024 Magnitude 7.5 Earthquake and the Associated Earthquake Swarm Beneath the Noto Peninsula, Central Japan - I

Type: Oral

Date: 5/3/2024

Presentation Time: 08:30 AM (local time)

Presenting Author: John

Student Presenter: No

Invited Presentation: 

Authors