Determine whether the apparent displacement overshoot is physical ground reversal

Establish whether the approximately 5–7% transient displacement excess and subsequent reverse motion recorded during the 2026 Kumamoto earthquake represent physical ground overshoot rather than a coherent residual artifact introduced by the secondary CCTV recording, using an independent observation such as the native CCTV file or another camera recording the same rupture.

Background

The study identifies a transient displacement maximum approximately 5–7% above the subsequent permanent-displacement level, followed by reverse motion toward the final plateau. This feature is robust across the two image-tracking methods, smoothing choices, and reference-region tests.

However, both methods analyze the same secondary recording of a CCTV display, so a coherent artifact shared by the analyses cannot be excluded. The available video also does not provide sufficient information to separate strike-slip and dip-slip components or relate the observation site to rupture-front arrest. Consequently, the authors treat the overshoot descriptively rather than as demonstrated physical ground reversal and state that independent recording evidence is needed.

References

These physical interpretations are intriguing, but none can yet be demonstrated for the present observation. Both tracking methods operate on the same secondary recording, so coherent residual motion introduced by the recording system could appear in both analyses. The spatial-control tests do not provide a reliable quantitative upper bound on such residual motion, and the apparent peak excess is more sensitive to target-region size than the principal rise time. Furthermore, the available video alone does not constrain the relationship between the observation site and rupture-front arrest, or separate the strike-slip and dip-slip components, sufficiently to associate the observed return with a specific dynamic mechanism. We therefore use apparent overshoot as a descriptive term for the video-derived transient excess and do not interpret the observed reverse motion as definitive evidence of physical ground reversal. Establishing physical overshoot would require an independent observation, ideally the native CCTV recording or another camera recording the same part of the rupture.

— Time-Resolved Surface-Fault Displacement During the 2026 Kumamoto Earthquake From CCTV Video  (2608.21045 - Enescu et al., 21 Aug 2026) in Section 4.3, “Apparent displacement overshoot and reversal,” p. 13