Discussion about this post

User's avatar
Roland Bürgmann's avatar

Kyle and Judith, thanks for another very thorough analysis. Your blogs and Quentin and Jean-Mathieu's follow-up work have provided a really interesting and high-level discussion on an important topic.

I agree that the lack of a short-term signal in the tiltmeter data of Hirose et al. (2024) (in addition to the seafloor pressure data described in Hino et al (2018 Mar Geophys Res) also suggests that there was no large hours-long precursor before the 2011 Tohoku-oki earthquake. However, another puzzle remains regarding the tilt data. Something else but postseismic slip seems to have produced the features seen in the tilt data after the March 9 foreshock.

You wrote

> Because the tilt meter data and the GPS displacement data are independent, the apparent

>agreement about the timing and shape of the crustal stretching suggests that they are measuring

> the same crustal deformation.

However, as the authors point out, the data do not appear to be capturing a coherent deformation signal associated with the March 9 foreshock that would be consistent with the GPS data (i.e., related to afterslip from that event). Fig. S5 of Hirose et al. (2024) shows a high-amplitude, but quite random distribution of post-March 9 tilt signals, - not at all like what the afterslip model (Fig. 4 of Hirose et al., 2024) predicts. Thus, some other foreshock-related process (Hirose et al. consider "instrument responses or mechanical coupling between the sensor and a borehole, in response to the strong ground shaking of the foreshock") appears to dominate the tilt observations and overwhelms the afterslip signal seen with GPS.

Expand full comment
Ross Stein's avatar

Very impressive analysis. Thank you for performing it.

Expand full comment
7 more comments...

No posts