Comment on: “Interseismic Strain Accumulation near Lisbon (Portugal) from Space Geodesy” by Fonseca et al. (2021)

The paper by Fonseca et al. (2021), hereafter referred as FON21, published in Geophysical Research Letters2 make several conclusions that are not convincingly supported by the evidence of the data that is made available. In this comment we will address the following statements: 1) FON21 “provides new evidence of sinistral simple shear driven by a NNE-SSW first-order tectonic lineament; 2) “PSInSAR vertical velocities corroborate qualitatively the GNSS strain-rate field, showing uplift/subsidence where the GNSS data indicate contraction/extension”; 3) FON21 proposes “the presence of a small block to the W of Lisbon moving independently toward the SW with a relative velocity of 0.96 ± 0.20 mm/yr”; 4) FON21 shows “that the contribution of intraplate faults to the seismic hazard in the LMA is more important than currently assumed”. We conclude that more evidence needs to be collected to confirm or infirm FON21 statements and conclusions. For the moment the proposal of an autonomous crustal block moving with significant velocity in relation to the neighboring domain should be considered speculative and unproved.

Consistent Estimation of Strain Rate Fields from GNSS Velocity Data Using Basis Function Expansion with ABIC

Present day crustal displacement rates can be accurately observed at stations of global navigation satellite system (GNSS), and crustal deformation has been investigated by estimating strain-rate fields from discrete GNSS data. The method proposed by Shen et al. (J Geophys Res 101:27957–27980, 1996) offers a simple formulation for simultaneously estimating smooth velocity and strain-rate fields, and it has contributed to clarify crustal deformation fields in many regions all over the world. However, in this paper, we point out three theoretical disadvantages of the method: mathematical inconsistency between estimated velocity and strain-rate fields, inability to objectively determine the optimal value of a hyperparameter that controls smoothness, and inaccurate estimation of uncertainty. As an alternative, we propose a method of basis function expansion with Akaike's Bayesian information criterion (ABIC), which overcomes the above difficulties. Application of the two methods to GNSS data in Japan reveals that the inconsistency in the method of Shen et al. is generally insignificant, but could be serious in regions with sparser observation stations such as in islet areas. More importantly, the method of basis function expansion with ABIC shows a significantly better performance than the method of Shen et al. in terms of the trade-off curve between the residual of fitting and the roughness of velocity field. The estimated strain-rate field with the basis function expansion clearly exhibits a low strain-rate zone in the forearc from the southern Tohoku district to central Japan. We also find that the Ou Backbone Range has several contractive spots around active volcanoes and that these locations well correspond to the subsidence areas detected by InSAR after the 2011 Tohoku-oki earthquake. Thus, the method of basis function expansion with ABIC would serve as an effective tool for estimating strain-rate fields from GNSS data.

Seismic observations of crevasse growth following rain-induced glacier acceleration, Haupapa/Tasman Glacier, New Zealand

Copyright © The Author(s) 2019 This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.. Changing rates of water input can affect both the flow of glaciers and ice sheets and their propensity to crevasse. Here we examine geodetic and seismic observations during two substantial (10-18-times background velocity) rain-induced glacier accelerations at Haupapa/Tasman Glacier, New Zealand. Changes in rain rate result in glacier acceleration and associated uplift, which propagate down-glacier. This pattern of acceleration results in a change to the strain rate field, which correlates with an order of magnitude increase in the apparent seismicity rate and an overall down-glacier migration in located seismicity. After each acceleration event the apparent seismicity rate decreases to below the pre-acceleration rate for 3 days. This suggests that seismic events associated with surface crevasse growth occur early during phases of glacier acceleration due to elevated extensional stresses, and then do not occur again until stresses recover.

Seismic observations of crevasse growth following rain-induced glacier acceleration, Haupapa/Tasman Glacier, New Zealand

Copyright © The Author(s) 2019 This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.. Changing rates of water input can affect both the flow of glaciers and ice sheets and their propensity to crevasse. Here we examine geodetic and seismic observations during two substantial (10-18-times background velocity) rain-induced glacier accelerations at Haupapa/Tasman Glacier, New Zealand. Changes in rain rate result in glacier acceleration and associated uplift, which propagate down-glacier. This pattern of acceleration results in a change to the strain rate field, which correlates with an order of magnitude increase in the apparent seismicity rate and an overall down-glacier migration in located seismicity. After each acceleration event the apparent seismicity rate decreases to below the pre-acceleration rate for 3 days. This suggests that seismic events associated with surface crevasse growth occur early during phases of glacier acceleration due to elevated extensional stresses, and then do not occur again until stresses recover.

Numerical Simulation on the Penetration Behavior of the Projectile during the Water Injection Stage of Water-Projectile-Assisted Injection Molding Process

Water-projectile-assisted injection molding (W-PAIM) is a novel molding process for plastic pipes with complicated shape. It utilizes high-pressure water as a power to push a solid projectile to penetrate through the melt to form a hollow space. In order to investigate the penetration behavior of the projectile during the water injection stage of W-PAIM process, numerical simulation of the water injection stage of a W-PAIM pipe with straight and curved segments was carried out. A turbulent flow for the driving water was considered in the motion equation, and the dynamic mesh technology was used to deal with the moving solid projectile. The simulation results, including RWT and the flow fields, were compared with those of water-assisted injection molding (WAIM) pipe with the same outer dimensions. It was found that the residual wall thickness (RWT) of the W-PAIM pipe is much thinner than that of the WAIM pipe. The projectile has a crucial influence on the RWT. The pressure fields of W-PAIM and WAIM are very similar in both straight and curved segments. The velocity field and strain rate field near the penetration front in W-PAIM are quite different from those in WAIM due to the drag flow caused by the projectile penetration.

Scaling in the Local Strain-Rate Field during Jerky Flow in an Al-3%Mg Alloy

Jerky flow in alloys, or the Portevin-Le Chatelier effect, presents an outstanding example of self-organization phenomena in plasticity. Recent acoustic emission investigations revealed that its microscopic dynamics is governed by scale invariance manifested as power-law statistics of intermittent events. As the macroscopic stress serrations show both scale invariance and characteristic scales, the micro-macro transition is an intricate question requiring an assessment of intermediate behaviors. The first attempt of such an investigation is undertaken in the present paper by virtue of a one-dimensional (1D) local extensometry technique and statistical analysis of time series. The data obtained complete the missing link and bear evidence to a coexistence of characteristic large events and power laws for smaller events. The scale separation is interpreted in terms of the phenomena of self-organized criticality and synchronization in complex systems. Furthermore, it is found that both the stress serrations and local strain-rate bursts agree with the so-called fluctuation scaling related to general mathematical laws and unifying various specific mechanisms proposed to explain scale invariance in diverse systems. Prospects of further investigations including the duality manifested by a wavy spatial organization of the local bursts of plastic deformation are discussed.