the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 Apr 2026
Constraints on the Lithospheric Structure and Rheology of Northern Chile from 8-year Post-Seismic Deformation following the Mw8.1 Iquique Earthquake
Abstract. Understanding and modeling the deformation following large earthquake is essential for characterizing the rheological structure and processes that release post-seismic stress. Here, we measured postseismic deformation over an 8-year period following the 2014 Mw8.1 Iquique earthquake using Sentinel-1 InSAR and GNSS time series in northern Chile and Bolivia. We jointly modeled the surface displacements caused by afterslip and viscoelastic relaxation using a two-dimensional finite element model. The combination of GNSS and InSAR data allows us to continuously map the temporal and spatial variations of the displacement field, especially in the vertical component, providing valuable constraints for modeling the rheological structure of the continental plate from the slab to the Altiplano. The amplitude of the uplift pattern claims for a weak zone below the western part of the Altiplano, where the volcanic arc is fed by partial melting. To reproduce the temporal evolution of post-seismic uplift, this weak zone must be governed by a Burgers rheology, combining a transient Kelvin body with a viscosity ηKwz = 2 × 1018 Pa.s and a Maxwell body with a viscosity ηMwz = 2 × 1019 Pa.s. To the west, our preferred model includes a cold nose rooting into the slab at a slab-mantle decoupling depth of dCN = 84 km. This near-trench elastic wedge, predicted by thermal models, drives mantle flow and generates surface uplift during post-seismic relaxation. By characterizing the post-seismic deformation field following the Iquique earthquake, our results refine the rheological structure below the Central Andes and define its response to stress changes down to short time scales.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-2003', Jeff Freymueller, 19 May 2026
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RC2: 'Comment on egusphere-2026-2003', Sabrina Metzger, 28 May 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2003/egusphere-2026-2003-RC2-supplement.pdf
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RC3: 'Comment on egusphere-2026-2003', Anonymous Referee #3, 01 Jun 2026
This paper combines 8 years of GNSS time series with 5 years of InSAR to characterize post-seismic deformation of a Mw8.1 earthquake Authors jointly inverted afterslip and viscoelastic relaxation using a 2D FEM that explored several parameters: afterslip geometry, structure of a weak upper plate, cold-nose decoupling depth, oceanic mantle viscosities. Authors preferred an elastic cold nose reaching slab-mantle decoupling depth and Burgers rheology for the weak zone.
This study has significant importance in understanding the deformation after a megathrust earthquake. They explored the particular time interval of an earthquake cycle that connects the short-term coseismic and long-term interseismic periods, which is often the most difficult time period to model and characterize. This paper has reasonably dealt with this difficulty. There are a few other strong points of this paper:
- The dataset is valuable; the longer observation window is a genuine advance
- The core conclusions are plausible and reasonably supported, especially the cold-nose result and weak-zone Burgers rheology result
However, several methodological choices warrant stronger justification.
- There is a 7-month InSAR gap, which means the early uplift signal that the paper argues requires a Kelvin body is dependent only on GNSS. The authors should state this limitation explicitly at the point where the Burgers conclusion is drawn, not only in the data section.
- I got a little confused with referencing InSAR with GNSS mentioned in section 3.1. Then, in section 6.3, authors state that GPS reference issue will propagate into InSAR flattening. Also, in section 5.3, authors note that the ascending InSAR track brings the “strongest constraint” on the optimal location of the cold nose limit. These statements seem contradictory, and I am having a hard time distinguishing an independent InSAR constraint from the one inherited through referencing. Shouldn’t a GNSS-only or InSAR-only fit, shown side by side, strengthen the argument?
- The parameter exploration (section 4.3) in this paper varies individually around a preferred model instead of jointly sampling the parameter space. If these parameters are coupled, few would definitely show trade-offs (such as afterslip amplitude/width vs near-field viscosity, dcn vs h vs Xcraton). Therefore, the sequential search in the paper risks settling in a local minimum and underestimating uncertainties. The authors should at minimum, in section 4.3, (i) state if and where joint exploration was performed, (ii) justify the order of parameter exploration, (ii) report uncertainties around preferred values rather than listing optimal point values (the reader cannot judge whether dcn = 84 km is meaningfully distinct from 80 or 88 km). The afterslip amplitude-width grid search is the right idea and should be extended to the parameters that most strongly trade off.
- One of the major limitations of the current methodology is how the geodetic signal is partitioned. From my reading (and please correct me if I am wrong), the partitioning is built into the model rather than derived from it. I see that depth, width, amplitude, and time function of afterslip are prescribed. I wonder how this mechanical decoupling between co-seismic viscoelastic run and afterslip would affect the final interpretation. In a self-consistent model, co-seismic and afterslip stresses both should load the viscoelastic medium, and the relaxation should modify the stress that drives the afterslip. Summing two independent runs neglects this coupling. The authors should at least argue why this is acceptable over a decadal window. This seems important since the afterslip is allowed to extend to the very depth range where the weak zone and decoupling begin to matter. The claim "the early uplift requires a transient Burgers rheology" is only as robust as the imposed afterslip vertical signature.
Minor comments:
- Line 8 (abstract): “The amplitude of the uplift pattern claims for a weak zone”. Replace the word “claims for” with “requires” or “calls for”.
- In the first paragraph of the introduction, fix the citation formats (currently: "?e.g.>[] pollitz2006post, panet2010upper, suito2017importance, Li2017PostseismicRheology, boulze2022post")
- Define what you mean by ‘weakened zone’ in the first paragraph of the introduction so that readers will understand the reason behind this characterization.
- Second from the last sentence in introduction reads,The use of a simple 2D model, rather than a 3D model, allows us to test 50 various configurations against the data.’ Authors should add another line after this that justifies their choice of isolated parameter testing in a 2D setting rather than doing co-evolution of parameters in a 3D setting.
- Can you the numbers such as 1.10^(20) to a consistent pattern of 1 * 10^(20). I mistook this for a decimal point first.
- Fix the section 5.1 heading. The wording does not make sense at all.
- In Figure B2, I see the x-axis titled ‘afterslip depth’ goes from 75-100. But Table 1 shows the exploration range of afterslip depth goes from 30-50 km. This is confusing and should be made internally consistent.
- A Kelvin rigidity of 136 GPa for the weak zone seems unusually high. Please provide a physical justification or clarify that this is an effective parameter rising from Burgers to Maxwell transposition
- The Luo and Wang (2021a) and (2021b) appear to be the exact same paper.
Citation: https://doi.org/10.5194/egusphere-2026-2003-RC3
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- 1
This paper presents a suite of 2D viscoelastic models for the postseismic deformation following the 2014 Iquique earthquake. The key finding is for a low viscosity weak zone (mantle wedge), which is required to explain the postseismic vertical displacements in particular. I think the paper is very well done, and the model they present represents a substantial improvement over past studies. They find that the vertical displacements are especially important in constraining elements of the model, because there are some much stronger tradeoffs within the model parameters when only the horizontal displacements are considered. (I think this is generally true for subduction zone postseismic studies).
The models are 2D rather than 3D. The advantage is that this makes the computational time much shorter, allowing a fuller exploration of the (multi-parameter) parameter space. But the cost is that the model becomes a bit inaccurate far from the trench, because in a 3D model the far field locations will “see” the edges of the rupture but in the 2D case there is no edge to the rupture as it is infinitely long. So the 3D model deformation would likely go to zero a bit closer to the trench than in the 2D model used here. I think in this case the use of a 2D model is OK because the main features that are being modeled and interpreted are close enough to the trench. It is possible that some optimal parameters values might change a bit in the case of a 3D model, but the basic structure they find should not change.
The authors consider a variety of geometric parameters for the viscoelastic structure, and systematically vary these values to find the optimal values. Their final model seems very sensible to me, and I think the basic geometry of an elastic cold nose and a low viscosity mantle wedge is a substantial improvement over previous studies. The “weak zone” that the authors identify really is the mantle wedge. I think it will be more clear to simply refer to it as the mantle wedge.
There are a lot of potential tradeoffs to explore in the model, starting with the contributions of afterslip vs viscoelastic relaxation, and also including potential variations of the viscoelastic geometry. It is a bit hard to keep track of all of the tests shown in Figures 7-15; this is a challenge for all such papers because there simply are so many things to test. I think the authors could help the reader a bit by providing a paragraph or two at the start of section 5 that would serve as a kind of “road map” to the rest of the section.
Line 124. “Therefore, we fixed tau to 45 days”. Based on what? The GNSS? You later get a different value for the GNSS. I suspect that it does not make much difference because you are modeling only the total deformation in the InSAR, but why the difference in time constant?
Figure 4, inset. I suggest using black rather than green. The green could set up an issue for colorblind readers, and black will be at least as clearly visible.
Minor corrections
Line 2. Change earthquake to earthquakes
Lines 8. I don’t know what you mean to say by “claims for a weak zone”. The verb is wrong.
Lines 20-21. Errors in references.
Line 30. Add “is” before “substantially”
Line 67. Change “is” to “was” at the start of the line
Line 97. Add SAR after interferometric
Line 129. Change cumulated to cumulative. Change from to for
Line 131. Change miss to lack
Line 134. Change cumulated to cumulative
Line 147. Change Bi-frequency to Dual-frequency.
Line 148. Change inverted to estimated
Line 149. Add the before VMF1. Add “mapping functions” after VMF1
Line 150. Change keep to estimate
Line 156. Add the before eight
Line 164. Change developped to developed.
Line 206. Change “As for” to “As with”
Line 251. Change is to are. Change parameter to parameters
Line 270. Add a comma after rheology
Line 271. Change transposed to translated
Line 353. Change “The afterslip” to “Afterslip”
Line 364. Change “add up” to “add constructively”
Line 370. Change “show that the” to “showed that”
Line 389. Change constraints to constrained
Line 393. Add “any” before “cold nose”
Line 399. Delete the comma after parameters