| 10 Feb 2026
Mantle Deformation Patterns Beneath the Central India Tectonic Zone: Evidence from SK(K)S Splitting Measurements in the Satpura Gondwana Basin and Adjacent Areas
Abstract. This study presents shear wave splitting (SWS) estimates for core-refracted SK(K)S phases utilizing data from nine seismic stations in the Central Indian Tectonic Zone (CITZ) that were temporarily operational between July 2023 and July 2025. The CITZ was formed during the Mesoproterozoic orogeny in central India, resulting from the collision of the northern Bundelkhand Craton with a jumble of South Indian Cratons. We used rotation-correlation and transverse energy minimization methodologies to ascertain the SWS parameters, the fast polarization directions (FPDs) and splitting delay times (δt). A total of 129 high-quality SWS measurements were obtained from 87 earthquakes (M>5.5) at epicentral distances between 84°–145° for SKS phases and 84°–180° for SKKS phases. The mean δts at each seismic station ranges from 0.7 to 1.4 seconds, demonstrating the upper mantle heterogeneity in the study region. Most stations show NE-SW FPDs, aligning with the Absolute Plate Motion (APM) of the Indian plate. The difference between mean FPD and APM direction at some stations suggests the presence of 10 fossilized anisotropic fabrics resulting from prior subduction events during the Mesoproterozoic Era. Seismic stations near the Deccan Volcanic Province and mantle dyke zones have lower δt (<1 second) values, indicating significant magmatism during the Cretaceous period. Our findings suggest that the mantle flow beneath the CITZ is affected by both the present APM direction of the Indian plate and lithospheric frozen anisotropy resulting from prior Mesoproterozoic orogeny and Cretaceous mantle plume activity.
Revision of Manuscript Number: egusphere-2025-6202
Title: Mantle Deformation Patterns Beneath the Central India Tectonic Zone: Evidence from SK(K)S Splitting Measurements in the Satpura Gondwana Basin and Adjacent Areas
Authors: Nitarani Bishoyi, Arun Kumar Dubey, and Ashwani Kant Tiwari
In the manuscript, the authors analysed data from nine seismological stations in the central Indian Tectonics zone that were installed in three phases during July 2023 to July 2025. The data acquired are analysed to obtain shear wave splitting parameters in the area and the results are discussed and interpreted in terms of the contribution of frozen-in and asthenospheric sources of anisotropy, corroborating previous interpretations done in the adjacent regions by several other authors. If interpretation and methodologies are not new for this kind of paper, the results presented are of interest for publication since covering part of the region not previously covered by this kind of analysis.
In general, the paper is well written and easy to follow. Most of the figures are clear and exhaustive and data are managed and treated in a properly way. That said, I have some issues about some aspects of the interpretation that I would like to be expanded and some other suggestions on how to interpret the data that I hope could be useful to revise the interpretation's part of the paper.
- I'm not very convinced by the reasons to associate the source of anisotropy with lithospheric and asthenosperic contribution. What I see in Figure 10 and what you explain in the text is that FPD, APM and GPS velocity are in agreement, and what I could think is that the deformation could occur on the entire volume from crust to upper mantle. This, in my opinion, is reasonable, but it is not clear why you associate so strictly the litho and asthenospheric contributions if all the directions are in agreement. How can you say that the deformation doesn't occur entirely in the asthenosphere? or completely in the lithosphere? How could you distinguish between these contributions only by comparing the vectors' direction? I think that a more detailed motivation and analysis about this issue could strengthen the whole interpretation of the results, which I would repeat, seems to be reasonable for me too.
- In several parts of the paper, the authors attest to the complexity of the anisotropic structure of the area (for example, line 184 "the splitting data may indicate a multilayered anisotropic structure"). These sentences should be justified through complex-layer modelling or classical FPD versus BAZ plots that software such as SplitLab could execute, but in no part of the paper is this shown or discussed. A part the software, there are several techniques to analysed the data trying to understand the presence of two anisotropic layer beneath a station, as the analysis of Fresnel Zones, the orientation of FPD based on back-azimuth or the comparison with other data as Pn data (sampling anisotropy in the shallower part of the upper mantle) and so on, just to be more precise on what you are saying in the interpretaion.
- Another issue that I would raise in this review is the use of the single shear wave splitting result. Why didn't you use or plot the null measurements? Especially where you have an asthenospheric upward, the amount of nulls should be consistent since the waves don't split horizontally, so this information could be useful in the region where the dykes occur. On the other hand, the discrepancy between SKS and SKKS direction should be an indication of a deformation that possibly occurs in the deeper part of the mantle, so a comparison of them could help the authors to discriminate better the source of anisotropy, confirming/not confirming their hypothesis.
In my version of the manuscript, I didn't find any supplementary material. I would encourage the authors to add at least a table with all the measurements obtained to reproduce the results, even for the seismological community working in the area or interested in the use of these data.
Other minor observation in the text:
- Line 4 and 104-109: if you don't use the results obtained in the Rotation Correction method, I think you can also remove the description ot the method itself. I know that SplitLab calculate in the same run, both the results but at the end, you use only one of the TEM techniques, so you can focus the description only on this. Alternatively, you can also decide to use only the results that give results similar in both cases, strengthening your final dataset with objective choices.
- Lines 35-40: What is the hypothesis that the authors prefer? Double-sided subduction? I suppose this from the cartoon in Figure 12, but in the text is not motivated properly.
- Lines 85-91: This paragraph seems out of place, but this is only my opinion
- Lines 159-160: the presence of complex mantle deformation should be examined in a better way; you can't attest it just in one phrase. The same applies to the presence of lithospheric strain and mantle flow relationships.
- Lines 183-186: As in the previous comment, the presence of the multilayered anisotropic structure should be justified better
- Line 200: DVP states for?
- Lines 200-202: The presence of the mantle plume could also be corroborated by the presence of null measurements
- Line 209: double citation of SG08
Comments on Figures:
- Figure 1: Please cite the DOI of the NCS network or some references about it. Have the 9 seismic stations recorded with a different DOI?
- Figures 2, 8 and 9: In my opinion, these figures are a bit "bare". Filling them with the names of the stations and the faults could help. I think it could also be useful to trace the region where the plumes are present.
- Figure 10: The word "inclination" should be "orientation", don't it?