the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 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.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-6202', Anonymous Referee #1, 16 Mar 2026
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RC2: 'Comment on egusphere-2025-6202', Anonymous Referee #2, 01 Apr 2026
This study addresses an important and under-explored region of the central Indian lithosphere, where the Central India Tectonic Zone sutures the northern and southern cratons. Understanding mantle deformation here is fundamental to questions of how cratons stitched together, how magmatism modified the lithosphere, and how deep anisotropic fabrics developed over time. The dataset has the potential to fill a gap in regional SKS measurements and contribute significantly to our understanding of lithospheric and upper-mantle structure beneath stable continental interiors. At the same time, the manuscript would benefit from moderate-to-major revisions to strengthen its impact and reliability, including greater engagement with established studies of different sources of anisotropy (including crustal LPO, SPO), transparent presentation of individual SKS measurements with uncertainties and earthquake metadata, clearer visualization of the regional tectonic context, and more detailed exploration of variability in individual SKS values. Incorporating lithospheric thickness estimates, plotting individual measurements (possibly at chosen piercing points,) and considering the contributions of crustal versus mantle sources would help clarify the physical interpretation of the results and improve reproducibility. Overall, the study addresses a key region with high potential impact, but addressing these points would substantially improve the rigor, clarity, and interpretative depth of the manuscript. I think this study fits very well with the scope of the journal and I recommend this mansucript for publication with moderate revisions.
Major Comments
Tectonic context visualisation: The manuscript discusses the CITZ as a major suture between northern and southern Indian cratons, but the figures don’t really show this clearly. Figure 1 doesn’t explicitly indicate the CITZ or the craton boundaries, so it’s hard to see how the sutures or faults relate to the tectonic story. Figure 2 shows a lot of local lithology, supracrustals, granitoids, basins, supergroups, but it’s hard to place that in the larger craton-scale context. A wider, simpler, regional tectonic map showing the two cratons, the CITZ, and major faults would help readers connect the field observations to the bigger tectonic picture.
The authors report performing SKS splitting analyses using both RC and TEM methods. However, the only measurements presented are in Table 1, which shows station-averaged values without uncertainties, making it difficult to assess the quality of the final results. In SKS studies, and generally as best practice, it is expected that all individual measurements be provided. Since the authors used two methods, even if only one forms the basis of their interpretation, the individual measurements, associated uncertainties, and earthquake metadata should be included. Providing these details is essential for evaluating the quality, reproducibility, and reliability of the results and would greatly enhance the transparency and rigor of the study.
I strongly suggest that the authors plot individual SKS measurements, similar to what is done for other stations in Figure 3, perhaps using color or symbol size to represent delay times. While rose diagrams (Fig. 8) are valuable, they empahsize quantity and can obscure the actual measurement values and variability. Plots of individual measurements, potentially at chosen piercing points (50, 100 or 200 km for example), could provide insight into the depth and lateral extent of the anisotropy. For example, if two nearby stations record different fast directions from the same earthquake, the overlap of the SKS Fresnel zones can constrain the minimum depth of the anisotropy source (e.g. Alsina and Snieder). Exploring this type of lateral and depth coherence would greatly improve understanding of the anisotropic structure beneath the network.
Station orientation and horizontal component alignment can influence SKS measurements. Even small misalignments can rotate the observed particle motion, affecting both the fast-axis direction and the split time, potentially introducing systematic errors. The authors could note whether any checks or corrections for station misalignment were applied and discuss how such uncertainties might impact their results. If station misalignment was not assessed prior to SKS splitting results, I believe this can even be done by comapring SKS source polarisaiton with theoretical backazimuths of analsyed earthquakes (like the shown example), so it could be a good post-analysis check as well.
It would be valuable to incorporate existing estimates of lithospheric and crustal thickness beneath the stations, for example from previous geophysical studies, to visualize how much the lithosphere could contribute to the observed SKS delay times. Cratons are generally very thick, and depending on crustal thickness, the lithospheric contribution to δt could range from roughly 0.04-0.2 s (Barruol & Mainprice, 1993). Plotting or summarizing this information alongside the SKS measurements would help assess the relative contributions of lithospheric versus deeper mantle anisotropy and provide context for interpreting the splitting results.
The authors link lower delay times values to mantle plume upwelling and Cretaceous magmatism, but could a plume formed millions of years ago could still influence present-day SKS measurements? Since India has drifted north since the Cretaceous, the spatial relationship between the original magmatism and the current station location should be addressed. Also the authors invoke the presence of dykes as evidence for magmatism which they relate directly to lower delay tiems. Hwoever, crustal features such as dike intrusions or aligned fabrics could contribute to the observed Delay times and fats axes in different ways, potentially producing different signatures from crustal LPO or SPO compared with mantle LPO (see articles by Fouch and Rondenay (2006), Meissner et al (2002), Mainprice & Nicolas (1989) and others by Karato, Zoback, Ribe, Crampin, Long).
More line-by-line comments:
L27: The CITZ is not clearly shown in Figure 1. It is unclear whether it is meant to represent a collection of sutures and faults shown in the figure, or if it is delimited by some other feature. This should be clarified. If the CITZ is an important suture between the northern and southern cratons, the boundaries of these cratons should also be indicated in Figure 1.
L33: “the northern Indian craton subducting beneath the southern Indian craton.” Since the CITZ formed during the Mesoproterozoic (~1.6–1.0 Ga), possibly before modern-style plate tectonics was fully established, and given that cratons are thick and buoyant, it may be clearer to describe this as underthrusting or collisional interactions along craton margins, rather than full-scale subduction, while acknowledging that the polarity and details of these collisions remain debated.
L55: The manuscript briefly mentions anisotropy may be due to mantle LPO, but given that the preceding paragraphs focus on crustal and lithospheric structures, it would be helpful to also discuss potential sources of anisotropy within the crust. For example, lattice-preferred orientation (LPO) of crustal minerals such as biotite, and shape-preferred orientation (SPO) of aligned grains or foliation, can influence shear-wave splitting in different ways. References such as Fouch and Rondenay (2006), Meissner et al (2002), and Mainprice & Nicolas (1989) provide detailed examples, though the authors should also consider additional established studies (for example by authors like Karato, Zoback, Ribe, Crampin, Long) to give a broader perspective. Including these sources would strengthen the link between observed anisotropy and deformation in both the crust and upper mantle.
L60: "moves parallel to it" - not always (see the references above).
L80: this is the first mention of a mantle plume. I suggest first describing it in the earlier tectonic pargaraphs rather than mentioning it so briefly at the end of a paragraph about seismic anisotropy studies in India.
L130: "The rose diagram for each split measurement (Figure 8) illustrates the variance and predominant orientation of FPDs at each seismic station." This statement should be interpreted cautiously. The apparent “predominant orientation” does not necessarily represent the true fast-axis direction, as it can be biased by the uneven distribution of earthquakes, which may preferentially sample only part of the anisotropic signal. At the same time, the large variability in measurements in Fig 7c,d is noteworthy and deserves careful exploration. I suggest that the authors report individual measurements with associated uncertainties and discuss how both earthquake distribution and potential multilayer or complex anisotropy contribute to the observed variance.
L141: Which absolute plate motion (APM) model did the authors use for this analysis? The resulting trench-parallel and trench-perpendicular components can vary depending on the chosen global model (e.g., Nuvel-1A, MORVEL) or reference frame (e.g., no-net-rotation, Eurasia-fixed, hotspot). Clarifying the specific model and reference frame is important I think.
L170: 'the measured δts varies from 0.74 seconds at station SG02 to 1.4 seconds" this should be shown and/or added as a dataset in the SI
L188: "The lithosphere-asthenosphere boundary (LAB)" It owuld be very good to add a map of the LAB here to support the tex
L193: 'may be located in locations with thicker lithosphere" add a value
L200-205: The paragraph links lower dt at SG02 to mantle plume upwelling and Cretaceous magmatism, but this raises a few points worth exploring further. If the mantle plume formed in the Cretaceous, could its effects still influence present-day SKS measurements, or would the signal primarily reflect frozen-in anisotropy? Considering that the Deccan plume (Reunion hotspot if I m not mistaken?) is now far south in the western Indian Ocean and India has drifted north since the Cretaceous, how might the original location of magmatism relate to current station positions? Finally, given the potential influence of crustal features, including dike intrusions or aligned fabrics, it may be valuable to consider the different signatures of crustal LPO and SPO versus mantle LPO (i.e. see my earlier comment about other articles the author sshould enagge with).
Figure comments
Figure 1 . I strongly suggest adding a wider tectonic figure here showing the cratons and the suture zones between them investigated with SKS in this study.
Figure 2 shows range of petrological regions, but it mixes many terms like supergroups, supracrustals, sediments, basins, traps, groups, granitoids. For a seismologist who may not be familiar with the local tecotnic framework, it is quite confusing and hard to connect all these lithosplogical regions with the tectonic context described in the main text. Where are the limit fo the Southern cratons in this figure? What is the area of the Satpura Gondwana Basin (or mobile belt?) here? Perhaps also add the recognized limits of the CITZ here as well.
Figure 7. This shows a large range of values for the same backazimuth. I wonder how it looks like for individual stations (rose diagrams such as the ones in Fig 8 are also representative but seeing the values in xy baz plots can even tell about 2d layer variabilitirs. Such a high variation in values of the same baz seems indicative of multiple layers to me).
Figure 12. The elevation profile appears to differ from the cross section shown below. What time frame does the sketch represent? If this region shifted northward or eroded over time, how did the topographic high develop in the backarc region relative to the subduction front? It would also be helpful to indicate the craton boundaries and thick roots on this section. Given that subduction along the CITZ occurred in the Mesoproterozoic, while magmatism related to the Deccan plume occurred in the Cenozoic, how should present-day SKS delay times be interpreted in the context of mantle upwelling?
Citation: https://doi.org/10.5194/egusphere-2025-6202-RC2
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- 1
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?