Seismic slip channeling along the East Anatolian Fault illuminates long-term supercycle behavior

Domain: earth_science
Published: 2024-10-16
Editorial outcome: major_revision

Abstract
The two Mw > 7.5 earthquakes that struck the East Anatolian Fault (EAF), Türkiye, in 2023 caused more slip than expected, indicating that they were potentially part of a supercycle, in which the occurrence probability of a large earthquake is determined by accumulated strain rather than time since the last large earthquake. Here, we show two potential supercycles along the EAF, analyzing earthquakes from the last two millennia. Within each supercycle, seismic ruptures originated in the northeast and progressively spread southwestward with an increasing number of earthquakes until a new supercycle began with another large earthquake in the northeast. To understand the supercycle behavior, we analyze the aftershock sequences of the four most recent Mw ≥ 6.1 mainshocks (2010–2023). This series of earthquakes progressed southwestward, characterized by an increasing diversity of focal mechanisms and a heightened dispersion of epicenters across a branched seismotectonic environment. Earthquakes in the northeast exhibit spatial and kinematic channeling along the master fault surface, effectively transferring slip southwestward and there potentially triggering dispersed and heterogeneous earthquakes. This spatiotemporal pattern seems connected with varying levels of a presumably-innate property of fault sections or regions, ruling the process of seismic slip channeling, which could also explain the behavior of long-term supercycles.

Introduction
Devastating earthquakes continue to surprise and give lessons to scientists, especially when these events exhibit unexpected characteristics1, such as the 2023 doublet of Mw > 7.5 earthquakes within a day along the same fault system in Türkiye2–9. Indeed, several great earthquakes in the past served as scientific watershed episodes. The Mw 7.9 San Francisco earthquake of 1906 sparked the development of the elastic rebound theory10, which is still used to describe the basics of earthquake cycles. Another significant event was the 1964 Alaskan Mw 9.2 earthquake with its associated tsunami. The earthquake served as unmistakable proof for the theory of plate tectonics11, while the tsunami resulted in the establishment of the NOAA Tsunami Warning Center, which has since saved lives in the Pacific region. Between 1939 and 1992, ten Mw ≥ 6.7 earthquakes that progressively unzipped ~1000 km of the North Anatolian Fault, Türkiye, taught geoscientists how secular stressing and static stress transfer after large earthquakes can trigger the next major event along the same fault system12,13.

Occurrences of temporally and spatially close earthquakes are hence unmissable opportunities to advance our understanding of active fault mechanics and regional hazards14. The most recent noteworthy instance with a significant impact on people and infrastructure is the aforementioned doublet of Mw > 7.5 earthquakes that occurred along the East Anatolian Fault (EAF)3,9,15–19.

To improve our knowledge of fault unzipping through multiple earthquakes and hence of seismic supercycles20, if that is truly the case for the EAF earthquakes3, we compare the seismotectonic features of the two 2023 mainshock-aftershock sequences near Pazarcık (Mw 7.7) and Elbistan (Mw 7.6), southwestern EAF, with those of the two previous Mw ≥ 6.1 sequences, which occurred in 2010 and 2020, respectively, near Kovancılar (Mw 6.1) and Elâzığ (Mw 6.8) along the northeastern EAF (Fig. 1). To do so, we gathered data mainly from the Türkiye’s Disaster and Emergency Management Authority, i.e., the AFAD databases, and from other historical databases (see “Methods”). We then place the four mainshock-aftershock sequences within a multimillennial context of historical seismicity25 and use them as proxies to interpret long-term earthquake supercycles. The analogy we propose between recent mainshock-aftershock sequences and long-term clusters of earthquakes, or possibly supercycles20, is based on a concept termed seismic slip channeling. For each investigated earthquake sequence, the degree of seismic slip channeling is calculated by examining some geometric parameters of faults and earthquakes; specifically, the distance between the epicenters of mainshocks or aftershocks and the EAF mapped master surface. This distance is compared, in a two-dimensional diagram, to the angle between azimuths of the EAF master surface and seismic slip vectors obtained from focal mechanisms.

The EAF is a major > 600 km long tectonic boundary in eastern Türkiye, separating the Anatolian, Arabian, and Eurasian plates, which come into contact at the Karliova triple junction located at the northeastern tip of the EAF (Fig. 1). The EAF has a general subvertical attitude, NE-SW strike, and left-lateral kinematics26–28. It is best defined as a complex and branched strike-slip fault system, which includes a segmented master fault surface, as is mapped on the Earth’s surface, and numerous subsidiary faults with different orientations and inclinations. In detail, the tectonic architecture of the EAF appears twisted and accompanied by variously oriented subsidiary faults between the Karliova triple junction and the 2010 Kovancılar mainshock epicenter (Fig. 1). Southwestward, the EAF becomes more linear and narrower where the 2010 Kovancılar and 2020 Elâzığ mainshock epicenters occurred, particularly in the area of the 2020 event. Further southwestward, the EAF becomes progressively more complex from a geometrical point of view, splitting into a few main branches, with fault segments oriented from E-W to N-S26–28. The two 2023 mainshocks occurred along two main branches of this southwestern portion of the EAF (Fig. 1).

In the area of the 2023 Pazarcık mainshock (Fig. 1), the EAF trace bends southward from the NE-SW strike to NNE-SSW, forming a releasing bend with an associated extensional basin developed within the general left-lateral kinematics of the entire fault system. The 2023 Pazarcık mainshock nucleated there on the Narlı fault zone and then spread along the EAF master surface, affecting both the Amanos segment to the south and the Pazarcık and Erkenek segments to the north16,19,29.

The following Mw 7.6 Elbistan mainshock originated along an E-W striking segment of the Çardak fault, 95 km to the NNE of the Pazarcık maishock epicenter (Fig. 1), and then spread westward to the Savrun fault and eastward through the Nurhak tectonic complexity, along a minor fault between the Malatya and Sürgü major faults. The Mw 7.6 mainshock triggered a series of aftershocks, including normal faulting earthquakes near the Savrun fault. Some aftershocks located to the north of the Çardak fault are compatible with a N-dipping fault16,19,29.

On a larger scale, all the aforementioned fault segments belong to the broad and complex EAF strike-slip system, in particular the branched southwestern part26–28. For the EAF, which is a plate boundary more than 600 km long, it is indeed reasonable to hypothesize a composite fault zone up to a few tens of km thick (< ~10% of the fault length), including several fault segments with slip distributed partly on the master fault and partly on subsidiary faults. The 2023 earthquakes demonstrate how complex a subvertical strike-slip plate boundary can be and thus how varied the seismic ruptures and slip propagation along the boundary are9,30,31. Fault stepovers as well as releasing and restraining bends or multiple fault segments variously oriented and inclined can partition, facilitate, or restrain the slip propagation along the fault system32,33. As this is one of the main focuses of our discussion, below, by using the seismic slip channeling, we aim at assessing such a slip complexity.

To further complicate the general seismotectonic architecture of the EAF, to the south of the 2023 Pazarcık earthquake epicenter, the EAF system joins with the strike-slip Dead Sea Fault system and the Cyprus compressional arc, which are both active plate boundaries of the eastern Mediterranean region34 (Fig. 1). These boundaries, particularly the Cyprus arc, may influence the seismotectonics of the southwestern section of the EAF as it will be briefly discussed below.

Our aim is to assess the extent to which seismic deformation is directed along or dispersed around the EAF master surface, particularly concerning seismic slip parallel, oblique, or perpendicular to the master surface. To do so, we use the aforementioned seismic slip channeling. Additionally, our goal is to comprehend whether the seismic slip channeling itself is connected with an innate property of fault sections or regions, rather than being influenced by specific earthquake characteristics, such as mainshock magnitude. Below, based on an analysis of earthquakes from the last two thousand years, we identify two possible supercycles along the EAF. Each supercycle began with a major earthquake in the northeast, followed by a southwestward trend in seismic activity. To investigate this pattern, we analyze aftershock sequences from the four most recent Mw ≥ 6.1 mainshocks (2010–2023), revealing, also in this case, a southwestward trend. This trend was distinguished by increased variability in focal mechanisms and broader epicenter dispersion in a complex seismotectonic setting. In the northeast, seismic activity was concentrated along the master fault, allowing slip to be transferred southwestward and potentially triggering more scattered earthquakes. This observed trend, attributed to a process we describe as seismic slip channeling, may help explain the long-term dynamics of supercycles along the EAF.

Results
Uncertainties and terminology
We acknowledge that our analyses of both recent (Figs. 1–3) and historical (Fig. 4) data are inevitably subject to uncertainties inherent in seismological catalogs. This applies also to the AFAD databases utilized here, which have intrinsic limitations regarding the precise location of instrumental earthquakes and their focal attributes22,35, as well as the intensity, magnitude, and location of historical earthquakes. However, it is important to acknowledge that the recording of the four recent seismic sequences (2010–2023) studied here benefited from a significant strengthening of the AFAD seismic network since 2007. This enhancement has led to improved detection thresholds and reduced location uncertainties26,35. Even though providing quantitative estimates of uncertainties is challenging, approximate estimates from first-order relocations of the four studied sequences indicate horizontal and vertical mean uncertainties around 3 and 4 km, respectively22,26,30. At the scale of investigation of the present study, such uncertainty in the epicenter location ensures that the observed differences in the aggregate dataset of our elaborations remain robust. In particular, uncertainty and errors should affect all four aftershock sequences roughly equally without changing the observed patterns.

Concerning the completeness of the AFAD catalog for instrumental earthquakes, many studies indicate a lower threshold of Mw around 3.0 or even less since 2010 in the EAF region21,26,35,36. Since our study focuses on earthquakes with Mw ≥ 4.0, we are confident that we are well above the catalog’s completeness threshold.

Furthermore, our calculation of seismic slip channeling employed a two-dimensional analysis (Fig. 3), despite the data being distributed in a three-dimensional space. For this reason, as we will explain below, our analysis assumes a subvertical EAF zone.

In this paper, we use the term premainshock to refer to Mw ≥ 4.0 earthquakes that occurred up to six months before one of the four studied mainshocks, within a radius of 50 km around the mainshock epicenter, and with a maximum depth of 25 km. The term aftershock is instead used for Mw ≥ 4.0 earthquakes occurring up to 1 month after one of the four studied mainshocks, within the same spatial parameters as for premainshocks.

Four recent sequences
Figures 1–3 depict seismological data from the four 2010–2023 Mw ≥ 6.1 mainshock-aftershock sequences. In ensemble, the sequences show a northeast-to-southwest migration and progressive seismic unzipping of the EAF37 (Fig. 1). The 2023 mainshock nodal planes are coaxial (parallel) with the local strikes of the EAF master surfaces, whereas the aftershock focal mechanisms are both geometrically and kinematically noncoaxial or poorly coaxial with the mainshocks and hence also with the local strikes of the EAF master surfaces (Figs. 1 and 2). In particular, attitudes of both nodal planes, slip vectors, and P- and T-axes from the aftershock focal mechanisms display great variability (Fig. 2c, d). In contrast, nodal planes of focal mechanisms from two premainshocks are coaxial with the nodal planes of the 2023 Pazarcık mainshock (Fig. 2c). In both the Pazarcık and Elbistan cases, several aftershock epicenters are located off the EAF master surface, especially in the Pazarcık instance (Fig. 2c, d).

Unlike the 2023 sequences, nodal planes of focal mechanisms from both the premainshocks and the aftershocks of the 2010 (Fig. 2a) and 2020 (Fig. 2b) sequences are geometrically and kinematically coaxial with the nodal planes of the related mainshocks, with corresponding P-axis attitudes that are clustered around the subhorizontal NNE trend, consistent with left-lateral displacements along the NE-SW striking EAF. Slip vectors from focal mechanisms are indeed horizontally clustered along the NE-SW trend and along the orthogonal one. Both in the 2010 sequence and in the 2020 one, most aftershock epicenters are located along and close to the EAF master surface, particularly in the 2020 instance (Fig. 2a, b). The coaxiality of focal mechanisms with respect to the EAF master surface is quantitatively described below (Fig. 3).

Seismic slip channeling
The four studied mainshock-aftershock sequences are hence heterogeneous in terms of slipping surface attitude and kinematics, as well as the epicenter locations with respect to the EAF master surface (Fig. 2). To evaluate all these parameters together, we develop the aforementioned concept of seismic slip channeling (Fig. 3), which expresses whether seismic slip is channeled along (close to) the master fault with a movement coaxial (parallel) to it, as determined by the focal mechanisms. Thus, the concept is directly related to the efficiency of the seismic displacement translation along and parallel to the master fault itself and establishes a bridge between seismological data and surface tectonics, i.e., the EAF mapped master surface. A pioneer study on this theme along the EAF was realized in 199138.

Assuming an early vertical attitude of the EAF strike-slip system26, we plotted the distance between earthquake epicenters and the EAF mapped master surface (i.e., the nearest main trace from each epicenter) against the small azimuthal angle between the local master surface itself and the seismic slip vectors derived from the focal mechanisms (Fig. 3 and Supplementary Fig. 1; “Methods” and Supplementary Information). In the same diagrams, with conventional color codes39, we also plotted the earthquake kinematics derived from the focal mechanisms. Last, since the amount of seismic slip is directly related to the earthquake magnitude, we presented this latter attribute through different marker sizes (Fig. 3). For the azimuth of the EAF mapped master surface, we utilize the mapping provided by previous studies27,28. As mentioned above, earthquake epicenters and seismic slip data are sourced from the instrumental seismicity catalog within the AFAD databases (“Methods”, Supplementary Information, Supplementary Figs. 1 and 2, Supplementary Tables 1–3, and Supplementary Data 1).

The main aim of the seismic slip channeling analysis is to render the geometric-kinematic complexity of mainshock-aftershock sequences9,16,29 in a graphic manner (Fig. 3), which shall be both easily comparable from sequence to sequence and analyzable with statistical methods (Fig. 3 and Supplementary Fig. 2). Each diagram of Fig. 3 is divided into four major fields that represent various gradations of seismic slip channeling: channeled, dispersed, parallel unchanneled, and unparallel channeled. The boundaries between different fields have been set arbitrarily based on data distributions. The two end-members are channeled slip, i.e., seismic slip parallel and close to the master fault, and dispersed slip, i.e., seismic slip unparallel to and off the master fault. The gray shading of each bin in Fig. 3, which includes a total of 16 square bins for each panel, represents the density distribution of events on the diagram plane, i.e., the number of events in each bin normalized by the total number of events of each sequence (Supplementary Fig. 2).

The 2010 and 2020 mainshock-aftershock sequences primarily comprise strike-slip channeled earthquakes that are thus kinematically coaxial with the master fault and close to it, particularly the 2020 sequence (Fig. 3a, b). In these two cases, the maximum density levels are relatively high (0.77 and 0.62 for the 2010 and 2020 sequences, respectively; Supplementary Fig. 2a, b) and fall in the most channeled bin. The two 2023 mainshock-aftershock sequences (Fig. 3c, d), instead, include earthquakes up to a few tens of km away from the master fault and characterized by strike-slip to normal-slip kinematics as well as some thrust-slip events. Indeed, these earthquakes only partially fall within the channeled field, spreading toward the other three fields, particularly for the 2023 Pazarcık sequence. While the maximum density levels also fall within the channeled field, they have lower values compared to the 2010 and 2020 sequences (0.24 and 0.27 for the Elbistan and Pazarcık sequences, respectively; Supplementary Fig. 2c, d). It is critical to note that in the two 2023 cases, aftershocks with extensional and reverse kinematics, which are significantly misaligned with the master fault and the mainshocks, occurred not only in the quadrants farthest from the master fault but also in the nearest ones (Fig. 3c, d). In contrast, in the 2010 and 2020 sequences—particularly the 2020 sequence—the azimuthal alignment between the aftershock slips and both the master fault and the mainshock slip is very pronounced, with an azimuthal distance generally less than 20° regardless of the distance from the master fault (Fig. 3a, b). In all four cases, no systematic patterns are detectable for the earthquake magnitude (Fig. 3).

In synthesis, based on the assumption that the master fault is the structure best capable of transferring (seismic) slip, Fig. 3 helps us determine how many earthquakes occurred along (or inversely far from) the master surface, particularly with slip parallel to the master surface itself. In other words, the figure illustrates how much seismic slip was transferred or diffused in these specific events, either over a narrow fault zone or a wider deformation area, respectively.

Earthquake supercycles
To analyze the time-space pattern of past destructive earthquakes along the EAF and frame the recent mainshock-aftershock sequences within a historical perspective, we built a diagram previously used to identify earthquake supercycles elsewhere20,40. We plotted the spatial and temporal distributions of destructive earthquakes (I0 ≥ IX and Mw ≥ 6.5) occurring between A.D. 1 and 2023 along the EAF (Fig. 4).

Being a time-line representation, this diagram (Fig. 4b) compresses the fault-epicenter information along the EAF master surface. Uncertainties and limits of the historical source material are reported above and in the historical catalogs41–43. In Fig. 4b, the uncertainty associated with the coseismic rupture lengths is represented by dashed lines. Moreover, we acknowledge that a large supercycle with a return period of ~900 years along the EAF was recently proposed9 and a general spatiotemporal southwestward migration of recent and past seismicity was previously documented37.

With triangular-shaped clusters of earthquakes, Fig. 4b shows three major earthquake-rich periods, ranging from A.D. 240 to 601 (or perhaps even 867), 1046 to 1408, and 1866 to 2023. At least for the two youngest and more complete periods, named unzipping episodes 1 and 2 in Fig. 4b, we observe a marked tendency of earthquake migration from northeast to southwest along the EAF, such that one or a few earthquakes in the northeast are followed by clusters of earthquakes toward the southwest, likely mirroring the EAF southwestern branched pattern (Fig. 4). The A.D. 1046 and 1866 earthquakes constitute the apices to the northeast of the two clusters, which tendentially evolve over time toward the southwest, where a greater number of earthquakes occur than toward the northeast. Within these clusters, there are also seismic episodes, such as that from A.D. 1114 to 1121 or that from 1872 to 1971, with migration in the opposite direction (northeastward) from the predominant one toward the southwest, thus testifying a predominant but non-unique tendency for earthquakes to migrate toward the southwest along the EAF (Fig. 4).

Methods
Instrumental earthquakes
For instrumental earthquakes (Figs. 1–4), we used the AFAD database. The selection of this database was guided by two primary criteria: territorial relevance and past experience.

Territorial Relevance: there is a general preference for national seismic catalogs when studying earthquakes within a specific territory. These catalogs are indeed tailored to the region, utilizing seismic networks that are specifically designed and calibrated for better detection and analysis of local earthquakes. Consequently, the AFAD database, being the national seismic catalog, was deemed most appropriate for our study.

Past Experience: in conducting this research, we reviewed recent and past articles on the same seismic sequences to determine which catalogs were used and the outcomes they provided. For the four seismic sequences analyzed in this manuscript, numerous significant articles have utilized the AFAD catalog (refer to citations within this paper). This extensive prior use underscore the reliability and relevance of the AFAD database for our research.

Moreover, the AFAD database uniquely encompasses all the necessary information for our study, including catalogs of focal mechanisms, instrumental earthquakes, and historical earthquakes. Ensuring data homogeneity is crucial, and the AFAD catalog was the only source that provided comprehensive and consistent data across all required parameters. For these reasons, we selected the AFAD database for our instrumental seismological analyses.

Historical earthquakes
For historical earthquakes (Fig. 4 that also includes some instrumental earthquakes), we used various databases (see below). Diagrams of Fig. 4 are inspired by previous works on earthquake supercycles20,40,60–63. The spatial and temporal distribution of destructive earthquakes (I0 ≥ IX and Mw ≥ 6.5) occurring between A.D. 1 and 2023 along the EAF was obtained merging data from the following databases: AFAD-Historical Earthquakes (2000 B.C.–1900 A.D., https://deprem.afad.gov.tr/event-historical); CFTI5Med-Catalogo dei Forti Terremoti in Italia (461 a.C.–1997) e nell’area Mediterranea (760 a.C.–1500; https://storing.ingv.it/cfti/cfti5/)42; GHEA-Global Historical Earthquake Archive (https://www.emidius.eu/GEH/map.php); AFAD-Instrumental Earthquakes Catalog (1900–Present M≥4.0, https://deprem.afad.gov.tr/event-instrumental). We preferred to consider only destructive earthquakes, thus making the catalog as homogeneous as possible throughout the entire timespan (A.D. 1–2023).

To build the diagrams of Fig. 4, we performed an analysis of the space-time rupture history of the EAF for the last ~2000 years, using the aforementioned earthquake databases for information about time of occurrence and intensity (Supplementary Table 3). On the basis of standard magnitude-intensity relationships, we associated (i) to intensity IX the magnitude range 6.5–6.9 and (ii) to intensity X the magnitude range 7–7.5. In particular, consistently with the EAF kinematics, to constrain the length of individual subsurface ruptures, we used the earthquake magnitude-rupture length scaling properly proposed for strike-slip earthquakes47. Obviously, in the case of recent earthquakes, these lengths, retrieved from empirical relationships47, may differ from the lengths measured with seismological or other modern methods. Based on the aforementioned magnitude ranges (i.e., 6.5–6.9 and 7–7.5), we obtained rupture lengths (RL) ranging between 30 (minimum RL for intensity IX) and 60 km (maximum RL for intensity IX), and between 60 (minimum RL for intensity X) and 120 km (maximum RL for intensity X), respectively. This is represented in the legend of Fig. 4 and provides a graphic representation of the uncertainty of the related data. These estimated lengths are plotted in (b) consistently with their time-space distribution along the EAF.

Seismic slip channeling appraisal
We elaborated the seismic slip channeling diagrams of Fig. 3 as follows.

Distance (km) along the abscissa axes is the orthogonal distance between each earthquake epicenter (earthquakes of Fig. 2) and the local EAF master surface (i.e., projecting each earthquake epicenter onto the nearest EAF segment along the line orthogonal to the EAF segment itself). Coordinates of earthquake epicenters are in Supplementary Table 2 and are obtained from the AFAD database (https://deprem.afad.gov.tr/event-focal-mechanism) whereas digital tracks of the EAF segments with related coordinates are available in the Supplementary Data 1 and are obtained from previous maps27,28. Distances plotted in the abscissa axes are in Supplementary Table 2.

Differential azimuth (°) is the small azimuthal angle between the local master surface itself and the seismic slip, this latter derived from the focal mechanisms using the WinTensor software64. Note that two seismic slip vectors can be retrieved from each focal mechanism. For the differential azimuth in these diagrams (Fig. 3), we considered the slip vector (of the two possible ones in each focal mechanism) minimizing the azimuthal difference (in degrees) with the local azimuth of the EAF master surface. Azimuths of seismic slip and EAF are in Supplementary Table 2 and are obtained, respectively, from the focal mechanisms (AFAD database; https://deprem.afad.gov.tr/event-focal-mechanism) and from previous maps of the EAF27,28 (see also Supplementary Data 1). Further technical information on the realization of Fig. 3 is provided together with Supplementary Fig. 1.

The gray shading of each bin in the figure, which includes a total of 16 square bins for each panel, represents the density distribution of events on the diagram plane, i.e., the number of events in each bin normalized by the total number of events of each sequence. Density values are displayed in Supplementary Fig. 2.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Review of “Seismic slip channeling along the East Anatolian Fault illuminates long-term supercycle behavior” by Billi et al. 2024\nBy M Abdelmeguid\nThis paper studies the seismic slip channeling along EAF fault with emphasis on recent and historical earthquakes to understand the nature of the supercycle behavior along the EAF. Understanding the earthquake supercycle is essential for assessing seismic risk and implementing appropriate mitigation measures to reduce the potential impact of future earthquakes along the EAF. By analyzing the main-shock aftershock pattern of four of the recent earthquakes along the EAF the authors draw a conclusion regarding the migration pattern of slip along the EAF transitioning from channeled at the northeast segments to more dispersed patterns near the southwest segment. The paper is well-written and informative.\nHowever, I have some general comments regarding the manuscript.\nWith a particularly large slip, the analysis of the more recent Turkey earthquakes in the context of a large supercycle with a return period of ~900 years has been previously explored by Xu et al. 2023. While the authors acknowledge that the classification of seismic events is not the main objective of their study, I think it’s important to put their work in the context of recent literature that explored similar aspects in detail.\nXu, L., Mohanna, S., Meng, L. et al. The overall-subshear and multi-segment rupture of the 2023 Mw7.8 Kahramanmaraş, Turkey earthquake in millennia supercycle. Commun Earth Environ 4, 379 (2023). https://doi.org/10.1038/s43247-023-01030-x\nTo conclude the overall supercycle behavior the author relies on a dataset of four distinct earthquakes. However, given the small sample size, it is unclear whether the data is sufficient. For example, the authors argue that earthquakes become more dispersed along the southwest direction (L235-237), however statistically speaking based on the contours in Figure 3, most of the main-shock aftershock distribution of the Elbistan Mw7.6 earthquake (particularly larger magnitude aftershocks as mentioned by the authors) lies within the channeled regions of Figure 3. It would be beneficial for the authors to include more quantitative statistical analysis beyond the statistical probability contours in Figure 3 (which are hard to read due to overlapping information) within the main text to support that conclusion.\nI think one of the most important figures in the manuscript is Figure 3. However, the authors only briefly discuss it in Lines 137-151. I think general readers would benefit from a more detailed explanation of the quantitative statistical features that are drawn out of the slip-channeling analysis.\nIn addition to the clear contrast between the magnitudes of the earthquakes compared, the authors explore alternative hypotheses to explain the spatial complexity of seismicity patterns. I completely agree with the authors that there are indeed multiple factors that could lead to such behavior (which probably explains the difference in magnitude). The authors explore fault maturity as one factor, it wasn’t clear to me how the authors concluded that the segment that hosted the 2010 and 2020 earthquakes was more mature without examining the historical slip accumulated in this region before those earthquakes. I would appreciate it if the authors could expand a bit on how they define maturity in the context of their work and how they reached that conclusion. On the other hand, if the authors are rather arriving at such a conclusion based on their analysis, I would argue that the data is insufficient as it would require a more detailed analysis of the fault zone structure (mapping of pre-existing fault networks, both surface and depth fractural distribution) and the historical slip along the main segment to reach such a conclusion. Some even argue that the whole EAF is an immature fault system.\nI also have an additional question, since Figure 3 is generated based on projections to EAF nearest segments do the same conclusions hold for a more updated EAF mapping that includes previously unmapped EAF segments that are now recognized post the 2023 Earthquake?\nFinally, I found the organization of the manuscript a bit confusing. The continuous flow of text without any headings made reading the manuscript difficult.\nSpecific comments:\nFigure 1: The subfigure is covering the labels of the Figure.\nL60-61: The author mentions “… is based on a novel concept termed seismic slip channeling, which is described below” However, the description of the seismic slip channeling comes 9 paragraphs later in lines 125. It would help the reader to understand the mechanism of analysis earlier in the manuscript.\nL93 and L96 reference Figure 3 before any mention of Figure 2\nL144: Can you please add numbers of the maximum probability levels so that readers can draw independent conclusions?\nL200: I think the authors raise an important point regarding rheological differences. However, based on my reading it is not clear if there are indeed observations of more ductile rheology toward the southwest matches. Which would indeed support a more complex distribution of slip (see Mia, Abdelmeguid, and Elbanna 2022,2023) If the reduced Vp/Vs ratio implies such a conclusion can the authors please explain it further for the general audience?\nFigure 3: The heading of panel d is wrong should be Kovancilar\nFigure 3: It would help the reader identify talking points if the authors add panel numbers and appropriately refer to them in the text\nFigure 4 : I don’t see the 2010 event within the unzipping episode 2.", "reviewer_2": "Review Report of manuscript titled \"Seismic slip channeling along the East Anatolian Fault illuminates long-term supercycle behavior\" by Andrea Billi et al. submitted to the Nature Communications.\nRemarks to the Authors\n______________________\nAlthough the topic of the manuscript is interesting and it provides lacking details about the 6th February 2023 Turkish (Türkiye) earthquake doublet, I reckon that it has some shortcomings in verifying the robustness of the results and estimations derived by current status of the study.\nI could not see any intriguing new results obtained from the current seismological analyses that I strongly recommend authors to convince readers and to confirm their findings with respect to many valuable pioneering papers that have already been published in high-impact journals like Science, Nature, GRL, JGR and regular journals like Tectonophysics, GJI, Seismological Research Letters, and emerging ones like The Seismic Record, Seismica to name among many others (see for example; International Seismological Center Online Event Bibliography http://www.isc.ac.uk/cgi-bin/ FormatBibprint.pl?evid=625614289). Thus, I value that this is not an objective way of conducting a decent research in order to augment the science for the society where remaining cultures' survival matters.\nThe Eastern Anatolia, and active tectonics of the Eastern Mediterranean Sea Region are one of the most and the best studied actively deforming continental regions in the world. But, the authors rarely make use of scholarly published papers over a century now and then. Thus, this makes the current study poorer and the ignorance of the valuable classical publications kills the draft manuscript. My summarized comments are:\n(1) The authors are using extremely selected publications, and this makes it not an objective way of study that does not support the advancement of science in a way to desired level. In this regard the present work seriously lacks of including already published plentiful literature on the historical and recent kinematic-dynamic rupture properties for which an exhaustive list can be easily made.\n(2) The authors never acknowledge the AFAD (Türkiye) where there are too many talented seismologists are securing and providing seismological data free of charge 7/24/365 to anybody interested.\n(3) The authors never discusses why they have chosen to use the AFAD catalogue as there are others, better located ones as well to implement for a better resolution.\nTEXT-FIGURES-TABLES-LABELS\n__________________________\n1- The national country name of Turkey is Türkiye (TÜRKİYE) both in English and Turkish approved by the United Nations General Assembly a few years ago. Thus, please correct it throughout the text and figures, tables, and supplements etc.\n2- Quality of figures and labeling the individual earthquakes with wrong referencing and naming them are confusing and format is not hostile (e.g. 6Feb23,Mw7.6? why not type it properly \"6 February 2023 Mw7.6\").\n3- Mark/label the sense of tectonic motions on the major faults and fault-zones properly in order to orient and to help the readers.\n4- Authors are directly using already published seismicity (PDE-Preliminarily Determined Epicenters) and earthquake focal mechanism catalogues after AFAD in Figures 2 and 3 (see figure captions at Figure 2. Earthquake focal mechanisms with magnitude Mw≥4.0 and depth in the 0-25 km range are from the AFAD database (https://deprem.afad.gov.tr/event-focal-mechanism). All these data are in Table S2, and at Figure 3. Distance (km) along the abscissa axes is the orthogonal distance between each earthquake epicenter (earthquakes of Fig. 2) and the local EAF segment (i.e. projecting each earthquake epicenter onto the nearest EAF segment along the line orthogonal to the EAF segment itself). Coordinates of earthquake epicenters are in Table S2 and are obtained from the AFAD database (https://deprem.afad.gov.tr/event-focal-mechanism).\nThis is NOT right as the responsible and knowledgeable expert seismologists know that these PDE catalogues contain too many errors. Hence, extensive studies should be individually conducted otherwise one can easily get/obtain similar PDE catalogues from the USGS-NEIC, EMSC, ISC, gCMT, GEOFON, GEOSCOPE, INGV, KOERI or else to compile them in a common format to introduce a known conventional and/or traditional methods. But, this is not the proper way of advancing science and to streamline the message in the right way. Nevertheless, that is the reason why it is crucial to study seismicity and source parameters of individual earthquakes by using multi-type multi-resolution data along with multidisciplinary approaches with state-of-art techniques in 1D, 2D and 3D combined with kinematic and dynamic modelling approaches or so.\nBesides, I see that Summary and Conclusions contain too strong statements that are not properly supported by the Data and the Methods. I reckon that this is not an objective way of conducting decent research in order to augment the science for the society. Therefore, I consider that this work is insufficient to be acceptable as in its present form to be published in high-impact journals like Nature Communications. Hence, I recommend REJECT and advise authors to enhance the current study to submit it elsewhere.", "reviewer_3": "I think the authors have proposed a good idea about how to quantify the spatial and temporal clustering characterization of each mainshock-aftershock sequence. However, the completeness of the earthquake catalog is still uncertain, and the authors didn’t discuss about it, especially the 2010 Kovancılar earthquake sequence. So I suggest that the authors make a major revision in this paper. Here are some major comments I have for this paper.\nBeside, I think the supplementary materials are not well organized, please follow the format instructions of Nature communication and re-organize it.\n1. Lines 102-103, How do you define premainshocks, and what’s the criterion you use to select the premainshocks?\n2. Statistically, the authors have classified all mainshock-aftershocks sequence into four types: channeled, dispersed, parallel unchanneled, and unparallel channeled. I wonder if you can discuss about the physical meaning of the paralleled unchanneled and unparalleled channeled, the factors that may affect the forming mechanism of them.\n3. Line 135, the authors should explain more details about the statistical method to calculate the spatial probability of each type of earthquakes, at least in the supplementary materials.\n4. Lines 162-164, the authors describe that in the unzipping episodes 1 and 2, a marked tendency earthquake clustering moving from northeast to southwest along EAF is observed. However, I found several rupture jumps toward the opposite directions, such as from 1114 to 1121, from 1872 to 1971, In addition, the uncertainty of rupture extent of each earthquake is not evaluated.", "reviewer_4": "This study examines characteristics of aftershock sequences of four recent EAF earthquakes and speculates about how these characteristics may be related to supercycle behavior on the fault. The mechanisms and characteristics of supercycle behavior are of great interest to the scientific community, in terms of understanding seismic hazard and earthquake processes on the EAF and on other faults that exhibit similar behavior.\nI reviewed a previous version of this paper that was submitted to Nature Geoscience. Most of my more minor comments have been addressed in this version, but many of my more significant concerns have been only partially or superficially addressed. While the authors propose some interesting hypotheses, overall I still find their arguments to be somewhat unconvincing and missing important points of discussion. This paper could be suitable for publication after significant revision. I summarize my major concerns below; more detailed comments can be found on the annotated manuscript.\nThe authors examine aftershock sequences of two 21st-century M6+ earthquakes along the northeast EAF as well as aftershock sequences of the two 2023 M7.5+ events, plotting the distance of each M4+ aftershock from the nearest main trace of the EAF against the angle between the EAF trace and the aftershock fault plane. They refer to aftershocks close to/far from the fault trace as “channeled”/”unchanneled” and to those with similar/different fault plane azimuths as “parallel”/”unparallel”. They find that the two M6+ events along the northeast EAF had dominantly parallel, channeled aftershocks that had universally strike-slip mechanisms, whereas the two 2023 events had significant numbers of unparallel, unchanneled events and a wide diversity of focal mechanisms.\nThe authors argue that the collective behavior of these four mainshock-aftershock sequences is illustrative of the longer-term behavior of the EAF. Based on the historical records of earthquakes in the region, the authors identify two supercycles during which rupture cascades began at the northeast end of the fault and dispersed southwestward. The authors hypothesize that the northeast EAF (perhaps being a simpler, more mature trace) can release tectonic strain more efficiently, transferring slip to the southwest where a more complex fault network results in more dispersed rupture sequences with diverse mechanisms.\nOverall, I find this chain of reasoning to be plausible. However, there are many significant potential confounding factors that might weaken the authors’ argument, which the paper still does not adequately discuss:\n1. The authors now mention up front that uncertainties exist in aftershock locations, focal mechanisms, and magnitudes. However, there is no discussion of the typical size of these uncertainties and whether they are large enough to potentially affect the results (i.e. Fig. 3).\n2. The “unchanneled” aftershocks of the 2023 earthquakes have potential causes that are not adequately addressed. The authors do now note that the M7.8 Pazarcik earthquake initiated on the Narli fault before propagating bilaterally on the EAF, but they do not elucidate that aftershocks along the Narli fault are clearly the dominant source of the sub-population of “unchanneled” aftershocks shown in Fig. 3a, rather than any inherent nature of the region. Similarly, the potential northward dip of the Cardak fault is mentioned but not discussed as a potential reason why the 2023 aftershocks are farther from the surface trace of the mainshock fault (and thus less “channeled”). A basic check would be, are the more distant aftershocks also deeper?\n3. In my previous review I noted that the major difference in magnitude between the 2023 and earlier events could account for much or all of the difference in diversity of the aftershocks. The authors now mention this as a hypothesis, but then go on to dismiss it without clear reasoning or evidence. The statement that the magnitude difference “cannot explain the varying levels of seismic slip channeling observed along the EAF” is not well supported.\n4. Assertions that the fault trace is simpler to the northeast, that more efficient slip channeling also enables aseismic slip, and that these factors explain why the 2023 earthquakes had larger than expected slip are also poorly supported. It is difficult to follow the arguments for these assertions."}, "author_response": "Dear Reviewers,\nthank you very much for your constructive efforts on our manuscript. We believe that these efforts have been fundamental to improve our material. Please, find below some general thoughts on our revisions and the point-by-point responses to your comments.\nSincerely,\nAndrea Billi and co-authors\nGeneral thoughts\nRegarding some main concerns aroused by the Reviewers:\n- We have significantly expanded the number of references (from 52 to 67) and used them to improve our manuscript (e.g., Lines 425-432 in the trackchange version of the manuscript, and elsewhere).\n- We have better explained the limits of our dataset in a specific section (Lines 144-165) and where possible over the entire manuscript (see Discussion and Conclusions). Coherently, we have also improved the Methods and Supplementary Information sections (Lines 857-956).\n- We have expanded our analyses adding Figs. S2 and S3 and coherently developed the description of results and their discussion (Lines 284-313).\n- As mentioned by some Reviewers, Fig. 3 is the core of this work (together with Fig. 4 indeed). For this reason, we have spent many new words and statements to explain it better, specifically in the two sections named ‘Seismic Slip Channeling’ and ‘Discussion’ (Lines 284-313, 418-490).\n- Furthermore, we would like to point out that the use of a national catalog (AFAD) for our study does not reduce the validity of our results. The same or similar dataset has been used by many colleagues, who published their results on Nature, Science, Nature Reviews Earth & Environment, and similar high-quality journals (see below our Response no. 18), without quantifying the uncertainty of the data and the related impact on the results, simply because it is not possible to evaluate such a general uncertainty (perhaps on individual events but not on entire datasets like ours). In particular:\nFirst of all, it is not certain that a reprocessed dataset gives better results with lower uncertainties than a national catalog.\nSecond, we conducted a study of four sequences covering the years 2010-2023 and almost 500 km in length. There are no reprocessed and homogeneous datasets for such a study (except those available on national catalogs such as AFAD).\nThird, there are no general and average values to evaluate the uncertainty of a seismic catalog. The uncertainty analysis, whenever possible, must be done on individual events. We are therefore not able to give a rough general assessment of the uncertainty of our results, as happens for all the thousands of articles that use national seismological catalogues.\nTo this latter end, an example above all: let's take the successful article (about 250 citations at the moment) by Bouchon et al. 2013 published on Nature Geoscience (6, 299–302, https://doi.org/10.1038/ngeo1770). The authors conducted a seismological analysis over the North Pacific area using USGS catalogs (not reprocessed). The heart of the publication is their Fig. 3, which shows the time evolution of the seismic moment released in the 50-km-radius zone surrounding the mainshock epicenters before interplate earthquakes. What is the seismic moment error? What is the error in the localization of earthquakes and therefore in the spatial sampling window? There are no answers. Yet that article remains a point of reference for understanding foreshocks, even though the authors used an unreprocessed catalog. Obviously, many other similar examples could be given.\nFor instance, a recent article on Science (Sigmundsson et al. 2018 https://doi.org/10.1126/science.adn28) investigated the 15-kilometer-long magma dike that formed beneath Grindavík, Iceland, in November 2023, which caused widespread damage and evacuation of the local population. The study combined satellite-based geodetic observations and seismic measurements. In particular, the authors used seismicity recorded by the Icelandic Meteorological Office (IMO), where earthquakes are recorded on the SIL national seismic network and automatically located by the SIL analysis system. The events are then manually reviewed, revised and updated as required, using a one-dimensional velocity model (SIL model), as is usually done for many if not all national seismic catalogs worldwide. Sigmundsson et al. used the revised part of the data published on the IMO national catalog, without acknowledging specific errors. Moreover, these same authors acknowledged that, to improve seismic monitoring of the ongoing unrest on the Reykjanes Peninsula, additional waveform data from eight stations owned by the Czech Academy of Sciences (CAS) and operated by Iceland GeoSurvey (ÍSOR) were used in the routine locations and integrated in the national catalog. Such seismic network integrations are frequent during seismic crises around the world and the results are normally integrated into the national seismic catalogs, so that users of these catalogs can take advantage of such an improvement; hence, reinforcing the idea that the use of national seismic catalogs does not at all reduce the science of the works that make use of them.\nReviewer #1\nReview of “Seismic slip channeling along the East Anatolian Fault illuminates long-term supercycle behavior” by Billi et al. 2024\nBy M Abdelmeguid\nThis paper studies the seismic slip channeling along EAF fault with emphasis on recent and historical earthquakes to understand the nature of the supercycle behavior along the EAF. Understanding the earthquake supercycle is essential for assessing seismic risk and implementing appropriate mitigation measures to reduce the potential impact of future earthquakes along the EAF. By analyzing the main-shock aftershock pattern of four of the recent earthquakes along the EAF the authors draw a conclusion regarding the migration pattern of slip along the EAF transitioning from channeled at the northeast segments to more dispersed patterns near the southwest segment. The paper is well-written and informative.\nHowever, I have some general comments regarding the manuscript.\nWith a particularly large slip, the analysis of the more recent Turkey earthquakes in the context of a large supercycle with a return period of ~900 years has been previously explored by Xu et al. 2023. While the authors acknowledge that the classification of seismic events is not the main objective of their study, I think it’s important to put their work in the context of recent literature that explored similar aspects in detail.\nXu, L., Mohanna, S., Meng, L. et al. The overall-subshear and multi-segment rupture of the 2023 Mw7.8 Kahramanmaraş, Turkey earthquake in millennia supercycle. Commun Earth Environ 4, 379 (2023). https://doi.org/10.1038/s43247-023-01030-x\n(1) We have now expanded this subject by properly acknowledging previous studies by Xu et al., 2023 and by Chen et al. 2024 (Lines 189-190 and 323-344).\nTo conclude the overall supercycle behavior the author relies on a dataset of four distinct earthquakes. However, given the small sample size, it is unclear whether the data is sufficient. For example, the authors argue that earthquakes become more dispersed along the southwest direction (L235-237), however statistically speaking based on the contours in Figure 3, most of the main-shock aftershock distribution of the Elbistan Mw7.6 earthquake (particularly larger magnitude aftershocks as mentioned by the authors) lies within the channeled regions of Figure 3. It would be beneficial for the authors to include more quantitative statistical analysis beyond the statistical probability contours in Figure 3 (which are hard to read due to overlapping information) within the main text to support that conclusion.\n(2) We agree with the reviewer and acknowledge the validity of pointing out the small sample size. With more data in the sequences under examination, indeed, we could have attempted to assess whether distributions exhibit clustering, inhibition, or complete spatial randomness. Unfortunately, we are not in that position. We concur with the reviewer that this figure (Fig. 3) is rich in information and there is a risk of losing the main message (i.e., earthquake sequences occurring in different segments of the EAF display different seismic slip channeling). To better emphasize this message, we have included two additional figures (Figs. S2 and S3), showing a clear difference in the differential azimuth-distance plane in terms of concentration of events with clear focusing in the “channeled” region for the 2010 and 2020 distribution and a more widespread distribution for the 2023 doublet (Fig. S3). These figures are now described and commented at Lines 230-313.\nI think one of the most important figures in the manuscript is Figure 3. However, the authors only briefly discuss it in Lines 137-151. I think general readers would benefit from a more detailed explanation of the quantitative statistical features that are drawn out of the slip-channeling analysis.\n(3) We have expanded the discussion of Fig. 3 at Lines 284-313 and added two new figures (Figs. S2 and S3) with new statistical analyses. See also our previous response (no. 2).\nIn addition to the clear contrast between the magnitudes of the earthquakes compared, the authors explore alternative hypotheses to explain the spatial complexity of seismicity patterns. I completely agree with the authors that there are indeed multiple factors that could lead to such behavior (which probably explains the difference in magnitude). The authors explore fault maturity as one factor, it wasn’t clear to me how the authors concluded that the segment that hosted the 2010 and 2020 earthquakes was more mature without examining the historical slip accumulated in this region before those earthquakes. I would appreciate it if the authors could expand a bit on how they define maturity in the context of their work and how they reached that conclusion. On the other hand, if the authors are rather arriving at such a conclusion based on their analysis, I would argue that the data is insufficient as it would require a more detailed analysis of the fault zone structure (mapping of pre-existing fault networks, both surface and depth fractural distribution) and the historical slip along the main segment to reach such a conclusion. Some even argue that the whole EAF is an immature fault system.\n(4) Our new statements at Lines 450-490 should better clarify this point. Although partially speculative (as it often happens in Discussion sections), we believe that this topic is relevant for the article and for the community of seismologists and tectonists. We believe that the task of an article in Nature Communications is also to discuss partially speculative themes to be strengthened in the future, in order to indicate future strategic research fields for the safety of people and infrastructures.\nI also have an additional question, since Figure 3 is generated based on projections to EAF nearest segments do the same conclusions hold for a more updated EAF mapping that includes previously unmapped EAF segments that are now recognized post the 2023 Earthquake?\n(5) It is true that new fault segments have been found and mapped after the 2023 earthquakes; most of these faults, however, are far from the EAF master surface as mapped by many studies (e.g., Duman et al., 2020; Taymazet al., 2021; and references therein) and should probably be considered as subsidiary faults with respect to the master one. Based on the assumption that the master fault is the structure that is most capable of best transferring slip, with Fig. 3 we are interested in understanding how many earthquakes occurred along (or inversely far from) the master surface, particularly with a slip parallel to the master surface itself (i.e., the seismic slip channeling, Fig. 3). In other words, we aim at understanding how much the fault system is able to transfer slip along itself (i.e. the master surface) or, conversely, to diffuse it in a broad deformation area/volume. This concept has obviously to do with our initial statement (Lines 14-17): ‘The two Mw>7.5 earthquakes that struck the East Anatolian Fault, Türkiye, in 2023 caused more slip than expected, indicating that they were potentially part of a supercycle, in which the probability of a large earthquake is determined by accumulated strain rather than time since the last large earthquake.’, from which a piece of final discussion derives (Lines 436-490). In our opinion, the seismic slip channeling (Fig. 3) can indeed contribute to understanding what ‘caused more slip than expected’, as is discussed in our manuscript. For this reason, we are not interested in mapping all subsidiary faults. We aim instead at measuring how on or off the master fault surface each earthquake occurred. In other words, we aim at measuring whether the seismic deformation is channelized along or dispersed around the EAF master surface (Fig. 3). All this is now expanded at Lines 69-78, 209-313, and in the Discussion section.\nFinally, I found the organization of the manuscript a bit confusing. The continuous flow of text without any headings made reading the manuscript difficult.\n(6) Done. We have used Headings and Subheadings in the new version of the manuscript.\nSpecific comments:\nFigure 1: The subfigure is covering the labels of the Figure.\n(7) Done. Please, see Fig. 1.\nL60-61: The author mentions “… is based on a novel concept termed seismic slip channeling, which is described below” However, the description of the seismic slip channeling comes 9 paragraphs later in lines 125. It would help the reader to understand the mechanism of analysis earlier in the manuscript.\n(8) We have now explained and expanded the concept of Seismic Slip Channeling at the beginning of the manuscript, i.e., Lines 69-78.\nL93 and L96 reference Figure 3 before any mention of Figure 2\n(9) Fig. 2 is now properly mentioned at Line 187.\nL144: Can you please add numbers of the maximum probability levels so that readers can draw independent conclusions?\n(10) Good point for a quantitative visualization. Following the reviewer suggestion, we have now provided the probability of each bin for the four investigated sequences. Instead of adding a value in Fig. 3, which is already very crowded, we have provided this information in Fig. S2 and mentioned it at Lines 287 and 293.\nL200: I think the authors raise an important point regarding rheological differences. However, based on my reading it is not clear if there are indeed observations of more ductile rheology toward the southwest matches. Which would indeed support a more complex distribution of slip (see Mia, Abdelmeguid, and Elbanna 2022,2023) If the reduced Vp/Vs ratio implies such a conclusion can the authors please explain it further for the general audience?\n(11) We have now expanded this theme at Lines 418-435. No, unfortunately the only available clues about a more plastic beheavior than elsewhere along the EAF are those mentioned in the paper: ‘In the case of the EAF, the shallowing of the Moho depth, reduced Vp/Vs ratio, and high heat flux values towards the southwest(49) may indicate a crustal rheology change in that direction, potentially resulting in a dispersed fault architecture (Fig. 1) and related dispersion of seismicity (Figs. 2-4).’\nFigure 3: The heading of panel d is wrong should be Kovancilar\n(12) Corrected. Thanks for spotting this issue.\nFigure 3: It would help the reader identify talking points if the authors add panel numbers and appropriately refer to them in the text\n(13) We do not exactly understand this point. If the reviewer is suggesting us to name the various panels of Figures 3 etc. with lettering such as (a), (b) etc. and to refer to them appropriately in the text (Figs. 3a, 3b, etc.), then that is exactly what we have done in the new version. Thank you!\nFigure 4 : I don’t see the 2010 event within the unzipping episode 2.\n(14) We agree with the Reviewer that the lack, in Fig. 4, of the 2010 earthquake appears as odd; however, the criteria used for earthquake selection along the EAF in Fig. 4 were: macroseismic intensity ≥ IX and magnitude ≥ 6.5. We preferred to consider only destructive earthquakes thus making the catalogue as homogeneous as possible throughout the entire time span (A.D. 1 - 2023). For this reason, the 2010 Mw=6.1 earthquake does not meet the assigned criteria and was therefore not included in this analysis. The aforementioned criteria are explained in the Methods and Supplementary Information (Lines 933-956).\nReviewer #2\nReview Report of manuscript titled \"Seismic slip channeling along the East Anatolian Fault illuminates long-term supercycle behavior\" by Andrea Billi et al. submitted to the Nature Communications.\nRemarks to the Authors\n______________________\nAlthough the topic of the manuscript is interesting and it provides lacking details about the 6th February 2023 Turkish (Türkiye) earthquake doublet, I reckon that it has some shortcomings in verifying the robustness of the results and estimations derived by current status of the study.\nI could not see any intriguing new results obtained from the current seismological analyses that I strongly recommend authors to convince readers and to confirm their findings with respect to many valuable pioneering papers that have already been published in high-impact journals like Science, Nature, GRL, JGR and regular journals like Tectonophysics, GJI, Seismological Research Letters, and emerging ones like The Seismic Record, Seismica to name among many others (see for example; International Seismological Center Online Event Bibliography http://www.isc.ac.uk/cgi-bin/ FormatBibprint.pl?evid=625614289). Thus, I value that this is not an objective way of conducting a decent research in order to augment the science for the society where remaining cultures' survival matters.\n(15) We believe that our manuscript has significantly improved thanks to the comments received during this submission and during the previous one to Nature Geoscience.\nFor the Reviewers, we would like to clarify that, if necessary, we can provide full documentation (including maintext with trackchange and related point-by-point explanation letter) of revisions made after the first submission to Nature Geoscience and before this submission to Nature Communications. Coherently with the lines indicated by the previous reviewers, we indeed did as much changes as possible before submitting the manuscript to Nature Communications. Please, do not hesitate to ask these documents that are ready and available in our PCs.\nThe Eastern Anatolia, and active tectonics of the Eastern Mediterranean Sea Region are one of the most and the best studied actively deforming continental regions in the world. But, the authors rarely make use of scholarly published papers over a century now and then.\nThus, this makes the current study poorer and the ignorance of the valuable classical publications kills the draft manuscript. My summarized comments are:\n(1) The authors are using extremely selected publications, and this makes it not an objective way of study that does not support the advancement of science in a way to desired level. In this regard the present work seriously lacks of including already published plentiful literature on the historical and recent kinematic-dynamic rupture properties for which an exhaustive list can be easily made.\n(16) Done. We have significantly expanded the number of cited articles that are now 67 instead of 52 in the former version. We used them to improve our manuscript (e.g., Lines 425-432 and elsewhere).\n(2) The authors never acknowledge the AFAD (Türkiye) where there are too many talented seismologists are securing and providing seismological data free of charge 7/24/365 to anybody interested.\n(17) AFAD is now mentioned at least 4 times at Lines 66, 147, 153, 228 + Figure captions + Methods + Supplementary Info, and eventually in the Acknowledgments.\n(3) The authors never discusses why they have chosen to use the AFAD catalogue as there are others, better located ones as well to implement for a better resolution.\n(18) There is no quantitative data that indicate a greater or lesser reliability, in general (on single events it is different, obviously), of one seismic catalog compared to another. The selection criteria that we used are therefore those used by most scientists and are essentially two: territoriality and past-recent experience.\nTerritoriality: generally, there is a tendency to favor national seismic catalogs, which include the earthquakes to be studied within their territory. These catalogs are, in fact, based on seismic networks specifically calibrated for better detection of earthquakes on the national territory. Experience: when approaching the study of one or more seismic sequences, recent and past articles on the same seismic sequences are consulted to see which catalogs have been used and which results have provided. In the case of the four seismic sequences studied in this manuscript, the significant articles that have considered them using the AFAD catalog are numerous (see below some of these articles). For these reasons our choice fell on the AFAD catalog.\nAlthough we believe that it is not necessary to disclose the aforementioned two criteria in the article because they are well known to the entire seismological community, we have added an ad hoc sentence in the Methods (Lines 878-895) and in Supplementary Information.\nFinally, the AFAD catalog is the only one that contains all the information we needed in this paper, i.e., databases of focal mechanisms, instrumental earthquakes, and historical earthquakes. Therefore, for homogeneity of the data, our choice fell on the AFAD catalog.\nTEXT-FIGURES-TABLES-LABELS\n__________________________\n1- The national country name of Turkey is Türkiye (TÜRKİYE) both in English and Turkish approved by the United Nations General Assembly a few years ago. Thus, please correct it throughout the text and figures, tables, and supplements etc.\n(19) Done. Please, see Fig. 1. Text also is checked and correct.\n2- Quality of figures and labeling the individual earthquakes with wrong referencing and naming them are confusing and format is not hostile (e.g. 6Feb23,Mw7.6? why not type it properly \"6 February 2023 Mw7.6\").\n(20) Done. Please, see all Figures.\n3- Mark/label the sense of tectonic motions on the major faults and fault-zones properly in order to orient and to help the readers.\n(21) Done. Please, see Fig. 1.\n4- Authors are directly using already published seismicity (PDE-Preliminarily Determined Epicenters) and earthquake focal mechanism catalogues after AFAD in Figures 2 and 3 (see figure captions at Figure 2. Earthquake focal mechanisms with magnitude Mw≥4.0 and depth in the 0-25 km range are from the AFAD database (https://deprem.afad.gov.tr/event-focal-mechanism). All these data are in Table S2, and at Figure 3. Distance (km) along the abscissa axes is the orthogonal distance between each earthquake epicenter (earthquakes of Fig. 2) and the local EAF segment (i.e. projecting each earthquake epicenter onto the nearest EAF segment along the line orthogonal to the EAF segment itself). Coordinates of earthquake epicenters are in Table S2 and are obtained from the AFAD database (https://deprem.afad.gov.tr/event-focal-mechanism).\nThis is NOT right as the responsible and knowledgeable expert seismologists know that these PDE catalogues contain too many errors. Hence, extensive studies should be individually conducted otherwise one can easily get/obtain similar PDE catalogues from the USGS-NEIC, EMSC, ISC, gCMT, GEOFON, GEOSCOPE, INGV, KOERI or else to compile them in a common format to introduce a known conventional and/or traditional methods. But, this is not the proper way of advancing science and to streamline the message in the right way. Nevertheless, that is the reason why it is crucial to study seismicity and source parameters of individual earthquakes by using multi-type multi-resolution data along with multidisciplinary approaches with state-of-art techniques in 1D, 2D and 3D combined with kinematic and dynamic modelling approaches or so.\n(22) Please, see above our Response no. 18 concerning seismic catalogs.\nMoreover, we are obviously aware that the seismic data reported in the seismic catalogs (may) contain uncertainties greater than those re-processed (this is not always the case in reality! Debatable!) by using 3D velocity models selected ad hoc for a specific region and the most suitable algorithms (e.g., Presti et al., 2019, https://doi.org/10.1785/0220190024, and references therein); however, experience teaches us that the direct use of national catalog data without ad hoc reprocessing is a very valid method used by many scientists.. The limits explained at Lines 144-165 should highlight the uncertainties of our results as wells as our awareness on the use of catalog data.\nBesides, I see that Summary and Conclusions contain too strong statements that are not properly supported by the Data and the Methods. I reckon that this is not an objective way of conducting decent research in order to augment the science for the society. Therefore, I consider that this work is insufficient to be acceptable as in its present form to be published in high-impact journals like Nature Communications. Hence, I recommend REJECT and advise authors to enhance the current study to submit it elsewhere.\n(23) Done. We have toned down our conclusions using ‘might’, ‘perhaps’, ‘would’, and ‘hypothesized’ at Lines 493-507.\nReviewer #3\nI think the authors have proposed a good idea about how to quantify the spatial and temporal clustering characterization of each mainshock-aftershock sequence. However, the completeness of the earthquake catalog is still uncertain, and the authors didn’t discuss about it, especially the 2010 Kovancılar earthquake sequence. So I suggest that the authors make a major revision in this paper. Here are some major comments I have for this paper.\nBeside, I think the supplementary materials are not well organized, please follow the format instructions of Nature communication and re-organize it.\n(24) The completeness of the earthquake dataset used in the present paper - for which we selected data with magnitude greater or equal to 4.0 - is based on the estimations reported for the AFAD catalog in Çıvgın and Scordilis (2019, https://doi.org/10.1007/s10950-019-09863-w) (see their Fig. 6 on time variation of the completeness magnitude). Their result indicates that, since 2010, the completeness magnitude in the Kovancilar area has been lower than 3.0. Other similar values of completeness values along the EAF may be found in Bulut et al., (2012, https://doi.org/10.1029/2011JB008966); Güvercin et al., (2022, https://doi.org/10.1093/gji/ggac045); Tan (2021, https://doi.org/10.1029/2011GL047702). We therefore believe that the used data are reliable. We have better clarified this in the revised manuscript at Lines 144-165.\n(25) As suggested by the Reviewer, we carefully consulted the instructions on this matter from Nature Communications (see below), in which however nothing is specified about the logical organization of the Supplementary Information. Although we believe that the current organization of the Supplementary Information is rational and convenient (i.e., figure by figure), we are certainly available to reorganize it, if specific journal instructions will arise.\nhttps://www.nature.com/documents/ncomms-submission-guide.pdf\n1. Lines 102-103, How do you define premainshocks, and what’s the criterion you use to select the premainshocks?\n(26) In our study, a premainshock is set arbitrarily and corresponds to an earthquake that preceded one of the four studied mainshocks by up to a maximum of six months within a radius of 50 km around the mainshock epicenter and maximum depth of 25 km. This is now explained at Lines 160-165.\n2. Statistically, the authors have classified all mainshock-aftershocks sequence into four types: channeled, dispersed, parallel unchanneled, and unparallel channeled. I wonder if you can discuss about the physical meaning of the paralleled unchanneled and unparalleled channeled, the factors that may affect the forming mechanism of them.\n(27) We absolutely agree with the Reviewer. We have not provided any explanations in this regard. This is an arbitrary subdivision (based on data distribution on the diagram itself) within an experimental diagram developed for the first time in this study. As such (arbitrary) therefore, we do not yet have an unequivocal physical explanation. We explained the graph in the discussion section. We have now explained better that this is an arbitrary subdivision that must be physically validated and explained in the future with further data (Lines 380-384).\n3. Line 135, the authors should explain more details about the statistical method to calculate the spatial probability of each type of earthquakes, at least in the supplementary materials.\n(28) The gray shading of each bin is proportional to the relative number of observations (number of observations in bin / total number of observations), and the sum of the bar heights is less than or equal to 1. This is now explained at Lines 280-283 and 580-581 (see also Figs. S2 and S3).\n4. Lines 162-164, the authors describe that in the unzipping episodes 1 and 2, a marked tendency earthquake clustering moving from northeast to southwest along EAF is observed. However, I found several rupture jumps toward the opposite directions, such as from 1114 to 1121, from 1872 to 1971, In addition, the uncertainty of rupture extent of each earthquake is not evaluated.\n(29) This theme (rupture jumps toward the opposite directions) was in fact already illustrated in the previous version but now we have explained it better by indicating the episodes mentioned by the Reviewer (Lines 353-354).\nConcerning the uncertainty of each earthquake's rupture extent, we have evaluated it by considering the uncertainty on the earthquake magnitude. A legend on Fig. 4 now explains that the dashed lines are expression of the uncertainty on the rupture length (Lines 602-606, 949-956). Note, however, that the impact of this uncertainty on our interpretations/conclusions is null. Our interpretations are not, in fact, based on the extent of the rupture.\nReviewer #4\nThis study examines characteristics of aftershock sequences of four recent EAF earthquakes and speculates about how these characteristics may be related to supercycle behavior on the fault. The mechanisms and characteristics of supercycle behavior are of great interest to the scientific community, in terms of understanding seismic hazard and earthquake processes on the EAF and on other faults that exhibit similar behavior.\nI reviewed a previous version of this paper that was submitted to Nature Geoscience. Most of my more minor comments have been addressed in this version, but many of my more significant concerns have been only partially or superficially addressed. While the authors propose some interesting hypotheses, overall I still find their arguments to be somewhat unconvincing and missing important points of discussion. This paper could be suitable for publication after significant revision. I summarize my major concerns below; more detailed comments can be found on the annotated manuscript.\n(30) We thank the Reviewer for these and previous comments. For the Reviewers, we would like to clarify that, if necessary, we can provide full documentation (including maintext with trackchange and related point-by-point explanation letter) of revisions made after the first submission to Nature Geoscience and before this submission to Nature Communications. Please, do not hesitate to ask these documents that are ready and available in our PCs.\nThe authors examine aftershock sequences of two 21st-century M6+ earthquakes along the northeast EAF as well as aftershock sequences of the two 2023 M7.5+ events, plotting the distance of each M4+ aftershock from the nearest main trace of the EAF against the angle between the EAF trace and the aftershock fault plane. They refer to aftershocks close to/far from the fault trace as “channeled”/”unchanneled” and to those with similar/different fault plane azimuths as “parallel”/”unparallel”. They find that the two M6+ events along the northeast EAF had dominantly parallel, channeled aftershocks that had universally strike-slip mechanisms, whereas the two 2023 events had significant numbers of unparallel, unchanneled events and a wide diversity of focal mechanisms.\nThe authors argue that the collective behavior of these four mainshock-aftershock sequences is illustrative of the longer-term behavior of the EAF. Based on the historical records of earthquakes in the region, the authors identify two supercycles during which rupture cascades began at the northeast end of the fault and dispersed southwestward. The authors hypothesize that the northeast EAF (perhaps being a simpler, more mature trace) can release tectonic strain more efficiently, transferring slip to the southwest where a more complex fault network results in more dispersed rupture sequences with diverse mechanisms.\nOverall, I find this chain of reasoning to be plausible. However, there are many significant potential confounding factors that might weaken the authors’ argument, which the paper still does not adequately discuss:\n1. The authors now mention up front that uncertainties exist in aftershock locations, focal mechanisms, and magnitudes. However, there is no discussion of the typical size of these uncertainties and whether they are large enough to potentially affect the results (i.e. Fig. 3).\n(31) We believe that our previous responses on seismological catalogs should fully respond to this comment. Please, see above our responses (no. 18 and 22).\nIt is not possible to quantify these uncertainties, especially considering that we are analyzing four sequences covering the 2010-2023 timespan and almost 500 km of fault length. This, however, does not reduce the validity of our results like all the cited articles (see the manuscript and Response no. 18) that use the same dataset, without having felt the need to specify that the dataset is obviously affected by uncertainties (as are all seismological datasets, both from national catalogs and from specific reprocessing) and that these uncertainties are impossible to evaluate in general as is equally impossible to evaluate the effect of such uncertainties on the results. See Lines 145-152.\n2. The “unchanneled” aftershocks of the 2023 earthquakes have potential causes that are not adequately addressed. The authors do now note that the M7.8 Pazarcik earthquake initiated on the Narli fault before propagating bilaterally on the EAF, but they do not elucidate that aftershocks along the Narli fault are clearly the dominant source of the sub-population of “unchanneled” aftershocks shown in Fig. 3a, rather than any inherent nature of the region. Similarly, the potential northward dip of the Cardak fault is mentioned but not discussed as a potential reason why the 2023 aftershocks are farther from the surface trace of the mainshock fault (and thus less “channeled”). A basic check would be, are the more distant aftershocks also deeper?\n(32) We believe that Fig. 3 is a concise way (in a 2D diagram) to express precisely what the Reviewer expresses in this comment. It is true, the 2023 earthquake was generated and then propagated along the fault planes (all earthquakes originate on a fault plane!) mentioned by the Reviewer and also in our text (Lines 82-140). But these faults are distant from the EAF master fault surface mapped in all geological maps, demonstrating the diffusion of seismic deformation and therefore its poor channeling along the master fault surface. This is what Fig. 3 demonstrates and what we believe is implicit in the Reviewer's comment. The concept has now been implemented at Lines 69-78, 125-135, and 210-313.\nPlease, read also one of our responses to Reviewer 1 (no. 5).\nEventually, please, note that the northward dip of the Cardak fault is debatable. In this article (https://doi.org/10.1016/j.eqs.2023.06.002), for instance, the Cardak fault is represented as subvertical (Fig. 2, g-g’ section).\nEventually, although the suggestion of analyzing the earthquake depth is theoretically suitable, in reality, the associated error (that is typically much larger than errors in Lat. and Long. of the corresponding epicenters) would prevent a reliable analysis.\nNote also that we are analyzing four sequences covering the 2010-2023 timespan and almost 500 km of fault length. There is no such a reprocessed and corrected dataset.\n3. In my previous review I noted that the major difference in magnitude between the 2023 and earlier events could account for much or all of the difference in diversity of the aftershocks. The authors now mention this as a hypothesis, but then go on to dismiss it without clear reasoning or evidence. The statement that the magnitude difference “cannot explain the varying levels of seismic slip channeling observed along the EAF” is not well supported.\n(33) We actually believe we haven't dismissed it. Doubts on the cause-effect relationships between seismotectonic characteristics of faults (including seismic slip channeling) are proposed in recent articles (Guo et al., 2023) and therefore should be considered seriously. This is what we try to do in the new text. In this regard we have inserted a new sentence on Lines 456-490: 'The seismic slip channeling addressed in this research does not deviate from this rule: are the varying degrees of seismic slip channeling the cause or result of the earthquakes' different energy levels? This uncertainty offers up new strategic avenues of study for seismic risk mitigation.' In fact, we believe that an article in Nature Communications also has the task of indicating new lines of research, in particular if they are strategic for human life and the salvation of infrastructures.\n4. Assertions that the fault trace is simpler to the northeast, that more efficient slip channeling also enables aseismic slip, and that these factors explain why the 2023 earthquakes had larger than expected slip are also poorly supported. It is difficult to follow the arguments for these assertions.\n(34) We have explained our motivations better at Lines 373-379.\nANNOTATIONs on the attached doc/pdf file.\n‘4_reviewer_attachment_1_1714074630’. We have carefully considered all comments annotated inside and coherently amended the manuscript. Please, find below these annotations with our detailed responses.\nAnd how big are those uncertainties, typically? Are they large enough to potentially impact the validity of your results? It's not enough to simply state that uncertainties exist.\n(35) We have clarified that it is not possible to quantify these uncertainties, especially considering that we are analyzing four sequences covering the 2010-2023 timespan and almost 500 km in length. This, however, does not reduce the validity of our results like all the cited articles (see Response no. 18) that use the same dataset, without having felt the need to specify that the dataset is obviously affected by uncertainties (as are all seismological datasets, both from national catalogs and from specific reprocessing) and that these uncertainties are impossible to evaluate in general like the effect of such uncertainties on the results. See Lines 145-152.\nThis is confusingly stated. Would it be correct to say “The 2023 mainshock nodal planes are coaxial wit the local strikes of the EAF master surfaces, whereas the aftershock focal mechanisms are both geometrically and kinematically noncoaxial with the mainshocks.”? If so I suggest that phrasing.\n(36) Rephrased as suggested by the Reviewer (Lines 190-193).\nAs I noted in my previous review, the initiation of the Pazarcik earthquake along the Narli fault is the primary reason for distant aftershocks in that case. The potential northward dip of the Cardak fault also may make aftershocks appear distant. While those issues are briefly mentioned above, they are not discussed in terms of their impact on the degree of \"channeling\" of the aftershocks.\n(37) The impact on the seismic slip channeling is exactly what we measure in Fig. 3. This is exactly our aim, not an error. The statements added at Lines 125-135 should now better explain what we mean. An almost 700 km long plate boundary includes a master surface and many subsidiary faults for a thickness of a least a few tens of km (1-10% of the fault length). See for instance the San Andreas Fault, the Alpine Fault or the North Anatolian Fault.\nMoreover, please, note that the northward dip of the Cardak fault is debatable. In Fig. 2 (g-g’ section) of this article (https://doi.org/10.1016/j.eqs.2023.06.002), the Cardak fault is represented as subvertical.\nUnclear why this follows.\n(38) This is now better explained at Lines 360-379. The aseismic motion along the EAF is not our aim in this paper. This is now clearly stated. Please, note that this inference is necessarily included in what is said in the Dal Zilio and Ampuero (2023) article. If the seismic slip of the 2023 earthquakes shows an excess of seismic slip compared to previous strong earthquakes along the same fault in adjacent segments, then we must necessarily hypothesize an aseismic slip in addition to the seismic one (Dal Zilio and Ampuero 2023). This is also consistent with the GPS data cited by Guvercin et al. (2022; https://doi.org/10.1093/gji/ggac045) and Guvercin (2023; doi: https://doi.org/10.1093/gji/ggac045), which shows a variation in slip rate moving along the fault from NE to SW, from around 10 mm/yr to 1-4 mm/yr, respectively. Evidently, to the NE we have to admit some aseismic slip compared to the SW. But we do not want to develop this topic further because it would be speculative in this article (Lines 378-379).\nI don't follow this reasoning either. In the first place, why would strain accumulated to the northeast be relevant to slip expected on a different fault section to the southwest?\n(39) For the same reason why: ‘Between 1939 and 1992, ten Mw≥6.7 earthquakes that progressively unzipped ~1,000 km of the North Anatolian Fault, Türkiye, taught geoscientists how secular stressing and static stress transfer after large earthquakes can trigger the next major event along the same fault system(12,13)’, as stated at Lines 40-43. But we do not want to open this discussion here and simply cite again the work by Dal Zilio and Ampuero (2023), who evocate this supercycle process of earthquake migration along the EAF (Lines 360-362). Same or similar concepts (NE-to-SW migration of seismicity) are also proposed in Chen et al. (2023) and Xu et al. (2023), who are properly cited in our manuscript.\nThis assertion is not well supported. *Why* is the difference in mainshock magnitude insufficient? You have shown that these other hypotheses *may* apply; certainly they can’t be ruled out, but I see no evidence or solid argument that they are required to explain the differences between the aftershock sequences.\n(40) We simply mention the review paper by Guo et al. (2023), where fault maturity depends on various seismological parameters, not only on earthquake magnitude. However, we have toned down most of this part of Discussion (456-490).\nA bit strange that the Cardak fault is considered part of the EAF but other faults between that and the main EAF trace are not (shown black on this map).\n(41) This figure has been improved. Most faults are below the beach balls as always happens with the focal mechanisms.\nRelative to what?\n(42) To fixed Eurasia (Line 531).\nPlease put these panels in order of earthquake occurrence, for clarity.\n(43) We have clarified our criteria at Lines 188-190.\nDid you mean \"associated with the main trace of the EAF?\"\n(44) This part has been rephrased (Lines 556-557).\nAs I commented on the previous draft, I suggest putting the four panels in order of occurrence. Also, the \"relative probability\" still does not seem to be explained anywhere (it should be here in the caption). I gather that it means the relative probability of an earthquake falling in that sub-quadrant, but I think it might be clearer to express it as percentage of earthquakes within each square.\n(45) We have clarified our criteria at Lines 188-190. The probability is now explained at Lines 580-581.\nAs I commented on the previous draft, It should be noted that the recent 7.8 earthquake had a rupture length of >300 km. Given that, perhaps there should be a mention that actual rupture lengths might have been significantly longer than estimated here?\n(46) This is now explained in the Methods (Lines 949-951)."}, {"round": 2, "reviewer_comments": {"reviewer_1": "Review of “Seismic slip channeling along the East Anatolian Fault illuminates long-term supercycle behavior” by Billi et al. 2024\nBy M Abdelmeguid\nI reviewed a previous version of this manuscript. The current, revised version is much improved and most of my initial concerns have been addressed. I also want to comment that I believe this work, serves a useful purpose in the field. While there are indeed several publications that report kinematic slip inversions for this earthquake or dynamic rupture models that fit the data. But very few of those explore the historical context or provide systematic spatiotemporal analysis for said observations.\nIn this revision, the authors have provided much-needed context and discussion of their analysis. I still have some concerns regarding the small sample size, however, I don’t believe that this diminishes the value of the paper.", "reviewer_3": "I think both the clarity and organization of the revised manuscript have been notably improved\nspecifically, the revison focuses on the degree of seismic slip channeling along the EAF master surface, avoiding unnecessary distraction, which\nenhances its accessibility.\nLine by line comments:\nLine 232 \"Fig. 3 helps us determining how many earthquakes occurred along (or inversely far from) the master surface, particularly with slip parallel to the master surface itself. \"\ndetermining should be determine\nLine 247 \"we acknowledge that a large supercycle with a return period of ~900 years along the EAF was recently proposed9 as well as a general spatiotemporal southwestward migration of recent...\", \"as well as\" is not proper here, it should be \"and\"\nLine 257 \"where a greater number of earthquakes occur than towards the...\", it should be \"toward\" here", "reviewer_4": "I thank the authors for the many improvements they have made to the paper. This draft is closer to being ready for publication, but a few issues throughout the text remain to be addressed, and the discussion section still requires substantial reorganization to flow logically. My major comments are below and more detailed comments on the annotated PDF.\nRegarding uncertainties in the catalog data, the authors still need to be a bit more quantitative and explicit. Their response to my previous comment, and argument in the paper, appears to be “other high profile papers have used these data without discussing uncertainties, so we can too.” Inadequate attention to and discussion of uncertainties is in fact a major problem throughout scientific publishing, so I do not find “others are also doing it wrong” to be a valid argument. Ideally, it should be possible to make a general statement, based on information from AFAD and some of the papers analyzing the catalog which the authors cite, about the likely typical uncertainties, along the lines of “based on past analyses, horizontal location errors for these epicenters are typically no more than 5 km” or whatever the distance is. If that’s truly not possible, an alternative would be to make the argument that uncertainty and errors should affect all four aftershock sequences roughly equally, so that the observed differences in the aggregate dataset should be robust. I should say that I don’t believe the likely uncertainties are big enough to invalidate the results of this paper—it just needs to be discussed more quantitatively and explicitly.\nThe density distributions in Fig. 3 are now much better explained. In fact, I think Fig. S3 and the associated explanation in the main text are unnecessary. You can get the point across more succinctly with a few suggested edits to the previous paragraph.\nI do strongly recommend reordering the panels in Figs. 2 and 3 to put the four mainshocks in order of occurrence. The current order is confusing and doesn’t seem to have a compelling reason behind it.\nSome points in the discussion still need to be better organized and clarified and others seem self-contradictory. If I may summarize, the main result/observation of the paper is that the aftershocks of the 2023 earthquakes are spread over a wider area and have more diverse slip planes and focal mechanisms than aftershocks of the 2010 and 2020 earthquakes. The authors name this property “slip channeling” and ultimately wish to argue that the difference in slip channeling explains longer-term features of earthquake behavior along the EAF. Such a causal link requires that the “slip channeling” be an innate property of feature of the fault sections or regions, as opposed to the variations being due to properties of these specific earthquakes (such as mainshock magnitude).\nI recommend that the authors start the discussion with the (null) hypothesis that the slip channeling is related to the mainshock magnitude, and first make the case that this hypothesis is insufficient before moving on to links with supercycle behavior and migration.\nIn my estimation, the broader scattering of aftershocks along the distance axis for the 2023 events can easily be explained by the greater magnitudes and by certain features of the specific 2023 ruptures, namely the initiation of the Pazarcik earthquake on the Narli fault and the potential northward dip of the Cardak fault. While the aftershocks along the Narli fault are indeed far from the EAF master fault, they are very close to *the specific fault rupture of the 2023 mainshock,* which includes the Narli fault. Similarly for the Cardak fault, if it does dip to the north, the aftershocks there may not actually be far from the master fault plane. Even if the depths are too uncertain to check this, the possibility should be explicitly mentioned in the discussion.\nThe wider spread in azimuth and slip sense for the 2023 aftershocks are a bit easier to defend as properties of the region rather than of these specific earthquakes. The authors should perhaps point out that while larger earthquakes are able to activate aftershocks over a wider area, thus including more diverse fault planes, the diversity in azimuth and mechanism is just as apparent among aftershocks very close to the master fault rupture. That lends credence to the idea that the southwest section of the EAF is inherently prone to “poor channeling” in comparison to the northeast section.\nOnce the argument is made that the degree of slip channeling is a regional property, then the authors can move on to the discussion of potential underlying mechanisms such as rock rheology and fault maturity, and finally at the end make the capstone argument that this along-strike variation in slip channeling is what produces the observed supercycle behavior.\nAnd please clarify the seemingly self-contradictory argument that the less efficient slip channeling in the southwest explains why the 2023 earthquakes had such high slip."}, "author_response": "Dear Reviewers,\nWe thank you sincerely for your help and support, which allowed us to significantly improve the manuscript and its scientific content. We have carefully considered your latest comments and have modified our material accordingly. Below you will find our answers and explanations, point by point, with precise references to the text and figures.\nSincerely\nAndrea Billi and coauthors\nREVIEWER COMMENTS\nReviewer #1 (Remarks to the Author):\nReview of “Seismic slip channeling along the East Anatolian Fault illuminates long-term supercycle behavior” by Billi et al. 2024\nBy M Abdelmeguid\nI reviewed a previous version of this manuscript. The current, revised version is much improved and most of my initial concerns have been addressed. I also want to comment that I believe this work, serves a useful purpose in the field. While there are indeed several publications that report kinematic slip inversions for this earthquake or dynamic rupture models that fit the data. But very few of those explore the historical context or provide systematic spatiotemporal analysis for said observations.\nIn this revision, the authors have provided much-needed context and discussion of their analysis. I still have some concerns regarding the small sample size, however, I don’t believe that this diminishes the value of the paper.\nReviewer #3 (Remarks to the Author):\nI think both the clarity and organization of the revised manuscript have been notably improved. Specifically, the revision focuses on the degree of seismic slip channeling along the EAF master surface, avoiding unnecessary distraction, which enhances its accessibility.\nWe thank Reviewer 3 very much for his appreciation and constructive help.\nLine by line comments:\nLine 232 \"Fig. 3 helps us determining how many earthquakes occurred along (or inversely far from) the master surface, particularly with slip parallel to the master surface itself. \"\ndetermining should be determine\nDone (Line 266).\nLine 247 \"we acknowledge that a large supercycle with a return period of ~900 years along the EAF was recently proposed9 as well as a general spatiotemporal southwestward migration of recent...\", \"as well as\" is not proper here, it should be \"and\"\nDone (Line 365).\nLine 257 \"where a greater number of earthquakes occur than towards the...\", it should be \"toward\" here\nReviewer #4 (Remarks to the Author):\nI thank the authors for the many improvements they have made to the paper. This draft is closer to being ready for publication, but a few issues throughout the text remain to be addressed, and the discussion section still requires substantial reorganization to flow logically. My major comments are below and more detailed comments on the annotated PDF.\nWe thank Reviewer 4 once again for his past and present comments. In particular, we believe that the suggestions regarding the logical reorganization of the Discussion and the seismic slip channeling as an innate attribute of fault zones/segments have significantly enhanced our work (Lines 27-30, 256-264, and 393-736). Thank you!\nAdditionally, we have carefully considered all comments annotated in the PDF file and have made consistent edits throughout the text.\nRegarding uncertainties in the catalog data, the authors still need to be a bit more quantitative and explicit. Their response to my previous comment, and argument in the paper, appears to be “other high profile papers have used these data without discussing uncertainties, so we can too.” Inadequate attention to and discussion of uncertainties is in fact a major problem throughout scientific publishing, so I do not find “others are also doing it wrong” to be a valid argument. Ideally, it should be possible to make a general statement, based on information from AFAD and some of the papers analyzing the catalog which the authors cite, about the likely typical uncertainties, along the lines of “based on past analyses, horizontal location errors for these epicenters are typically no more than 5 km” or whatever the distance is. If that’s truly not possible, an alternative would be to make the argument that uncertainty and errors should affect all four aftershock sequences roughly equally, so that the observed differences in the aggregate dataset should be robust. I should say that I don’t believe the likely uncertainties are big enough to invalidate the results of this paper—it just needs to be discussed more quantitatively and explicitly.\nDone (Lines 136-153).\nDone (Lines 246-269). We have omitted Fig. S3 and improved the text concerning Fig. 3 by including all edits suggested in the PDF file.\nI do strongly recommend reordering the panels in Figs. 2 and 3 to put the four mainshocks in order of occurrence. The current order is confusing and doesn’t seem to have a compelling reason behind it.\nDone. We have reordered the panels of Figures 2, 3, and S2 in chronological order, from oldest to youngest sequences (2010, 2020, 2023a, and 2023b).\nSome points in the discussion still need to be better organized and clarified and others seem self-contradictory. If I may summarize, the main result/observation of the paper is that the aftershocks of the 2023 earthquakes are spread over a wider area and have more diverse slip planes and focal mechanisms than aftershocks of the 2010 and 2020 earthquakes. The authors name this property “slip channeling” and ultimately wish to argue that the difference in slip channeling explains longer-term features of earthquake behavior along the EAF. Such a causal link requires that the “slip channeling” be an innate property of feature of the fault sections or regions, as opposed to the variations being due to properties of these specific earthquakes (such as mainshock magnitude).\nThanks a lot! This is a very good synthesis with useful suggestions.\nWe have entirely reordered the Discussion section following the Reviewer’s suggestions (Lines 380-738): (1) from the null hypothesis (i.e. the relationship between seismic slip channeling and mainshock magnitude), (2) to alternative hypotheses (i.e., the seismic slip channeling as an innate attribute of fault zones/segments), and (3) finally to the relationship between seismic slip channeling and earthquake supercycles. See also Lines 27-30 and 256-264.\nWe have also solved the contradictory section at the end of the Discussion, advancing the hypothesis of aseismic slip connected with well channeled segments of the fault. In our opinion, some aseismic slip in the northeastern section of the EAF may compensate for the observed deficit of seismic slip when compared to the 2023 earthquakes toward the southwestern section. In addition, the well channeled nature of the northeastern section is consistent with the hypothesis of some aseismic slip there (Lines 747-764).\nDone (Lines 380-738).\nIn my estimation, the broader scattering of aftershocks along the distance axis for the 2023 events can easily be explained by the greater magnitudes and by certain features of the specific 2023 ruptures, namely the initiation of the Pazarcik earthquake on the Narli fault and the potential northward dip of the Cardak fault. While the aftershocks along the Narli fault are indeed far from the EAF master fault, they are very close to *the specific fault rupture of the 2023 mainshock,* which includes the Narli fault. Similarly for the Cardak fault, if it does dip to the north, the aftershocks there may not actually be far from the master fault plane. Even if the depths are too uncertain to check this, the possibility should be explicitly mentioned in the discussion.\nDone (Lines 727-736).\nThe wider spread in azimuth and slip sense for the 2023 aftershocks are a bit easier to defend as properties of the region rather than of these specific earthquakes. The authors should perhaps point out that while larger earthquakes are able to activate aftershocks over a wider area, thus including more diverse fault planes, the diversity in azimuth and mechanism is just as apparent among aftershocks very close to the master fault rupture. That lends credence to the idea that the southwest section of the EAF is inherently prone to “poor channeling” in comparison to the northeast section.\nDone (Lines 393-665).\nOnce the argument is made that the degree of slip channeling is a regional property, then the authors can move on to the discussion of potential underlying mechanisms such as rock rheology and fault maturity, and finally at the end make the capstone argument that this along-strike variation in slip channeling is what produces the observed supercycle behavior.\nAnd please clarify the seemingly self-contradictory argument that the less efficient slip channeling in the southwest explains why the 2023 earthquakes had such high slip.\nDone (Lines 747-764).\n6"}]

Decision letter