# Accretion versus erosion and sediment transfer balance near the subduction interface

Serge Lallemand, Michel Peyret, Diane Arcay, Arnauld Heuret

► To cite this version:

Serge Lallemand, Michel Peyret, Diane Arcay, Arnauld Heuret. Accretion versus erosion and sediment transfer balance near the subduction interface. Comptes Rendus. Géoscience, 2024, Géodynamique des continents et des océans – Hommage à Jean Aubouin, 356 (S2), pp.27-51. 10.5802/crgeos.252. hal-04618375

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https://hal.science/hal-04618375

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Distributed under a Creative Commons Attribution 4.0 International License
# Accretion versus erosion and sediment transfer balance near the subduction interface

Serge Lallemand, Michel Peyret, Diane Arcay, Arnauld Heuret

► To cite this version:

Serge Lallemand, Michel Peyret, Diane Arcay, Arnauld Heuret. Accretion versus erosion and sediment transfer balance near the subduction interface. Comptes Rendus. Géoscience, 2024, Géodynamique des continents et des océans – Hommage à Jean Aubouin, 356 (S2), pp.27-51. 10.5802/crgeos.252. hal-04618375

HAL Id: hal-04618375

https://hal.science/hal-04618375v1

Submitted on 21 Jun 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Comptes Rendus
## Géoscience
### Sciences de la Planète

Serge Lallemand, Michel Peyret, Diane Arcay and Arnauld Heuret

**Accretion versus erosion and sediment transfer balance near the subduction interface**

Volume 356, Special Issue S2 (2024), p. 27-51

Online since: 3 April 2024

**Part of Special Issue:** Geodynamics of Continents and Oceans – A tribute to Jean Aubouin

**Guest editors:** Olivier Fabbri (Université de Franche-Comté, UMR CNRS 6249, Besançon), Michel Faure (Université d'Orléans-BRGM, UMR CNRS 7325, Institut des Sciences de la Terre, Orléans), Jacky Ferrière (Université de Lille, faculté des Sciences), Laurent Jolivet (Sorbonne Université, ISTE, UMR 7193, Paris) and Sylvie Leroy (Sorbonne Université, CNRS-INSU, ISTE, Paris)

https://doi.org/10.5802/crgeos.252

<figure><img src="image_2.png" /></figure>

This article is licensed under the
CREATIVE COMMONS ATTRIBUTION 4.0 INTERNATIONAL LICENSE.

http://creativecommons.org/licenses/by/4.0/
# Comptes Rendus
## Géoscience
### Sciences de la Planète

Serge Lallemand, Michel Peyret, Diane Arcay and Arnauld Heuret

**Accretion versus erosion and sediment transfer balance near the subduction interface**

Volume 356, Special Issue S2 (2024), p. 27-51

Online since: 3 April 2024

**Part of Special Issue:** Geodynamics of Continents and Oceans – A tribute to Jean Aubouin

**Guest editors:** Olivier Fabbri (Université de Franche-Comté, UMR CNRS 6249, Besançon), Michel Faure (Université d'Orléans-BRGM, UMR CNRS 7325, Institut des Sciences de la Terre, Orléans), Jacky Ferrière (Université de Lille, faculté des Sciences), Laurent Jolivet (Sorbonne Université, ISTE, UMR 7193, Paris) and Sylvie Leroy (Sorbonne Université, CNRS-INSU, ISTE, Paris)

https://doi.org/10.5802/crgeos.252

<figure><img src="image_2.png" /></figure>

This article is licensed under the
CREATIVE COMMONS ATTRIBUTION 4.0 INTERNATIONAL LICENSE.

http://creativecommons.org/licenses/by/4.0/

<figure><img src="image_3.png" /></figure>
Research article

Geodynamics of Continents and Oceans – A tribute to Jean Aubouin

# Accretion versus erosion and sediment transfer balance near the subduction interface

Serge Lallemand<sup>®,*,a</sup>, Michel Peyret<sup>®,a</sup>, Diane Arcay<sup>®,a</sup> and Arnauld Heuret<sup>®,b</sup>

E-mail: serge.lallemand@umontpellier.fr (S. Lallemand)

**Abstract.** The nature and amount of sediment transferred from one plate to the other near the subduction interface partly determines the tectonic and seismogenic regime of a margin. Examination of over 500 multichannel seismic lines has enabled us to build up a global database of subduction zone front characteristics at unprecedented spatial resolution. The total thickness of sediment in the trench below the deformation front, as well as that of the subduction channel at a distance from the trench, combined with other indices such as the tectonic regime of the forearc or the migration of the volcanic front, have enabled us to revisit the accretionary or erosional character of active margins. Preliminary conclusions, based on ~3/4 of sufficiently documented subduction zones, show a predominance of the erosive character of subduction over the last million years. The flux of solid matter through the shallow part of the subduction channel is of the order of 1.5 km³/yr, and that of pore fluids 0.4 km³/yr. Some subduction zones, such as the Mediterranean, are characterized by exceptional solid flux in the channel, while fluid flux is comparatively moderate. This is due to the fact that channel sediments are compacted even before subduction. Overall, fluid flux in the channel is greater under erosive margins, due to the higher rate of subduction and often higher porosity. Maximum porosity in the channel is reached when there is neither accretion nor tectonic erosion.

**Keywords.** Subduction, Active margins, Oceanic trenches, Subduction channel, Accretion, Erosion, Sediment flux.

Manuscript received 5 July 2023, revised 20 November 2023, accepted 21 December 2023.

## 1. Introduction

The existence of erosive processes responsible for the destruction of some active margins was first considered in the early 1970s along the Chilean subduction based on a mass balance deficit between sediment inputs from the Andes and those actually observed along the margin and in the trench [Scholl et al.,

1970], as well as a distribution of plutons showing an eastward rejuvenation from Jurassic in the coast to Cenozoic in the Cordillera [Rutland, 1971]. A little later, deep ocean drilling on active margins in Central America, the Marianas, Japan, or Peru provided additional support for the tectonic erosion process that explained both the anomalous subsidence of these margins (not explained by thermal contraction or sediment loading) and the landward migration of the volcanic front [Moore et al., 1986, Natland and Tarney, 1981, Bloomer, 1983, von Huene

<footnote><sup>a</sup> Geosciences Montpellier, CNRS, Université de Montpellier, Université des Antilles, France</footnote>

<footnote><sup>b</sup> Geosciences Montpellier, CNRS, Université de Montpellier, Université des Antilles, Université de Guyane, France</footnote>

<footnote>* Corresponding author</footnote>
Research article

Geodynamics of Continents and Oceans – A tribute to Jean Aubouin

# Accretion versus erosion and sediment transfer balance near the subduction interface

Serge Lallemand<sup>®,*,a</sup>, Michel Peyret<sup>®,a</sup>, Diane Arcay<sup>®,a</sup> and Arnauld Heuret<sup>®,b</sup>

E-mail: serge.lallemand@umontpellier.fr (S. Lallemand)

**Abstract.** The nature and amount of sediment transferred from one plate to the other near the subduction interface partly determines the tectonic and seismogenic regime of a margin. Examination of over 500 multichannel seismic lines has enabled us to build up a global database of subduction zone front characteristics at unprecedented spatial resolution. The total thickness of sediment in the trench below the deformation front, as well as that of the subduction channel at a distance from the trench, combined with other indices such as the tectonic regime of the forearc or the migration of the volcanic front, have enabled us to revisit the accretionary or erosional character of active margins. Preliminary conclusions, based on ~3/4 of sufficiently documented subduction zones, show a predominance of the erosive character of subduction over the last million years. The flux of solid matter through the shallow part of the subduction channel is of the order of 1.5 km³/yr, and that of pore fluids 0.4 km³/yr. Some subduction zones, such as the Mediterranean, are characterized by exceptional solid flux in the channel, while fluid flux is comparatively moderate. This is due to the fact that channel sediments are compacted even before subduction. Overall, fluid flux in the channel is greater under erosive margins, due to the higher rate of subduction and often higher porosity. Maximum porosity in the channel is reached when there is neither accretion nor tectonic erosion.

**Keywords.** Subduction, Active margins, Oceanic trenches, Subduction channel, Accretion, Erosion, Sediment flux.

Manuscript received 5 July 2023, revised 20 November 2023, accepted 21 December 2023.

## 1. Introduction

The existence of erosive processes responsible for the destruction of some active margins was first considered in the early 1970s along the Chilean subduction based on a mass balance deficit between sediment inputs from the Andes and those actually observed along the margin and in the trench [Scholl et al.,

1970], as well as a distribution of plutons showing an eastward rejuvenation from Jurassic in the coast to Cenozoic in the Cordillera [Rutland, 1971]. A little later, deep ocean drilling on active margins in Central America, the Marianas, Japan, or Peru provided additional support for the tectonic erosion process that explained both the anomalous subsidence of these margins (not explained by thermal contraction or sediment loading) and the landward migration of the volcanic front [Moore et al., 1986, Natland and Tarney, 1981, Bloomer, 1983, von Huene

<footnote><sup>a</sup> Geosciences Montpellier, CNRS, Université de Montpellier, Université des Antilles, France</footnote>

<footnote><sup>b</sup> Geosciences Montpellier, CNRS, Université de Montpellier, Université des Antilles, Université de Guyane, France</footnote>

<footnote>* Corresponding author</footnote>
et al., 1982, Suess et al., 1988). These findings have challenged the established model of active margin growth by sediment accretion at the foot of the landward slope [e.g., Seely, 1979]. Aubouin et al. [1984, 1985], following an exploration of the Guatemalan margin [von Huene and Aubouin, 1982], introduced the concept of convergent-extensional margin, reflecting that many active margins are cut by normal faults as in passive margins [see also Ferrière and Faure, 2024]. Proposals to classify active margins on the basis of their accretionary or erosive characteristics have emerged since the 1990s as discoveries were made [von Huene and Scholl, 1991, Clift and Vannucchi, 2004]. Nowadays, most authors still refer to these early classifications that deserve to be updated, now that we have additional observations.

Another descriptive feature of active margins concerns the amount of sediment available at the trench versus that present between the plate interface and the top of the igneous oceanic crust, that we will further call the “subduction channel”. The thickness of this channel often reflects the erosive or non-erosive behavior of the subduction. Similarly, many authors suggested a causal link between an excess of sediment present in the trench and the generation of mega-earthquakes [Ruff, 1989, Heuret et al., 2012, Scholl et al., 2015].

Even more recently, Lallemand et al. [2018] and van Rijsingen et al. [2018, 2019] showed that a high ocean floor roughness at 80–100 km wavelengths tended to reduce interseismic coupling on the subduction interface, and hence earthquake magnitude. Seno [2017] was the first to point out that it was not so much the thickness of the sediments at the trench but those actually present in the subduction channel which could condition the seismogenic behavior of the interface. Here, we propose to complete and revise the databases describing active margins from the wealth of work done along subduction zones, in order to verify the assertions made since the 1980s, which were based on a limited number of reference seismic profiles.

Based on a comprehensive review of interpreted seismic profiles published in the literature, we present not only an updated compilation of trench sediment thickness at an unprecedented density but we also provide a first order thickness of the subduction channel on the depth range over which it is imaged. This new database allows us to signifi-

cantly revise the characterization (accretionary versus erosive) of active margins, as well as the solid and fluid fractions of sediment flowing through the subduction channel.

## 2. The NE Japan margin as a case study

Tremendous improvements have been done in the processing of multichannel seismic lines since the 1980’s. It concerns both the penetration depth and the resolution of the data. Figure 1 is an example of the progress made, allowing the NE Japan margin to be imaged with unprecedented accuracy [Park et al., 2021]. The observation of widespread shallow normal faults cutting through the Neogene sedimentary cover of the margin had already been reported [von Huene and Lallemand, 1990] but not their deeper extent. In their interpretation, Park et al. [2021] identified some of these at depths greater than 20 km. Their shallow dip suggests the reactivation of former splay faults into normal faults as similarly observed off Ecuador [Collot et al., 2008] or at the transition from Alaska and Aleutian subduction zones [Kahrizi et al., 2024]. A tiny accretionary wedge (see thrust faults in red in Figure 1), limited to the foot of the margin, reworks the material slided from the margin rather than those deposited in the trench to the extent that the latter is empty of terrigenous deposits. Truncation of margin’s basal reflections along the subduction interface (see green arrow labelled “basal erosion” in Figure 1), seaward deepening of a Miocene subaerial unconformity and sampling of Early Miocene arc volcanic rocks at less than 100 km (see projection of DSDP site 439 in Figure 1) from the present trench attest for subcrustal tectonic erosion since at least 20 Ma [von Huene et al., 1980, von Huene and Lallemand, 1990]. Evidence for landward migration of the volcanic front through time has been reported by Ohguchi et al. [1989]. The >200 km progressive landward migration of the volcanic front is illustrated in the Figure 1 insert. Downdip thickening of the subduction channel primarily observed by von Huene et al. [1994] further north was later observed all along the NE Japan margin [Tsuru et al., 2002]. The thickness of the channel can locally reach up to 3 km–100 km north of the line shown in Figure 1.

Given the progress made and the multitude of seismic lines acquired along the subduction zones since the 1980’s and 1990’s, we have undertaken to
et al., 1982, Suess et al., 1988). These findings have challenged the established model of active margin growth by sediment accretion at the foot of the landward slope [e.g., Seely, 1979]. Aubouin et al. [1984, 1985], following an exploration of the Guatemalan margin [von Huene and Aubouin, 1982], introduced the concept of convergent-extensional margin, reflecting that many active margins are cut by normal faults as in passive margins [see also Ferrière and Faure, 2024]. Proposals to classify active margins on the basis of their accretionary or erosive characteristics have emerged since the 1990s as discoveries were made [von Huene and Scholl, 1991, Clift and Vannucchi, 2004]. Nowadays, most authors still refer to these early classifications that deserve to be updated, now that we have additional observations.

Another descriptive feature of active margins concerns the amount of sediment available at the trench versus that present between the plate interface and the top of the igneous oceanic crust, that we will further call the “subduction channel”. The thickness of this channel often reflects the erosive or non-erosive behavior of the subduction. Similarly, many authors suggested a causal link between an excess of sediment present in the trench and the generation of mega-earthquakes [Ruff, 1989, Heuret et al., 2012, Scholl et al., 2015].

Even more recently, Lallemand et al. [2018] and van Rijsingen et al. [2018, 2019] showed that a high ocean floor roughness at 80–100 km wavelengths tended to reduce interseismic coupling on the subduction interface, and hence earthquake magnitude. Seno [2017] was the first to point out that it was not so much the thickness of the sediments at the trench but those actually present in the subduction channel which could condition the seismogenic behavior of the interface. Here, we propose to complete and revise the databases describing active margins from the wealth of work done along subduction zones, in order to verify the assertions made since the 1980s, which were based on a limited number of reference seismic profiles.

Based on a comprehensive review of interpreted seismic profiles published in the literature, we present not only an updated compilation of trench sediment thickness at an unprecedented density but we also provide a first order thickness of the subduction channel on the depth range over which it is imaged. This new database allows us to signifi-

cantly revise the characterization (accretionary versus erosive) of active margins, as well as the solid and fluid fractions of sediment flowing through the subduction channel.

## 2. The NE Japan margin as a case study

Tremendous improvements have been done in the processing of multichannel seismic lines since the 1980’s. It concerns both the penetration depth and the resolution of the data. Figure 1 is an example of the progress made, allowing the NE Japan margin to be imaged with unprecedented accuracy [Park et al., 2021]. The observation of widespread shallow normal faults cutting through the Neogene sedimentary cover of the margin had already been reported [von Huene and Lallemand, 1990] but not their deeper extent. In their interpretation, Park et al. [2021] identified some of these at depths greater than 20 km. Their shallow dip suggests the reactivation of former splay faults into normal faults as similarly observed off Ecuador [Collot et al., 2008] or at the transition from Alaska and Aleutian subduction zones [Kahrizi et al., 2024]. A tiny accretionary wedge (see thrust faults in red in Figure 1), limited to the foot of the margin, reworks the material slided from the margin rather than those deposited in the trench to the extent that the latter is empty of terrigenous deposits. Truncation of margin’s basal reflections along the subduction interface (see green arrow labelled “basal erosion” in Figure 1), seaward deepening of a Miocene subaerial unconformity and sampling of Early Miocene arc volcanic rocks at less than 100 km (see projection of DSDP site 439 in Figure 1) from the present trench attest for subcrustal tectonic erosion since at least 20 Ma [von Huene et al., 1980, von Huene and Lallemand, 1990]. Evidence for landward migration of the volcanic front through time has been reported by Ohguchi et al. [1989]. The >200 km progressive landward migration of the volcanic front is illustrated in the Figure 1 insert. Downdip thickening of the subduction channel primarily observed by von Huene et al. [1994] further north was later observed all along the NE Japan margin [Tsuru et al., 2002]. The thickness of the channel can locally reach up to 3 km–100 km north of the line shown in Figure 1.

Given the progress made and the multitude of seismic lines acquired along the subduction zones since the 1980’s and 1990’s, we have undertaken to
<figure><img src="image_3.png" /></figure>

**Figure 1.** Pre-stack depth migrated seismic profile across Japan margin off Ishinomaki Cape modified from Park et al. [2021]. Note the extent of normal faults (in dark blue) beyond the Moho, and the restriction of the thrust faults (in red) to the frontal part of the margin. The subduction channel, the top of which is delimited by the dashed pale blue line, is well imaged down to 19 km. $T_{channel}$ refers to the thickness of the subduction channel, $T_{sed}$ is the trench fill sediment thickness measured at deformation front (maximum thickness) and $T_{SP}$ is the average sediment thickness covering the subducting plate away from the trench. Updip and downdip limit of the seismogenic zone based on historical ruptures after Nishikawa et al. [2023]. Considering a subduction rate of 92 mm/yr, the subducting oceanic crust near the red star (2011 Tohoku Eq hypocenter) began to underthrust ~1 Ma ago. The projection of the DSDP site 439, distant of ~200 km from the present-day active volcanic front, where Early Miocene arc volcanic rocks were drilled beneath a subaerial unconformity is shown in purple. Insert: Location of seismic line and volcanic front since 21 Ma after Lallemand [1995].

update the submap database (submap.fr) concerning not only the sediment thickness at the trench $T_{sed}$, but also that of the sediment cover of the lower plate away from the trench $T_{SP}$, and especially that of the subduction channel $T_{channel}$ (see Figure 1). On the basis of these elements as well as the morphology of the margin and any additional elements such as the position of the volcanic arc in the past, we were led to revisit the classification of active margins into accretion versus erosion.

**3. Dominantly accretionary versus erosive margins over the last million years**

Sorting active margins into accretionary or erosive types (Figure 2) has long been challenging because the net growth or decrease of the volume of a margin can only be considered over a period that allows the integration of spatial (along and across strike) and

temporal variations, typically from 1 to several million years. Thus, the presence or absence of an active accretionary prism, especially at the margin front, is not sufficient to characterize the margin regime.

For a long time, authors have described the structural complexity of active margins based on the nature of rocks outcropping in the inner forearcs or on seismic reflection images, shedding light on the first ~10 km of crust [e.g., Cloos and Shreve, 1988a,b, von Huene and Scholl, 1991]. Thus, the notions of wedge-shaped or channel-like subducted sedimentary units were later imaged, for example, by Tsuru et al. [2002] beneath the NE Japan margin. Underplating of sedimentary units that were first underthrust, then incorporated into the margin and ultimately exhumed from large depths as attested by their blueschist and eclogitic facies, was primarily suspected in the Franciscan complex in California [Platt, 1975, Cloos, 1986] and then in numerous ancient accretionary systems [Angiboust et al., 2021].
<figure><img src="image_4.png" /></figure>

**Figure 1.** Pre-stack depth migrated seismic profile across Japan margin off Ishinomaki Cape modified from Park et al. [2021]. Note the extent of normal faults (in dark blue) beyond the Moho, and the restriction of the thrust faults (in red) to the frontal part of the margin. The subduction channel, the top of which is delimited by the dashed pale blue line, is well imaged down to 19 km. $T_{channel}$ refers to the thickness of the subduction channel, $T_{sed}$ is the trench fill sediment thickness measured at deformation front (maximum thickness) and $T_{SP}$ is the average sediment thickness covering the subducting plate away from the trench. Updip and downdip limit of the seismogenic zone based on historical ruptures after Nishikawa et al. [2023]. Considering a subduction rate of 92 mm/yr, the subducting oceanic crust near the red star (2011 Tohoku Eq hypocenter) began to underthrust ~1 Ma ago. The projection of the DSDP site 439, distant of ~200 km from the present-day active volcanic front, where Early Miocene arc volcanic rocks were drilled beneath a subaerial unconformity is shown in purple. Insert: Location of seismic line and volcanic front since 21 Ma after Lallemand [1995].

update the submap database (submap.fr) concerning not only the sediment thickness at the trench $T_{sed}$, but also that of the sediment cover of the lower plate away from the trench $T_{SP}$, and especially that of the subduction channel $T_{channel}$ (see Figure 1). On the basis of these elements as well as the morphology of the margin and any additional elements such as the position of the volcanic arc in the past, we were led to revisit the classification of active margins into accretion versus erosion.

**3. Dominantly accretionary versus erosive margins over the last million years**

Sorting active margins into accretionary or erosive types (Figure 2) has long been challenging because the net growth or decrease of the volume of a margin can only be considered over a period that allows the integration of spatial (along and across strike) and

temporal variations, typically from 1 to several million years. Thus, the presence or absence of an active accretionary prism, especially at the margin front, is not sufficient to characterize the margin regime.

For a long time, authors have described the structural complexity of active margins based on the nature of rocks outcropping in the inner forearcs or on seismic reflection images, shedding light on the first ~10 km of crust [e.g., Cloos and Shreve, 1988a,b, von Huene and Scholl, 1991]. Thus, the notions of wedge-shaped or channel-like subducted sedimentary units were later imaged, for example, by Tsuru et al. [2002] beneath the NE Japan margin. Underplating of sedimentary units that were first underthrust, then incorporated into the margin and ultimately exhumed from large depths as attested by their blueschist and eclogitic facies, was primarily suspected in the Franciscan complex in California [Platt, 1975, Cloos, 1986] and then in numerous ancient accretionary systems [Angiboust et al., 2021].
<figure><img src="image_4.png" /></figure>

**Figure 2.** Sketch showing two types of active margins. Left: Typical accretionary margin undergoing frontal and subcrustal (underplating) accretion of sediment transferred from the trench or the subduction channel respectively (see small arrows at the base of accretionary wedge). The wedge is growing through time, loading and deflecting the subducting plate (former seafloor in dashed line). The volcanic arc is generally stable with respect to the overlying plate. The tectonic regime is generally compressive. Subcrustal removal may occur (see question mark) so that we prefer to describe this case as dominantly accretionary. Right: Typical erosive margin undergoing frontal and subcrustal tectonic erosion feeding the subduction channel that thickens downdip. The margin is generally narrow because it oversteepens with time, with a maximum of subsidence trenchward, and lacks of significant accretionary wedge. The volcanic arc often migrates landward as the margin shrinks and thins (former seafloor in dashed line). The tectonic regime is generally extensional. Underplating at large depths may happen (see question mark) so that we prefer to describe this case as dominantly erosive.

The detailed exploration of subduction interfaces, such as in Ecuador, Chile or Japan for example [e.g., Collot et al., 2008, Contreras-Reyes et al., 2010, Park et al., 2021], shows that the processes of growth or consumption of the margins evolve in space and time. It is now possible to detect evidence of subcrustal erosion down to depths of 20 km on a seismic profile (Figure 1) and to record uplift in the innermost parts potentially corresponding to the underplating of deeper sedimentary units like in Chile [Angiboust et al., 2021].

von Huene and Scholl [1991] and then Clift and Vannucchi [2004] attempted to estimate the net volume of sedimentary material that is accreted at convergent margins or subducted beneath the basement rocks. The former authors thus classified the margins according to whether or not they are building an accretionary prism while recognizing that the present state does not necessarily reflect the past regime and that visible accretion can mask a deep erosive process. From seismic profiles distributed over 3/4 of the subduction zones, they concluded that 56% of the margins presented an accretionary regime against 44% non-accretionary. The latter authors calculated mass balances for subduction margins

over longer periods—typically >10 m.y.—and then classified the subduction margins into accretionary versus erosive. This had the effect of switching some segments initially identified as accretionary, into erosive segments like Japan, Mexico, Panama, Colombia, Ecuador, N-Peru or Manila. More recently, Festa et al. [2018] compiled both classifications by retaining the intent of that of Clift and Vannucchi on the long-term behavior. Noda [2016] proposed a classification of forearc basins based on material transfer between the converging plates like von Huene and Scholl (accretion versus non-accretion) but also on long-term strain field in the basin (compressional versus extensional).

The thickness of sediments observed at a subduction trench $T_{sed}$ has been shown to be an important parameter not only in terms of material fluxes [Scholl et al., 1970, von Huene and Scholl, 1991, Clift and Vannucchi, 2004] but also as a parameter that may partly control the seismogenic and tsunamogenic character of the subduction interface, in particular through the fluid content of the subducted section [Ruff, 1989, Le Pichon et al., 1993, Heuret et al., 2012, Scholl et al., 2015, Festa et al., 2018, Brizzi et al., 2018, 2020, Geersen, 2019]. At the same time, many
<figure><img src="image_5.png" /></figure>

**Figure 2.** Sketch showing two types of active margins. Left: Typical accretionary margin undergoing frontal and subcrustal (underplating) accretion of sediment transferred from the trench or the subduction channel respectively (see small arrows at the base of accretionary wedge). The wedge is growing through time, loading and deflecting the subducting plate (former seafloor in dashed line). The volcanic arc is generally stable with respect to the overlying plate. The tectonic regime is generally compressive. Subcrustal removal may occur (see question mark) so that we prefer to describe this case as dominantly accretionary. Right: Typical erosive margin undergoing frontal and subcrustal tectonic erosion feeding the subduction channel that thickens downdip. The margin is generally narrow because it oversteepens with time, with a maximum of subsidence trenchward, and lacks of significant accretionary wedge. The volcanic arc often migrates landward as the margin shrinks and thins (former seafloor in dashed line). The tectonic regime is generally extensional. Underplating at large depths may happen (see question mark) so that we prefer to describe this case as dominantly erosive.

The detailed exploration of subduction interfaces, such as in Ecuador, Chile or Japan for example [e.g., Collot et al., 2008, Contreras-Reyes et al., 2010, Park et al., 2021], shows that the processes of growth or consumption of the margins evolve in space and time. It is now possible to detect evidence of subcrustal erosion down to depths of 20 km on a seismic profile (Figure 1) and to record uplift in the innermost parts potentially corresponding to the underplating of deeper sedimentary units like in Chile [Angiboust et al., 2021].

von Huene and Scholl [1991] and then Clift and Vannucchi [2004] attempted to estimate the net volume of sedimentary material that is accreted at convergent margins or subducted beneath the basement rocks. The former authors thus classified the margins according to whether or not they are building an accretionary prism while recognizing that the present state does not necessarily reflect the past regime and that visible accretion can mask a deep erosive process. From seismic profiles distributed over 3/4 of the subduction zones, they concluded that 56% of the margins presented an accretionary regime against 44% non-accretionary. The latter authors calculated mass balances for subduction margins

over longer periods—typically >10 m.y.—and then classified the subduction margins into accretionary versus erosive. This had the effect of switching some segments initially identified as accretionary, into erosive segments like Japan, Mexico, Panama, Colombia, Ecuador, N-Peru or Manila. More recently, Festa et al. [2018] compiled both classifications by retaining the intent of that of Clift and Vannucchi on the long-term behavior. Noda [2016] proposed a classification of forearc basins based on material transfer between the converging plates like von Huene and Scholl (accretion versus non-accretion) but also on long-term strain field in the basin (compressional versus extensional).

The thickness of sediments observed at a subduction trench $T_{sed}$ has been shown to be an important parameter not only in terms of material fluxes [Scholl et al., 1970, von Huene and Scholl, 1991, Clift and Vannucchi, 2004] but also as a parameter that may partly control the seismogenic and tsunamogenic character of the subduction interface, in particular through the fluid content of the subducted section [Ruff, 1989, Le Pichon et al., 1993, Heuret et al., 2012, Scholl et al., 2015, Festa et al., 2018, Brizzi et al., 2018, 2020, Geersen, 2019]. At the same time, many
<figure><img src="image_5.png" /><figcaption>**Figure 3.** Distribution of “dominantly accretionary” (blue trenches) and “dominantly erosive” (red trenches) margins. Grey trenches correspond either to convergent margins where continental crust subducts like north of Australia, or where we do not have enough data to decipher which type is dominant. MED = Mediterranean, SEA = Southeast Asia, NPA = North Pacific, SWP = Southwest Pacific, SAM = South America.</figcaption></figure>

authors pointed out the bias of considering only $T_{sed}$ insofar as all or part of the sediments present in the trench could be accreted to the margin and there was ample evidence of material transfer to the margin or to the subduction channel [Heuret et al., 2012, Scholl et al., 2015, Seno, 2017].

The difficulty today, if one wants to test the role of the sedimentary thickness available at the foot of the margin $T_{sed}$ or the one effectively dragged into the subduction $T_{channel}$, is to have a reliable database.

Apart from the pioneering work of Ruff [1989] who characterized the 19 margin segments that hosted an earthquake of $M_w > 8$ according to the presence or absence of an accretionary prism (ETS = Excess Trench Sediment) or horsts and grabens (HGS) on the subducting plate, there are few studies [von Huene and Scholl, 1991, Heuret et al., 2012, Scholl et al., 2015, Seno, 2017], all based on a limited number of observations, then extrapolated.

A close examination of the subduction zones shows that the lateral variations along strike and downdip are sometimes very important. This is why we have undertaken to gather as many observations as possible to upgrade the existing datasets.

Here, we will consider the mid-term behavior (a few m.y.) of the margin based on criteria such as (1) the down-dip variations of the thickness (thickening/thinning) of the subduction channel, (2) the tectonic regime (compressional/extensional) of the margin overriding the subduction interface, (3) its vertical motion (subsidence/uplift), and (4) the migration of the volcanic arc (landward/seaward) (Figure 2). By doing this along 3/4 of the subduction zones, mostly the same as von Huene and Scholl [1991] and Festa et al. [2018], we have increased the proportion of dominantly erosive margins (see Table 1 and Figure 3).

# 4. Methodology

## 4.1. Sediment thicknesses estimation

We have (re)analyzed more than 500 multichannel seismic profiles published in 170+ articles covering 88% of the oceanic subduction zones (see Table S1 in Supplementary Material). We still lack precise information for some subduction zones: Solomons,
<figure><img src="image_6.png" /><figcaption>**Figure 3.** Distribution of “dominantly accretionary” (blue trenches) and “dominantly erosive” (red trenches) margins. Grey trenches correspond either to convergent margins where continental crust subducts like north of Australia, or where we do not have enough data to decipher which type is dominant. MED = Mediterranean, SEA = Southeast Asia, NPA = North Pacific, SWP = Southwest Pacific, SAM = South America.</figcaption></figure>

authors pointed out the bias of considering only $T_{sed}$ insofar as all or part of the sediments present in the trench could be accreted to the margin and there was ample evidence of material transfer to the margin or to the subduction channel [Heuret et al., 2012, Scholl et al., 2015, Seno, 2017].

The difficulty today, if one wants to test the role of the sedimentary thickness available at the foot of the margin $T_{sed}$ or the one effectively dragged into the subduction $T_{channel}$, is to have a reliable database.

Apart from the pioneering work of Ruff [1989] who characterized the 19 margin segments that hosted an earthquake of $M_w > 8$ according to the presence or absence of an accretionary prism (ETS = Excess Trench Sediment) or horsts and grabens (HGS) on the subducting plate, there are few studies [von Huene and Scholl, 1991, Heuret et al., 2012, Scholl et al., 2015, Seno, 2017], all based on a limited number of observations, then extrapolated.

A close examination of the subduction zones shows that the lateral variations along strike and downdip are sometimes very important. This is why we have undertaken to gather as many observations as possible to upgrade the existing datasets.

Here, we will consider the mid-term behavior (a few m.y.) of the margin based on criteria such as (1) the down-dip variations of the thickness (thickening/thinning) of the subduction channel, (2) the tectonic regime (compressional/extensional) of the margin overriding the subduction interface, (3) its vertical motion (subsidence/uplift), and (4) the migration of the volcanic arc (landward/seaward) (Figure 2). By doing this along 3/4 of the subduction zones, mostly the same as von Huene and Scholl [1991] and Festa et al. [2018], we have increased the proportion of dominantly erosive margins (see Table 1 and Figure 3).

# 4. Methodology

## 4.1. Sediment thicknesses estimation

We have (re)analyzed more than 500 multichannel seismic profiles published in 170+ articles covering 88% of the oceanic subduction zones (see Table S1 in Supplementary Material). We still lack precise information for some subduction zones: Solomons,
<table><caption>**Table 1.** Comparison between global classifications of margin types with respective segments lengths (this study)</caption><thead><tr><th rowspan="2">Trench name</th><th rowspan="2">Trench length (km)</th><th colspan="2">von Huene & Scholl (1991)<br>based on the active building (or not) of an accretionary wedge</th><th colspan="2">Clift & Vannuchi (2004)<br>based on mass-balance over ~10 Myrs</th><th colspan="2">Festa & al. (2018)<br>essentially compiled former studies over long periods</th><th colspan="3">This study based on global margin's behavior over few Myrs and MCS data, independent from earlier compilations</th><th rowspan="2">Agreement with previous global studies</th></tr><tr><th>accreting</th><th>non-accreting</th><th>accretionary</th><th>erosive</th><th>accretionary</th><th>erosive</th><th>accretionary</th><th>erosive</th><th>undetermined</th></tr></thead><tbody><tr><td>Calabria</td><td>600</td><td></td><td></td><td>x</td><td></td><td>x</td><td></td><td>600</td><td></td><td></td><td>yes</td></tr><tr><td>Aegean - Cyprean</td><td>1800</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>1800</td><td></td><td></td><td>yes</td></tr><tr><td>Makran</td><td>600</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>600</td><td></td><td></td><td>yes</td></tr><tr><td>Japan</td><td>700</td><td>x</td><td></td><td></td><td>x</td><td></td><td>x</td><td></td><td>700</td><td></td><td>partly</td></tr><tr><td>Kurils - Kamtchatka</td><td>2150</td><td></td><td>x</td><td></td><td>x</td><td></td><td>x</td><td>1250</td><td>900</td><td></td><td>partly</td></tr><tr><td>C - W-Aleutians</td><td>2300</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td></td><td>700</td><td>1600</td><td>partly</td></tr><tr><td>Alaska</td><td>1500</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>1500</td><td></td><td></td><td>yes</td></tr><tr><td>Vancouver</td><td>400</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>400</td><td></td><td></td><td>yes</td></tr><tr><td>Cascadia</td><td>850</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>850</td><td></td><td></td><td>yes</td></tr><tr><td>Central America</td><td>3500</td><td>x</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td>300</td><td>3200</td><td></td><td>partly</td></tr><tr><td>N-Panama</td><td>700</td><td></td><td></td><td></td><td></td><td></td><td></td><td>700</td><td></td><td></td><td>new</td></tr><tr><td>S-Caribbeans</td><td>1700</td><td></td><td></td><td></td><td></td><td></td><td></td><td>1700</td><td></td><td></td><td>new</td></tr><tr><td>Muertos</td><td>700</td><td></td><td></td><td></td><td></td><td></td><td></td><td>700</td><td></td><td></td><td>new</td></tr><tr><td>Hispaniola - PRVI</td><td>700</td><td></td><td>x</td><td></td><td></td><td></td><td>x</td><td></td><td>600</td><td>100</td><td>yes</td></tr><tr><td>Lesser Antilles</td><td>1500</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>500</td><td>1000</td><td></td><td>partly</td></tr><tr><td>Colombia</td><td>600</td><td>x</td><td></td><td></td><td>x</td><td></td><td>x</td><td>200</td><td>400</td><td></td><td>partly</td></tr><tr><td>Ecuador</td><td>450</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td></td><td>450</td><td></td><td>partly</td></tr><tr><td>Peru</td><td>2200</td><td>x</td><td>x</td><td>x</td><td></td><td>x</td><td></td><td>2200</td><td></td><td></td><td>partly</td></tr><tr><td>Chile</td><td>4350</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>1200</td><td>3150</td><td></td><td>partly</td></tr><tr><td>S-Sandwich</td><td>1100</td><td></td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>1100</td><td></td><td>yes</td></tr><tr><td>Andaman</td><td>1000</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>1000</td><td></td><td></td><td>yes</td></tr><tr><td>Sumatra</td><td>2150</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>2150</td><td></td><td></td><td>yes</td></tr><tr><td>Java</td><td>1350</td><td>x</td><td></td><td>x</td><td></td><td></td><td>x</td><td></td><td>1350</td><td></td><td>partly</td></tr><tr><td>Timor</td><td>500</td><td>x</td><td></td><td></td><td></td><td></td><td>x</td><td></td><td>150</td><td>350</td><td>partly</td></tr><tr><td>Flores</td><td>570</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>570</td><td>new</td></tr><tr><td>Wetar</td><td>350</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>350</td><td>new</td></tr><tr><td>Banda incl. Seram</td><td>2000</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>2000</td><td>new</td></tr><tr><td>Halmahera</td><td>700</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>700</td><td></td></tr><tr><td>North Sulawesi</td><td>440</td><td>x</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>440</td><td></td></tr><tr><td>Sangihe</td><td>1300</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1300</td><td></td></tr><tr><td>East-Luzon</td><td>300</td><td>x</td><td></td><td></td><td></td><td>x</td><td></td><td></td><td></td><td>300</td><td></td></tr><tr><td>Philippines</td><td>1380</td><td></td><td>x</td><td></td><td>x</td><td></td><td></td><td></td><td></td><td>1380</td><td></td></tr><tr><td>Cotobato</td><td>380</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>380</td><td></td></tr><tr><td>Sulu</td><td>200</td><td>x</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>200</td><td></td></tr><tr><td>Manila</td><td>1200</td><td>x</td><td></td><td></td><td>x</td><td>x</td><td></td><td>1200</td><td></td><td></td><td>partly</td></tr><tr><td>Ryukyus incl. W-Gagua</td><td>1600</td><td></td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>150</td><td>1450</td><td></td><td>partly</td></tr><tr><td>Nankai</td><td>400</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>400</td><td></td><td></td><td>yes</td></tr><tr><td>Izu-Bonin</td><td>1000</td><td></td><td>x</td><td>x</td><td>x</td><td>x</td><td></td><td></td><td>1000</td><td></td><td>yes</td></tr><tr><td>Mariana</td><td>2400</td><td></td><td>x</td><td>x</td><td></td><td>x</td><td></td><td></td><td>2400</td><td></td><td>yes</td></tr><tr><td>Yap</td><td>600</td><td></td><td>x</td><td></td><td></td><td></td><td></td><td></td><td>600</td><td></td><td>yes</td></tr><tr><td>Palau</td><td>220</td><td></td><td>x</td><td></td><td></td><td></td><td></td><td></td><td>220</td><td></td><td>yes</td></tr><tr><td>Trobriand</td><td>650</td><td>x</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>650</td><td></td></tr><tr><td>New Britain</td><td>550</td><td>x</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>550</td><td>partly</td></tr><tr><td>Solomons</td><td>1850</td><td></td><td>x</td><td>x</td><td>x</td><td></td><td></td><td></td><td></td><td>1850</td><td></td></tr><tr><td>New Hebrides</td><td>1250</td><td></td><td>x</td><td></td><td></td><td></td><td></td><td></td><td>1250</td><td></td><td>yes</td></tr><tr><td>Tonga</td><td>1250</td><td></td><td>x</td><td>x</td><td>x</td><td></td><td></td><td></td><td>1250</td><td></td><td>yes</td></tr><tr><td>Kermadec</td><td>1500</td><td></td><td>x</td><td></td><td>x</td><td></td><td></td><td></td><td>1500</td><td></td><td>yes</td></tr><tr><td>Hikurangi</td><td>650</td><td>x</td><td></td><td></td><td></td><td></td><td></td><td>500</td><td>150</td><td></td><td>partly</td></tr><tr><td>Puysegur</td><td>500</td><td></td><td></td><td></td><td></td><td></td><td></td><td>100</td><td>400</td><td></td><td>new</td></tr><tr><td>Macquarie</td><td>200</td><td></td><td>x</td><td></td><td></td><td></td><td></td><td></td><td></td><td>200</td><td></td></tr><tr><td>Hjort</td><td>550</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>550</td><td></td></tr><tr><td></td><td>57390</td><td></td><td></td><td></td><td></td><td></td><td></td><td>18500</td><td>25420</td><td>13470</td><td></td></tr></tbody></table>

Blue (accretion) and red (erosion) trench lengths highlight major changes with respect to earlier classifications.

Halmahera, Philippines, Sulu, Cotobato, Sangihe, N-Sulawesi. Only the data we were able to verify are reported in this study. Instead of providing average values based on one or two profiles, we list measured values of $Z_t$, $T_{SP}$, $T_{sed}$ and $T_{channel}$ line by line even when distant by only few kilometers (see Figures 1 and 4 for definition and Table S1 (Supplementary Material) for access to the complete database).
<table><caption>**Table 1.** Comparison between global classifications of margin types with respective segments lengths (this study)</caption><thead><tr><th rowspan="2">Trench name</th><th rowspan="2">Trench length (km)</th><th colspan="2">von Huene & Scholl (1991)<br>based on the active building (or not) of an accretionary wedge</th><th colspan="2">Clift & Vannuchi (2004)<br>based on mass-balance over ~10 Myrs</th><th colspan="2">Festa & al. (2018)<br>essentially compiled former studies over long periods</th><th colspan="3">This study based on global margin's behavior over few Myrs and MCS data, independent from earlier compilations</th><th rowspan="2">Agreement with previous global studies</th></tr><tr><th>accreting</th><th>non-accreting</th><th>accretionary</th><th>erosive</th><th>accretionary</th><th>erosive</th><th>accretionary</th><th>erosive</th><th>undetermined</th></tr></thead><tbody><tr><td>Calabria</td><td>600</td><td></td><td></td><td>x</td><td></td><td>x</td><td></td><td>600</td><td></td><td></td><td>yes</td></tr><tr><td>Aegean - Cyprean</td><td>1800</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>1800</td><td></td><td></td><td>yes</td></tr><tr><td>Makran</td><td>600</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>600</td><td></td><td></td><td>yes</td></tr><tr><td>Japan</td><td>700</td><td>x</td><td></td><td></td><td>x</td><td></td><td>x</td><td></td><td>700</td><td></td><td>partly</td></tr><tr><td>Kurils - Kamtchatka</td><td>2150</td><td></td><td>x</td><td></td><td>x</td><td></td><td>x</td><td>1250</td><td>900</td><td></td><td>partly</td></tr><tr><td>C - W-Aleutians</td><td>2300</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td></td><td>700</td><td>1600</td><td>partly</td></tr><tr><td>Alaska</td><td>1500</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>1500</td><td></td><td></td><td>yes</td></tr><tr><td>Vancouver</td><td>400</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>400</td><td></td><td></td><td>yes</td></tr><tr><td>Cascadia</td><td>850</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>850</td><td></td><td></td><td>yes</td></tr><tr><td>Central America</td><td>3500</td><td>x</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td>300</td><td>3200</td><td></td><td>partly</td></tr><tr><td>N-Panama</td><td>700</td><td></td><td></td><td></td><td></td><td></td><td></td><td>700</td><td></td><td></td><td>new</td></tr><tr><td>S-Caribbeans</td><td>1700</td><td></td><td></td><td></td><td></td><td></td><td></td><td>1700</td><td></td><td></td><td>new</td></tr><tr><td>Muertos</td><td>700</td><td></td><td></td><td></td><td></td><td></td><td></td><td>700</td><td></td><td></td><td>new</td></tr><tr><td>Hispaniola - PRVI</td><td>700</td><td></td><td>x</td><td></td><td></td><td></td><td>x</td><td></td><td>600</td><td>100</td><td>yes</td></tr><tr><td>Lesser Antilles</td><td>1500</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>500</td><td>1000</td><td></td><td>partly</td></tr><tr><td>Colombia</td><td>600</td><td>x</td><td></td><td></td><td>x</td><td></td><td>x</td><td>200</td><td>400</td><td></td><td>partly</td></tr><tr><td>Ecuador</td><td>450</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td></td><td>450</td><td></td><td>partly</td></tr><tr><td>Peru</td><td>2200</td><td>x</td><td>x</td><td>x</td><td></td><td>x</td><td></td><td>2200</td><td></td><td></td><td>partly</td></tr><tr><td>Chile</td><td>4350</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>1200</td><td>3150</td><td></td><td>partly</td></tr><tr><td>S-Sandwich</td><td>1100</td><td></td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>1100</td><td></td><td>yes</td></tr><tr><td>Andaman</td><td>1000</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>1000</td><td></td><td></td><td>yes</td></tr><tr><td>Sumatra</td><td>2150</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>2150</td><td></td><td></td><td>yes</td></tr><tr><td>Java</td><td>1350</td><td>x</td><td></td><td>x</td><td></td><td></td><td>x</td><td></td><td>1350</td><td></td><td>partly</td></tr><tr><td>Timor</td><td>500</td><td>x</td><td></td><td></td><td></td><td></td><td></td><td></td><td>150</td><td>350</td><td>partly</td></tr><tr><td>Flores</td><td>570</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>570</td><td>new</td></tr><tr><td>Wetar</td><td>350</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>350</td><td>new</td></tr><tr><td>Banda incl. Seram</td><td>2000</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>2000</td><td>new</td></tr><tr><td>Halmahera</td><td>700</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>700</td><td></td></tr><tr><td>North Sulawesi</td><td>440</td><td>x</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>440</td><td></td></tr><tr><td>Sangihe</td><td>1300</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1300</td><td></td></tr><tr><td>East-Luzon</td><td>300</td><td>x</td><td></td><td></td><td></td><td>x</td><td></td><td></td><td></td><td>300</td><td></td></tr><tr><td>Philippines</td><td>1380</td><td></td><td>x</td><td></td><td>x</td><td></td><td></td><td></td><td></td><td>1380</td><td></td></tr><tr><td>Cotobato</td><td>380</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>380</td><td></td></tr><tr><td>Sulu</td><td>200</td><td>x</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>200</td><td></td></tr><tr><td>Manila</td><td>1200</td><td>x</td><td></td><td></td><td>x</td><td>x</td><td></td><td>1200</td><td></td><td></td><td>partly</td></tr><tr><td>Ryukyus incl. W-Gagua</td><td>1600</td><td></td><td>x</td><td>x</td><td>x</td><td>x</td><td>x</td><td>150</td><td>1450</td><td></td><td>partly</td></tr><tr><td>Nankai</td><td>400</td><td>x</td><td></td><td>x</td><td></td><td>x</td><td></td><td>400</td><td></td><td></td><td>yes</td></tr><tr><td>Izu-Bonin</td><td>1000</td><td></td><td>x</td><td>x</td><td>x</td><td>x</td><td></td><td></td><td>1000</td><td></td><td>yes</td></tr><tr><td>Mariana</td><td>2400</td><td></td><td>x</td><td>x</td><td>x</td><td>x</td><td></td><td></td><td>2400</td><td></td><td>yes</td></tr><tr><td>Yap</td><td>600</td><td></td><td>x</td><td></td><td></td><td></td><td></td><td></td><td>600</td><td></td><td>yes</td></tr><tr><td>Palau</td><td>220</td><td></td><td>x</td><td></td><td></td><td></td><td></td><td></td><td>220</td><td></td><td>yes</td></tr><tr><td>Trobriand</td><td>650</td><td>x</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>650</td><td></td></tr><tr><td>New Britain</td><td>550</td><td>x</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>550</td><td>partly</td></tr><tr><td>Solomons</td><td>1850</td><td></td><td>x</td><td>x</td><td>x</td><td></td><td></td><td></td><td></td><td>1850</td><td></td></tr><tr><td>New Hebrides</td><td>1250</td><td></td><td>x</td><td></td><td></td><td></td><td></td><td></td><td>1250</td><td></td><td>yes</td></tr><tr><td>Tonga</td><td>1250</td><td></td><td>x</td><td>x</td><td>x</td><td></td><td></td><td></td><td>1250</td><td></td><td>yes</td></tr><tr><td>Kermadec</td><td>1500</td><td></td><td>x</td><td>x</td><td>x</td><td></td><td></td><td></td><td>1500</td><td></td><td>yes</td></tr><tr><td>Hikurangi</td><td>650</td><td>x</td><td></td><td></td><td></td><td></td><td></td><td>500</td><td>150</td><td></td><td>partly</td></tr><tr><td>Puysegur</td><td>500</td><td></td><td></td><td></td><td></td><td></td><td></td><td>100</td><td>400</td><td></td><td>new</td></tr><tr><td>Macquarie</td><td>200</td><td></td><td>x</td><td></td><td></td><td></td><td></td><td></td><td></td><td>200</td><td></td></tr><tr><td>Hjort</td><td>550</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>550</td><td></td></tr></tbody><tfoot><tr><td></td><td>57390</td><td></td><td></td><td></td><td></td><td></td><td></td><td>18500</td><td>25420</td><td>13470</td><td></td></tr></tfoot></table>

Blue (accretion) and red (erosion) trench lengths highlight major changes with respect to earlier classifications.

Halmahera, Philippines, Sulu, Cotobato, Sangihe, N-Sulawesi. Only the data we were able to verify are reported in this study. Instead of providing average values based on one or two profiles, we list measured values of $Z_t$, $T_{SP}$, $T_{sed}$ and $T_{channel}$ line by line even when distant by only few kilometers (see Figures 1 and 4 for definition and Table S1 (Supplementary Material) for access to the complete database).
<figure><img src="image_6.png" /><figcaption>**Figure 4.** The calculation of porosity in the subduction channel at a distance of ~15 km from the deformation front is performed differently depending on whether the channel thickness $T_{\text{channel}}$ is greater or smaller than the $T_{\text{sed\_co}}$ threshold value corresponding to $T_{\text{sed}} \times K_{\text{co}}$. If there is frontal accretion, then only the already compacted basal section ($T_{\text{sed\_base}}$) of the trench sediments will be entrained, whereas if there is no accretion, the entire $T_{\text{sed}}$ thickness will be entrained ($T_{\text{sed\_base}} = T_{\text{sed}}$). In addition, sediments eroded from the sole of the margin may be added to the subducted section.</figcaption></figure>

Each line, generally normal to the trench, is located by its intersection (latitude, longitude) with the trench. $Z_t$ is the trench depth in kilometers measured on the seismic line. $T_{SP}$ is the average sediment thickness covering the subducting plate away from the trench measured on the seismic line. We do not specify the distance from the deformation front at which we measure $T_{SP}$, as this can vary enormously depending on terrigenous inputs. Our aim is to provide a value for the thickness of the oceanic crust away from the terrigenous inputs that concentrate in the trench. This can be very close to the deformation front if there are no terrigenous inputs, as along most intra-oceanic subduction zones, or several hundred km away if the trench coincides with a detrital fan, as in Cascadia or in the Bay of Bengal. $T_{\text{sed}}$ is the trench fill sediment thickness measured at deformation front down to the top of the oceanic crust and $T_{\text{channel}}$ refers to the thickness of the subduction channel between the plate boundary and the top of oceanic crust, close or near the updip limit of the seismogenic zone, as defined for example in Heuret et al. [2011]. We will further consider a mean distance of ~15 km from the deformation front, given that it may vary from 10 to 30–40 km. As often observed, the thickness of the channel may vary significantly as pore fluids are expelled downdip but also as a function material transfer from or to the margin. This, in conjunction with the fact that the channel imagery is highly variable depending on the quality of the seismic data, especially at great depths (a depth of 20 km, as shown in Figure 1, remains exceptional), means that the

value provided should not be considered as an absolute value but rather as an averaged representative value of the profile. The thicknesses in kilometers are either issued from depth sections or converted from two-way-travel time sections using simplistic empirical laws assuming that sound velocities range from 2 to 3 km/s depending on the thickness for the trench fill sediment. It has sometimes happened that very different values are proposed for sections-depths of the same seismic line in different papers. In this case, we decided after a short investigation which solution made the most sense to us. Again, we do not claim here to provide an exact value that would require knowledge of the seismic velocities on the section-time concerned but an order of magnitude that is close to reality. By doing this, we can reasonably assume an average error between 10 and 20% depending on the quality of the seismic data. The density of the dataset varies greatly from region to region. We extrapolated the margin type to along-strike distances never greater than 200 km when the lateral variations seemed minor. Regarding $T_{\text{sed}}$ and $T_{\text{channel}}$, we did not extrapolate at distances larger than 50 km away from a line. In order to feed the submap database with a step distance of around 2°, we sometimes had to extrapolate the values of $T_{\text{sed}}$, $T_{\text{channel}}$ and $T_{\text{SP}}$ along the trenches, based on the nearest measurement, but also on morphological criteria such as the bathymetric profile of the trench. In such case, the symbols of the parameters are then accompanied by an asterisk, $T_{\text{sed}}^*$, $T_{\text{SP}}^*$, $T_{\text{channel}}^*$. We provide the source for each seismic line.
<figure><img src="image_7.png" /><figcaption>**Figure 4.** The calculation of porosity in the subduction channel at a distance of ~15 km from the deformation front is performed differently depending on whether the channel thickness $T_{\text{channel}}$ is greater or smaller than the $T_{\text{sed\_co}}$ threshold value corresponding to $T_{\text{sed}} \times K_{\text{co}}$. If there is frontal accretion, then only the already compacted basal section ($T_{\text{sed\_base}}$) of the trench sediments will be entrained, whereas if there is no accretion, the entire $T_{\text{sed}}$ thickness will be entrained ($T_{\text{sed\_base}} = T_{\text{sed}}$). In addition, sediments eroded from the sole of the margin may be added to the subducted section.</figcaption></figure>

Each line, generally normal to the trench, is located by its intersection (latitude, longitude) with the trench. $Z_t$ is the trench depth in kilometers measured on the seismic line. $T_{SP}$ is the average sediment thickness covering the subducting plate away from the trench measured on the seismic line. We do not specify the distance from the deformation front at which we measure $T_{SP}$, as this can vary enormously depending on terrigenous inputs. Our aim is to provide a value for the thickness of the oceanic crust away from the terrigenous inputs that concentrate in the trench. This can be very close to the deformation front if there are no terrigenous inputs, as along most intra-oceanic subduction zones, or several hundred km away if the trench coincides with a detrital fan, as in Cascadia or in the Bay of Bengal. $T_{\text{sed}}$ is the trench fill sediment thickness measured at deformation front down to the top of the oceanic crust and $T_{\text{channel}}$ refers to the thickness of the subduction channel between the plate boundary and the top of oceanic crust, close or near the updip limit of the seismogenic zone, as defined for example in Heuret et al. [2011]. We will further consider a mean distance of ~15 km from the deformation front, given that it may vary from 10 to 30–40 km. As often observed, the thickness of the channel may vary significantly as pore fluids are expelled downdip but also as a function material transfer from or to the margin. This, in conjunction with the fact that the channel imagery is highly variable depending on the quality of the seismic data, especially at great depths (a depth of 20 km, as shown in Figure 1, remains exceptional), means that the

value provided should not be considered as an absolute value but rather as an averaged representative value of the profile. The thicknesses in kilometers are either issued from depth sections or converted from two-way-travel time sections using simplistic empirical laws assuming that sound velocities range from 2 to 3 km/s depending on the thickness for the trench fill sediment. It has sometimes happened that very different values are proposed for sections-depths of the same seismic line in different papers. In this case, we decided after a short investigation which solution made the most sense to us. Again, we do not claim here to provide an exact value that would require knowledge of the seismic velocities on the section-time concerned but an order of magnitude that is close to reality. By doing this, we can reasonably assume an average error between 10 and 20% depending on the quality of the seismic data. The density of the dataset varies greatly from region to region. We extrapolated the margin type to along-strike distances never greater than 200 km when the lateral variations seemed minor. Regarding $T_{\text{sed}}$ and $T_{\text{channel}}$, we did not extrapolate at distances larger than 50 km away from a line. In order to feed the submap database with a step distance of around 2°, we sometimes had to extrapolate the values of $T_{\text{sed}}$, $T_{\text{channel}}$ and $T_{\text{SP}}$ along the trenches, based on the nearest measurement, but also on morphological criteria such as the bathymetric profile of the trench. In such case, the symbols of the parameters are then accompanied by an asterisk, $T_{\text{sed}}^*$, $T_{\text{SP}}^*$, $T_{\text{channel}}^*$. We provide the source for each seismic line.
## 4.2. Margin type characterization

The margin type MT “dominantly accretionary” or “dominantly erosive” over the last few million years has been updated (Figures 2 and 3) mainly based on data from the literature but also according to the criteria mentioned in previous section ($T_{sed}-T_{channel}$, extensional versus compressional regime, margin subsidence/uplift, volcanic front migration).

Raw data set is accessible as supplementary information. Mean values every ~200 km of trench are accessible on line at the following url: submap.fr.

## 4.3. Sediment flux calculation

To estimate the balance of solid or fluid fraction transiting through the subduction channel, we need to estimate the porosity of the sequence in the channel, as well as its thickness. To do this, we convert the depth versus porosity curves of trench floor sedimentary deposits obtained from DSDP and ODP cores and seismic velocities [Figure S1 in Supplementary Material extrapolated in depth from von Huene and Scholl, 1991] into a thickness versus mean porosity curve (Figure S2 in Supplementary Material). Then, we considered 2 distinct cases, depending on whether part of the sedimentary sequence was frontally accreted or not (Figure 4). In the first case (frontal accretion), the channel thickness $T_{channel}$ will be less than that of the sedimentary sequence at the trench $T_{sed}$ compacted by a factor $K_{co}$, i.e. $T_{sed\_co}$. It means that the incoming section subducting at trench consists only in the lower part of the trench sediment section further called $T_{sed\_base}$. This implies that the mean porosity of the subducting sediment layer $\Phi_{sed\_base}$ is less than that of the whole trench sequence, i.e., $\Phi_{sed}$. The average porosity in the channel $\Phi_{channel}$ will be reduced by a factor $K_r$ compared with that of the subducted section $\Phi_{sed\_base}$. The second case, without frontal accretion, generally corresponds to subcrustal erosion if $T_{channel}$ is greater than $T_{sed\_co}$. The channel sequence will therefore be composed of a basal section issued from the trench $T_{sed\_co}$ with a porosity $\theta_{sed\_co}$, and an upper section issued from margin removal $T_{ero}$ with an average porosity $\Phi_{ero} < 10\%$ [Saffer and Tobin, 2011] that we set to 5%. Details of the calculations used to determine an average porosity reduction coefficient $K_r$ between the incoming section at the trench and the

channel at an average distance of ~15 km from the deformation front are given in the Supplementary Material, as well as for the compaction coefficient $K_{co}$ between the thickness of incoming sediment and that in the channel. The compaction coefficient $K_{co}$ naturally depends on the initial porosity measured at the trench in the incoming sequence, i.e., $\Phi_{sed}$ or $\Phi_{sed\_base}$.

Calculating the solid and fluid fluxes entrained in each subduction zone requires processing the data obtained along the 535 unevenly distributed profiles in such a way as to provide the relevant information per representative transect along each subduction zone. Of the 260 submap database transects, only 116 were able to be assigned with a mean $T_{channel}$ value, due to their proximity to a seismic line allowing the channel to be imaged at a distance of at least 10 km from the deformation front. We therefore first estimated the solid and fluid fractions along each of the 116 constrained transects (in green in Table S2 in Supplementary Material) using the estimated porosity $\Phi_{channel}$, and then calculated the fluxes per km of trench by multiplying the solid or liquid fraction by the normal component of the subduction velocity recently updated in the submap database (Table S2). We then extrapolated these values along the subduction zones, weighting them by the width sampled on each transect, which enabled us to cover around 70% of the total length of the subduction zones.

# 5. Results

## 5.1. Margin type

Our updated dataset allowed us to significantly modify the distribution of margin types and, at the end, increase the proportion of “dominantly erosive” margins compared with former studies. We count in this study (see Table 1 and Table S1 in Supplementary Material for details and references) 25,420 km of “dominantly erosive” margins, 18,500 km of “dominantly accretionary” margins and 13,470 km of either undetermined type or where oceanic subduction laterally switches into continental subduction like north of Hispaniola or Australia. In such cases, it is impossible to measure the sediment thickness because the continental basement is either poorly defined or not imaged at all. Based on the 3/4 of subduction zones for which it has been possible
## 4.2. Margin type characterization

The margin type MT “dominantly accretionary” or “dominantly erosive” over the last few million years has been updated (Figures 2 and 3) mainly based on data from the literature but also according to the criteria mentioned in previous section ($T_{sed}-T_{channel}$, extensional versus compressional regime, margin subsidence/uplift, volcanic front migration).

Raw data set is accessible as supplementary information. Mean values every ~200 km of trench are accessible on line at the following url: submap.fr.

## 4.3. Sediment flux calculation

To estimate the balance of solid or fluid fraction transiting through the subduction channel, we need to estimate the porosity of the sequence in the channel, as well as its thickness. To do this, we convert the depth versus porosity curves of trench floor sedimentary deposits obtained from DSDP and ODP cores and seismic velocities [Figure S1 in Supplementary Material extrapolated in depth from von Huene and Scholl, 1991] into a thickness versus mean porosity curve (Figure S2 in Supplementary Material). Then, we considered 2 distinct cases, depending on whether part of the sedimentary sequence was frontally accreted or not (Figure 4). In the first case (frontal accretion), the channel thickness $T_{channel}$ will be less than that of the sedimentary sequence at the trench $T_{sed}$ compacted by a factor $K_{co}$, i.e. $T_{sed\_co}$. It means that the incoming section subducting at trench consists only in the lower part of the trench sediment section further called $T_{sed\_base}$. This implies that the mean porosity of the subducting sediment layer $\Phi_{sed\_base}$ is less than that of the whole trench sequence, i.e., $\Phi_{sed}$. The average porosity in the channel $\Phi_{channel}$ will be reduced by a factor $K_r$ compared with that of the subducted section $\Phi_{sed\_base}$. The second case, without frontal accretion, generally corresponds to subcrustal erosion if $T_{channel}$ is greater than $T_{sed\_co}$. The channel sequence will therefore be composed of a basal section issued from the trench $T_{sed\_co}$ with a porosity $\theta_{sed\_co}$, and an upper section issued from margin removal $T_{ero}$ with an average porosity $\Phi_{ero} < 10\%$ [Saffer and Tobin, 2011] that we set to 5%. Details of the calculations used to determine an average porosity reduction coefficient $K_r$ between the incoming section at the trench and the

channel at an average distance of ~15 km from the deformation front are given in the Supplementary Material, as well as for the compaction coefficient $K_{co}$ between the thickness of incoming sediment and that in the channel. The compaction coefficient $K_{co}$ naturally depends on the initial porosity measured at the trench in the incoming sequence, i.e., $\Phi_{sed}$ or $\Phi_{sed\_base}$.

Calculating the solid and fluid fluxes entrained in each subduction zone requires processing the data obtained along the 535 unevenly distributed profiles in such a way as to provide the relevant information per representative transect along each subduction zone. Of the 260 submap database transects, only 116 were able to be assigned with a mean $T_{channel}$ value, due to their proximity to a seismic line allowing the channel to be imaged at a distance of at least 10 km from the deformation front. We therefore first estimated the solid and fluid fractions along each of the 116 constrained transects (in green in Table S2 in Supplementary Material) using the estimated porosity $\Phi_{channel}$, and then calculated the fluxes per km of trench by multiplying the solid or liquid fraction by the normal component of the subduction velocity recently updated in the submap database (Table S2). We then extrapolated these values along the subduction zones, weighting them by the width sampled on each transect, which enabled us to cover around 70% of the total length of the subduction zones.

# 5. Results

## 5.1. Margin type

Our updated dataset allowed us to significantly modify the distribution of margin types and, at the end, increase the proportion of “dominantly erosive” margins compared with former studies. We count in this study (see Table 1 and Table S1 in Supplementary Material for details and references) 25,420 km of “dominantly erosive” margins, 18,500 km of “dominantly accretionary” margins and 13,470 km of either undetermined type or where oceanic subduction laterally switches into continental subduction like north of Hispaniola or Australia. In such cases, it is impossible to measure the sediment thickness because the continental basement is either poorly defined or not imaged at all. Based on the 3/4 of subduction zones for which it has been possible
to determine the dominant margin regime, at least
in the submerged part, we observe 42% accret-
ing margins (25,420 km) and 58% eroding margins
(18,500 km). However, we do not rule out the possi-
bility that some erosive margins may simultaneously
record subcrustal accretion far from the deformation
front or that some margins assumed to be accreting
are subject to deep subcrustal erosion.

We confirm the accretionary character of the
Mediterranean, Makran, South Lesser Antilles,
Sumatra-Andaman, Alaska, Cascadia, Nankai and
South Hikurangi margins (Figure 3). We also con-
firm the erosional character of the Puerto Rico,
South Sandwich, New Hebrides, Izu-Bonin-Mariana
or Tonga-Kermadec margins. Some inconsisten-
cies with previous classifications (Table 1) are
linked to the time period concerned (current ver-
sus 1–2 m.y. versus 10 m.y.). Discrepancy is great-
est when von Huene and Scholl [1991] list non-
accretionary margins, while we list erosive margins.
When re-examining the type of margin, we based
our analysis—as indicated above—on a set of crite-
ria and not just on the excess or deficit of sediment
present in the subduction channel (see Table 2). The
differences with earlier studies include about 600 km
of the Lesser Antilles margin north of its intercept
with the Tiburon Ridge. The forearc underwent there
a dramatic subsidence and extension since middle
Miocene (~16 Ma) which is attributed to severe basal
erosion following the subduction of the southern
extent of the Bahamas Bank [Boucard et al., 2021].
Further west, the Puerto-Rico-Virgin-Islands mar-
gin recorded an even stronger episode of tectonic
erosion [Grindlay et al., 2005]. Most of the Central
America forearc turned into “dominantly erosive”
margins [Prada et al., 2023] except the northernmost
and southernmost terminations [Bartolomé et al.,
2011, MacKay and Moore, 1990]. The Central Aleu-
tians margin is currently considered as accretionary
based on the well-developed accretionary wedge but
Jicha and Kay [2018] demonstrated that the landward
arc migration increased to the west and is great-
est over the last 5 m.y. Furthermore, they interpret
adakite-like lavas as additional evidence for ongoing
subduction-erosion. Northeast Japan and Northern
Andes (South Colombia–Ecuador–Peru) turned to
exhibit all characters of subduction-erosion even if
some local sediment accretion may occur at the mar-
gin front [e.g., Collot et al., 2004, Marcaillou et al.,

2006]. The Chilean margin shows lateral variations
already highlighted in previous classifications, with a
predominantly erosive behavior, albeit accretionary
evidence in the center. On the other hand, the loca-
tion of accretionary sectors between 33.4 and 38.2°S
and south of 54.1°S is more precise in our study. We
agree with Festa et al. [2018] that the margin south of
Java is dominantly erosive and that the Manila sub-
duction zone is accretionary over its entire length.
The Ryukyu margin is still dominantly erosive but
we have changed the status of its southernmost
termination, between Taiwan and the intersection
with the Gagua ridge where sedimentary accretion
dominates [Lallemand et al., 2013, Nishizawa et al.,
2017]. Finally, we have characterized new margins
such as in the Caribbean Sea (North-Panama, South-
Caribbeans, Muertos) exhibiting sedimentary accre-
tion or Puysegur south of New Zealand being mainly
erosive.

5.2. *Total sediment thickness in the trench and the subduction channel*

Based on a re-examination of 500 multichannel seis-
mic lines across the subduction zones, we have
updated the database firstly published by Heuret
et al. [2012] not only regarding the thickness of in-
coming sediment Tsed but also those of the subduc-
tion channel Tchannel when available as well as those
of the sedimentary cover away from the trench area
(TSP, see Table S1 for data and references line by line).
An extract of the database each 2° is provided on the
submap web-tool (submap.fr). We have chosen to
represent the Tsed and Tchannel data in visual form
with a color code against the margin types (see ex-
planations in Figure 5). The maximum thickness of
sediment available in the trench Tsed is plotted on
the ocean side. The thickness of the channel is rep-
resented indirectly by subtracting it from the thick-
ness of the sediments in the trench (Tsed-Tchannel),
so that negative values (in red) indicate an excess of
subducted sediments over incoming sediments, and
positive values (in blue) indicate a deficit of sedi-
ments when the upper (or entire) section of enter-
ing sediment accrete at the margin front, for exam-
ple. In absolute terms, knowing that subducted sedi-
ments are compacting, it would be necessary to com-
pare Tchannel and Tsed_co, but as the difference is
minor, we have contented ourselves with plotting
to determine the dominant margin regime, at least
in the submerged part, we observe 42% accret-
ing margins (25,420 km) and 58% eroding margins
(18,500 km). However, we do not rule out the possi-
bility that some erosive margins may simultaneously
record subcrustal accretion far from the deformation
front or that some margins assumed to be accreting
are subject to deep subcrustal erosion.

We confirm the accretionary character of the
Mediterranean, Makran, South Lesser Antilles,
Sumatra-Andaman, Alaska, Cascadia, Nankai and
South Hikurangi margins (Figure 3). We also con-
firm the erosional character of the Puerto Rico,
South Sandwich, New Hebrides, Izu-Bonin-Mariana
or Tonga-Kermadec margins. Some inconsisten-
cies with previous classifications (Table 1) are
linked to the time period concerned (current ver-
sus 1–2 m.y. versus 10 m.y.). Discrepancy is great-
est when von Huene and Scholl [1991] list non-
accretionary margins, while we list erosive margins.
When re-examining the type of margin, we based
our analysis—as indicated above—on a set of crite-
ria and not just on the excess or deficit of sediment
present in the subduction channel (see Table 2). The
differences with earlier studies include about 600 km
of the Lesser Antilles margin north of its intercept
with the Tiburon Ridge. The forearc underwent there
a dramatic subsidence and extension since middle
Miocene (~16 Ma) which is attributed to severe basal
erosion following the subduction of the southern
extent of the Bahamas Bank [Boucard et al., 2021].
Further west, the Puerto-Rico-Virgin-Islands mar-
gin recorded an even stronger episode of tectonic
erosion [Grindlay et al., 2005]. Most of the Central
America forearc turned into “dominantly erosive”
margins [Prada et al., 2023] except the northernmost
and southernmost terminations [Bartolomé et al.,
2011, MacKay and Moore, 1990]. The Central Aleu-
tians margin is currently considered as accretionary
based on the well-developed accretionary wedge but
Jicha and Kay [2018] demonstrated that the landward
arc migration increased to the west and is great-
est over the last 5 m.y. Furthermore, they interpret
adakite-like lavas as additional evidence for ongoing
subduction-erosion. Northeast Japan and Northern
Andes (South Colombia–Ecuador–Peru) turned to
exhibit all characters of subduction-erosion even if
some local sediment accretion may occur at the mar-
gin front [e.g., Collot et al., 2004, Marcaillou et al.,

2006]. The Chilean margin shows lateral variations already highlighted in previous classifications, with a predominantly erosive behavior, albeit accretionary evidence in the center. On the other hand, the location of accretionary sectors between 33.4 and 38.2°S and south of 54.1°S is more precise in our study. We agree with Festa et al. [2018] that the margin south of Java is dominantly erosive and that the Manila subduction zone is accretionary over its entire length. The Ryukyu margin is still dominantly erosive but we have changed the status of its southernmost termination, between Taiwan and the intersection with the Gagua ridge where sedimentary accretion dominates [Lallemand et al., 2013, Nishizawa et al., 2017]. Finally, we have characterized new margins such as in the Caribbean Sea (North-Panama, South-Caribbeans, Muertos) exhibiting sedimentary accretion or Puysegur south of New Zealand being mainly erosive.

5.2. *Total sediment thickness in the trench and the subduction channel*

Based on a re-examination of 500 multichannel seis-
mic lines across the subduction zones, we have
updated the database firstly published by Heuret
et al. [2012] not only regarding the thickness of in-
coming sediment Tsed but also those of the subduc-
tion channel Tchannel when available as well as those
of the sedimentary cover away from the trench area
(TSP, see Table S1 for data and references line by line).
An extract of the database each 2° is provided on the
submap web-tool (submap.fr). We have chosen to
represent the Tsed and Tchannel data in visual form
with a color code against the margin types (see ex-
planations in Figure 5). The maximum thickness of
sediment available in the trench Tsed is plotted on
the ocean side. The thickness of the channel is rep-
resented indirectly by subtracting it from the thick-
ness of the sediments in the trench (Tsed-Tchannel),
so that negative values (in red) indicate an excess of
subducted sediments over incoming sediments, and
positive values (in blue) indicate a deficit of sedi-
ments when the upper (or entire) section of enter-
ing sediment accrete at the margin front, for exam-
ple. In absolute terms, knowing that subducted sedi-
ments are compacting, it would be necessary to com-
pare Tchannel and Tsed_co, but as the difference is
minor, we have contented ourselves with plotting
<table><caption>**Table 2.** Digest of Table S1 in Supplementary Material</caption><thead><tr><th>region</th><th>trench segments</th><th>mean T<sub>sed</sub></th><th>mean T<sub>channel</sub></th><th>mean T<sub>sed</sub> - T<sub>channel</sub></th><th>compressional vs extensional margin (C,E)</th><th>margin's subsidence vs uplift (Su,Up)</th><th>evidence for landward volcanic front migration</th><th>MT</th><th>sources</th></tr></thead><tbody><tr><td rowspan="3">MED</td><td>Calabria</td><td>6.4</td><td>3.2</td><td>3.2</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Gallen et al. (2023)</td></tr><tr><td>Aegean</td><td>9.9</td><td>4.8</td><td>5.1</td><td>E</td><td>Up</td><td></td><td>accretional</td><td>Strobl et al. (2014), Gallen et al. (2014)</td></tr><tr><td>Cyprean</td><td>8</td><td></td><td></td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Vidal et al. (2009)</td></tr><tr><td rowspan="10">MAK</td><td>Makran</td><td>6.7</td><td>3.8</td><td>2.9</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Panaz et al. (2022)</td></tr><tr><td>North-east Japan</td><td>0.4</td><td>1.4</td><td>-1</td><td>E</td><td>Su</td><td>x</td><td>accretional</td><td></td></tr><tr><td>South Kurils 41.2-46.9°N</td><td>0.5</td><td>0.5</td><td>0</td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Klaeschen et al. (1994), Schnürle et al. (1995)</td></tr><tr><td>North Kurils - South Kamchatka 47-51°N</td><td>0.5</td><td>0.5</td><td>0</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Klaeschen et al. (1994)</td></tr><tr><td>North Kamchatka</td><td>0.7</td><td></td><td></td><td></td><td></td><td></td><td>undetermined</td><td>Barenov et al. (2022), Gnbidenko et al. (1983)</td></tr><tr><td>West Aleutians 164-177°E</td><td>1.6</td><td></td><td></td><td></td><td></td><td></td><td>undetermined</td><td></td></tr><tr><td>Central Aleutians 179-187.4°E</td><td>2</td><td>1.4</td><td>0.6</td><td>C</td><td></td><td>x</td><td>accretional</td><td>McCarthy and Scholl (1985), Jicha & Kay (2018)</td></tr><tr><td>East Aleutians 189-195°E</td><td>1.7</td><td>1.9</td><td>-0.2</td><td>C/E</td><td></td><td></td><td>undetermined</td><td></td></tr><tr><td>West Alaska 197-205°E</td><td>1.3</td><td>1</td><td>0.3</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>von Huene et al. (2016), Kahrtz et al. (2024)</td></tr><tr><td>East Alaska 205-215.8°E</td><td>2.5</td><td>1.6</td><td>0.9</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>von Huene et al. (1999), Fruehn et al. (1999)</td></tr><tr><td rowspan="10">N-PAC</td><td>Cascadia</td><td>3.3</td><td>0.6</td><td>2.7</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Davis et al. (1990)</td></tr><tr><td>Central America - 29°N</td><td>1.1</td><td></td><td></td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Michaud et al. (1996), Bartolomé et al. (2011)</td></tr><tr><td>Central America 8.4-19.1°N</td><td>0.6</td><td>0.7</td><td>-0.1</td><td>C</td><td></td><td></td><td>accretional</td><td>Aubouin et al. (1964), von Huene and Ranero (2000)</td></tr><tr><td>Central America 6.7-6.8°N</td><td>1.3</td><td>0.4</td><td>0.9</td><td>C</td><td></td><td></td><td>accretional</td><td>MacKay and Moore (1990), Silver et al. (1990)</td></tr><tr><td>Panama</td><td>2</td><td></td><td></td><td>C</td><td></td><td></td><td>accretional</td><td>Silver et al. (1990)</td></tr><tr><td>Venezuela</td><td>3.2</td><td>0.9</td><td>2.3</td><td>C</td><td></td><td></td><td>accretional</td><td>Kroehler et al. (2011)</td></tr><tr><td>Muertos</td><td>1</td><td>0.5</td><td>0.5</td><td>C/E</td><td></td><td></td><td>accretional</td><td>Granja-Bruna et al. (2009, 2014)</td></tr><tr><td>Hispaniola</td><td>2.5</td><td></td><td></td><td>C/E</td><td>Up</td><td></td><td>accretional</td><td>Rodriguez-Zunero et al. (2020)</td></tr><tr><td>Puerto-Rico</td><td>1.9</td><td></td><td></td><td>E</td><td>Up/Su</td><td></td><td>accretional</td><td>TenBrink et al. (2005)</td></tr><tr><td>Northern Lesser Antilles 17-20°N</td><td>0.5</td><td>0.3</td><td>0.2</td><td>C</td><td>Su</td><td>x</td><td>accretional</td><td>Boucard et al. (2021)</td></tr><tr><td rowspan="10">CARIBBEANS</td><td>Northern Lesser Antilles 11-16°N</td><td>4.4</td><td>1.5</td><td>2.9</td><td>C/E</td><td></td><td></td><td>accretional</td><td>Gomez et al. (2018), Deville (2023)</td></tr><tr><td>North Colombia 5 - 7°N</td><td>0.9</td><td>0.4</td><td>0.5</td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Westbrook et al. (1995)</td></tr><tr><td>Colombia 1.7 - 3.5°N</td><td>3.3</td><td>1.4</td><td>1.9</td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Colot et al. (2004, 2008)</td></tr><tr><td>Ecuador</td><td>0.5</td><td>0.5</td><td>0</td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Colot et al. (2004, 2008)</td></tr><tr><td>Peru</td><td>0.8</td><td>0.8</td><td>0</td><td>E</td><td>Su</td><td>x</td><td>accretional</td><td>von Huene et al. (1989, 1996)</td></tr><tr><td>North Chile 19-33.3°S</td><td>0.4</td><td>1</td><td>-0.6</td><td>E</td><td></td><td></td><td>accretional</td><td>Petersen et al. (2022)</td></tr><tr><td>Central Chile 33.4-38.2°S</td><td>2</td><td>0.9</td><td>1.1</td><td>C</td><td></td><td></td><td>accretional</td><td>Grevenyer et al. (2003)</td></tr><tr><td>South Chile 39-53.5°S</td><td>1.9</td><td>1.7</td><td>0.2</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Schernath et al. (2009)</td></tr><tr><td>South Chile 54.1-57.5°S</td><td>2.8</td><td>1.3</td><td>1.5</td><td>C/E</td><td>Up/Su</td><td></td><td>accretional</td><td>Polonia et al. (2007)</td></tr><tr><td rowspan="10">S-AMERICA</td><td>Northern Lesser Antilles 11-16°N</td><td>0.7</td><td></td><td></td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Vanneste and Lartenschuch (2002)</td></tr><tr><td>Andaman - North Sumatra 1.6 - 14°N</td><td>3.7</td><td>0.3</td><td>3.4</td><td>C/E</td><td>Up/Su</td><td></td><td>accretional</td><td>Moeremans et al. (2014), McNeill et al. (2014)</td></tr><tr><td>Sumatra 0 - 8°S</td><td>1.5</td><td>0.1</td><td>1.4</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>McNeill et al. (2014)</td></tr><tr><td>Java 105 - 117°E</td><td>0.8</td><td>0.7</td><td>0.1</td><td>C</td><td></td><td></td><td>accretional</td><td>Kopp (2011)</td></tr><tr><td>Aru</td><td>1.4</td><td></td><td></td><td>C</td><td></td><td></td><td>undetermined</td><td></td></tr><tr><td>Flores</td><td>1.2</td><td></td><td></td><td>C</td><td>Up</td><td></td><td>undetermined</td><td>Milson et al. (1996)</td></tr><tr><td>Wetar</td><td>1</td><td></td><td></td><td>C</td><td>Up</td><td></td><td>undetermined</td><td>Silver et al. (1983)</td></tr><tr><td>Seram</td><td>1</td><td></td><td></td><td>C</td><td></td><td></td><td>undetermined</td><td>Silver et al. (1983)</td></tr><tr><td>South Manila 14 - 16.7°N</td><td>0.4</td><td>0.4</td><td>0.6</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Pairault et al. (2003)</td></tr><tr><td>North Manila 17 - 24°N</td><td>2</td><td>0</td><td>2</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Hayes and Lewis (1984)</td></tr><tr><td>South Ryukyu 122.5 - 123.1°E</td><td>4.3</td><td>1.1</td><td>3.2</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Ku and Hsu (2009)</td></tr><tr><td>Ryukyu 124 - 133°E</td><td>0.4</td><td>0</td><td>0.4</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Schnürle et al. (1998), Lallemand et al. (1999), Font et Lallemand (2009)</td></tr><tr><td rowspan="10">SE-ASIA</td><td>Nankai</td><td>1.6</td><td>0.6</td><td>1</td><td>C</td><td>Su</td><td></td><td>accretional</td><td>Nishizawa et al. (2017), Okamura et al. (2017)</td></tr><tr><td>Izu-Bonin-North Mariana 19 - 33°N</td><td>0.3</td><td>0.6</td><td>-0.1</td><td>C</td><td>Up</td><td>x</td><td>accretional</td><td>Park et al. (2000), Kodaira et al. (2002)</td></tr><tr><td>Mariana 16.4 - 17.9°N</td><td>0.5</td><td>0.6</td><td>-0.1</td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Takahashi et al. (1998)</td></tr><tr><td>South Mariana 10.8 - 16.2°N</td><td>0.3</td><td>0.4</td><td>-0.1</td><td>E</td><td>Su</td><td>x</td><td>accretional</td><td>Oakley et al. (2008)</td></tr><tr><td>Yap-Palau</td><td>0.2</td><td></td><td></td><td>C/E</td><td></td><td></td><td>accretional</td><td>Oakley et al. (2008), Ribeiro et al. (2013)</td></tr><tr><td>North New-Hebrides 12 - 17.2°S</td><td>1.6</td><td>1.6</td><td>0</td><td>C/E</td><td>Up</td><td></td><td>accretional</td><td>Yang et al. (2018), Dong et al. (2018), Zhang et al. (2019)</td></tr><tr><td>South New-Hebrides 17.5 - 23°S</td><td>0.4</td><td>1.6</td><td>-1.2</td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Colot et al. (1985, 1992), Fisher et al. (1986, 1991)</td></tr><tr><td>Tonga</td><td>0.4</td><td>0</td><td>0.4</td><td>E</td><td>Su</td><td>x</td><td>accretional</td><td>Fisher et al. (1986)</td></tr><tr><td>Kermadec 26.7 - 37.1°S</td><td>0.5</td><td>0</td><td>0.5</td><td>E</td><td>Su</td><td>x</td><td>accretional</td><td>Contreras-Reyes et al. (2011), Stratford et al. (2015)</td></tr><tr><td>North Hikurangi 37.8 - 39°S</td><td>1.1</td><td>0</td><td>1.1</td><td>C/E</td><td>Su</td><td></td><td>accretional</td><td>Funnell et al. (2017), Stratford et al. (2015)</td></tr><tr><td>North Hikurangi 39.1 - 42.3°S</td><td>4.4</td><td>1</td><td>3.4</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Schernath et al. (2010), Gase et al. (2021)</td></tr><tr><td>North Puyssegur 45.2 - 45.7°S</td><td>2.7</td><td>0.4</td><td>2.3</td><td>C</td><td></td><td></td><td>accretional</td><td>Barker et al. (2009), Gase et al. (2021, 2022)</td></tr><tr><td rowspan="2">SW-PAC</td><td>South Puyssegur 46 - 49°S</td><td>1.4</td><td>1.2</td><td>0.2</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Lebrun et al. (2000), Lamarche et Lebrun (2000)</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>undetermined</td><td>Colot et al. (1995)</td></tr></tbody></table>

Trench segments by region (MED = Mediterranean, MAK = Makran, N-PAC = North Pacific, CARIBBEANS, S-AMERICA = Andes and S-Sandwich, SE-ASIA = Philippine Sea and Sunda, SW-PAC = Southwest Pacific) were firstly defined according to margin type MT, then sediment thickness at trench $T_{sed}$ and finally sediment thickness below the plate boundary $T_{channel}$, each of them showing little variations within a given trench segment. Mean thickness values are reported in km for each segment.

$T_{sed} - T_{channel}$. As the spacing between seismic profiles is extremely variable from one region to another, from less than 1 km to over 100 km, we plotted the average of $T_{sed}$ and $T_{sed}^*$ or $T_{channel}$ and $T_{channel}^*$ values as a colored bar every km, perpendicular to the trench, within a sliding window of 100 km along the trench. In other words, empty sectors mean that no values could be measured or estimated at a distance of less than 50 km.

Figure 5 and Table 2 show that we now have an almost complete coverage of $T_{sed}$ and less coverage of $T_{channel}$. Generally speaking, and with rare

exceptions, an excess of sediment in the channel in relation to the thickness of the incoming section highlights the erosive nature of the margin. Positive $T_{sed} - T_{channel}$ values, reflecting frontal accretion, are sometimes associated with margins with a dominant erosive character (e.g., Central Aleutians 179-187.4°E, Colombia 1.7-3.5°N, North Hikurangi 37.8-39°S). Most of the time, this is due to a bias in $T_{channel}$ estimation, when its measurement could only be carried out at a short distance from the trench and is not corrected for compaction. For this reason, this value should be used with caution.
<table><caption>**Table 2.** Digest of Table S1 in Supplementary Material</caption><thead><tr><th>region</th><th>trench segments</th><th>mean T<sub>sed</sub></th><th>mean T<sub>channel</sub></th><th>mean T<sub>sed</sub> - T<sub>channel</sub></th><th>compressional vs extensional margin (C,E)</th><th>margin's subsidence vs uplift (Su,Up)</th><th>evidence for landward volcanic front migration</th><th>MT</th><th>sources</th></tr></thead><tbody><tr><td rowspan="3">MED</td><td>Calabria</td><td>6.4</td><td>3.2</td><td>3.2</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Gallen et al. (2023)</td></tr><tr><td>Aegean</td><td>9.9</td><td>4.8</td><td>5.1</td><td>E</td><td>Up</td><td></td><td>accretional</td><td>Strobl et al. (2014), Gallen et al. (2014)</td></tr><tr><td>Cyprean</td><td>8</td><td></td><td></td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Vidal et al. (2009)</td></tr><tr><td rowspan="10">MAK</td><td>Makran</td><td>6.7</td><td>3.8</td><td>2.9</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Panaz et al. (2022)</td></tr><tr><td>North-east Japan</td><td>0.4</td><td>1.4</td><td>-1</td><td>E</td><td>Su</td><td>x</td><td>accretional</td><td></td></tr><tr><td>South Kurils 41.2-46.9°N</td><td>0.5</td><td>0.5</td><td>0</td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Klaeschen et al. (1994), Schnürle et al. (1995)</td></tr><tr><td>North Kurils - South Kamchatka 47-51°N</td><td>0.5</td><td>0.5</td><td>0</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Klaeschen et al. (1994)</td></tr><tr><td>North Kamchatka</td><td>0.7</td><td></td><td></td><td></td><td></td><td></td><td>undetermined</td><td>Barenov et al. (2022), Gnbidenko et al. (1983)</td></tr><tr><td>West Aleutians 164-177°E</td><td>1.6</td><td></td><td></td><td></td><td></td><td></td><td>undetermined</td><td></td></tr><tr><td>Central Aleutians 179-187.4°E</td><td>2</td><td>1.4</td><td>0.6</td><td>C</td><td></td><td>x</td><td>accretional</td><td>McCarthy and Scholl (1985), Jicha & Kay (2018)</td></tr><tr><td>East Aleutians 189-195°E</td><td>1.7</td><td>1.9</td><td>-0.2</td><td>C/E</td><td></td><td></td><td>undetermined</td><td></td></tr><tr><td>West Alaska 197-205°E</td><td>1.3</td><td>1</td><td>0.3</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>von Huene et al. (2016), Kahrtz et al. (2024)</td></tr><tr><td>East Alaska 205-215.8°E</td><td>2.5</td><td>1.6</td><td>0.9</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>von Huene et al. (1999), Fruehn et al. (1999)</td></tr><tr><td rowspan="10">N-PAC</td><td>Cascadia</td><td>3.3</td><td>0.6</td><td>2.7</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Davis et al. (1990)</td></tr><tr><td>Central America - 29°N</td><td>1.1</td><td></td><td></td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Michaud et al. (1996), Bartolomé et al. (2011)</td></tr><tr><td>Central America 8.4-19.1°N</td><td>0.6</td><td>0.7</td><td>-0.1</td><td>C</td><td></td><td></td><td>accretional</td><td>Aubouin et al. (1964), von Huene and Ranero (2000)</td></tr><tr><td>Central America 6.7-6.8°N</td><td>1.3</td><td>0.4</td><td>0.9</td><td>C</td><td></td><td></td><td>accretional</td><td>MacKay and Moore (1990), Silver et al. (1990)</td></tr><tr><td>Panama</td><td>2</td><td></td><td></td><td>C</td><td></td><td></td><td>accretional</td><td>Silver et al. (1990)</td></tr><tr><td>Venezuela</td><td>3.2</td><td>0.9</td><td>2.3</td><td>C</td><td></td><td></td><td>accretional</td><td>Kroehler et al. (2011)</td></tr><tr><td>Muertos</td><td>1</td><td>0.5</td><td>0.5</td><td>C/E</td><td></td><td></td><td>accretional</td><td>Granja-Bruna et al. (2009, 2014)</td></tr><tr><td>Hispaniola</td><td>2.5</td><td></td><td></td><td>C/E</td><td>Up</td><td></td><td>accretional</td><td>Rodriguez-Zunero et al. (2020)</td></tr><tr><td>Puerto-Rico</td><td>1.9</td><td></td><td></td><td>E</td><td>Up/Su</td><td></td><td>accretional</td><td>TenBrink et al. (2005)</td></tr><tr><td>Northern Lesser Antilles 17-20°N</td><td>0.5</td><td>0.3</td><td>0.2</td><td>C</td><td>Su</td><td>x</td><td>accretional</td><td>Boucard et al. (2021)</td></tr><tr><td rowspan="10">CARIBBEANS</td><td>Northern Lesser Antilles 11-16°N</td><td>4.4</td><td>1.5</td><td>2.9</td><td>C/E</td><td></td><td></td><td>accretional</td><td>Gomez et al. (2018), Deville (2023)</td></tr><tr><td>North Colombia 5 - 7°N</td><td>0.9</td><td>0.4</td><td>0.5</td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Westbrook et al. (1995)</td></tr><tr><td>Colombia 1.7 - 3.5°N</td><td>3.3</td><td>1.4</td><td>1.9</td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Colot et al. (2004, 2008)</td></tr><tr><td>Ecuador</td><td>0.5</td><td>0.5</td><td>0</td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Colot et al. (2004, 2008)</td></tr><tr><td>Peru</td><td>0.8</td><td>0.8</td><td>0</td><td>E</td><td>Su</td><td>x</td><td>accretional</td><td>von Huene et al. (1989, 1996)</td></tr><tr><td>North Chile 19-33.3°S</td><td>0.4</td><td>1</td><td>-0.6</td><td>E</td><td></td><td></td><td>accretional</td><td>Petersen et al. (2022)</td></tr><tr><td>Central Chile 33.4-38.2°S</td><td>2</td><td>0.9</td><td>1.1</td><td>C</td><td></td><td></td><td>accretional</td><td>Grevenyer et al. (2003)</td></tr><tr><td>South Chile 39-53.5°S</td><td>1.9</td><td>1.7</td><td>0.2</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Schernath et al. (2009)</td></tr><tr><td>South Chile 54.1-57.5°S</td><td>2.8</td><td>1.3</td><td>1.5</td><td>C/E</td><td>Up/Su</td><td></td><td>accretional</td><td>Polonia et al. (2007)</td></tr><tr><td rowspan="10">S-AMERICA</td><td>Northern Lesser Antilles 11-16°N</td><td>0.7</td><td></td><td></td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Vanneste and Lartenschich (2002)</td></tr><tr><td>Andaman - North Sumatra 1.6 - 14°N</td><td>3.7</td><td>0.3</td><td>3.4</td><td>C/E</td><td>Up/Su</td><td></td><td>accretional</td><td>Moeremans et al. (2014), McNeill et al. (2014)</td></tr><tr><td>Sumatra 0 - 8°S</td><td>1.5</td><td>0.1</td><td>1.4</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>McNeill et al. (2014)</td></tr><tr><td>Java 105 - 117°E</td><td>0.8</td><td>0.7</td><td>0.1</td><td>C</td><td></td><td></td><td>accretional</td><td>Kopp (2011)</td></tr><tr><td>Aru</td><td>1.4</td><td></td><td></td><td>C</td><td></td><td></td><td>undetermined</td><td></td></tr><tr><td>Flores</td><td>1.2</td><td></td><td></td><td>C</td><td>Up</td><td></td><td>undetermined</td><td>Milson et al. (1996)</td></tr><tr><td>Wetar</td><td>1</td><td></td><td></td><td>C</td><td>Up</td><td></td><td>undetermined</td><td>Silver et al. (1983)</td></tr><tr><td>Seram</td><td>1</td><td></td><td></td><td>C</td><td></td><td></td><td>undetermined</td><td>Silver et al. (1983)</td></tr><tr><td>South Manila 14 - 16.7°N</td><td>0.4</td><td>0.4</td><td>0.6</td><td>C</td><td>Up</td><td></td><td>undetermined</td><td>Pairault et al. (2003)</td></tr><tr><td>North Manila 17 - 24°N</td><td>2</td><td>0</td><td>2</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Hayes and Lewis (1984)</td></tr><tr><td>South Ryukyu 122.5 - 123.1°E</td><td>4.3</td><td>1.1</td><td>3.2</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Ku and Hsu (2009)</td></tr><tr><td>Ryukyu 124 - 133°E</td><td>0.4</td><td>0</td><td>0.4</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Schnürle et al. (1998), Lallemand et al. (1999), Font et Lallemand (2009)</td></tr><tr><td rowspan="10">SE-ASIA</td><td>Nankai</td><td>1.6</td><td>0.6</td><td>1</td><td>C</td><td>Su</td><td></td><td>accretional</td><td>Nishizawa et al. (2017), Okamura et al. (2017)</td></tr><tr><td>Izu-Bonin-North Mariana 19 - 33°N</td><td>0.3</td><td>0.6</td><td>-0.1</td><td>C</td><td>Up</td><td>x</td><td>accretional</td><td>Park et al. (2000), Kodaira et al. (2002)</td></tr><tr><td>Mariana 16.4 - 17.9°N</td><td>0.5</td><td>0.6</td><td>-0.1</td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Takahashi et al. (1998)</td></tr><tr><td>South Mariana 10.8 - 16.2°N</td><td>0.3</td><td>0.4</td><td>-0.1</td><td>E</td><td>Su</td><td>x</td><td>accretional</td><td>Oakley et al. (2008)</td></tr><tr><td>Yap-Palau</td><td>0.2</td><td></td><td></td><td>C/E</td><td></td><td></td><td>accretional</td><td>Oakley et al. (2008), Ribeiro et al. (2013)</td></tr><tr><td>North New-Hebrides 12 - 17.2°S</td><td>1.6</td><td>1.6</td><td>0</td><td>C/E</td><td>Up</td><td></td><td>accretional</td><td>Yang et al. (2018), Dong et al. (2018), Zhang et al. (2019)</td></tr><tr><td>South New-Hebrides 17.5 - 23°S</td><td>0.4</td><td>1.6</td><td>-1.2</td><td>E</td><td>Su</td><td></td><td>accretional</td><td>Colot et al. (1985, 1992), Fisher et al. (1986, 1991)</td></tr><tr><td>Tonga</td><td>0.4</td><td>0</td><td>0.4</td><td>E</td><td>Su</td><td>x</td><td>accretional</td><td>Fisher et al. (1986)</td></tr><tr><td>Kermadec 26.7 - 37.1°S</td><td>0.5</td><td>0</td><td>0.5</td><td>E</td><td>Su</td><td>x</td><td>accretional</td><td>Contreras-Reyes et al. (2011), Stratford et al. (2015)</td></tr><tr><td>North Hikurangi 37.8 - 39°S</td><td>1.1</td><td>0</td><td>1.1</td><td>C/E</td><td>Su</td><td></td><td>accretional</td><td>Funnell et al. (2017), Stratford et al. (2015)</td></tr><tr><td>North Hikurangi 39.1 - 42.3°S</td><td>4.4</td><td>1</td><td>3.4</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Schernath et al. (2010), Gase et al. (2021)</td></tr><tr><td>North Puyssegur 45.2 - 45.7°S</td><td>2.7</td><td>0.4</td><td>2.3</td><td>C</td><td></td><td></td><td>accretional</td><td>Barker et al. (2009), Gase et al. (2021, 2022)</td></tr><tr><td rowspan="2">SW-PAC</td><td>South Puyssegur 46 - 49°S</td><td>1.4</td><td>1.2</td><td>0.2</td><td>C</td><td>Up</td><td></td><td>accretional</td><td>Lebrun et al. (2000), Lamarche et Lebrun (2000)</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>undetermined</td><td>Colot et al. (1995)</td></tr></tbody></table>

Trench segments by region (MED = Mediterranean, MAK = Makran, N-PAC = North Pacific, CARIBBEANS, S-AMERICA = Andes and S-Sandwich, SE-ASIA = Philippine Sea and Sunda, SW-PAC = Southwest Pacific) were firstly defined according to margin type MT, then sediment thickness at trench $T_{sed}$ and finally sediment thickness below the plate boundary $T_{channel}$, each of them showing little variations within a given trench segment. Mean thickness values are reported in km for each segment.

$T_{sed} - T_{channel}$. As the spacing between seismic profiles is extremely variable from one region to another, from less than 1 km to over 100 km, we plotted the average of $T_{sed}$ and $T_{sed}^*$ or $T_{channel}$ and $T_{channel}^*$ values as a colored bar every km, perpendicular to the trench, within a sliding window of 100 km along the trench. In other words, empty sectors mean that no values could be measured or estimated at a distance of less than 50 km.

Figure 5 and Table 2 show that we now have an almost complete coverage of $T_{sed}$ and less coverage of $T_{channel}$. Generally speaking, and with rare

exceptions, an excess of sediment in the channel in relation to the thickness of the incoming section highlights the erosive nature of the margin. Positive $T_{sed} - T_{channel}$ values, reflecting frontal accretion, are sometimes associated with margins with a dominant erosive character (e.g., Central Aleutians 179-187.4°E, Colombia 1.7-3.5°N, North Hikurangi 37.8-39°S). Most of the time, this is due to a bias in $T_{channel}$ estimation, when its measurement could only be carried out at a short distance from the trench and is not corrected for compaction. For this reason, this value should be used with caution.
<figure><img src="image_7.png" /></figure>

**Figure 5.** Close-up view of margin type and related mean sediment thickness available at trench and within the subduction channel in the North Pacific area. Total sediment thickness in the trench $T_{sed}$ is plotted in yellow to green colors seaward of the trench axis at the resolution of available MCS data. Landward of the trench axis, we plotted the difference in thickness between the incoming sediments and those of the subduction channel $T_{sed}-T_{channel}$. Blue colors mean that the upper part of trench sediment is offscrapped to build the accretionary wedge like off Kamtchatka, whereas red colors mean that the thickness of the subduction channel exceeds those of the entering section like off Tohoku (NE Japan). EUR: Eurasian plate. NAM: North American plate. PAC: Pacific plate.

At the world scale (Figure 6), we observe that thin trench fill, typically less than 0.8 km, often faces erosive margins (South Kuril Islands, NE Japan, Izu-Bonin-Mariana, Ryukyu, Java, Northern Lesser Antilles, Northern Andes, Tonga-Kermadec, New-Hebrides) and thick trench fill, typically more than 0.8 km, often faces accreting margins (Nankai, Manila, Sumatra-Andaman, Alaska, Cascadia, South-ern Lesser Antilles, Panama-Venezuela, Hikurangi, Makran or Mediterranean). However, there are some exceptions to this association, such as Northern Kuril-Kamtchatka where accretionary processes may prevail while $T_{sed}$ does not exceed 0.7 km [Gnibidenko et al., 1983, Klaeschen et al., 1994, Baranov et al., 2022]. We classified the Colombia margin as subject to subduction erosion while mean $T_{sed}$ between 1.7°N and 3.5°S is 3.3 km and mean $T_{channel}$ is 1.4 km. According to Collot et al. [2008], coeval basal erosion of the outer wedge proceeds pervasively together with deeper underplating with a balance in favor of erosion over the mid-term. Splay faults are activated as new plate boundaries as margin slices are progressively dragged down the

subduction zone. As described above, despite the 2 km sediment thickness in the trench in the central Aleutians between 179 and 187.4°E, the recent landward migration of the arc as well as the composition of the lavas argues for deep tectonic erosion [Jicha and Kay, 2018]. South Chile, between 39 and 53°S, North New-Hebrides, between 12 and 17.2°S, South Puysegur, between 46 and 49°S, Hispaniola and Puerto-Rico combine trench sediment thicknesses more than 1.4 km, thick subduction channels (≥1.2 km) and typical characteristics of erosive margins (narrow, steep, sometimes extensional).

We observe large variations of $T_{sed}$ from one trench to another: 0.54 ± 0.4 km from NE Japan to Kamtchatka, 1.98 ± 1.0 km along the Aleutians-Alaska or 3.27 ± 0.5 km off Cascadia, but also from one profile to the adjacent one, even at short spacing interval like in the central Aleutians for example. Significant local variations in sediment thickness along the trenches are often due to major offsets in the subducting basement, linked to the presence of seamounts or fracture zones, for example.
<figure><img src="image_8.png" /><figcaption>**Figure 5.** Close-up view of margin type and related mean sediment thickness available at trench and within the subduction channel in the North Pacific area. Total sediment thickness in the trench *T*<sub>sed</sub> is plotted in yellow to green colors seaward of the trench axis at the resolution of available MCS data. Landward of the trench axis, we plotted the difference in thickness between the incoming sediments and those of the subduction channel *T*<sub>sed</sub>–*T*<sub>channel</sub>. Blue colors mean that the upper part of trench sediment is offscrapped to build the accretionary wedge like off Kamtchatka, whereas red colors mean that the thickness of the subduction channel exceeds those of the entering section like off Tohoku (NE Japan). EUR: Eurasian plate. NAM: North American plate. PAC: Pacific plate.</figcaption></figure>

At the world scale (Figure 6), we observe that thin trench fill, typically less than 0.8 km, often faces erosive margins (South Kuril Islands, NE Japan, Izu-Bonin-Mariana, Ryukyu, Java, Northern Lesser Antilles, Northern Andes, Tonga-Kermadec, New-Hebrides) and thick trench fill, typically more than 0.8 km, often faces accreting margins (Nankai, Manila, Sumatra-Andaman, Alaska, Cascadia, South-ern Lesser Antilles, Panama-Venezuela, Hikurangi, Makran or Mediterranean). However, there are some exceptions to this association, such as Northern Kuril-Kamtchatka where accretionary processes may prevail while *T*<sub>sed</sub> does not exceed 0.7 km [Gnibidenko et al., 1983, Klaeschen et al., 1994, Baranov et al., 2022]. We classified the Colombia margin as subject to subduction erosion while mean *T*<sub>sed</sub> between 1.7°N and 3.5°S is 3.3 km and mean *T*<sub>channel</sub> is 1.4 km. According to Collot et al. [2008], coeval basal erosion of the outer wedge proceeds pervasively together with deeper underplating with a balance in favor of erosion over the mid-term. Splay faults are activated as new plate boundaries as margin slices are progressively dragged down the

subduction zone. As described above, despite the 2 km sediment thickness in the trench in the central Aleutians between 179 and 187.4°E, the recent landward migration of the arc as well as the composition of the lavas argues for deep tectonic erosion [Jicha and Kay, 2018]. South Chile, between 39 and 53°S, North New-Hebrides, between 12 and 17.2°S, South Puysegur, between 46 and 49°S, Hispaniola and Puerto-Rico combine trench sediment thicknesses more than 1.4 km, thick subduction channels (≥1.2 km) and typical characteristics of erosive margins (narrow, steep, sometimes extensional).

We observe large variations of *T*<sub>sed</sub> from one trench to another: 0.54 ± 0.4 km from NE Japan to Kamtchatka, 1.98 ± 1.0 km along the Aleutians-Alaska or 3.27 ± 0.5 km off Cascadia, but also from one profile to the adjacent one, even at short spacing interval like in the central Aleutians for example. Significant local variations in sediment thickness along the trenches are often due to major offsets in the subducting basement, linked to the presence of seamounts or fracture zones, for example.
<figure><img src="image_8.png" /></figure>

**Figure 6.** Margin type and related mean sediment thickness available at trench and within the subduction channel around the world except the North Pacific area. See also explanations in legend of Figure 5. AFR = Africa plate, ANT = Antarctica plate, ARA = Arabia plate, COC = Cocos plate, IND = India plate, NAZ = Nazca plate, PHS = Philippine Sea plate, SAM = South America plate, SCO = Scotia plate.

### 5.3. Volumes of solid and fluid transiting through the subduction channel

The large number of observations taken along most of the subduction zones enables us to update estimates of solid and fluid fluxes through the subduction channel. In order to compare our results with those proposed by von Huene and Scholl [1991], we attempted to use a similar approach. First, we determined the solid and liquid fraction of the subducted sedimentary section on the basis of average porosity (see Section 4). The major differences, apart from the quantity of data analyzed, consist in measuring the thickness of the channel at an average dis-

tance of ~15 km from the deformation front, taking into account compaction in the channel, updating subduction velocities and sometimes differences in trench length (see Supplementary Material for details on the procedure). We then estimated material fluxes per km of trench in areas where we had Tchannel values, and extrapolated these data along the subduction zone. In the absence of constraints on a given subduction zone, such as the Sunda region north of Australia, New Britain and the Solomons, Izu-Bonin, Yap-Palau, Puerto-Rico, Panama, Hjort or South Sandwich, we did not provide estimates. The details of the calculations are provided in the Supplementary material (Table S2) and average porosities
<figure><img src="image_9.png" /><figcaption>**Figure 6.** Margin type and related mean sediment thickness available at trench and within the subduction channel around the world except the North Pacific area. See also explanations in legend of Figure 5. AFR = Africa plate, ANT = Antarctica plate, ARA = Arabia plate, COC = Cocos plate, IND = India plate, NAZ = Nazca plate, PHS = Philippine Sea plate, SAM = South America plate, SCO = Scotia plate.</figcaption></figure>

### 5.3. Volumes of solid and fluid transiting through the subduction channel

The large number of observations taken along most of the subduction zones enables us to update estimates of solid and fluid fluxes through the subduction channel. In order to compare our results with those proposed by von Huene and Scholl [1991], we attempted to use a similar approach. First, we determined the solid and liquid fraction of the subducted sedimentary section on the basis of average porosity (see Section 4). The major differences, apart from the quantity of data analyzed, consist in measuring the thickness of the channel at an average dis-

tance of ~15 km from the deformation front, taking into account compaction in the channel, updating subduction velocities and sometimes differences in trench length (see Supplementary Material for details on the procedure). We then estimated material fluxes per km of trench in areas where we had Tchannel values, and extrapolated these data along the subduction zone. In the absence of constraints on a given subduction zone, such as the Sunda region north of Australia, New Britain and the Solomons, Izu-Bonin, Yap-Palau, Puerto-Rico, Panama, Hjort or South Sandwich, we did not provide estimates. The details of the calculations are provided in the Supplementary material (Table S2) and average porosities
and fluxes values per km of constrained trench and per trench are given in Table 3.

Our results show very strong variations from one subduction zone to another, between sectors where fluxes are gigantic, as in the Aegean, Central America, Chile, New Hebrides and Aleutians, and sectors where fluxes are negligible, as in the Andaman- Sumatra, Ryukyus or Tonga-Kermadec zones. We also note that pore water fluxes are certainly also significant in the same regions where solid fluxes are important, but not in the same proportions. For example, most of the water flowing through the subduction channel is concentrated under Central America, Peru-Chile, and under the New Hebrides, Kuril Islands and Aleutians. In particular, the Aegean subduction zone is characterized by the largest solid flow for a very small fluid flow. On the basis of 70% cumulative trench length, we estimate that every million of years for the past few million years, 1463 km³ and 396 km³ of solid sediment and pore water respectively have been transiting through the subduction channel, having subducted some ~15 km from the deformation front. In Table 3, we report the values obtained by von Huene and Scholl [1991], bearing in mind that they only provided solid fluxes based on the porosity of the sediment column estimated at the trench. Surprisingly, in the end, we arrive at the same order of magnitude for solid flux, i.e. 1.5 km³/yr along 70% of the subduction zones. In detail, we can see large discrepancies with our estimates (e.g., Aegean, Japan, Central America, Ryukyus, Nankai, New Hebrides, Cascadia, Andaman, Sumatra, Tonga, Kermadec), which can be explained by the smaller number of constrained transects more than 30 years ago, but also by the fact that we have taken into account the first stages of compaction.

# 6. Discussion

## 6.1. *T<sub>sed</sub> and T<sub>channel</sub> may be decorrelated*

We have reported the values of Table 2, mean T<sub>sed</sub>, mean T<sub>channel</sub> and margin type MT for each trench segment, on a diagram (Figure 8) after sorting the trench segments, first based on their associated MT and second based on decreasing T<sub>sed</sub>.

Although not all trench segments have information on the thickness of sediment in the subduction

channel, we note that, apart from the major accretionary prisms: Mediterranean, Makran or Southern Lesser Antilles, there is no obvious correspondence or proportionality between the thickness of incoming sediment and that of the channel. However, we note that T<sub>channel</sub> is systematically lower than T<sub>sed</sub> in accreting margins, whereas it is more or less close to T<sub>sed</sub> in eroding margins. This diagram provides information primarily on the thickness of frontally accreted sediment or, on the contrary, the material removed from the prism (subcrustal erosion) that feeds the subduction channel at the front of the prism where it can still be imaged seismically. Even if, overall, the erosive margins are characterized by a small gap between T<sub>sed</sub> and T<sub>channel</sub>, we can see that frontal accretion is carried over along some trench segments, such as in southern Colombia, central Aleutians, Kermadec or the Ryukyus. This means that deep subcrustal erosion of the margin exceeds frontal accretion in these areas.

## 6.2. Porosity variations in the subduction channel

The sediment porosity in the subduction channel Φ<sub>channel</sub> depends on those of the incoming sequence (beneath the accreted sequence in case of frontal accretion, Φ<sub>sed_base</sub>), a porosity reduction factor K<sub>r</sub>, and the porosity Φ<sub>ero</sub> of the material subcrustally eroded from the margin (in case of erosion). Assuming K<sub>r</sub> = 0.85 and Φ<sub>ero</sub> = 5%, it is possible to express Φ<sub>channel</sub> as a function of T<sub>sed</sub> and T<sub>channel</sub> (see Section 4 and Supplementary Material). Figure 9 shows that maximum porosities are obtained close to the threshold value where T<sub>channel</sub> = T<sub>sed_co</sub> is represented by the straight line. The values obtained on the 116 constrained transects are plotted on the diagram, with triangles representing cases with frontal accretion (below the threshold line) and dots representing cases with erosion (above the threshold line). A wide dispersion can be observed, reflecting the variety of thicknesses in the trench T<sub>sed</sub> as well as those in the channel T<sub>channel</sub>, but on average, porosities are slightly higher for erosive margins, despite the fact that some of the subducted material only has a porosity of 5%. This is because the entire sequence at the trench is subducted under erosive conditions, and the upper part of the sequence at the trench also has the highest porosity.
and fluxes values per km of constrained trench and per trench are given in Table 3.

Our results show very strong variations from one subduction zone to another, between sectors where fluxes are gigantic, as in the Aegean, Central America, Chile, New Hebrides and Aleutians, and sectors where fluxes are negligible, as in the Andaman- Sumatra, Ryukyus or Tonga-Kermadec zones. We also note that pore water fluxes are certainly also significant in the same regions where solid fluxes are important, but not in the same proportions. For example, most of the water flowing through the subduction channel is concentrated under Central America, Peru-Chile, and under the New Hebrides, Kuril Islands and Aleutians. In particular, the Aegean subduction zone is characterized by the largest solid flow for a very small fluid flow. On the basis of 70% cumulative trench length, we estimate that every million of years for the past few million years, 1463 km³ and 396 km³ of solid sediment and pore water respectively have been transiting through the subduction channel, having subducted some ~15 km from the deformation front. In Table 3, we report the values obtained by von Huene and Scholl [1991], bearing in mind that they only provided solid fluxes based on the porosity of the sediment column estimated at the trench. Surprisingly, in the end, we arrive at the same order of magnitude for solid flux, i.e. 1.5 km³/yr along 70% of the subduction zones. In detail, we can see large discrepancies with our estimates (e.g., Aegean, Japan, Central America, Ryukyus, Nankai, New Hebrides, Cascadia, Andaman, Sumatra, Tonga, Kermadec), which can be explained by the smaller number of constrained transects more than 30 years ago, but also by the fact that we have taken into account the first stages of compaction.

# 6. Discussion

## 6.1. *T<sub>sed</sub> and T<sub>channel</sub> may be decorrelated*

We have reported the values of Table 2, mean T<sub>sed</sub>, mean T<sub>channel</sub> and margin type MT for each trench segment, on a diagram (Figure 8) after sorting the trench segments, first based on their associated MT and second based on decreasing T<sub>sed</sub>.

Although not all trench segments have information on the thickness of sediment in the subduction

channel, we note that, apart from the major accretionary prisms: Mediterranean, Makran or Southern Lesser Antilles, there is no obvious correspondence or proportionality between the thickness of incoming sediment and that of the channel. However, we note that T<sub>channel</sub> is systematically lower than T<sub>sed</sub> in accreting margins, whereas it is more or less close to T<sub>sed</sub> in eroding margins. This diagram provides information primarily on the thickness of frontally accreted sediment or, on the contrary, the material removed from the prism (subcrustal erosion) that feeds the subduction channel at the front of the prism where it can still be imaged seismically. Even if, overall, the erosive margins are characterized by a small gap between T<sub>sed</sub> and T<sub>channel</sub>, we can see that frontal accretion is carried over along some trench segments, such as in southern Colombia, central Aleutians, Kermadec or the Ryukyus. This means that deep subcrustal erosion of the margin exceeds frontal accretion in these areas.

## 6.2. Porosity variations in the subduction channel

The sediment porosity in the subduction channel Φ<sub>channel</sub> depends on those of the incoming sequence (beneath the accreted sequence in case of frontal accretion, Φ<sub>sed_base</sub>), a porosity reduction factor K<sub>r</sub>, and the porosity Φ<sub>ero</sub> of the material subcrustally eroded from the margin (in case of erosion). Assuming K<sub>r</sub> = 0.85 and Φ<sub>ero</sub> = 5%, it is possible to express Φ<sub>channel</sub> as a function of T<sub>sed</sub> and T<sub>channel</sub> (see Section 4 and Supplementary Material). Figure 9 shows that maximum porosities are obtained close to the threshold value where T<sub>channel</sub> = T<sub>sed_co</sub> is represented by the straight line. The values obtained on the 116 constrained transects are plotted on the diagram, with triangles representing cases with frontal accretion (below the threshold line) and dots representing cases with erosion (above the threshold line). A wide dispersion can be observed, reflecting the variety of thicknesses in the trench T<sub>sed</sub> as well as those in the channel T<sub>channel</sub>, but on average, porosities are slightly higher for erosive margins, despite the fact that some of the subducted material only has a porosity of 5%. This is because the entire sequence at the trench is subducted under erosive conditions, and the upper part of the sequence at the trench also has the highest porosity.
<figure><img src="image_9.png" /></figure>

**Figure 7.** Map of solid (sediment) and fluid (pore water) fluxes estimated from the solid and fluid fractions of the subduction channel, having travelled approximately 15 km from the deformation front, by subduction zone in thousands of km³ per million years.

<figure><img src="image_10.png" /></figure>

**Figure 8.** Diagram sorting the trench segments first as a function of margin type (grey domains) and second as a function of decreasing T<sub>sed</sub> mean values (blue dots and curve). Superimposed are the T<sub>channel</sub> mean values (orange) when available. Note that T<sub>channel</sub> is often equal or larger than T<sub>sed</sub> for dominantly erosive trench segments.
<figure><img src="image_10.png" /></figure>

**Figure 7.** Map of solid (sediment) and fluid (pore water) fluxes estimated from the solid and fluid fractions of the subduction channel, having travelled approximately 15 km from the deformation front, by subduction zone in thousands of km³ per million years.

<figure><img src="image_11.png" /></figure>

**Figure 8.** Diagram sorting the trench segments first as a function of margin type (grey domains) and second as a function of decreasing T<sub>sed</sub> mean values (blue dots and curve). Superimposed are the T<sub>channel</sub> mean values (orange) when available. Note that T<sub>channel</sub> is often equal or larger than T<sub>sed</sub> for dominantly erosive trench segments.
<table><caption>**Table 3.** Mean porosities Φ<sub>sed</sub> and Φ<sub>channel</sub> and solid and fluid fluxes dragged into the subduction channel per km of trench and extrapolated per trench</caption><thead><tr><th rowspan="3">Trench name</th><th rowspan="3">Trench length (km)</th><th colspan="5">This study</th><th colspan="4">von Huene & Scholl (1991)</th></tr><tr><th rowspan="2">Mean porosity in the trench fill at deformation front Φsed</th><th rowspan="2">Mean porosity in the channel 15 km landward of deformation front Φchannel</th><th rowspan="2">Estimated fraction subducted km3/m.y./km of constrained trench</th><th rowspan="2">Extrapolated fraction subducted x1000 km3/m.y./trench</th><th rowspan="2">Estimated fraction subducted km3/m.y./km of constrained trench</th><th rowspan="2">Extrapolated fraction subducted x1000 km3/m.y./trench</th><th rowspan="2">Mean porosity in the trench fill at deformation front</th><th rowspan="2">Estimated fraction subducted km3/m.y./km of trench</th><th rowspan="2">Extrapolated fraction subducted x1000 km3/m.y./trench</th></tr><tr><th colspan="2">solid</th><th colspan="2">fluid</th></tr></thead><tbody><tr><td>Calabria</td><td>600</td><td>22.3</td><td>13.9</td><td>23.6</td><td>14.1</td><td>4.0</td><td>2.4</td><td></td><td></td><td></td></tr><tr><td>Aegean -Cyprean</td><td>1800</td><td>17.2</td><td>7.7</td><td>153.9</td><td>277.0</td><td>12.3</td><td>22.1</td><td>24.0</td><td>66.7</td><td>100.0</td></tr><tr><td>Makran</td><td>600</td><td>21.8</td><td>12.5</td><td>97.4</td><td>58.4</td><td>14.4</td><td>8.6</td><td>22.5</td><td>113.7</td><td>108.0</td></tr><tr><td>Japan</td><td>700</td><td>53.7</td><td>15.8</td><td>111.4</td><td>77.9</td><td>20.1</td><td>14.1</td><td>46.3</td><td>36.3</td><td>29.0</td></tr><tr><td>Kurils - Kamtchatka</td><td>2150</td><td>50.2</td><td>37.3</td><td>26.0</td><td>56.0</td><td>15.3</td><td>32.8</td><td>40.0</td><td>21.8</td><td>48.0</td></tr><tr><td>C- W-Aleutians</td><td>2300</td><td>35.1</td><td>25.4</td><td>70.6</td><td>162.5</td><td>24.0</td><td>55.1</td><td>33.0</td><td>65.6</td><td>177.0</td></tr><tr><td>Alaska</td><td>1500</td><td>34.8</td><td>24.6</td><td>52.8</td><td>79.1</td><td>16.8</td><td>25.2</td><td></td><td></td><td></td></tr><tr><td>Vancouver</td><td>400</td><td>29.3</td><td>17.3</td><td>13.0</td><td>5.2</td><td>3.3</td><td>1.3</td><td>33.0</td><td>32.5</td><td>13.0</td></tr><tr><td>Cascadia</td><td>850</td><td>27.4</td><td>17.1</td><td>16.9</td><td>14.4</td><td>3.5</td><td>3.0</td><td>33.0</td><td>37.8</td><td>34.0</td></tr><tr><td>Central America</td><td>3500</td><td>47.1</td><td>29.5</td><td>43.0</td><td>150.5</td><td>16.9</td><td>62.5</td><td>43.1</td><td>20.0</td><td>58.0</td></tr><tr><td>N-Panama</td><td>700</td><td>33.4</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>S-Caribbeans</td><td>1700</td><td>30.3</td><td>21.1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Muertos</td><td>700</td><td>44.0</td><td>30.5</td><td>0.7</td><td>0.5</td><td>0.3</td><td>0.2</td><td></td><td></td><td></td></tr><tr><td>Hispaniola - PRVI</td><td>700</td><td>35.6</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Lesser Antilles</td><td>1500</td><td>42.7</td><td>24.8</td><td>13.1</td><td>19.6</td><td>2.7</td><td>4.1</td><td>31.0</td><td>23.8</td><td>19.0</td></tr><tr><td>Colombia</td><td>600</td><td>34.7</td><td>22.2</td><td>22.6</td><td>13.5</td><td>5.9</td><td>3.5</td><td>36.7</td><td>53.3</td><td>56.0</td></tr><tr><td>Ecuador</td><td>450</td><td>57.1</td><td>21.6</td><td>25.1</td><td>11.3</td><td>7.0</td><td>3.2</td><td>42.0</td><td>46.7</td><td>70.0</td></tr><tr><td>Peru</td><td>2200</td><td>48.8</td><td>24.9</td><td>40.9</td><td>90.0</td><td>12.5</td><td>27.5</td><td>36.7</td><td>30.7</td><td>135.0</td></tr><tr><td>Chile</td><td>4350</td><td>43.8</td><td>21.8</td><td>44.7</td><td>194.5</td><td>12.2</td><td>53.0</td><td>40.0</td><td>5.0</td><td>4.0</td></tr><tr><td>S-Sandwich</td><td>1100</td><td>45.5</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Andaman</td><td>1000</td><td>29.5</td><td></td><td>0.0</td><td>0.0</td><td>0.0</td><td>0.0</td><td>24.0</td><td>80.0</td><td>120.0</td></tr><tr><td>Sumatra</td><td>2150</td><td>36.3</td><td>28.9</td><td>3.0</td><td>6.4</td><td>1.3</td><td>2.7</td><td></td><td>46.8</td><td>96.0</td></tr><tr><td>Java</td><td>1350</td><td>40.7</td><td>23.6</td><td>33.3</td><td>45.0</td><td>10.3</td><td>13.9</td><td>36.7</td><td>56.9</td><td>37.0</td></tr><tr><td>Timor</td><td>500</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Flores</td><td>570</td><td>39.9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Wetar</td><td>350</td><td>45.7</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Banda incl. Seram</td><td>2000</td><td></td><td></td><td></td><td></td><td></td><td></td><td>33.0</td><td>46.8</td><td>96.0</td></tr><tr><td>Halmahera</td><td>700</td><td></td><td></td><td></td><td></td><td></td><td></td><td>42.0</td><td>13.3</td><td>8.0</td></tr><tr><td>North Sulawesi</td><td>440</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Sangihe</td><td>1300</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>East-Luzon</td><td>300</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Philippines</td><td>1380</td><td>54.8</td><td></td><td></td><td></td><td></td><td></td><td>40.0</td><td>21.3</td><td>33.0</td></tr><tr><td>Cotobato</td><td>380</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Sulu</td><td>200</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Manila</td><td>1200</td><td>35.5</td><td>27.5</td><td>10.3</td><td>12.3</td><td>4.2</td><td>5.0</td><td>36.7</td><td>6.7</td><td>7.0</td></tr><tr><td>Ryukus incl. W-Gagua</td><td>1600</td><td>47.6</td><td>15.3</td><td>2.6</td><td>4.2</td><td>0.5</td><td>0.8</td><td></td><td>14.1</td><td>19.0</td></tr><tr><td>Nankai</td><td>400</td><td>38.0</td><td>25.2</td><td>8.1</td><td>3.3</td><td>2.7</td><td>1.1</td><td>36.7</td><td>22.5</td><td>18.0</td></tr><tr><td>Izu-Bonin</td><td>1000</td><td>57.7</td><td></td><td></td><td></td><td></td><td></td><td>40.0</td><td>25.0</td><td>25.0</td></tr><tr><td>Mariana</td><td>2400</td><td>55.9</td><td>34.9</td><td>19.8</td><td>47.5</td><td>10.5</td><td>25.2</td><td>40.0</td><td>21.7</td><td>52.0</td></tr><tr><td>Yap</td><td>600</td><td>60.1</td><td></td><td></td><td></td><td></td><td></td><td>40.0</td><td>5.5</td><td>3.0</td></tr><tr><td>Palau</td><td>220</td><td>60.1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Trobriand</td><td>650</td><td></td><td></td><td></td><td></td><td></td><td></td><td>33.0</td><td>21.5</td><td>14.0</td></tr><tr><td>New Britain</td><td>550</td><td>44.9</td><td></td><td></td><td></td><td></td><td></td><td>42.0</td><td>51.1</td><td>46.0</td></tr><tr><td>Solomons</td><td>1850</td><td>53.8</td><td></td><td></td><td></td><td></td><td></td><td>40.0</td><td>26.7</td><td>28.0</td></tr><tr><td>New Hebrides</td><td>1250</td><td>49.5</td><td>23.5</td><td>83.8</td><td>104.7</td><td>20.6</td><td>25.8</td><td>40.0</td><td>23.9</td><td>43.0</td></tr><tr><td>Tonga</td><td>1250</td><td>57.7</td><td></td><td>0.0</td><td>0.0</td><td>0.0</td><td>0.0</td><td>40.0</td><td>40.7</td><td>55.0</td></tr><tr><td>Kermadec</td><td>1500</td><td>54.3</td><td></td><td>0.0</td><td>0.0</td><td>0.0</td><td>0.0</td><td>40.0</td><td>17.1</td><td>24.0</td></tr><tr><td>Hikurangi</td><td>650</td><td>30.9</td><td>13.5</td><td>14.4</td><td>9.3</td><td>2.4</td><td>1.6</td><td>33.0</td><td>31.7</td><td>19.0</td></tr><tr><td>Puysegur</td><td>500</td><td>42.5</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Macquarie</td><td>200</td><td></td><td></td><td></td><td></td><td></td><td></td><td>40.0</td><td>6.0</td><td>3.0</td></tr><tr><td>Hjort</td><td>550</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Sums</td><td>57390</td><td></td><td></td><td></td><td>1457.4</td><td></td><td>394.6</td><td></td><td></td><td>1597.0</td></tr></tbody></table>

The last 3 columns are values of Φ<sub>sed</sub> and material fluxes reported from von Huene and Scholl [1991] for comparison, given that the mode of calculations slightly differs (see main text).

## 6.3. Solid and fluid volumes dragged at depth within the subduction channel

Given that we only estimate the volumes of solid or fluid transiting through the shallow subduction

channel, and therefore do not predict transfers between the margin and the subducting plate that may occur deeper down, we have nevertheless updated previous estimates. Our first observation is that T<sub>channel</sub> determines the volume of subducted ma-
<table><caption>**Table 3.** Mean porosities Φ<sub>sed</sub> and Φ<sub>channel</sub> and solid and fluid fluxes dragged into the subduction channel per km of trench and extrapolated per trench</caption><thead><tr><th rowspan="3">Trench name</th><th rowspan="3">Trench length (km)</th><th colspan="6">This study</th><th colspan="3">von Huene & Scholl (1991)</th></tr><tr><th rowspan="2">Mean porosity in the trench fill at deformation front Φsed</th><th rowspan="2">Mean porosity in the channel 15 km landward of deformation front Φchannel</th><th colspan="2">Estimated fraction subducted km3/m.y./km of constrained trench</th><th colspan="2">Estimated fraction subducted km3/m.y./km of constrained trench</th><th rowspan="2">Mean porosity in the trench fill at deformation front</th><th rowspan="2">Estimated fraction subducted km3/m.y./km of trench</th><th rowspan="2">Extrapolated fraction subducted km3/m.y./trench</th></tr><tr><th>solid</th><th>fluid</th><th>solid</th><th>fluid</th></tr></thead><tbody><tr><td>Calabria</td><td>600</td><td>22.3</td><td>13.9</td><td>23.6</td><td>14.1</td><td>4.0</td><td>2.4</td><td></td><td></td><td></td></tr><tr><td>Aegean - Cyprean</td><td>1800</td><td>17.2</td><td>7.7</td><td>153.9</td><td>277.0</td><td>12.3</td><td>22.1</td><td>24.0</td><td>66.7</td><td>100.0</td></tr><tr><td>Makran</td><td>600</td><td>21.8</td><td>12.5</td><td>97.4</td><td>58.4</td><td>14.4</td><td>8.6</td><td>22.5</td><td>113.7</td><td>108.0</td></tr><tr><td>Japan</td><td>700</td><td>53.7</td><td>15.8</td><td>111.4</td><td>77.9</td><td>20.1</td><td>14.1</td><td>46.3</td><td>36.3</td><td>29.0</td></tr><tr><td>Kurils - Kamtchatka</td><td>2150</td><td>50.2</td><td>37.3</td><td>26.0</td><td>56.0</td><td>15.3</td><td>32.8</td><td>40.0</td><td>21.8</td><td>48.0</td></tr><tr><td>C- W-Aleutians</td><td>2300</td><td>35.1</td><td>25.4</td><td>70.6</td><td>162.5</td><td>24.0</td><td>55.1</td><td>33.0</td><td>65.6</td><td>177.0</td></tr><tr><td>Alaska</td><td>1500</td><td>34.8</td><td>24.6</td><td>52.8</td><td>79.1</td><td>16.8</td><td>25.2</td><td></td><td></td><td></td></tr><tr><td>Vancouver</td><td>400</td><td>29.3</td><td>17.3</td><td>13.0</td><td>5.2</td><td>3.3</td><td>1.3</td><td>33.0</td><td>32.5</td><td>13.0</td></tr><tr><td>Cascadia</td><td>850</td><td>27.4</td><td>17.1</td><td>16.9</td><td>14.4</td><td>3.5</td><td>3.0</td><td>33.0</td><td>37.8</td><td>34.0</td></tr><tr><td>Central America</td><td>3500</td><td>47.1</td><td>29.5</td><td>43.0</td><td>150.5</td><td>16.9</td><td>62.5</td><td>43.1</td><td>20.0</td><td>58.0</td></tr><tr><td>N-Panama</td><td>700</td><td>33.4</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>S-Caribbeans</td><td>1700</td><td>30.3</td><td>21.1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Muertos</td><td>700</td><td>44.0</td><td>30.5</td><td>0.7</td><td>0.5</td><td>0.3</td><td>0.2</td><td></td><td></td><td></td></tr><tr><td>Hispaniola - PRVI</td><td>700</td><td>35.6</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Lesser Antilles</td><td>1500</td><td>42.7</td><td>24.8</td><td>13.1</td><td>19.6</td><td>2.7</td><td>4.1</td><td>31.0</td><td>23.8</td><td>19.0</td></tr><tr><td>Colombia</td><td>600</td><td>34.7</td><td>22.2</td><td>22.6</td><td>13.5</td><td>5.9</td><td>3.5</td><td>36.7</td><td>53.3</td><td>56.0</td></tr><tr><td>Ecuador</td><td>450</td><td>57.1</td><td>21.6</td><td>25.1</td><td>11.3</td><td>7.0</td><td>3.2</td><td>42.0</td><td>46.7</td><td>70.0</td></tr><tr><td>Peru</td><td>2200</td><td>48.8</td><td>24.9</td><td>40.9</td><td>90.0</td><td>12.5</td><td>27.5</td><td>36.7</td><td>30.7</td><td>135.0</td></tr><tr><td>Chile</td><td>4350</td><td>43.8</td><td>21.8</td><td>44.7</td><td>194.5</td><td>12.2</td><td>53.0</td><td>40.0</td><td>5.0</td><td>4.0</td></tr><tr><td>S-Sandwich</td><td>1100</td><td>45.5</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Andaman</td><td>1000</td><td>29.5</td><td></td><td>0.0</td><td>0.0</td><td>0.0</td><td>0.0</td><td>24.0</td><td>80.0</td><td>120.0</td></tr><tr><td>Sumatra</td><td>2150</td><td>36.3</td><td>28.9</td><td>3.0</td><td>6.4</td><td>1.3</td><td>2.7</td><td></td><td>46.8</td><td>96.0</td></tr><tr><td>Java</td><td>1350</td><td>40.7</td><td>23.6</td><td>33.3</td><td>45.0</td><td>10.3</td><td>13.9</td><td>36.7</td><td>56.9</td><td>37.0</td></tr><tr><td>Timor</td><td>500</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Flores</td><td>570</td><td>39.9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Wetar</td><td>350</td><td>45.7</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Banda incl. Seram</td><td>2000</td><td></td><td></td><td></td><td></td><td></td><td></td><td>33.0</td><td>46.8</td><td>96.0</td></tr><tr><td>Halmahera</td><td>700</td><td></td><td></td><td></td><td></td><td></td><td></td><td>42.0</td><td>13.3</td><td>8.0</td></tr><tr><td>North Sulawesi</td><td>440</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Sangihe</td><td>1300</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>East-Luzon</td><td>300</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Philippines</td><td>1380</td><td>54.8</td><td></td><td></td><td></td><td></td><td></td><td>40.0</td><td>21.3</td><td>33.0</td></tr><tr><td>Cotobato</td><td>380</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Sulu</td><td>200</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Manila</td><td>1200</td><td>35.5</td><td>27.5</td><td>10.3</td><td>12.3</td><td>4.2</td><td>5.0</td><td>36.7</td><td>6.7</td><td>7.0</td></tr><tr><td>Ryukus incl. W-Gagua</td><td>1600</td><td>47.6</td><td>15.3</td><td>2.6</td><td>4.2</td><td>0.5</td><td>0.8</td><td></td><td>14.1</td><td>19.0</td></tr><tr><td>Nankai</td><td>400</td><td>38.0</td><td>25.2</td><td>8.1</td><td>3.3</td><td>2.7</td><td>1.1</td><td>36.7</td><td>22.5</td><td>18.0</td></tr><tr><td>Izu-Bonin</td><td>1000</td><td>57.7</td><td></td><td></td><td></td><td></td><td></td><td>40.0</td><td>25.0</td><td>25.0</td></tr><tr><td>Mariana</td><td>2400</td><td>55.9</td><td>34.9</td><td>19.8</td><td>47.5</td><td>10.5</td><td>25.2</td><td>40.0</td><td>21.7</td><td>52.0</td></tr><tr><td>Yap</td><td>600</td><td>60.1</td><td></td><td></td><td></td><td></td><td></td><td>40.0</td><td>5.5</td><td>3.0</td></tr><tr><td>Palau</td><td>220</td><td>60.1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Trobriand</td><td>650</td><td></td><td></td><td></td><td></td><td></td><td></td><td>33.0</td><td>21.5</td><td>14.0</td></tr><tr><td>New Britain</td><td>550</td><td>44.9</td><td></td><td></td><td></td><td></td><td></td><td>42.0</td><td>51.1</td><td>46.0</td></tr><tr><td>Solomons</td><td>1850</td><td>53.8</td><td></td><td></td><td></td><td></td><td></td><td>40.0</td><td>26.7</td><td>28.0</td></tr><tr><td>New Hebrides</td><td>1250</td><td>49.5</td><td>23.5</td><td>83.8</td><td>104.7</td><td>20.6</td><td>25.8</td><td>40.0</td><td>23.9</td><td>43.0</td></tr><tr><td>Tonga</td><td>1250</td><td>57.7</td><td></td><td>0.0</td><td>0.0</td><td>0.0</td><td>0.0</td><td>40.0</td><td>40.7</td><td>55.0</td></tr><tr><td>Kermadec</td><td>1500</td><td>54.3</td><td></td><td>0.0</td><td>0.0</td><td>0.0</td><td>0.0</td><td>40.0</td><td>17.1</td><td>24.0</td></tr><tr><td>Hikurangi</td><td>650</td><td>30.9</td><td>13.5</td><td>14.4</td><td>9.3</td><td>2.4</td><td>1.6</td><td>33.0</td><td>31.7</td><td>19.0</td></tr><tr><td>Puysegur</td><td>500</td><td>42.5</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Macquarie</td><td>200</td><td></td><td></td><td></td><td></td><td></td><td></td><td>40.0</td><td>6.0</td><td>3.0</td></tr><tr><td>Hjort</td><td>550</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Sums</td><td>57390</td><td></td><td></td><td></td><td>1457.4</td><td></td><td>394.6</td><td></td><td></td><td>1597.0</td></tr></tbody></table>

The last 3 columns are values of Φ<sub>sed</sub> and material fluxes reported from von Huene and Scholl [1991] for comparison, given that the mode of calculations slightly differs (see main text).

## 6.3. Solid and fluid volumes dragged at depth within the subduction channel

Given that we only estimate the volumes of solid or fluid transiting through the shallow subduction

channel, and therefore do not predict transfers between the margin and the subducting plate that may occur deeper down, we have nevertheless updated previous estimates. Our first observation is that T<sub>channel</sub> determines the volume of subducted ma-
<figure><img src="image_11.png" /></figure>

**Figure 9.** Predicted mean porosity in the subduction channel at a distance of ~15 km from the deformation front as a function of *T*<sub>sed</sub> and *T*<sub>channel</sub>. The dots (erosive margins) and triangles (accretionary margins) represent the values corresponding to the 116 transects for which we have measured both *T*<sub>channel</sub> and *T*<sub>sed</sub> (Table S2). We have also drawn the threshold line between frontal accretion and subcrustal erosion when *T*<sub>channel</sub> = *T*<sub>sed_co</sub>.

terial, whereas T_sed will have essentially an effect
on Φ_sed. Indeed, some subduction zones charac-
terized by thick trench fill like Andaman, Sumatra
or Cascadia-Vancouver are associated with very lit-
tle sediment flux. The reason is that most of the
sedimentary pile at trench is accreted frontally. The
flux of solid material dragged in depth is decorre-
lated from the subduction rate as illustrated by the
Aegean–Cyprean subduction zone which allows the
most solid sediment to pass through (Figure 7), while
the average subduction rate (normal component) is
only 27 mm/yr (Table S2). This is due to the fact
that the thickness of the incoming sediments is great
(as is the length of the trench), but as a result their
porosity is low (17.2%), as they were already com-
pacted before subducting into the channel. As a re-
sult, the volume of fluid entrained in this subduc-

tion zone is comparatively very low. Another ob-
servation is that the greatest volumes of fluid in the
channel globally subduct along erosive margins. This
may result from the combination of a larger channel
porosity and a higher subduction rate. As indicated
above (Section 5), our overall values for subducted
solid matter flux are comparable to those estimated
by von Huene and Scholl [1991]. In contrast, the vol-
ume of subducted fluid is significantly lower in our
study, mainly due to the fact that we took into ac-
count both the “pre-compaction” of incoming sedi-
ments in accretion cases and then applied a porosity
reduction factor in the channel. In the end, we ob-
tain ~0.4 km³/yr of fluids entrained in the channel
along 40,450 km of trench, whereas von Huene and
Scholl [1991] proposed ~0.8 km³/yr along 43,450 km
of trench.

6.4. *T*<sub>sed</sub> *and* *seismogenic potential along the subduction interface*

As we have already pointed out, several studies
suggest that subduction mega-earthquakes oc-
cur preferentially along opposite sediment-filled
trenches [Ruff, 1989, Heuret et al., 2012, Scholl et al.,
2015]. Geersen [2019] noted that sediment-starved
trenches and rough subducting plates are conducive
to tsunami earthquakes. As Geersen, some of the
formerly cited authors consider that T_sed alone is
not a good proxy, as the thickness of sediment over-
lying the subducting plate in the seismogenic zone
can sometimes differ quite widely from that avail-
able in the trench. Scholl et al. [2015], for example,
noted the correspondence between most M<sub>w</sub> ≥ 8.5
earthquakes and high T_sed values, but pointed out
that some M<sub>w</sub> ≥ 8.0 earthquakes could sometimes
occur along weakly sediment-filled trenches facing
erosive margins, i.e., the products of subcrustal ero-
sion thicken the subduction channel. Seno [2017]
comes to the same conclusion and then provides a
rough estimate of the correction to be made to T_sed.
As can be seen, the general idea is that interseismic
coupling seems to be stronger with a smooth sub-
duction interface [Lallemand et al., 2018] and a large
radius of curvature [Bletery et al., 2016], hence the
concern to describe the roughness of this interface
as closely as possible. While it remains impossible
to image the interface over the entire depth range of
the seismogenic zone, we provide here an estimate of
<figure><img src="image_12.png" /></figure>

**Figure 9.** Predicted mean porosity in the subduction channel at a distance of ~15 km from the deformation front as a function of *T*<sub>sed</sub> and *T*<sub>channel</sub>. The dots (erosive margins) and triangles (accretionary margins) represent the values corresponding to the 116 transects for which we have measured both *T*<sub>channel</sub> and *T*<sub>sed</sub> (Table S2). We have also drawn the threshold line between frontal accretion and subcrustal erosion when *T*<sub>channel</sub> = *T*<sub>sed_co</sub>.

terial, whereas T_sed will have essentially an effect
on Φ_sed. Indeed, some subduction zones charac-
terized by thick trench fill like Andaman, Sumatra
or Cascadia-Vancouver are associated with very lit-
tle sediment flux. The reason is that most of the
sedimentary pile at trench is accreted frontally. The
flux of solid material dragged in depth is decorre-
lated from the subduction rate as illustrated by the
Aegean–Cyprean subduction zone which allows the
most solid sediment to pass through (Figure 7), while
the average subduction rate (normal component) is
only 27 mm/yr (Table S2). This is due to the fact
that the thickness of the incoming sediments is great
(as is the length of the trench), but as a result their
porosity is low (17.2%), as they were already com-
pacted before subducting into the channel. As a re-
sult, the volume of fluid entrained in this subduc-

tion zone is comparatively very low. Another ob-
servation is that the greatest volumes of fluid in the
channel globally subduct along erosive margins. This
may result from the combination of a larger channel
porosity and a higher subduction rate. As indicated
above (Section 5), our overall values for subducted
solid matter flux are comparable to those estimated
by von Huene and Scholl [1991]. In contrast, the vol-
ume of subducted fluid is significantly lower in our
study, mainly due to the fact that we took into ac-
count both the “pre-compaction” of incoming sedi-
ments in accretion cases and then applied a porosity
reduction factor in the channel. In the end, we ob-
tain ~0.4 km³/yr of fluids entrained in the channel
along 40,450 km of trench, whereas von Huene and
Scholl [1991] proposed ~0.8 km³/yr along 43,450 km
of trench.

6.4. *T*<sub>sed</sub> and seismogenic potential along the subduction interface

As we have already pointed out, several studies
suggest that subduction mega-earthquakes oc-
cur preferentially along opposite sediment-filled
trenches [Ruff, 1989, Heuret et al., 2012, Scholl et al.,
2015]. Geersen [2019] noted that sediment-starved
trenches and rough subducting plates are conducive
to tsunami earthquakes. As Geersen, some of the
formerly cited authors consider that T_sed alone is
not a good proxy, as the thickness of sediment over-
lying the subducting plate in the seismogenic zone
can sometimes differ quite widely from that avail-
able in the trench. Scholl et al. [2015], for example,
noted the correspondence between most M<sub>w</sub> ≥ 8.5
earthquakes and high T_sed values, but pointed out
that some M<sub>w</sub> ≥ 8.0 earthquakes could sometimes
occur along weakly sediment-filled trenches facing
erosive margins, i.e., the products of subcrustal ero-
sion thicken the subduction channel. Seno [2017]
comes to the same conclusion and then provides a
rough estimate of the correction to be made to T_sed.
As can be seen, the general idea is that interseismic
coupling seems to be stronger with a smooth sub-
duction interface [Lallemand et al., 2018] and a large
radius of curvature [Bletery et al., 2016], hence the
concern to describe the roughness of this interface
as closely as possible. While it remains impossible
to image the interface over the entire depth range of
the seismogenic zone, we provide here an estimate of
$T_{\text{channel}}$ close or at the updip limit of the seismogenic zone [~11 ± 4 km in average according to Heuret et al., 2011] in a number of regions. The analysis of this new dataset with the objective to evaluate and eventually revisit our former conclusions based on a less complete dataset is under process.

## 6.5. *Nature of the incoming sediment*

It is not just the thickness of the sediments in the trench or channel that is important, but recent studies show that their nature and spatial distribution are likely to play a role in seismogenic potential. It appears that the mud-rich mass transport deposits (MTDs) modify the architecture and properties of the subduction channel [Festa et al., 2018, Geersen et al., 2020]. Heterogeneous fabric and fluid content possibly favor slow ruptures, particularly in shallow parts. Magmatic intrusions (sills) within the sedimentary cover appear as patches in few areas around the rupture area of the 2011 Tohoku earthquake. Fugie et al. [2020] thus suggest that disturbance and thermal metamorphism associated with this recent volcanic activity modify and shape the size and distribution of interplate earthquakes off NE Japan. In the Nankai subduction zone, Park and Jamali Hondori [2023] suggest that the underthrust turbidites cause low pore-fluid overpressure and high effective vertical stress across the decollement inhibiting the slow earthquakes occurrence. Similar heterogeneities were also found in the shallow part of the subduction interface along the Hikurangi margin [Gase et al., 2022]. There, they consist of pelagic carbonates versus heterogeneous volcaniclastics. The presence of pelagic carbonates above thickened non-volcanic siliciclastic sediments plays a key role in smoothing the rough topography of the subducting plate and higher coupling that could be prone to large ruptures. In this study, we do not directly address the question of the nature of the incoming sediments, as this would require lengthy developments, but we provide whenever possible a proxy for the contribution of terrigenous inputs via the submarine drainage network thanks to the difference between $T_{\text{sed}}$ and $T_{\text{SP}}$ (Table S1). Unsurprisingly, we find the great detrital fans such as the Nile in the Mediterranean, the Indus or Bengal in the Makran and Andaman, the Astoria and Nitinat in the Cascades or the Orinoco in the Lesser Antilles.

## 6.6. *Uncertainties on plate interface transient migration*

Mass transfer occurs in the vicinity of the plate boundary landward of the deformation front from the subducting to the overriding plate (underplating) or the opposite (basal erosion). By nature, field evidences of erosive structures in the vicinity of exhumed subduction channels are tiny [Bachmann et al., 2009, Vannucchi et al., 2010]. Such a mass transfer process assumes that the subduction interface migrates upwards pervasively via hydrofracturing of the overriding plate sole [e.g., von Huene et al., 2004] or transiently in the wake of a seamount, for example [e.g., Lallemand et al., 1994]. Similarly, certain discontinuities along the interface, such as variations in fluid pressure or rheology, can cause downward migration of the décollement, leading to the incorporation of a subduction channel slice at the margin [underplating, Sample and Moore, 1987, von Huene and Scholl, 1991, Raimbourg et al., 2019, Angiboust et al., 2021]. Today, it is relatively easy to trace the décollement at shallow levels, based on seismic reflection amplitudes and polarity reversals. Sometimes, we can observe the ghosts of abandoned paleo-décollements such as in the Nankai accretionary wedge [deep strong reflector of Park et al., 2002]. Based on the estimates of basal versus internal friction along the Chilean margin, Cubas et al. [2022] were able to characterize the sectors of the subduction interface where deformation was distributed, i.e. where forethrusts paralleled the interface. The authors interpret this type of condition (small differences in friction) as favorable to underplating, but it could just as easily favor basal erosion. The distribution of the deformation around the plate interface over the last Ma makes analysis (margin type, $T_{\text{channel}}$) complex on the basis of the current image of the margin alone.

## 7. Conclusion

We provide in this study an exhaustive database describing the lateral variations of the sediment thickness covering the oceanic plate when approaching a subduction zone, at the deformation front in the trench and in the shallow portion (<20 km) of the subduction channel. The unprecedented density of the data acquired opens the door to future
$T_{\text{channel}}$ close or at the updip limit of the seismogenic zone [~11 ± 4 km in average according to Heuret et al., 2011] in a number of regions. The analysis of this new dataset with the objective to evaluate and eventually revisit our former conclusions based on a less complete dataset is under process.

## 6.5. *Nature of the incoming sediment*

It is not just the thickness of the sediments in the trench or channel that is important, but recent studies show that their nature and spatial distribution are likely to play a role in seismogenic potential. It appears that the mud-rich mass transport deposits (MTDs) modify the architecture and properties of the subduction channel [Festa et al., 2018, Geersen et al., 2020]. Heterogeneous fabric and fluid content possibly favor slow ruptures, particularly in shallow parts. Magmatic intrusions (sills) within the sedimentary cover appear as patches in few areas around the rupture area of the 2011 Tohoku earthquake. Fugie et al. [2020] thus suggest that disturbance and thermal metamorphism associated with this recent volcanic activity modify and shape the size and distribution of interplate earthquakes off NE Japan. In the Nankai subduction zone, Park and Jamali Hondori [2023] suggest that the underthrust turbidites cause low pore-fluid overpressure and high effective vertical stress across the decollement inhibiting the slow earthquakes occurrence. Similar heterogeneities were also found in the shallow part of the subduction interface along the Hikurangi margin [Gase et al., 2022]. There, they consist of pelagic carbonates versus heterogeneous volcaniclastics. The presence of pelagic carbonates above thickened non-volcanic siliciclastic sediments plays a key role in smoothing the rough topography of the subducting plate and higher coupling that could be prone to large ruptures. In this study, we do not directly address the question of the nature of the incoming sediments, as this would require lengthy developments, but we provide whenever possible a proxy for the contribution of terrigenous inputs via the submarine drainage network thanks to the difference between $T_{\text{sed}}$ and $T_{\text{SP}}$ (Table S1). Unsurprisingly, we find the great detrital fans such as the Nile in the Mediterranean, the Indus or Bengal in the Makran and Andaman, the Astoria and Nitinat in the Cascades or the Orinoco in the Lesser Antilles.

## 6.6. *Uncertainties on plate interface transient migration*

Mass transfer occurs in the vicinity of the plate boundary landward of the deformation front from the subducting to the overriding plate (underplating) or the opposite (basal erosion). By nature, field evidences of erosive structures in the vicinity of exhumed subduction channels are tiny [Bachmann et al., 2009, Vannucchi et al., 2010]. Such a mass transfer process assumes that the subduction interface migrates upwards pervasively via hydrofracturing of the overriding plate sole [e.g., von Huene et al., 2004] or transiently in the wake of a seamount, for example [e.g., Lallemand et al., 1994]. Similarly, certain discontinuities along the interface, such as variations in fluid pressure or rheology, can cause downward migration of the décollement, leading to the incorporation of a subduction channel slice at the margin [underplating, Sample and Moore, 1987, von Huene and Scholl, 1991, Raimbourg et al., 2019, Angiboust et al., 2021]. Today, it is relatively easy to trace the décollement at shallow levels, based on seismic reflection amplitudes and polarity reversals. Sometimes, we can observe the ghosts of abandoned paleo-décollements such as in the Nankai accretionary wedge [deep strong reflector of Park et al., 2002]. Based on the estimates of basal versus internal friction along the Chilean margin, Cubas et al. [2022] were able to characterize the sectors of the subduction interface where deformation was distributed, i.e. where forethrusts paralleled the interface. The authors interpret this type of condition (small differences in friction) as favorable to underplating, but it could just as easily favor basal erosion. The distribution of the deformation around the plate interface over the last Ma makes analysis (margin type, $T_{\text{channel}}$) complex on the basis of the current image of the margin alone.

## 7. Conclusion

We provide in this study an exhaustive database describing the lateral variations of the sediment thickness covering the oceanic plate when approaching a subduction zone, at the deformation front in the trench and in the shallow portion (<20 km) of the subduction channel. The unprecedented density of the data acquired opens the door to future
multivariate analyses, notably concerning the dependence of the seismogenic behavior of the subduction interface on the thickness of the subduction channel versus that of the sediments present in the trench. A mass balance of material transfer from the trench to depths through the subduction channel, as proposed by von Huene and Scholl [1991], is updated by analyzing fluxes, knowing the convergence rate and making assumptions on the sediment porosity, over the last m.y. Maximum porosity in the channel is reached when there is no accretion or tectonic erosion.

With the caveat that the observations used to carry out this study can be traced back to the last m.y., while the seismic lines or morphology reflect the current to recent state, and the vertical motions of the margin or the migration of the volcanic arc incorporates a longer period, we propose an adjustment in the tectonic style of certain margins, with a final erosive dominance.

## Dedication

The first author would like to dedicate this study to Roland von Huene, Jean Aubouin's partner at a time when the process of subcrustal tectonic erosion of active margins had only just been revealed and was the subject of much criticism.

## Declaration of interests

The authors do not work for, advise, own shares in, or receive funds from any organization that could benefit from this article, and have declared no affiliations other than their research organizations.

## Acknowledgements

We are grateful to Jin-Oh Park who kindly provided us the seismic line of Figure 1. We would like to thank Hugues Raimbourg for his detailed review, and in particular his encouragement to revisit material balance on the basis of our new data. We would also like to thank the anonymous reviewer. Finally, the first author is particularly grateful to one of the co-editors of this special issue, Laurent Jolivet, for prompting him to update his knowledge of a subject that first attracted his attention some thirty years ago.

## Supplementary data

Supporting information for this article is available on the journal's website under https://doi.org/10.5802/crgeos.252 or from the author.

## References

Angiboust, S., Menant, A., Gerya, T., and Oncken, O. (2021). The rise and demise of deep accretionary wedges: A long-term field and numerical modeling perspective. *Geosphere*, 17(X), 1–35.

Aubouin, J., Bourgois, J., and Azéma, J. (1984). A new type of active margin: the convergent-extensional margin, as exemplified by the Middle America trench off Guatemala. *Earth Planet. Sci. Lett.*, 67(2), 211–218.

Aubouin, J., Bourgois, J., and Azéma, J. (1985). Two types of active margins: convergent-compressional margins and convergent-extensional margins. In Nasu, N. et al., editors, *Formation of Active Ocean Margins*, pages 109–129. TERRAPUB, Tokyo.

Bachmann, R., Oncken, O., Glodny, J., Seifert, W., Georgieva, V., and Sudo, M. (2009). Exposed plate interface in the European Alps reveals fabric styles and gradients related to an ancient seismogenic coupling zone. *J. Geophys. Res.*, 114, 1–23.

Baranov, B. V., Tsukanov, N. V., Gaedicke, C., Freitag, R., and Dozorova, K. A. (2022). Morphology and structural features of the subduction zone in the vicinity of Kuril–Kamchatka–Aleutian junction. *Oceanology*, 62(4), 528–539.

Barker, D. H. N., Sutherland, R., Henrys, S., and Banister, S. (2009). Geometry of the Hikurangi subduction thrust and upper plate, North Island, New Zealand. *Geochem. Geophys. Geosyst.*, 10(2), article no. Q02007.

Bartolomé, R., Danobeitia, J., Michaud, F., Cordoba, D., and Delgado-Argote, L. A. (2011). Imaging the seismic crustal structure of the Western Mexican margin between 19°N and 21°N. *Pure Appl. Geophys.*, 168, 1373–1389.

Bletery, Q., Thomas, A. M., Rempel, A. W., Karlstrom, L., Sladen, A., and De Barros, L. (2016). Mega-earthquakes rupture flat megathrusts. *Science*, 354(6315), 1027–1031.
multivariate analyses, notably concerning the dependence of the seismogenic behavior of the subduction interface on the thickness of the subduction channel versus that of the sediments present in the trench. A mass balance of material transfer from the trench to depths through the subduction channel, as proposed by von Huene and Scholl [1991], is updated by analyzing fluxes, knowing the convergence rate and making assumptions on the sediment porosity, over the last m.y. Maximum porosity in the channel is reached when there is no accretion or tectonic erosion.

With the caveat that the observations used to carry out this study can be traced back to the last m.y., while the seismic lines or morphology reflect the current to recent state, and the vertical motions of the margin or the migration of the volcanic arc incorporates a longer period, we propose an adjustment in the tectonic style of certain margins, with a final erosive dominance.

## Dedication

The first author would like to dedicate this study to Roland von Huene, Jean Aubouin's partner at a time when the process of subcrustal tectonic erosion of active margins had only just been revealed and was the subject of much criticism.

## Declaration of interests

The authors do not work for, advise, own shares in, or receive funds from any organization that could benefit from this article, and have declared no affiliations other than their research organizations.

## Acknowledgements

We are grateful to Jin-Oh Park who kindly provided us the seismic line of Figure 1. We would like to thank Hugues Raimbourg for his detailed review, and in particular his encouragement to revisit material balance on the basis of our new data. We would also like to thank the anonymous reviewer. Finally, the first author is particularly grateful to one of the co-editors of this special issue, Laurent Jolivet, for prompting him to update his knowledge of a subject that first attracted his attention some thirty years ago.

## Supplementary data

Supporting information for this article is available on the journal's website under https://doi.org/10.5802/crgeos.252 or from the author.

## References

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Aubouin, J., Bourgois, J., and Azéma, J. (1984). A new type of active margin: the convergent-extensional margin, as exemplified by the Middle America trench off Guatemala. *Earth Planet. Sci. Lett.*, 67(2), 211–218.

Aubouin, J., Bourgois, J., and Azéma, J. (1985). Two types of active margins: convergent-compressional margins and convergent-extensional margins. In Nasu, N. et al., editors, *Formation of Active Ocean Margins*, pages 109–129. TERRAPUB, Tokyo.

Bachmann, R., Oncken, O., Glodny, J., Seifert, W., Georgieva, V., and Sudo, M. (2009). Exposed plate interface in the European Alps reveals fabric styles and gradients related to an ancient seismogenic coupling zone. *J. Geophys. Res.*, 114, 1–23.

Baranov, B. V., Tsukanov, N. V., Gaedicke, C., Freitag, R., and Dozorova, K. A. (2022). Morphology and structural features of the subduction zone in the vicinity of Kuril–Kamchatka–Aleutian junction. *Oceanology*, 62(4), 528–539.

Barker, D. H. N., Sutherland, R., Henrys, S., and Banister, S. (2009). Geometry of the Hikurangi subduction thrust and upper plate, North Island, New Zealand. *Geochem. Geophys. Geosyst.*, 10(2), article no. Q02007.

Bartolomé, R., Danobeitia, J., Michaud, F., Cordoba, D., and Delgado-Argote, L. A. (2011). Imaging the seismic crustal structure of the Western Mexican margin between 19°N and 21°N. *Pure Appl. Geophys.*, 168, 1373–1389.

Bletery, Q., Thomas, A. M., Rempel, A. W., Karlstrom, L., Sladen, A., and De Barros, L. (2016). Mega-earthquakes rupture flat megathrusts. *Science*, 354(6315), 1027–1031.
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Brizzi, S., Sandri, L., Funiciello, F., Corbi, F., Piromallo, C., and Heuret, A. (2018). Multivariate statistical analysis to investigate the subduction zone parameters favoring the occurrence of giant megathrust earthquakes. *Tectonophysics*, 728–729, 92–103.

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Boucard, M., Marcaillou, B., Lebrun, J.-F., Lallencin, M., Klingelhoefer, F., Laigle, M., Lallemand, S., Schenini, L., Graindorge, D., Cornée, J.-J., Münch, P., Philippon, M., and the AntiTheSis and GARAnti Scientific teams (2021). Paleogene V-shaped basins and Neogene subsidence of the Northern Lesser Antilles forearc. *Tectonics*, 40, article no. e2020TC006524.

Brizzi, S., Sandri, L., Funiciello, F., Corbi, F., Piromallo, C., and Heuret, A. (2018). Multivariate statistical analysis to investigate the subduction zone parameters favoring the occurrence of giant megathrust earthquakes. *Tectonophysics*, 728–729, 92–103.

Brizzi, S., van Zelst, I., Funiciello, F., Corbi, F., and van Dinther, Y. (2020). How sediment thickness influences subduction dynamics and seismicity. *J. Geophys. Res.: Solid Earth*, 125, article no. e2019JB018964.

Clift, P. and Vannucchi, P. (2004). Controls on tectonic accretion versus erosion in subduction zones: Implications for the origin and recycling of the continental crust. *Rev. Geophys.*, 42(2), article no. RG2001.

Cloos, M. (1986). Blueschists in the Franciscan Complex of California: Petrotectonic constraints on uplift mechanisms. In *Blueschists and Eclogites*, Geological Society of America Memoir, 164, pages 77–93. Geological Society of America.

Cloos, M. and Shreve, R. L. (1988a). Subduction-channel model of prism accretion, melange formation, sediment subduction, and subduction erosion at convergent plate margins: 1. Background and description. *Pure Appl. Geophys.*, 128(3/4), 455–500.

Cloos, M. and Shreve, R. L. (1988b). Subduction-channel model of prism accretion, melange formation, sediment subduction, and subduction erosion at convergent plate margins: 1. Implications and discussion. *Pure Appl. Geophys.*, 128(3/4), 501–545.

Collot, J.-Y., Agudelo, W., Ribodetti, A., and Marcaillou, B. (2008). Origin of a crustal splay fault and its relation to the seismogenic zone and underplating at the erosional north Ecuador–south Colom-

bia oceanic margin. *J. Geophys. Res.*, 113, article no. B12102.

Collot, J. Y., Daniel, J., and Burne, R. V. (1985). Recent tectonics associated with the subduction/collision of the d'Entrecasteaux zone in the central New Hebrides. *Tectonophysics*, 112(1–4), 325–356.

Collot, J. Y., Lallemand, S., Pelletier, B., Bissen, J. P., Glaçon, G., Fisher, M. A., Greene, H. G., Boulin, J., Daniek, J., and Monzier, M. (1992). Geology of the d'Entrecasteaux-New Hebrides Arc collision zone: results from a deep submersible survey. *Tectonophysics*, 212(3–4), 213–241.

Collot, J. Y., Lamarche, G., Wood, R. A., Delteil, J., Bosson, M., Lebrun, J. F., and Coffin, M. F. (1995). Morphostructure of an incipient subduction zone along a transform plate boundary: Puysegur Ridge and Trench. *Geology*, 23(6), 519–522.

Collot, J.-Y., Marcaillou, B., Sage, F., Michaud, F., Agudelo, W., Charvis, P., Graindorge, D., Gutscher, M.-A., and Spence, G. (2004). Are rupture zone limits of great subduction earthquakes controlled by upper plate structures? Evidence from multichannel seismic reflection data acquired across the northern Ecuador–southwest Colombia margin. *J. Geophys. Res.*, 109, article no. B11103.

Contreras-Reyes, E., Flueh, E. R., and Grevemeyer, I. (2010). Tectonic control on sediment accretion and subduction off south central Chile: Implications for coseismic rupture processes of the 1960 and 2010 megathrust earthquakes. *Tectonics*, 29, article no. TC6018.

Contreras-Reyes, E., Grevemeyer, I., Watts, A. B., Flueh, E. R., Peirce, C., Moeller, S., and Papenberg, C. (2011). Deep seismic structure of the Tonga subduction zone: Implications for mantle hydration, tectonic erosion, and arc magmatism. *J. Geophys. Res.: Solid Earth*, 116(B10), article no. B10103.

Cubas, N., Agard, P., and Tissandier, R. (2022). Earthquake ruptures and topography of the Chilean margin controlled by plate interface deformation. *Solid Earth*, 13(3), 779–792.

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Ferrière, J. and Faure, M. (2024). Jean Aubouin et les chaînes de montagnes: des observations aux synthèses. L'itinéraire scientifique d'un géologue au rayonnement international. *C. R. Géosci.*, 356(S2), 7–25. (this issue).

Festa, A., Dilek, Y., Mittempergher, S., Ogata, K., Pini, G. A., and Remitti, F. (2018). Does subduction of mass transport deposits (MTDs) control seismic behavior of shallow-level megathrusts at convergent margins? *Gondwana Res.*, 60, 186–193.

Fisher, M. A. (1986). Tectonic processes at the collision of the d'Entrecasteaux zone and the New-Hebrides island arc. *J. Geophys. Res.: Solid Earth*, 91(B10), 10470–10486.

Fisher, M. A., Collot, J. Y., and Geist, E. L. (1991). The collision zone between the North d'Entrecasteaux Ridge and the New Hebrides Island Arc: 2. Structure from multichannel seismic data. *J. Geophys. Res.: Solid Earth*, 96(B3), 4479–4495.

Font, Y. and Lallemand, S. (2009). Subducting oceanic high causes compressional faulting in southernmost Ryukyu forearc as revealed by hypocentral determinations of earthquakes and reflection/refraction seismic data. *Tectonophysics*, 466(3–4), 255–267.

Fruehn, J., von Huene, R., and Fisher, M. A. (1999). Accretion in the wake of terrane collision: The Neogene accretionary wedge off Kenai Peninsula, Alaska. *Tectonics*, 18(2), 263–277.

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Lamarche, G. and Lebrun, J. F. (2000). Transition from strike-slip faulting to oblique subduction: active tectonics at the Puysegur Margin, South New
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Granja Bruña, J. L., Ten Brink, U. S., Carbó-Gorosabel, A., Muñoz-Martín, A., and Ballesteros, M. G. (2009). Morphotectonics of the central Muertos thrust belt and Muertos Trough (northeastern Caribbean). *Mar. Geol.*, 263(1–4), 7–33.

Grevemeyer, I., Diaz-Naveas, J. L., Ranero, C. R., Villinger, H. W., and Leg, O. D. P. (2003). Heat flow over the descending Nazca plate in central Chile, 32 S to 41 S: Observations from ODP Leg 202 and the occurrence of natural gas hydrates. *Earth Planet. Sci. Lett.*, 213(3–4), 285–298.

Grindlay, N. R., Mann, P., Dolan, J. F., and van Gestel, J.-P. (2005). Neotectonics and subsidence of the northern Puerto-Rico-Virgin Islands margin in response to the oblique subduction of high-standing ridges. In Mann, P., editor, *Active Tectonics and Seismic Hazards of Puerto-Rico, the Virgin Islands, and Offshore Areas*, Geological Society, London, Special Publications, 385, pages 31–60. Geological Society of London.

Hayes, D. E. and Lewis, S. D. (1984). A geophysical study of the Manila Trench, Luzon, Philippines: 1. Crustal structure, gravity, and regional tectonic evolution. *J. Geophys. Res.: Solid Earth*, 89(B11), 9171–9195.

Heuret, A., Conrad, C., Funiciello, F., Lallemand, S., and Sandri, L. (2012). Relation between subduction megathrust earthquakes, trench sediment thickness and upper plate strain. *Geophys. Res. Lett.*, 39(5), article no. L05304.

Heuret, A., Lallemand, S., Funiciello, F., Piromallo, C., and Faccenna, C. (2011). Physical characteristics of subduction interface type seismogenic zones revisited. *Geochem. Geophys. Geosyst.*, 12, article no. Q01004.

Jicha, B. R. and Kay, S. M. (2018). Quantifying arc migration and the role of forearc subduction erosion in the central Aleutians. *J. Volcanol. Geotherm. Res.*, 360, 84–99.

Kahrizi, A., Delescluse, M., Chamot-Rooke, N., Pubellier, M., Bécel, A., Shillington, D., Nedimovic, M., and Bulois, C. (2024). Extensional forearc structures at the transition from Alaska to Aleutian Subduction Zone: slip partitioning, terranes and large earthquakes. *C. R. Géosci.*, 356(S2), 53–77. (this issue).

Klaeschen, D., Belykh, I., Gnibidenko, H., Patrikeyev,

S., and von Huene, R. (1994). Structure of the Kuril trench from seismic reflection records. *J. Geophys. Res.*, 99(B12), 24173–24188.

Kodaira, S., Kurashimo, E., Park, J. O., Takahashi, N., Nakanishi, A., Miura, S., Iwasaki, T., Hirata, N., Ito, K., and Kaneda, Y. (2002). Structural factors controlling the rupture process of a megathrust earthquake at the Nankai trough seismogenic zone. *Geophys. J. Int.*, 149(3), 815–835.

Kopp, H. (2011). The Java convergent margin: structure, seismogenesis and subduction processes. *Geol. Soc., Lond., Spec. Publ.*, 355(1), 111–137.

Kroehler, M. E., Mann, P., Escalona, A., and Christeson, G. L. (2011). Late Cretaceous-Miocene diachronous onset of back thrusting along the South Caribbean deformed belt and its importance for understanding processes of arc collision and crustal growth. *Tectonics*, 30(6), article no. TC6003.

Ku, C. Y. and Hsu, S. K. (2009). Crustal structure and deformation at the northern Manila Trench between Taiwan and Luzon islands. *Tectonophysics*, 466(3–4), 229–240.

Lallemand, S., Liu, C. S., Dominguez, S., Schnürle, P., and Malavieille, J. (1999). Trench-parallel stretching and folding of forearc basins and lateral migration of the accretionary wedge in the southern Ryukyus: A case of strain partition caused by oblique convergence. *Tectonics*, 18(2), 231–247.

Lallemand, S., Peyret, M., van Rijsingen, E., Arcay, D., and Heuret, A. (2018). Roughness characteristics of oceanic seafloor prior to subduction in relation to the seismogenic potential of subduction zones. *Geochem. Geophys. Geosyst.*, 19, 2121–2146.

Lallemand, S., Theunissen, T., Schnürle, P., Lee, C. S., Liu, C. S., and Font, Y. (2013). Indentation of the Philippine Sea plate by the Eurasia plate in Taiwan: Details from recent marine seismological experiments. *Tectonophysics*, 594, 60–79.

Lallemand, S. E. (1995). High rates of arc consumption by subduction processes: some consequences. *Geology*, 6, 551–554.

Lallemand, S. E., Schnürle, P., and Malavieille, J. (1994). Coulomb theory applied to accretionary and nonaccretionary wedges: Possible causes for tectonic erosion and/or frontal accretion. *J. Geophys. Res.: Solid Earth*, 99(B6), 12033–12055.

Lamarche, G. and Lebrun, J. F. (2000). Transition from strike-slip faulting to oblique subduction: active tectonics at the Puysegur Margin, South New