Crustal Structure of the Nankai Subduction Zone Revealed by Two Decades of Onshore‐Offshore and Ocean‐Bottom Seismic Data: Implications for the Dimensions and Slip Behavior of the Seismogenic Zone

Bassett, Dan; Arnulf, A. F.; Kodaira, Shuichi; Nakanishi, Ayako; Harding, A. J.; Moore, Gregory F.

doi:10.1029/2022jb024992

Cited by 5 publications

(1 citation statement)

References 111 publications

(273 reference statements)

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“…Instead, this depth corresponds in warm active margins to the region affected by slow earthquakes (e.g. Bassett et al, 2022;Fig.6b), inferred to occur on the interface itself (so, probably in a sedimentary-rich environment).…”

Section: Garnet As a Witness Of Ancient Unstable Slip Eventsmentioning

confidence: 97%

Garnet fracturing reveals ancient unstable slip events hosted in plate interface metasediments

Angiboust,

Ioannidi,

Muldashev

2023

Preprint

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A paradox exists between the great number of intermediate-depth earthquakes occurring along active subduction interfaces worldwide and the extreme scarcity of paleo-seismic events recorded in exhumed metasedimentary rocks from ancient subduction zones. Recrystallization, shearing as well as exhumation-related overprinting generally contribute to the nearly-complete erasing of markers of unstable slip events in metamorphic rocks. We herein focus on a sample from an ancient deep thrust from a Cretaceous High-Pressure paleo-accretionary complex in Chilean Patagonia. A representative, moderately foliated micaschist exhibits broken garnet crystals that host a dense network of healed micro-fractures. While garnet fragments appear thoroughly disaggregated along the main foliation, the matrix that has completely recrystallized hardly records brittle deformation. We employ a 2D visco-elasto-plastic numerical modelling approach in order to investigate the mechanical conditions that enable the fracturing of isolated garnet grains in a relatively weak matrix. The rupture of these stiff grains is achieved in our models at strain rates faster than 10-10 /s to 10-12 /s for elevated pore fluid pressures (80 to 99% of the lithostatic value, respectively). Since high pore fluid pressures prevail in deep subduction interface settings, it is suggested that the rupture of these garnet crystals occurred through cataclastic deformation via (transient) slip rate acceleration, perhaps as a consequence of localized slip associated with slow to normal earthquakes. Upon slip rate deceleration, viscous disaggregation of the broken garnet clasts occurred along with the erasing of the matrix cataclastic fabric.

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Section: Garnet As a Witness Of Ancient Unstable Slip Eventsmentioning

confidence: 97%

Garnet fracturing reveals ancient unstable slip events hosted in plate interface metasediments

Angiboust,

Ioannidi,

Muldashev

2023

Preprint

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Deep plutonic bodies over low-frequency earthquakes revealed from receiver-side Green's functions

Sawaki,

Ito,

Garcia

et al. 2024

Tectonophysics

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Structural Controls on Megathrust Slip Behavior Inferred From a 3D, Crustal‐Scale, P‐Wave Velocity Model of the Alaska Peninsula Subduction Zone

Acquisto,

Bécel,

Canales

et al. 2024

JGR Solid Earth

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In subduction zones, along‐strike and downdip variations in megathrust slip behavior are linked to changes in properties of the subducting and overriding plates. Although marine geophysical methods provide insights into subduction zone structures, most surveys consist of sparse 2D profiles, limiting our understanding of first‐order controls. Here, we use active‐source seismic data to derive a 3D crustal‐scale P‐wave velocity model of the Alaska Peninsula subduction zone that encompasses both plates and spans the Semidi segment and SW Kodiak asperity. Our results reveal modest variations within the incoming plate, attributed to a series of fracture zones, seamounts and their associated basement swell, collectively contributing to plate hydration. Basement swell appears to modulate the distribution and type of sediment entering the trench, likely impacting observed variations in slip behavior. The overriding plate exhibits significant heterogeneity. The updip limit and width of the dynamic backstop are similar between the SW Kodiak asperity and eastern Semidi segment, but differ significantly from the Western Semidi segment. These distinctions likely account for differences in earthquake rupture patterns and interseismic coupling among these segments. Additionally, high‐velocities in the mid‐lower forearc crust coincide with the location of megathrust slip during the Mw 8.2 2021 Chignik event. We interpret these velocities as intracrustal intrusions that contributed to the deep rupture of the 2021 event. Our findings suggest that the contrasting structural and material properties of both the incoming and overriding plates influence the spatially complex and semi‐persistent segmentation of the megathrust offshore the Alaska Peninsula.

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Crustal Structure of the Nankai Subduction Zone Revealed by Two Decades of Onshore‐Offshore and Ocean‐Bottom Seismic Data: Implications for the Dimensions and Slip Behavior of the Seismogenic Zone

Cited by 5 publications

References 111 publications

Garnet fracturing reveals ancient unstable slip events hosted in plate interface metasediments

Garnet fracturing reveals ancient unstable slip events hosted in plate interface metasediments

Deep plutonic bodies over low-frequency earthquakes revealed from receiver-side Green's functions

Structural Controls on Megathrust Slip Behavior Inferred From a 3D, Crustal‐Scale, P‐Wave Velocity Model of the Alaska Peninsula Subduction Zone

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