Subduction Dynamics and Deep Seismicity

Subduction zones are convergent plate boundaries where one lithospheric plate descends into the mantle beneath another. The physical and chemical processes within the downgoing slab—from dehydration of hydrous minerals through phase transformations to interactions with the surrounding mantle—govern the occurrence of earthquakes at depths ranging from a few kilometres to over 700 km. Shallow events are driven by frictional faulting on the plate interface, whereas intermediate- and deep-focus earthquakes involve mechanisms such as dehydration embrittlement, thermal shear instability and transformational faulting in metastable mineral phases. Seismic imaging reveals double seismic zones within many slabs, reflecting dehydration reactions in the crust and mantle lithosphere. The global distribution of deep earthquakes illuminates slab morphology, thermal structure and rheology, with implications for mantle circulation, volcanic arc genesis and seismic hazard assessment in subduction regions worldwide.

Research from Nature Portfolio

Recent high‐resolution seismological analyses of an Mw 8.3 earthquake at ~600 km depth beneath the Sea of Okhotsk have identified a small ultralow‐velocity anomaly (~30×60×60 km, −18 ± 2 % P‐wave perturbation) adjacent to the slab at the 660 km discontinuity. This volatile‐rich melted zone provides buoyancy that stresses the slab towards thermal runaway and explains the propagation of very large ruptures beyond metastable olivine domains. Laboratory experiments on chlorite‐bearing peridotite under pressures up to 2.5 GPa and temperatures around 700 °C have demonstrated that partial chlorite dehydration forms Ca‐amphibole along nascent faults, triggering intermediate‐depth seismicity in the lower plane of double seismic zones. Teleseismic double‐difference tomography of the Izu–Bonin slab has resolved a tear in the transition zone, folding and overturning of slab segments, and localisation of the 680 km‐deep Bonin earthquake at the edge of an overturned slab. These studies collectively link mineral dehydration, slab geometry and mantle interactions to the initiation and propagation of deep‐focus earthquakes.

Subduction Dynamics and Deep Seismicity publication trend

The graph below shows the total number of articles in subduction dynamics and deep seismicity across all publications each year (not limited to Nature Index journals).

Technical terms

Subducting slab: The portion of the oceanic lithosphere that descends beneath another plate into the mantle.

Deep‐focus earthquake: Seismic event occurring at depths greater than 300 km, often linked to transformational faulting or dehydration embrittlement.

Double seismic zone: Two parallel planes of seismicity within a downgoing slab, reflecting dehydration reactions in crustal and mantle layers.

Dehydration embrittlement: Process whereby water released from hydrous minerals reduces rock strength and triggers brittle failure at high pressures.

Metastable olivine wedge: A region of preserved olivine in the slab at mantle transition‐zone conditions, which transforms to spinel under stress and contributes to deep rupture.

P‐wave velocity anomaly: Localised region where compressional wave speed is significantly reduced, indicating compositional or thermal heterogeneity.

References

1. Subslab ultra low velocity anomaly uncovered by and facilitating the largest deep earthquake. Nature Communications (2024).
2. Impact of chlorite dehydration on intermediate-depth earthquakes in subducting slabs. Communications Earth & Environment (2023).
3. Slab morphology and deformation beneath Izu-Bonin. Nature Communications (2019).
4. Earthquakes track subduction fluids from slab source to mantle wedge sink. Science Advances (2019).
5. ISC‐EHB 1964–2016, an Improved Data Set for Studies of Earth Structure and Global Seismicity. Earth and Space Science (2020).