TY - JOUR

T1 - Global Constraints on Intermediate-Depth Intraslab Stresses From Slab Geometries and Mechanisms of Double Seismic Zone Earthquakes

AU - Sippl, Christian

AU - Dielforder, Armin

AU - John, Timm

AU - Schmalholz, Stefan

N1 - Funding Information: We thank the editor Claudio Faccenna, and an anonymous reviewer whose comments helped to improve the manuscript. C. Sippl has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (ERC Starting grant MILESTONE, StG2020‐947856). T. John was supported by Deutsche Forschungsgemeinschaft (DFG) in the framework of the priority program SPP 2017 “Mountain Building in Four Dimensions (MB‐4D)” by grant JO 349/12–1. S.M. Schmalholz was supported by the University of Lausanne. Figures were prepared using Matplotlib (Hunter, 2007 ) and the basemap library ( https://matplotlib.org/basemap/ ).

PY - 2022/9/6

Y1 - 2022/9/6

N2 - Double seismic zones (DSZs), parallel planes of intermediate-depth earthquakes inside oceanic slabs, have been observed in a number of subduction zones and may be a ubiquitous feature of downgoing oceanic plates. Focal mechanism observations from DSZ earthquakes sample the intraslab stress field at two distinct depth levels within the downgoing lithosphere. A pattern of downdip compressive over downdip extensive events was early on interpreted to indicate an unbending-dominated intraslab stress field. In the present study, we show that the intraslab stress field in the depth range of DSZs is much more variable than previously thought. Compiling DSZ locations and mechanisms from literature, we observe that the “classical” pattern of compressive over extensive events is only observed at about half of the DSZ locations around the globe. The occurrence of extensional mechanisms across both planes accounts for most other regions. To obtain an independent estimate of the bending state of slabs at intermediate depths, we compute (un)bending estimates from slab geometries taken from the slab2 compilation of slab surface depths. We find no clear global prevalence of slab unbending at intermediate depths, and the occurrence of DSZ seismicity does not appear to be limited to regions of slab (un)bending. Focal mechanism observations are frequently inconsistent with (un)bending estimates from slab geometries, which may imply that bending stresses are not always prevalent, and that other stress types such as in-plane tension due to slab pull or shallow compression due to friction along the plate interface may also play an important role.

AB - Double seismic zones (DSZs), parallel planes of intermediate-depth earthquakes inside oceanic slabs, have been observed in a number of subduction zones and may be a ubiquitous feature of downgoing oceanic plates. Focal mechanism observations from DSZ earthquakes sample the intraslab stress field at two distinct depth levels within the downgoing lithosphere. A pattern of downdip compressive over downdip extensive events was early on interpreted to indicate an unbending-dominated intraslab stress field. In the present study, we show that the intraslab stress field in the depth range of DSZs is much more variable than previously thought. Compiling DSZ locations and mechanisms from literature, we observe that the “classical” pattern of compressive over extensive events is only observed at about half of the DSZ locations around the globe. The occurrence of extensional mechanisms across both planes accounts for most other regions. To obtain an independent estimate of the bending state of slabs at intermediate depths, we compute (un)bending estimates from slab geometries taken from the slab2 compilation of slab surface depths. We find no clear global prevalence of slab unbending at intermediate depths, and the occurrence of DSZ seismicity does not appear to be limited to regions of slab (un)bending. Focal mechanism observations are frequently inconsistent with (un)bending estimates from slab geometries, which may imply that bending stresses are not always prevalent, and that other stress types such as in-plane tension due to slab pull or shallow compression due to friction along the plate interface may also play an important role.

KW - bending stresses

KW - double seismic zone

KW - in-plane stresses

KW - intraslab stress field

KW - subduction zone

UR - http://www.scopus.com/inward/record.url?scp=85139155226&partnerID=8YFLogxK

U2 - 10.1029/2022GC010498

DO - 10.1029/2022GC010498

M3 - Article

VL - 23

JO - Geochemistry, Geophysics, Geosystems

JF - Geochemistry, Geophysics, Geosystems

SN - 1525-2027

IS - 9

M1 - e2022GC010498

ER -