Focal Mechanisms of Intraslab Earthquakes: Insights From Pseudotachylytes in Mantle Units

E. Hosseinzadehsabeti, E. C. Ferré, T. B. Andersen, J. W. Geissman, D. Bilardello, G. Di Toro

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Devastating seismic events occur mainly in subduction zones, and a significant percentage of them are intraslab earthquakes. The geologic record of these events holds valuable information that needs to be investigated for a comprehensive seismic risk assessment. Here we investigate pseudotachylytes formed in oceanic peridotites and that are interpreted to result from intraslab seismic rupture. Each vein has recorded the seismic slip direction and slip sense of a single coseismic shear-heating event. The well-preserved exposures, showing individual veins up to 7 m in length and about 3 cm in width, of Cima di Gratera, in the Schistes Lustrés ophiolitic units of Corsica, offer unparalleled opportunities to investigate intraslab rupture kinematics in mantle rocks. The principal ferromagnetic phase in these rocks is a Ti-poor magnetite. We use the anisotropy of magnetic susceptibility (AMS) recorded in pseudotachylyte generation veins (bulk susceptibilities range from 600 to 20,000 × 10−6 [SI] volume, with P′ ranging from 1.05 to 2.5) to reconstruct the co-seismic deformation parameters, that is, fault plane attitude, direction and sense of slip. These new results, internally consistent at the vein level, span across oblate and prolate symmetries and reveal that seismic deformation recorded in these veins was kinematically diverse and included mostly normal mechanisms acting along the same subduction zone. In addition, our investigations show that the magnetic fabric of peridotite-hosted pseudotachylytes provides key information bearing on the complex dynamics of frictional melts at a unprecedently high spatial resolution.

Original languageEnglish (US)
Article numbere2020JB021479
JournalJournal of Geophysical Research: Solid Earth
Volume126
Issue number4
DOIs
StatePublished - Apr 1 2021

Bibliographical note

Funding Information:
This research was funded by two Geological Society of America graduate research grants to Elham Hosseinzadehsabeti during her doctoral research. Authors kindly thank Sarah Friedman for the SEM images she acquired at Montana State University, Billings. This work was supported by the National Science Foundation (Instrumentation and Facilities grant EAR-0521558 to ECF). Funding to T. B. Andersen was from CoE-grant 223272 from the Research Council of Norway. The IRM is a US National multi-user facility supported through the Instrumentation and Facilities program of the National Science Foundation, Earth Sciences Division, and by funding from the University of Minnesota. Two anonymous reviewers, the Associate Editor and the Editor (R. Abercrombie) are thanked for their constructive input.

Funding Information:
This research was funded by two Geological Society of America graduate research grants to Elham Hosseinzadehsabeti during her doctoral research. Authors kindly thank Sarah Friedman for the SEM images she acquired at Montana State University, Billings. This work was supported by the National Science Foundation (Instrumentation and Facilities grant EAR‐0521558 to ECF). Funding to T. B. Andersen was from CoE‐grant 223272 from the Research Council of Norway. The IRM is a US National multi‐user facility supported through the Instrumentation and Facilities program of the National Science Foundation, Earth Sciences Division, and by funding from the University of Minnesota. Two anonymous reviewers, the Associate Editor and the Editor (R. Abercrombie) are thanked for their constructive input.

Publisher Copyright:
© 2021. American Geophysical Union. All Rights Reserved.

Keywords

  • earthquake
  • kinematic
  • mantle
  • pseudotachylyte
  • seismic deformation
  • subduction

Fingerprint

Dive into the research topics of 'Focal Mechanisms of Intraslab Earthquakes: Insights From Pseudotachylytes in Mantle Units'. Together they form a unique fingerprint.

Cite this