Journal
TECTONICS
Volume 39, Issue 8, Pages -Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2019TC005894
Keywords
earthquakes</AUTHOR_KEYWORD>; seismicity</AUTHOR_KEYWORD>; slabs</AUTHOR_KEYWORD>; subduction</AUTHOR_KEYWORD>
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Funding
- Australian Research Council [DP150102887]
- AuScope
- Baragwanath Geology Research Scholarship
- Australian Government
- Government of Western Australia
- Nectar Research Cloud, a collaborative Australian research platform - National Collaborative Research Infrastructure Strategy (NCRIS).
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Earthquake moment tensors in eastern Pacific (ePac) slabs typically show downdip tensional (DT) axes, whereas in the western Pacific (wPac), they typically show downdip compressional (DC) axes or have mixed orientations indicative of unbending. Prevailing conceptual models emphasize uniform stress/deformation modes, that is, bulk slab stretching or shortening, as the dominant control on intermediate depth seismic expression. In contrast, we propose that a diversity of seismic expression, including DT- and DC-dominated regions, is consistent with expectations of flexural strain accumulation, based on systemic differences in slab geometry. Our analysis reveals two largely unrecognized features of ePac intraslab seismicity. First, earthquake clusters consistent with slab unbending are present in ePac slabs, albeit at much shallower depths than typical of wPac slabs. Second, intermediate depth ePac DT seismicity is strongly localized to the upper half of zones undergoing curvature increase, such as flat slab segments. Our study highlights how the seismic expression of slab flexure is impacted by the relative contribution of brittle and ductile deformation. The strongly asymmetric temperature structure that is preserved in sinking slabs means that seismicity disproportionately records the deformation regime in the colder part of the slab, above the neutral plane of bending. The expression of in-plane stress may be discernible in terms of a systematic modifying effect on the seismic expression of flexure.
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