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TitleHidden roughness of subducting seafloor and implications for megathrust seismogenesis: example from northern Manila Trench
AuthorTan, H; Gao, X; Wang, KORCID logo; Gao, J; He, J
SourceGeophysical Research Letters 2022 p. 1-9, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20220229
PublisherAmerican Geophysical Union
Mediapaper; digital; on-line
File formatpdf; html
AreaChina; Philippines; Malaysia
Lat/Long WENS 109.0000 125.0000 24.0000 5.0000
SubjectsScience and Technology; Nature and Environment; marine geology; seismicity; Manila Trench
Illustrationslocation maps; charts; graphs; diagrams
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2022 08 24
AbstractA smooth subducting seafloor usually leads to a smooth megathrust, which promotes great earthquakes. We present a case study at the northern Manila Trench to emphasize that the process depends also on sediment accretion and deformation. Here, a very rugged igneous basement is hidden beneath a smooth sediment cover on the incoming seafloor. Seismic imaging indicates that most of the sediment is scraped off at the trench, resulting in an uneven décollement interrupted by partially exposed subducted seamounts. New thermal models confirm the presence of large frictional heating, also consistent with a rough and strong megathrust. Our findings in conjunction with the low degree of megathrust locking reported in the literature are compatible with the notion of strong creep. Consequent implications to regional seismic and tsunami hazards call for further investigations, especially with new seafloor geodetic monitoring and improved paleoseismic studies.
Summary(Plain Language Summary, not published)
Great earthquakes, usually accompanied with large tsunamis, tend to occur in subduction zones where the megathrust fault is smooth. In appraising the potential of such great earthquakes, it is customary to use the ruggedness of the incoming seafloor before subduction to represent the roughness of the megathrust. In this work, we conduct a case study at the northern Manila Trench subduction zone to demonstrate that a smooth incoming seafloor does not always lead to a smooth megathrust. If the seafloor smoothness owes to a thick sediment cover, a rugged basement hidden beneath the sediment can still lead to a rough megathrust if most of the sediment is scraped off when the seafloor is subducted. We show seismic imaging results that indicate sediment scraping-off at the trench to expose basement relief such as seamounts. The lack of a very smooth megathrust suggests lower potential for great earthquakes, but an accurate assessment of regional seismic and tsunami hazards requires other independent observations that help to constrain strain accumulation across the trench and earthquake history. This study has important implications to the Cascadia subduction zone where the incoming seafloor is also smoothed by a thick sediment cover.

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