| Title | Hidden roughness of subducting seafloor and implications for megathrust seismogenesis: example from northern Manila Trench |
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| Author | Tan, H; Gao, X; Wang, K ; Gao, J; He, J |
| Source | Geophysical Research Letters 2022 p. 1-9, https://doi.org/10.1029/2022GL100146  Open Access |
| Image |  |
| Year | 2022 |
| Alt Series | Natural Resources Canada, Contribution Series 20220229 |
| Publisher | American Geophysical Union |
| Document | serial |
| Lang. | English |
| Media | paper; digital; on-line |
| File format | pdf; html |
| Area | China; Philippines; Malaysia |
| Lat/Long WENS | 109.0000 125.0000 24.0000 5.0000 |
| Subjects | Science and Technology; Nature and Environment; marine geology; seismicity; Manila Trench |
| Illustrations | location maps; charts; graphs; diagrams |
| Program | Public Safety Geoscience Assessing Earthquake Geohazards |
| Released | 2022 08 24 |
| Abstract | A 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. |
| GEOSCAN ID | 330590 |
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