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Our article on the co-location of the downdip end of seismic coupling and the continental shelf break is finally published and formatted in JGR Solid Earth: https://doi.org/10.1029/2020JB019589
Here is what @seismolucy, Noah Finnegan & @jaodynamics and I found:
… 1/9
Here is what @seismolucy, Noah Finnegan & @jaodynamics and I found:
… 1/9
At subduction zones, most of the deformation is accommodated by repeated earthquakes. Does the landscape record a trace of this deformation or are interseismic and coseismic deformation perfectly balanced? 2/9
When we looked closely where the locking depth appear in the landscape, we realized that they lined up with the edges of erosive shelf breaks (<200m deep). 
3/9
3/9
We compiled the locking depths of coseismic ruptures around the ring of fire and found that their downdip end matches the location of the shelf break [see inset distributions]. This observation holds with the addition of well-resolved interseismic high coupling footprints. 4/9
![We compiled the locking depths of coseismic ruptures around the ring of fire and found that their downdip end matches the location of the shelf break [see inset distributions]. This observation holds with the addition of well-resolved interseismic high coupling footprints. 4/9](https://pbs.twimg.com/media/Es1qiiBXEAIC016.jpg "We compiled the locking depths of coseismic ruptures around the ring of fire and found that their downdip end matches the location of the shelf break [see inset distributions]. This observation holds with the addition of well-resolved interseismic high coupling footprints. 4/9")
![We compiled the locking depths of coseismic ruptures around the ring of fire and found that their downdip end matches the location of the shelf break [see inset distributions]. This observation holds with the addition of well-resolved interseismic high coupling footprints. 4/9](https://pbs.twimg.com/media/Es1m1lJW8AMO67a.jpg "We compiled the locking depths of coseismic ruptures around the ring of fire and found that their downdip end matches the location of the shelf break [see inset distributions]. This observation holds with the addition of well-resolved interseismic high coupling footprints. 4/9")
This pattern can be explained if a fraction of the interseismic deformation is permanent (brittle rock fatigue, pressure‐solution creep…), as a result, a hinge line separates a subsiding zone seaward, and an uplifting zone landward.
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5/9
-- 5/9
But why does the shelf break match the uplift hinge line (above the locking depth) & not the coastline? Surface processes!
The hinge line is a tectonically meaningful
: will erode the shelf landward from it as a function of power, rock strength, uplift rate, etc. 6/9
The hinge line is a tectonically meaningful
: will erode the shelf landward from it as a function of power, rock strength, uplift rate, etc. 6/9
This means that if the shelf is narrow, the coastline is effectively very close to the locking depth as was observed by Ruff&Tichelaar in Chile & other places. Also we can’t use the shelf break as a guide if it is is built by sediment accumulation, e.g. Colombia, Alaska. 7/9
Subduction morphology integrates 100s of EQ cycles and could inform the persistence of seismic coupling patterns through time: sharp features = stable locking depth; rolling topo = varying locking depth. Could be partly responsible for contrast between Japan and Cascadia? 8/9
“And what about all these sites that do not fit the story?” I hear. Well this baseline could help identify sites where subduction morphology is transient / current surveyed coupling pattern differs from the long-term / other deformation mechanisms prime / & many more factors 9/9
