What fraction of a subduction zone’s energy budget goes into building and shaping subduction zone land- and seascapes?

Earthquakes along faults between the subduction trench and arc, as well as along the megathrust trigger ground failures, excite tsunamis that can devastate coastlines and traverse oceans, and damage the built environment surrounding subduction zones.  Over the long term, megathrust earthquakes largely facilitate the subduction of ocean crust far from the continent, while land- and sea-scape building processes are strongly impacted by faulting and folding of rock lying within the region between the subduction trench and the volcanic arc.  Both types of earthquakes have the potential to profoundly impact civilization and infrastructure. Motions within the upper plate may be particularly impactful to people and communities because they occur within the region where humans and their enterprises exist – they may directly rupture the land surface beneath cities, or rupture underwater in areas close enough to shore to cause damaging shaking inland.  

 

Despite the hazards posed by earthquakes, ground failures, and tsunamis within these subduction-zone land- and seascapes, we still lack understanding of the controls on the amount of subduction-zone convergence that is taken up between the trench and arc. How is deformation partitioned among the myriad of deformational processes within the forearc and how does movement associated with these processes contribute to the tectonic and erosive energy budget of a subduction zone? The long-term evolution of the subduction zone system is also fueled by energy contributed by the addition of heat and mass through magma beneath volcanoes, and the variable weight and erosive powers of ice and water as glaciers and sea level respond to changing climate. The study of the total subduction-zone energy budget is enabled by recent advances in our ability to image the topography, bathymetry, and shallow subsurface of land- and seascapes at high resolution. This allows us, for the first time, to gain both a detailed and synoptic view of the way in which areas between the trench and volcanic arc deform in four dimensions.  High-precision satellite geodesy, repeat laser altimetry, drone-based imaging technologies, new submarine monitoring and imaging technologies, and high resolution optical and multispectral imagery can now quantify Earth’s continuous deformation and erosion in near-real time. State-of-the-art numerical models that couple the action of surface processes and subduction-zone geodynamics allow us to link these observations to the energetics and dynamics of the processes that shape subduction-zone land- and seascapes. These new developments promise to enable new fundamental discoveries into the controls on the partitioning of deformation within the subduction zone system, which is central to understanding the risks that consequent hazardous tectonic events pose to communities living within subduction-zone land- and seascapes, by allowing us to answer the questions: How much permanent deformation is absorbed in the forearc and what factors control this?; and, How do upper plate structures that modify land- and seascapes contribute to subduction zone hazards?

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