Over 5000+ marine terraces record tectonics of the Japan arc and hint at essential controls on their creation and preservation.
Authors: Malatesta Luca C. , Huppert Kimberly L. , Finnegan Noah J. 
Published: February 2023

In 1978, &#332;ta and Yoshikawa published a pioneering study describing four distinct zones of marine terrace patterns in Japan and linked them to the large geodynamic processes controlling deformation across the arc. We repeat the exercise of &#332;ta and Yoshikawa (1978) with a large dataset of 5352 marine terraces of presumed last interglacial high stand age (~120 ka). The data is a subset from the Atlas of Marine Terraces by Koike and Machida (2001) later digitized by Nomura et al. (2016).Consistent with &#332;ta and Yoshikawa (1978), we find that, along the subductions, terraces show a near systematic increase in elevation toward the trench reflecting non-recoverable deformation linked to the earthquake cycle. The Pacific Coast has over 1000 terraces that show remarkable regularity in elevation (between 25 and 50 m above sea level, masl). Meanwhile, on the back arc side, terrace elevation can vary over short distances (<20 km) between ~0 and 150 masl. We can identify the signature of the Niigata-Kobe Tectonic Zone responsible for the small block tilting noted by &#332;ta and Yoshikawa (1978) along the coast of the back arc.The large terrace dataset allows us to probe controls on the generation and preservation of marine terraces. Because terrace elevation does not necessarily reflect the elevation of a marine high stand, without absolute dates and depth indicators we avoid using the terraces to calculate rock uplift rates. Instead we use their elevations as an indicator of relative patterns in rock uplift. We identify three main boundary envelopes to the distribution of presumed MIS 5e terraces when the entire dataset is displayed as a function of their mean elevation and surface area, and attribute it to potential controls:There are no large terraces preserved at low elevation because waves can more easily erode platforms that reside in or near the swash zone.
Terrace surface area reaches a maximum around 30 masl before declining again with higher elevation because faster rock uplift rates reduce the time that waves have to erode any given bedrock elevation.
The minimum area of terraces increases with elevation because under faster rock uplift, subaerial erosion processes tend to be more efficient and destroy small platforms.
Further study of the dataset &#8212;in particular accounting for local variations in wave power and rock type &#8212; will provide valuable insights to universal controls on marine terrace creation and preservation.&#160;Koike, K., & Machida, H. (2001). Atlas of Quaternary Marine Terraces in the Japanese Islands. Tokyo: University of Tokyo Press.Nomura K., Tanikawa S.-I. et al. (2016). Compilation of Information on Uplift of the Last Hundred Thousand Years in the Japanese Islands. JAEA reports, (JAEA-Data/Code 2016-015). https://doi.org/10.11484/jaea-data-code-2016-015Ota, Y., & Yoshikawa, T. (1978). Regional characteristics and their geodynamic implications of late quaternary tectonic movement deduced from deformed former shorelines in japan. Journal of Physics of the Earth, 26(Supplement), S379&#8211;S389. https://doi.org/10.4294/jpe1952.26.Supplement_S379