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Malatesta, L.*; Huppert, K.*; Weiss, N.-M.*; Asiedu, R.*; Finnegan, N.*; 末岡 茂
no journal, ,
Erosive marine terraces offer a precious record of crustal strain across hundreds of earthquake cycles along subduction zones. The predominant paradigm that terrace steps correctly reflect unique sea level high stands is significantly weakened when considering the continuous work of wave erosion regardless of sea level stand. A better understanding of the actual information encoded in erosive marine terraces hinges on grasping the dominant processes that control their generation and preservation. Here, we exploit a large dataset of 5352 marine terraces of presumed last interglacial high stand age combined a reconstruction of local wave power around the archipelago. 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: 1) There are no large terraces preserved at low elevation because waves can more easily erode platforms that reside in or near the swash zone, 2) 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, 3) 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 - in particular accounting for lithology - will provide valuable insights to universal controls on marine terrace creation and preservation.
Malatesta, L.*; Huppert, K.*; 末岡 茂; Finnegan, N.*; Asiedu, R.*; Weiss, N.-M.*
no journal, ,
A dataset of over 6000 wave-cut marine terraces of presumed Last Interglacial high-stand age (~120 ka) around the Japan islands provides an unprecedented access to the controls on the generation and preservation of marine terraces. The data is a subset from the Atlas of Marine Terraces later digitized, and carefully corrected and redrawn by ourselves. The terrace dataset is complemented by wave power estimates from NOAA WaveWatch III and bedrock lithology information from the Geological Survey of Japan. Each individual terrace is matched with topographic information, local wave condition, lithology, and local relief. Along the subductions, terraces show an increase in elevation toward the trench reflecting non-recoverable deformation linked to the earthquake cycle. On the back arc side, terrace elevation can vary between ~0 and 150 masl over short distances (
20 km). We can identify the signature of the Niigata-Kobe Tectonic Zone responsible for the small block tilting noted by Ota and Yoshikawa (1978) along the coast of the back arc. Ongoing study of the dataset provides valuable insights to universal controls on marine terrace creation and preservation. We use their elevations as an indicator of relative patterns in rock uplift (precise ages and corresponding sea level stage are rarely available). At the time of abstract submission, we have identified the following: There are no large terraces preserved at low elevation as waves may more easily erode platforms residing 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 may reduce the time that waves have to erode any given bedrock elevation. The minimum area of terraces increases with elevation as subaerial erosion processes would tend to be more efficient under faster rock uplift. Lithology does not play a first-order role in controlling the distribution of terraces across elevation and wave power.