Seafloor Displacement After the 2011 Tohoku‐oki Earthquake in the Northern Japan Trench Examined by Repeated Bathymetric Surveys

Abstract

We conducted multibeam bathymetric surveys crossing the northern Japan Trench offshore Sanriku and examined seafloor displacement by means of the difference in bathymetry before and after the 11 March 2011 Tohoku‐oki earthquake. The seafloor displacements were less than several meters in vertical displacement and less than 20 m in trench‐normal horizontal displacement; consequently, lower amplitude seafloor displacements were evaluated. Comparatively, the landward lower slope near the trench was uplifted, the middle slope was subsided, and the midslope terrace was depressed after the earthquake. Therefore, localized very large fault slip or very large submarine landslide is unlikely. Instead, smaller uplift of the lower slope near the trench extending broader along the trench seems to be plausible explanation for the devastating tsunami source in the northern Japan Trench area.

Seafloor Geodesy in Shallow Water With GPS on an Anchored Spar Buoy

“…Several methods have been developed to measure seafloor motion, including the following: Bottom pressure (e.g., Chadwick et al, ; Chierici et al, ) GPS acoustic (e.g., Chadwell & Spiess, ; Sato et al, ; Spiess, ; Spiess et al, ; Yokota et al, ) Direct‐path acoustic ranging (e.g., Chadwick & Stapp, ; Osada et al, ; McGuire & Collins, ) Multibeam sonar surveying (e.g., DeSanto et al, ; Fujiwara et al, ) Strainmeter and tiltmeter systems (e.g., Anderson et al, ; Zumberge et al, ) …”

Event Stratigraphy in a Hadal Oceanic Trench: The Japan Trench as Sedimentary Archive Recording Recurrent Giant Subduction Zone Earthquakes and Their Role in Organic Carbon Export to the Deep Sea

“…We acquired high-resolution bathymetry data along the entire trench axis during the R/V Sonne SO251-1 cruise in October 2016 (Fujiwara et al, 2017;Strasser et al, 2017;Kioka et al, 2019). The data were acquired by a 12 kHz frequency KONGSBERG EM122 system equipped on R/V Sonne, which has 432 beams with a transducer of 0.5 (transmission) by 1 (receiving) degrees, and a dual swath (multiping) function.…”

“…We combined a modern digital evaluation model (DEM) calculated from bathymetry data at the water depths of <∼6,000 m acquired before 2011 by the Japanese research cruises (Hydrographic and Oceanographic Department Japan Coast Guard and JAMSTEC, 2011) with our post 2011 earthquake data (>5500 m depth) acquired during the R/V Sonne SO251-1 cruise (Fujiwara et al, 2017;Strasser et al, 2017;Kioka et al, 2019). This allows analyzing the flow network of potential sediment pathways across the margin into the trench and estimating relative contribution of sediment volume that can be routed into individual terminal trench basins.…”

Correlation of frontal prism structures and slope failures near the trench axis with shallow megathrust slip at the Japan Trench

“…Another characteristic is a proposed tsunami source region at around 39°-40°N, to the north of the large shallow slip area identified by tsunami data analyses [4][5][6] . Seafloor geodetic observations 7 and estimates of seafloor displacement based on bathymetric datasets [8][9][10][11] are strong evidence with which to examine the propagation of fault slip towards the seafloor through the trench axis area. Research using differential bathymetry has shown that seafloor displacement during the Tohoku earthquake was > 50 m near the trench axis at 38°05′-38°35′N, where the large slip occurred during the Tohoku earthquake 8,9 , but was not significant outside of this area 10,11 (Fig.…”