{"id":2932,"date":"2020-09-01T10:21:10","date_gmt":"2020-09-01T01:21:10","guid":{"rendered":"http:\/\/www.eri.u-tokyo.ac.jp\/en\/?p=2932"},"modified":"2020-09-01T10:22:49","modified_gmt":"2020-09-01T01:22:49","slug":"marine-sediment-characterized-by-ocean-bottom-fiber-optic-seismology","status":"publish","type":"post","link":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/research\/2932\/","title":{"rendered":"Marine Sediment Characterized by Ocean-Bottom Fiber-Optic Seismology"},"content":{"rendered":"\n

Spica, Z. J.,\u00a0Nishida, K.,\u00a0Akuhara, T.,\u00a0P\u00e9tr\u00e9lis, F.,\u00a0Shinohara, M., &\u00a0Yamada, T.\u00a0(2020).\u00a0Marine sediment characterized by ocean\u2010bottom fiber\u2010optic seismology.\u00a0Geophysical Research Letters<\/em>,\u00a047,\u00a0e2020GL088360.\u00a0https:\/\/doi.org\/10.1029\/2020GL088360<\/a><\/p>\n\n\n\n

Abstract<\/strong>
The Sanriku ocean\u2010bottom seismometer system uses an optical fiber cable to guarantee real\u2010time observations at the seafloor. A dark fiber connected to a Distributed Acoustic Sensing (DAS) interrogator converted the cable in an array of 19,000 seismic sensors. We use these measurements to constrain the velocity structure under a section of the cable. Our analysis relies on 24\u2009hr of ambient seismic field recordings. We obtain a high\u2010resolution 2\u2010D shear\u2010wave velocity profile by inverting multimode dispersion curves extracted from frequency\u2010wave number analysis. We also produce a reflection image from autocorrelations of ambient seismic field, highlighting strong impedance contrasts at the interface between the sedimentary layers and the basement. In addition, earthquake wavefield analysis and modeling help to further constrain the sediment properties under the cable. Our results show for the first time that ocean\u2010bottom DAS can produce detailed images of the subsurface, opening new opportunities for cost\u2010effective ocean\u2010bottom imaging in the future.<\/p>\n\n\n\n

\"\"
Map showing the location of the telecommunication fiber\u2010optic cable off the shore of Sanriku. The gray section of the cable, which is used in our analyses, is buried under 60\u201370\u2009cm of sediment, while the black section lies directly on the seafloor by gravity. The white dots depict the accelerometers, and the white squares are the pressure gauges. The pink star depicts the location of an earthquake (2019\u201002\u201014T21:10:50; Mw = 3.0) recorded by DAS and shown in Figure 3c. The red star depicts the location of another earthquake recorded only by the OBS systems (2018\u201001\u201030T17:20:56.31; Mw = 3.1; depth = 30.9\u2009km) and showed in Figure 4.<\/figcaption><\/figure>\n\n\n\n
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(a) Power spectral densities along the cable every 500 channel, as shown in Figure\u00a02a<\/a>\u00a0(oceanward). (b) Two\u2010dimensional shear\u2010wave velocity profile obtained from the inversion of the dispersion curves at each subset of 1,000 channels, as shown in Figure S3. (c) Reflection image from autocorrelations of ASF. All autocorrelation functions are band\u2010pass filtered between 0.8 and 4.5\u2009Hz. The yellow box highlights potential velocity contrast corresponding to a four\u2010way travel time reflected\u00a0S<\/em>\u00a0waves. A zoom in the yellow box is shown in Figure S4d. (d)\u00a0S<\/em>\u00a0wave arrivals with automatic gain control for an earthquake recorded by the array as shown in Figure\u00a01<\/a>. In the green area, the\u00a0S<\/em>\u00a0wave arrives after the\u00a0S<\/em>\u00a0wave in the purple area, which suggests a lower velocity zone. The inverted V shapes that may characterize fault zones are highlighted with a red arrow and a red question mark. These fault\u2010zone regions are sometimes associated with amplification effects observed in the autocorrelation functions. Other amplification or scattering effects (orange arrow and blue box) may also be explained by localized tube waves or basin\u2010edge scattering. (e) Geological interpretation that combines the observations of all panels. <\/figcaption><\/figure>\n","protected":false},"excerpt":{"rendered":"

Spica, Z. J.,\u00a0Nishida, K.,\u00a0Akuhara, T.,\u00a0P\u00e9tr\u00e9lis, F.,\u00a0Shinohara, M., &\u00a0Yamada, T.\u00a0(2020).\u00a0Marine sediment … Continue reading “Marine Sediment Characterized by Ocean-Bottom Fiber-Optic Seismology”<\/span><\/a><\/p>\n","protected":false},"author":9,"featured_media":2933,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11],"tags":[],"class_list":["post-2932","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research"],"_links":{"self":[{"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/posts\/2932"}],"collection":[{"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/users\/9"}],"replies":[{"embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/comments?post=2932"}],"version-history":[{"count":3,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/posts\/2932\/revisions"}],"predecessor-version":[{"id":2937,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/posts\/2932\/revisions\/2937"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/media\/2933"}],"wp:attachment":[{"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/media?parent=2932"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/categories?post=2932"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.eri.u-tokyo.ac.jp\/en\/wp-json\/wp\/v2\/tags?post=2932"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}