{"created":"2021-03-01T06:51:32.134346+00:00","id":32820,"links":{},"metadata":{"_buckets":{"deposit":"f3177424-d325-467e-b2e9-59b9b4f9fb74"},"_deposit":{"id":"32820","owner":"1","owners":[],"pid":{"revision_id":0,"type":"depid","value":"32820"},"status":"published"},"_oai":{"id":"oai:repository.dl.itc.u-tokyo.ac.jp:00032820","sets":["80:4535:4747:4753","9:504:4538:4749:4754"]},"author_link":["127771","127770"],"item_4_alternative_title_1":{"attribute_name":"その他のタイトル","attribute_value_mlt":[{"subitem_alternative_title":"大和海盆の地震波構造とその形成過程"}]},"item_4_biblio_info_7":{"attribute_name":"書誌情報","attribute_value_mlt":[{"bibliographicIssueDates":{"bibliographicIssueDate":"1988-11-11","bibliographicIssueDateType":"Issued"},"bibliographicIssueNumber":"2","bibliographicPageEnd":"86","bibliographicPageStart":"51","bibliographicVolumeNumber":"63","bibliographic_titles":[{"bibliographic_title":"東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo"}]}]},"item_4_description_13":{"attribute_name":"フォーマット","attribute_value_mlt":[{"subitem_description":"application/pdf","subitem_description_type":"Other"}]},"item_4_description_5":{"attribute_name":"抄録","attribute_value_mlt":[{"subitem_description":"Seismic refraction/reflection experiments were carried out in the Yamato Basin during the DELP-85 cruise. Twenty ocean bottom seismometers were deployed along two refraction lines crossing each other perpendicularly, namely Line A (230 km long trending NE-SW) and Line B (130 km long trending NW-SE). A large amount of explosives and a large volume airgum were used as sound sources. Record sections of Line A and Line B are systematically different in both the cross-over distances of Pn and the distances of critical PmP arrival. To explain these differences, Pn anisotropy is required. In order to derive a precise seismic structure including lateral inhomogeneity, two-dimensional analyses were performed using ray tracing and synthetic seismograms. To satisfy both the gravity anomalies and the refraction data, the Moho must be shallower than 17.0 km, and almost flat along both Line A and Line B. When the Moho depth is assumed to be 16.5 km, the anisotropic Pn true velocities are 8.3km/s for Line B and 7.65 km/s for Line A, respectively. Although various seismic models of the Yamato Basin can be made to satisfy observed travel time patterns as well as amplitudes within the accuracy of 0.1 sec, a general feature of velocity distribution suggest that the crust of the Yamato Basin is classified into oceanic crust. However, the crustal thickness is 13-15 km which is almost twice as thick as that of the normal oceanic crust. It is supposed that the drastic change of the paleomagnetic declination of the Japan Arc at about 15 Ma were mainly caused by the opening of the Yamato Basin. This abnormally thick crust of the Yamato Basin might be due to unknown petrological as well as kinematical processes induced by rapid opening of the basin.","subitem_description_type":"Abstract"},{"subitem_description":"1985年のDELP航海では日本海大和海盆において屈折法地震探査が行なわれた.測線A(NE-SW,230km)およびこれと直交する測線B(NW-SE,130km)上に20台の海底地震計を配置し,エアガン,総計5トンの火薬を人工震源として用いた.本研究ではこのとき得られたデータを基に大和海盆の地殻および上部マントルの精密な地震波速度構造を求め,同海盆の形成過程を考察する.両測線の記録断面を比較すると,Pnが初動として始めて出現する距離,およびモホ面からの臨界反射とみられる相の到達距離に系統的な差異が認められる.これらのことは,南東-北西方向に速く東西-北東方向に遅いP波速度異方性が上部マントルに存在することを示している.詳しい構造解析は2次元波線追跡法による理論走時および理論波形と観測波形を比較し,試行錯誤をくりかえしてモデリングをおこなった.重力異常の観測値と矛盾しない解としては,モホ面の深さ16.5kmで両測線ともにほぼ平坦なモホ面を持ち,Pn速度は測線AB各々7.65km/sおよび8.3km/sとなるモデルが最も適当であると思われる.この他にも,理論走時を観測走時に0.1秒以内の精度で合わせ,理論記象も観測波形をほぼ満足するモデルとしては,測線交点におけるモホ面の深さ16kmから18kmの範囲で,測線Bに沿ったモホ面の形状および下部地殻の速度勾配等を変えることによって,多様な解が存在し得る.しかし,重力異常を満足するためには深さ17km以浅でほぼ平坦なモホ面の形状が要求される.上述のモデルはいずれも地殻上部で速度が連続的に大きな速度勾配で増加し,地殻下部には7.0km/s前後で速度勾配の小さい海洋第3層に相当する層が存在するなど,速度分布に関しては典型的な海洋性地殻の特徴を備えている.しかし,地殻の厚さは13～15kmで,通常の海洋地殻の2倍近くに達する特異なものである.約15Maの古地磁気偏角の急激な変化は,大和海盆のこの時期の急激な拡大によってもたらされたと考えられる.異常に厚い地殻の形成は,このような拡大速度の下で未知の地殻形成メカニズムが働いたことによるのかもしれない.","subitem_description_type":"Abstract"}]},"item_4_full_name_3":{"attribute_name":"著者別名","attribute_value_mlt":[{"nameIdentifiers":[{"nameIdentifier":"127771","nameIdentifierScheme":"WEKO"}],"names":[{"name":"片尾, 浩"}]}]},"item_4_identifier_registration":{"attribute_name":"ID登録","attribute_value_mlt":[{"subitem_identifier_reg_text":"10.15083/0000032820","subitem_identifier_reg_type":"JaLC"}]},"item_4_publisher_20":{"attribute_name":"出版者","attribute_value_mlt":[{"subitem_publisher":"東京大学地震研究所"}]},"item_4_source_id_10":{"attribute_name":"書誌レコードID","attribute_value_mlt":[{"subitem_source_identifier":"AN00162258","subitem_source_identifier_type":"NCID"}]},"item_4_source_id_8":{"attribute_name":"ISSN","attribute_value_mlt":[{"subitem_source_identifier":"00408972","subitem_source_identifier_type":"ISSN"}]},"item_4_subject_15":{"attribute_name":"日本十進分類法","attribute_value_mlt":[{"subitem_subject":"453","subitem_subject_scheme":"NDC"}]},"item_4_text_21":{"attribute_name":"出版者別名","attribute_value_mlt":[{"subitem_text_value":"Earthquake Research Institute, University of Tokyo"}]},"item_4_text_4":{"attribute_name":"著者所属","attribute_value_mlt":[{"subitem_text_value":"地震研究所"}]},"item_creator":{"attribute_name":"著者","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"Kato, Hiroshi"}],"nameIdentifiers":[{"nameIdentifier":"127770","nameIdentifierScheme":"WEKO"}]}]},"item_files":{"attribute_name":"ファイル情報","attribute_type":"file","attribute_value_mlt":[{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2017-06-26"}],"displaytype":"detail","filename":"ji0632001.pdf","filesize":[{"value":"2.9 MB"}],"format":"application/pdf","licensetype":"license_note","mimetype":"application/pdf","url":{"label":"ji0632001.pdf","url":"https://repository.dl.itc.u-tokyo.ac.jp/record/32820/files/ji0632001.pdf"},"version_id":"d31c1886-6aa6-4c67-9bf3-d1abb9246e88"}]},"item_language":{"attribute_name":"言語","attribute_value_mlt":[{"subitem_language":"eng"}]},"item_resource_type":{"attribute_name":"資源タイプ","attribute_value_mlt":[{"resourcetype":"departmental bulletin paper","resourceuri":"http://purl.org/coar/resource_type/c_6501"}]},"item_title":"Seismic Structure and Formation of the Yamato Basin","item_titles":{"attribute_name":"タイトル","attribute_value_mlt":[{"subitem_title":"Seismic Structure and Formation of the Yamato Basin","subitem_title_language":"en"}]},"item_type_id":"4","owner":"1","path":["4753","4754"],"pubdate":{"attribute_name":"PubDate","attribute_value":"2008-05-30"},"publish_date":"2008-05-30","publish_status":"0","recid":"32820","relation_version_is_last":true,"title":["Seismic Structure and Formation of the Yamato Basin"],"weko_creator_id":"1","weko_shared_id":-1},"updated":"2022-12-19T05:17:30.116798+00:00"}