੅ࡄݪਫ਼ࡄݪ༭࣬ȁల 68 ࣢ȁ2005 ා 9 ࠮ܿڠشཡब ࢹ௮ζΛάϋΈڔ૬໐౷̩̿ܖ૧̱̞८၄ਹ༹ࣣͅ ٜ৷Ƚض฽ৣ༹ΟȜΗ͈͒ഐဥ̷͈͂ࠫڙȽୌධ඾ུࡪ̤̫ͥͅࢩ ໌നഓ࿟ɖ Improved Mapping Method for Deep Crustal Imaging - Application to Wide-angle Refl ection Data in the Southwest Japan Arc and its Interpretation - Tetsuya TAKEDA Solid Earth Research Group, National Research Institute for Earth Science and Disaster Prevention, Japan [email protected] Abstract Wide-angle refl ection data often show remarkable refl ections from the deep crust. In order to obtain new images of crustal inhomogeneity beneath the southwest Japan arc, I propose an improved mapping method designed for sparse wide-angle refl ection data. The method, an improved form of the Common Scatter-Point (CSP) stacking method, has the advantages of both the Common Mid-Point (CMP) and CSP stacking methods, which means that it can add a migration effect to the CMP method, and has less of the ghost curves that results from the CSP method. When applied to two sets of wide-angle reflection data (the 1988 Kawachinagano-Kiwa profile and the 1989 Fujihashi-Kamigori profile), the method provided clear images of the subducting Philippine Sea plate and the island-arc’s lower crust. The main results are as follows: (1) Intra-plate seismic activity is concentrated within the oceanic mantle, which suggests that the oceanic mantle may be subject to dehydration embrittlement; and (2) The lower crust beneath the southwest Japan arc has strong inhomogeneity, with a wavelength ranging from several to a dozen kilometers, which may result from crustal reconstruction due to igneous activity that has occurred since the Cretaceous. Key words : Common Scatter-Point (CSP) stacking method, Wide-angle refl ection, The 1988 Kawachinagano-Kiwa profi le, The 1989 Fujihashi-Kamigori profi le, The Philippine Sea plate ͛ͅ ͊ Allmendinger et al., 1986ȫȅ̹͘Ȅߠ୬༹ٜଢ଼̲͉̽̀͢ͅ .1 ́ٮޏࢹ௮ౝऔ͈࡛ે ଔ೰̯̹ͦ Moho ࿂͉ȄႲ௽എ́ౙ੗̈́௸ഽະႲ௽ڔఱၘ౷ 1.1 Ȅ1980 ාయͤ͢ COCORPȪ႕̢͊ Brown, ̷̜ͥ͂ͦ́͘ࣉ̢̧̹̦ͣͦ̀Ȅ৘षͅං̹ͣͦ฽ৣ͉́ڔȁఱၘ౷ 1991ȫ͞ LithoprobeȪ ႕ ̢ ͊ Cook et al., 1992ȫ͂ ̞̹̽ ౯࿂଎͉́ Moho ࿂͈Ⴒ௽଻͉ߊ໦എ̱̥ͅంह̱̤̀ͣ ̭̜͂ͥ́ٮޏࢹ௮ౝऔ̦ ̴ȄMoho ࿂͉ 3-5km ͈໙̹ͬ̽͜ໝॠ̈́ڔఱܰ࿅ίυΐͿ·Π͈͂ࣞ͜ྟഽ͈૬໐౷ ৘ঔ̯̠̹ͦͥ̈́̽͢ͅȅౝऔ͉ͅఱၾ͈ܥऺ̦ൎව̯ ̦ྶ̥̹ͣ͂̈́̽Ȫ႕̢͊ Hale and Thompson, 1982ȫḙ̏ ڔȄྟ̈́਋૦ത͂อૼതͬ෻౾̱̹۷௶ͬ৘࡛̱̀ఱၾ ͈̠͢ͅȄ฽ৣ༹ٜଢ଼̽̀͢ͅਲြ౶ͤං̥̹̈́̽౷ͦ අ͈ڔΟȜΗ̦৾ං̯̠̹ͦͥ̈́̽͢ͅȅࣞྟഽ۷௶ͤ͢ͅ ૬໐͈๷ळࢹ௮̦ଔ೰̧̠́ͥ̈́ͤ͢ͅȄఱၘ౷͈ ၑٜ̳ͥષ́ఉఱ࣓̈́ࡃ̱̹ͬȅͬاஃ໐ࢹ௮ౝऔ͞୞࿳ౝऔ̈́̓ͅঀဥ̱̞̹̀฽ৣ༹ٜଢ଼ ಭ͞ૺ ࢹ௮ౝऔ͈࡛ેڔෝ̱ͅȄ̷ͦ́͘นட̱̥͂௴̢̥ͣͦ̈́̽ 1.2 ോࡪ౷خ൵ව͈ͬ ࢹ଼̯ͦͥ඾ུ͉́Ȅบ෫౷ૼ൲̥ͣڔഎȹͅζΛάϋΈ̳̭ͥ͂ͅ ȁ༷֚Ȅോࡪ౷ژ૬໐͈ࢹ௮ͬȸণڔ౷̹ ฽ৣ༹Ȫߠ୬༹ȫౝऔ̦ಎ૤ͅڙచચഎͅถ௄ ࡄݪΈσȜί̽̀͢ͅࢩ͉͂ڔȄ൫ྶ̈́ષ໐౷ض̱̹ࢗȅ̷଼͈ࠫ ,อࡉ̦̜̹̽Ȫ႕̢ ̧࣐̹ͩͦ̀Ȫ႕̢͊Ȅบ෫౷ૼ൲ࡄݪΈσȜίȄ1985͈ڔ໐౷ئȪlaminateȫࢹ௮ͬࠁ଼̳ͥ ੅ࡄݪਫ਼ȁࡥఘ౷ݩࡄݪ໐࿝ܿڠشɖඊၛ࣐ଽ༹૽ȁཡब Ƚ!175 Ƚ ੅ࡄݪਫ਼ࡄݪ༭࣬ȁల 68 ࣢ȁ2005 ා 9 ࠮ܿڠشཡब Ȅ႕̢͊ಎ໐඾ུͅ ̞͈̈́̓̾̀ͅમळ݈̈́ა̳̭̦ͬͥ͂ඳ̱̥̹̽ȅ̥ͣض1999ȫȅ๞̷͉͈ͣͦͣౝऔࠫ Ȅਲြ͈฽ৣ༹͈ٜଢ଼਀༹͉Ȅ਋͉̱̀۾࢜ ȁ̹͘਀༹༷ͅئȄତ km ಼̢ͬͥષͅئঝݿ୼Ƚ୓ؖࢹ௮஌̫̤ͥ ࣞྟഽ۷௶͈ΟȜΗͬచય̱͈͂̀ئ100m ո ̦ڞۼ๕͈૙̞֑̞ͬ঵̾൐߹০͈ݙ౯௄ࢹ௮ͬྶ̥ͣͅ ૦തܖ͈ ฽ৣ༹ΟȜΗ͈͒ഐဥ͉ேڙȄ۷௶തྟഽ͈೩̞ࢩ̤ͤ ͅڔ໐౷ئȪIkami et al., 1986, Takeda et al., 2004ȫȄ̷͈̱ ٮະ޳ৗ଻̦̜̭ͥ͂ͬা̱̹Ȫ໌ന , 1997ȫȅ̹͘ ೰̱̞̞̀̈́ȅ̷͈̹͛Ȅષܱ͈ࡄݪ̤̫ͥͅഐဥࡠ̞ޑ͉ ఊ໹ဢίτȜΠ͈ೆ͙ࣺ͙ͤ͢ͅࠁ଼̯̹ͦോࡪ̜́ͥ ͉ౙͅΟȜΗ̺̫͈࿚ఴ͉̩́̈́Ȅ਀༹ুఘ͜ͅ࿚ఴ̦ ෇̯ ̜ͥ͂࡞̢ͥȅઐോȪ1999ȫ͉Ȅ฽ৣ༹ٜଢ଼਀༹͈֚̾́ږ൐ཤ඾ུ͉́Ȅષ໐ζϋΠσͬഥͩͥ෨ȪPnȫ̥ͣ ۾ͅا५έυϋΠ ̜ͥ८၄ਹ༹ࣣͬဥ̞̹฽ৣ༹౷ૼౝऔ͈ࣞୈഽغȄ̤̱ͤ̀اMoho ࿂͈૬̯͉ఱ̧̩་ ͥͦ ೰̱ب͜ஜࡪ௰͉́ 32-35km ͂̽͂͜͜૬̞̦Ȅ෸ࡪ௰́ ̱̞̀͂͛̀ͥ͘ȅ̷͈ಎ́๞͉Ȅକ໹฽ৣ࿂ͬͤ͢ ಎ૤̳͂ͥහփ͈ͬڙ࿂฽ৣ෨͈฽ৣޢાࣣͅȄ̷͈̹ اถ̦ڔఱฺ̽̀ͅ౷ڐ27km ͂ஃ̩̤̈́̽̀ͤȄ෸ࡪ ͉ սඤ͈ΠτȜΑ͈͙ͬਹࣣ̳̭ͥ͂ͤ͢ͅȄS/Nํڙબݶͬা̱̹ȪIwasaki et al., 2001ȫȅ̱̥̱̦̈́ ८၄̞̱ͥ̀ Ȅ৽̱͂̀ P ෨ȆS ෨̷͈͞฽ৣ෨൝ ๤ͬ࢜ષ̵଼̯̭̱̞ͥ͂ࢗ̀ͥͅḙ͈̏ાࣣȄέτΥ͉ضḘ͈̏ͦͣࠫͣ ͦͥ͘ΠτȜΑ͈͙ͬਹ̧ࣣ̳ͥ͂ͅ S/N܄௢শͬঀဥ̱̹ߠ୬༹ٜଢ଼ͅջ̞̽̀ͥȅߠ୬༹ٜଢ଼ͅ σΖȜϋ͈ͅ ۼ ࢹ௮͈ͺ;Πρͼϋͬೕ͚̭͂ ๤̦डఱ͂̈́ͥȅొ̱Ḙ͈̏਀༹͉ࣞྟഽȪ1 ȡ 100mڔഽࢹ௮̥ͣȄ౷௸ͥ͢ ౷ૼౝऔΟȜۼȫͅอૼത̤͍͢਋૦തͬ෻౾̱̹࢟֔ڞ ະ޳ৗ଻͞ Moho ࿂͈ࠁે͈ڔȄ଒ೄ༷͈࢜౷̧̦͉ͥ́ ࢹ௮̞͈݈̾̀ͅა͉ඳ̱̞ȅ Η͈͒ഐဥͬே೰̱̞̹̀ͥ͛Ȅႋ୪̳ͥ۷௶ത͈෨ࠁڔ଻ৗ̞̹͂̽๷ळ̈́౷͞ ՛̞மྟ̈́ΟȜΗ͈͒ഐဥ͉ࣉၪ̯̞̞ͦ̀̈́ȅ̦۾߃ා͈ౠႹോ̤̫ͥͅ TASPȪSato et al.,1998ȫ͞൐ཤ඾ུ ͈௖ ฽ৣ෨ͬঀဥ̳ͥषͅ࿚ఴ͂̈́ͥ෨ࠁ͈ΑΠڙ౯ࣣ൳۷௶ȪIwasaki et al., 1999ȫْ͈͉̈́̓ࠗ́Ȅ̞͘ ̹͘Ȅࢩ؍ ฽ৣ༹ڙ࡞ݞ̯̞̞ͦ̀̈́ȅࢩ̱̀۾ͅضષૼ࡙͈৽ႁ̜́ͤૼ࡙෨ࠁௌैȆ౷ૼ෨΀ΥσΆȜ τΛΙϋΈ࢘ၘ͞ ฽ৣ༹ΟȜڙෝ̈́ΨͼήτȜΗȜૼ࡙ Vibroseis® ͬ ΟȜῌ฽ৣ༹ٜଢ଼ͬ൵ව̳̹͉ͥ͛ͅȄࢩخ಺ା͞Ⴒ௽อૼ̦ อ̦ຈါ̜́ͥȅٳ਀༹͈̹̱اࢹ௮ౝऔ͂൳೾ഽ͈ Η͈අಭͅඅڔൎව̱̀ȄLithoprobe ͈̈́̓ఱၘ౷ Ȅ႕̢͊Ȅ൐ཤ඾ 1.4 ུࡄݪ͈࿒എضෝ̹͂̈́̽ȅ̷͈ࠫخ̦௶ࣞྟഽ۷ ฽ৣ༹ౝऔ͉́΀ڙୢၴ५౷͉́Ȅၰზ͈ݙ౯௄̽̀͢ͅ؋̱ષ̬ͣͦ ȁบ෫౷ૼ൲ࡄݪΈσȜίͥ͢ͅࢩུ͈ ෇̯̹ͦȪ໹ന ΥσΆȜ͈ఱ̧̞ఱ࿪ၾ͈Θͼ΢ζͼΠૼ࡙ͬঀဥ̱̀ږpop-up ࢹ௮̦ࠁ଼̯̞̭̦ͦ̀ͥ͂ ͥ ̦̭̳́͂ͥ௶૬໐̥͈ͣ฽ৣ෨ͬ͜۷ڔȄ1999ȫȅొ̱Ȅോࡪ̤̫ͥͅࢹ௮ౝऔ๊͉֚́എͅ ̞̹ͥ͛Ȅ౷̥͕ ૬ڔఞ̯ͦͥȅ৘षͅ෨ࠁܱ჏ͬವ͛ͥ͂Ȅ౷ܢ̧͂ͥ ͛ȄΘ̹̞ޑ౷൲ΦͼΒ̦ఱ̧̩Ȅ̹͘౷ૼ෨͈ࡘଚ͜ ෇̧̳̭̦ͥ͂́ږ฽ৣ෨ͬڙͼ΢ζͼΠͅ๤͓̀΀ΥσΆȜ͈઀̯̞ Vibroseis® ͉́ ໐̥͈ͣ૦໙͈ఱ̧̞ࢩ ࢹ௮͈ଔ೰๊͉֚ͅ ͥȪ଎ 1.1ȫȅ฽ৣ༹ٜଢ଼͉࡛हٜ̽͂ࣞ͜͜௨ഽ̈́ͼιȜڔMoho ࿂ͅో̳͕ͥ̓૬໐͈́͘౷ ະ͈ڔ໐౷ئ਀༹̜́ͤȄMoho ࿂͈ࠁે̳ͥ͞ރࣾඳ̜́ͥȅ ΐͬ೹ ̜ࠧ́ͥȅخ฽ৣ༹ΟȜΗ͈͒฽ৣ༹ٜଢ଼͈൵ව ޳ৗࢹ௮݈ͬა̳ͥષ́฽ৣ༹ٜଢ଼͉ຈါະڙࢩ 1.3 ฽ৣ༹ΟȜΗͬঀ̽̀෨൲ા஠ఘͬ฽ৣ༹എͅڙࢩ ζΛάϋΈ̳ͥࡄݪ͉Ḙ̏ͦ́͘ͅ Chang et al.Ȫ1989ȫ͞ Zelt et al.Ȫ 1998ȫ̈́̓ͤ͢ͅ༭̯̞࣬ͦ̀ͥȅChang et al. ฽ৣڙȪ1989ȫ͉Ȅධୌ΂·ργζ̤̞̀৾ͅං̯̹ͦࢩ ༹ΟȜῌਹࣣஜခࡠओ໦ζͼΈτȜΏοϋ༹ͬഐဥ̱ ৽ಫ̱̀ͬٮȄอૼതྟഽ̦઀̯̞̭͂ͥ͢ͅഐဥࡠ̦̹ ̞ͥȅZelt et al.Ȫ 1998ȫ͉Ȅsynthetic ͈෨ࠁΟȜΗͬै଼ OBHȪ Ocean-Bottom Hydrophoneȫ۷௶͈ΟȜΗٜଢ଼ ̱̀ ฽ৣ༹ΟȜΗ͈͒ਹࣣஜڙ࿅̱̹ΞΑΠͬ৘ঔ̱Ȅࢩͬ ෝ଻ͬ࠿خσΪγΛέ૬ഽζͼΈτȜΏοϋ༹͈ഐဥ΅ ฽ৣ෨ͬဥ̞̀૬໐͈ͼιȜΐڙȄࢩضબ̱̹ȅ̷͈ࠫ 2km ͉ڞۼ ෝ̜̦́ͥȄOBHخζΛάϋΈ̳̭͉ͥ͂ͬ ոඤ́Ȅࠗॳͅဥ̞ͥ௸ഽࢹ௮κΟσ͈௸ഽࢋओ͉ 4% ո ଎ 1.1 บ෫౷ૼ൲۷௶ΈσȜίͥ͢ͅߠ୬༹ౝऔ͈۷௶෨ ૬໐̥͈ͣڔષߴ௶஌ S-1ȫȅ౷ . ޘඤ̫̞́̈́ͦ͊̈́ͣ̈́͂ঐഊ̱̞̀ͥȅ඾ུ̤̫̭ͥͅ ࠁ႕Ȫ1989 ා൥ ս̹ͦ͘ႀ֖ȫȅܱ́ڙ෇̧́ͥȪঅږ฽ৣ෨ͬڙࡄݪ͉Ȅ݌֔Ȫ1991ȫ͞ Matsu’ura et al.Ȫ1991ȫͬ ࢩ̠͈̈́͢ എ̈́฽ৣ༹ٜଢ଼ ჏͉ 6km/sec ́ reduce ̱̜̀ͥȅུܖȅ݌֔Ȫ1991ȫ͉̞͕̞̈́̓ͭ͂̀ੰ ༹̜́ͥ CMP ਹ༹ࣣͬဥ̞̀ζΛάϋΈ̱̤̀ͤḘ̏ͦ Fig. 1.1 Example of the record section of the refraction survey ంह̳ͥཤ߹০͈฽ৣ࿂ Ȫthe 1989 Fujihashi-Kamigori profi leȫ conducted by theͅڔ໐౷ئ͈ئչ฼ോܮͤ͢ͅ ೆ͙ࣺ͚έͻςάϋ٬ίτȜΠ͈ષ࿂ͬ௴̢̭ͥ͂ͅ Research Group for Explosion SeismologyȪRGESȫ. The͞ CMP reduction velocity is 6km/sec. Wide-angle refl ections from ̢̀ح̱̹ࢗȅ̱̥̱Ȅ۷௶തྟഽ̦೩଼̞̭͂ͅ ਹ༹ࣣٜͥ͢ͅଢ଼ͬဥ̞̹̹͛ȄႲ௽଻̧̦͉̱̽ͤ͂ the crustal lower part are identifi ed in the area enclosed by .฽ৣ࿂̥͉ͣȄέͻςάϋ٬ίτȜΠ͈ࠁે͞պ౾ the trapezoid̞̈́ Ƚ!176 Ƚ ࢹ௮ζΛάϋΈȽ໌നڔ૬໐౷̩̿ܖ૧̱̞८၄ਹ༹ࣣͅ ฽ৣ෨ͬဥ̞̀෨൲ા஠ఘͬζΛ ນ 2.1 Lithoprobe ْࠗͥ͢ͅ Southern Canadian Cordelleraڙࡄݪ͉́Ȅࢩ̷ུ̭́ ࢹ௮ͬȸণ ̤̫ͥͅఱၘ૬໐ࢹ௮ౝऔȪCook et al., 1992ȫ͂ڔάϋΈ̳̭ͥ͂ͤ͢ͅȄോࡪ̤̫ͥͅ૬໐౷ ષߴ௶஌ͅ . ޘഎȹͅ௴̢̭ͥ͂ͬদ͙ͥȅ̱̥̱Ȅஜ੆͈̠͢ͅਲ บ෫౷ૼ൲ࡄݪΈσȜίͥ͢ͅ൥ژ ฽ৣ༹ౝऔȪบ෫౷ૼ൲ࡄݪΈσȜίȄڙ฽ৣ༹ΟȜΗͬঀဥ̱̀૬໐౷ ̤̫ͥࢩڙြ͈਀༹͉́மྟ̈́ࢩ ڛࢹ௮ͬζΛάϋΈ̳̭͉ͥ͂ඳ̱̞ḙ̷ུ̏́ࡄݪ́ 1995ȫ͈͂ॽအ๤ڔ ෝ̈́૧̱̞ζΛάϋΈ਀ Table 2.1 Specification comparison between a continental deepخ฽ৣ༹ΟȜῌഐဥڙȄࢩ͉ อ̳ͥȅ̷̱̀Ȅ৘षͅ۷௶̯̹ͦ 2 ΓΛΠ͈ࢩ seismic survey of the Southern Canadian Cordelleraٳ༹ͬ ฽ৣ༹ΟȜῌഐဥ̱Ḙ̷̏́ංͣͦͥͼιȜΐ̥ͣ ȪCook et al., 1992ȫ from the Lithoprobe project, andڙ ೆ͙ࣺ͚έͻςάϋ٬ίτȜΠ͈պ౾͞ࠁેͅ a wide-angle reflection/refraction survey from theͅئോࡪ Fujihashi-Kamigori profileȪ Research Group for 1989 ئޏ۪·ȅ̹͘Ȅ։̈́ͥΞ·ΠΣΛ̳̥ͥͣͅྶ̞̀̾ .*૧ Explosion Seismology, 1995̳ͥ۾ະ޳ৗ଻͞ Moho ࿂͈අಭ͈ͅڔ໐౷ئ̫̤ͥͅ ̱̞౶ࡉͬං̭ͥ͂ͬ࿒എ̳͂ͥȅ อٳ૧̱̞਀༹ .2 อ̜̹̽̀ͅٳ਀༹ 2.1 ฽ৣ༹ΟȜΗ͈අಭ̞̾̀ͅ୰ྶ̳ͥȅਲြڙड੝ͅࢩ ฽ৣ༹ౝऔ͈ॽအ͉Ȅ฽ৣ༹ٜଢ଼͈́͘ੜڙ඾ུ͈́ࢩ͈ ḙ͉̏ͦࢃ͈ζͼΈτȜΏοϋੜၑ͈षȄୃ̧̦ͥ́͂ ̳ͥڛၑͬே೰̱̹ Lithoprobe ْ͈ࠗࢹ௮ౝऔ͈ॽအ͂๤ ࢹ௮ͬζΛάϋΈ̳̹ͥ͛ͅఱ་ਹါ̜́ͥȅئอૼതȆ਋૦തྟഽ͉઀̯̞ȅ֚႕̱͂̀ȄLithoprobe ̱̩౷͂ ْ̤̫ࠗͥͅධಎ؇΃΢Οͻͺϋ५ࠏ̤̫ͥͅఱၘ૬໐ ȁ௽̞̀Ȅ̽͂͜͜ഥൡഎ̈́਀༹̜́ͥ CMP ਹ༹ࣣ͂ζ ࢹ௮ౝऔȪCook et al., 1992ȫ͂บ෫౷ૼ൲ࡄݪΈσȜίͅ ͼΈτȜΏοϋ਀༹͈̜֚̾́ͥ८၄ਹ༹ࣣ̞̾̀ͅત ࢹ௮ౝऔȪบ ̳ٚͥḙ͈̏ 2 ͈̾యນഎ̈́ζΛάϋΈ਀༹ͬ႕͂ͤͅȄڔ౷༷̤̫ͥͅോࡪ౷ܪ඾ུ͈ಎ໐Ȇ߃ͥ͢ ෫౷ૼ൲ࡄݪΈσȜίȄ1995ȫ͈ॽအͬນ 2.1 ͅা̳ȅോ ̷͈ͦͣ਀༹͈ࡔၑ̷͈͂࿚ఴതͬၑٜ̱̹ષ́Ȅ૧̱ อ৾ͤͅழ͚̭̳͂ͥͅȅٳ਀༹̞ ۼࢹ௮ౝऔ͉ఱၘ૬໐ࢹ௮ౝऔͅచ̱̀Ȅ਋૦തڔࡪ౷ ȄංͣͦͥΟȜΗ͈ 2.2 CMP ਹ༹ࣣ̜ͤ́ 500/1 ͉ڞۼ30Ȅอૼത/1 ͉ڞ ࢹ௮ౝऔ͈ΟȜΗͬဥ̞ 2.2.1 CMP ਹ༹ࣣ͈ࡔၑڔओ͉๛̞͛̈́ȅോࡪ౷ڒၾഎ ͅئఱ̧̞̹͛Ȫ໹ ȁࡔၑͬ୰ྶ̳̹ͥ͛ͅȄ଎ 2.1Ȫaȫ́া̳̠̈́͢౷̦ڞۼ฽ৣ༹ٜଢ଼࣐̠ͬાࣣ͉Ȅ۷௶ത̀ ೰̱Ȅ౷ນ͉ͅอૼبକ໹̈́฽ৣ࿂̦̜ͥକ໹ 2 ௄ࢹ௮ͬ ͉۾޳ 1.5kmȫȄ๊֚ͅႋ୪̳ͥΠτȜΑ͈͂฽ৣ෨͈௖ ՛̞ȅ̷͈̹͛Ȅ฽ৣ෨͈պ௖̦ఁ̴ͩȄζΛάϋΈ̱ ത͂਋૦ത̦୭౾̯̞ͦ̀ͥાࣣͬࣉ̢ͥȅ଎ಎ͈๔࣢ͬ อૼڎ͜Ⴒ௽̳ͥ฽ৣ࿂͈ठ࡛͉ඳ̱̞ȅ̹͘Ȅૼ࡙͉஠̀ ૦̜̽̀ͥอૼത͂਋૦ത͈ழ̵͙ࣣ̤̞ͩ̀ͅȄ̀ ฽ৣ࿂́฽ৣ̱̀చ͂̈́ͥ਋૦ത͈ئΘͼ΢ζͼΠૼ࡙̜̹́ͥ͛Ȅอૼത͈ૼ࡙෨ࠁ̷͈͞ ത̥ͣ੄̹෨̦౷ ழ̵̷͙ࣣ̤̞͈ͩ̀ͅ฽ৣത͉֚ڎ΀ΥσΆȜ͈౷ૼ෨་۟࢘ၚྀ͉ٝ։̈́ͤȄ̷ͦͣͬଷ ͅൢ಍̧̳ͥ͂Ȅ ࢄ̳̭͉ͥ͂ඳ̱̞ȅ̷͈̹͛։̈́ͥอૼത͈ΟȜΗͬ ౿̳ͥḙ̏ͦͬވ೒฽ৣത͂ࡤ͐ȅCMP ͉͂ȄCommon ௶೒฽ৣത͈փ̜́ͥȩ̭͈͈̏͂۷ވਹࣣੜၑ̳ͥष͉ͅಕփ̦ຈါ̜́ͥȅ MidPoint ͈ၞ́ ̺̦Ȅခ၌̈́ത̜ͥ͜ȅ̴͘ૼ࡙̦஠̀Θͼ΢ζͼΠ ܱ჏͉଎ 2.1Ȫbȫ͈̠̈́ͤ͢ͅȄ฽ৣ෨௢শ͉஼ެ஌ͬຝ ೒฽ৣതೄષ͈౷ນވอ෫̜͈́ͥ́ȄΨͼήυ΍ͼΑ͈̠̈́͢ఈ͈ଷࢄૼ࡙ ̩ḙ͈̏ͦͣ۷௶ܱ჏̜̹̥ͬ͜ ૬໐͈ౝऔ͉ͅޭ͛̀ ͈൳֚ത́อૼ͂਋૦̱̹̥͈̠ͬ͢ͅ་̳̭۟ͥ͂ͬڔ͜΀ΥσΆȜ̦ఱ̧̩Ȅ౷ͤ͢ ခ̜࢘́ͥȅ̹͘Ȅ͂͂͜͜ߠ୬༹ͥ͢ͅ௸ഽࢹ௮ଔ೰ NMO ༞ୃ͂ࡤ͐ȅNMO ༞ୃͤ͢ͅ฽ৣ෨͉պ௖̦ఁ̽ Ⴅͅ໼͍Ȩ̭͈͈̏͂༞ୃ̯̹ܱͦ჏ͬΔυ΂έ֚؍̀ ࿒എ̱̹͂ౝऔ̜̹́ͥ͛௶஌ಿ̦ಿ̩୭೰̱̜̀ͤͬ ૬໐ͬ೒ͥߠ୬෨ ΓΛΠ௢শܱ჏͂ࡤ͐ȅ̷̱̀൳̲ CMP ͬ̾͜Δυ΂έڔȪ150-200kmȫȄζϋΠσ͉̲ͬ͛౷ ޑ૬໐͈́͘௸ഽࢹ௮ͬୈഽ̩͢ଔ೰̳̭ͥ͂ ΓΛΠ௢শܱ჏ͬ௷̵̱ࣣ̭ͩͥ͂ͤ͢ͅȄ฽ৣ෨͉ڔȄ౷̥ͣ ෝ̜́ͥȅ฽ৣ༹ٜଢ଼́௸ഽࢹ௮ͬݥ͉͛ͥͅȄ֚ ಺̯ͦͥḙ͈̏௷̵̱ࣣ͈̭ͩ͂ͬ CMP ਹࣣ͂ࡤ͐ȅ֚خ̦ ഽٜଢ଼࣐̠ͬȅ௸ഽٜଢ଼͉͂Ȅକ໹ఉ௄ࢹ௮͈ા ༷Ȅ஼ެ஌ͬຝ̥̞̈́ఈ͈෨Ȫ႕̢͊Ȅೄో P ෨͞ S ෨Ȅ௸๊ͅ Ⴅͅպ֚؍ࣣ͈฽ৣ෨௢শ̦߃যഎͅ஼ެ஌ͬຝ̩଻ৗͬ၌ဥ̱̀Ȅ multipleȄນ࿂෨̈́̓ȫ͉ȄNMO ༞ୃ̽̀͢ͅ အș̈́௸ഽ͈͂́͜ࢃ੆͈Δυ΂έΓΛΠ௢শܱ჏ͬै ௖̦ఁ̞̹ͩ̈́͛ͅ௷̵̱ࣣͩ̀͜ޑ಺̯̭͉ͦͥ͂̈́ ଼̱௷̵̧̱ࣣ̹ͩ͂ͅȄ̽͂͜͜฽ৣ෨͈૦໙̦ޑ̩ ̞ȅρϋΘθΦͼΒ͜௖फ़̯ͦȄ௷̵̱ࣣ̹ͩତȪਹࣣତȫ ̷࡛̹͈͈ͦͬ͜૬̯͈௸ഽ̳͈̜͂ͥ́ͥ͜ȅ̱̥̱Ȅ n ͅ؊̲̀ȄS/N ๤͉ n1/2 ෼͂̈́ͥȅ̷̱̀Ḙ͈̏ௌैͬ ͼιȜ͈ئഎ۰༒ͅ౷ڛോࡪ͈ΟȜῌഐဥ̳ͥાࣣȄ ஠̀ CMP ࣐̠̭́͂ͤ͢ͅȄ๤̞ޑະ޳ৗ଻༹͈༷͈̭ͬ ͛Ȅ௸ഽ ΐͬං̧̭̦ͥ͂́ͥḙ͈̏਀༹͈၌ത͉ȄΟȜΗତ̦̹ͥͦٸ৘ष͈฽ৣ෨௢শ̦஼ެ஌̥ͣఱ̧̩ ฽ৣ༹ΟȜ ઁ̞̈́ાࣣ́͜ࢃ੆̳ͥζͼΈτȜΏοϋੜၑ͈̠̈́͢ڙٜଢ଼̳̭͉ͥ͂ඳ̱̞ȅ̷ͦͅచ̱̀Ȅࢩ ȅକ໹̧༷̜̭̞̯̭࢜ͥ́͂̈́ܳ֨ͬاΉ͉Ȅߠ୬༹ٜଢ଼̽̀͢ͅ৘षͅ௢শࠗॳ࣐̞ͬȄ௸ ͼιȜΐ͈Ⴆ ఱ̧̩̞̈́ࢹ௮͈ાࣣ͉ͅȄ̥̈́ͤୃ̦اഽࢹ௮ͬ౶̭ͥ ͈௸ഽࢹ௮་௸̈́ږഽࢹ௮ͬݥ̞̹͛̀ͥ͛Ȅͤ͢ୃ Ƚ!177 Ƚ ੅ࡄݪਫ਼ࡄݪ༭࣬ȁల 68 ࣢ȁ2005 ා 9 ࠮ܿڠشཡब ਋૦തȫȄȪbȫNMO ༞ୃஜ͈͉ڙอૼതȄঅ͉ڙါȅȪaȫକ໹ 2 ௄κΟσȪ२ٽ଎ 2.1 CMP ਹ༹ࣣ͈ ෨ࠁȄȪcȫNMO ༞ୃࢃ͈۷௶෨ࠁȄȪdȫCMP ਹࣣࢃ͈Δυ΂έΓΛΠ௢শܱ჏௶۷ Fig. 2.1 Scheme of the Common Mid-PointȪCMPȫ stacking method.Ȫ aȫ Simple model with a single horizontal refl ectorȪ triangles and squares indicate shot points and receivers, respectivelyȫȪbȫBefore NMO correctionȪ cȫAfter NMO correctionȪdȫCMP stacking after NMO correction. ෝ̜́ͥȅخζΛάϋΈ̦̈́ږ 2.2.2 CMP ਹ༹ࣣ͈࿚ఴത CMP ਹ༹ࣣ͉́Ȅ1ȫ฽ৣ࿂̦କ໹̜́ͥȄ2ȫକ໹༷࢜ ஜ೹̱̞͂̀ͥȅ̷͈̭̞͕͉ͬ͂̈́̓ͭ͂اഽ་௸ͅ ζΛͅږ͛Ȅ߹০͈઀̯̞฽ৣ࿂͈ાࣣ͉̥̈́ͤͅୃ̹ άϋΈ̧̦́ͥȄݢ߹০ͬ̾͜฽ৣ࿂̦̜ͥાࣣ͞କ໹ ༷࢜ͅఱ̧̈́ະ޳ৗ̦̜ͥાࣣ͉ͅȄୃ̱̞պ౾ͅζΛ άϋΈ̧̞̞̠́̈́͂ࠧത̦̜ͥȅ̱̹̦̽̀Ȅോࡪ͈ ͛କ໹༷͈࢜௸ഽ་̹͈ޏ۪·ໝॠ̈́Ξ·ΠΣΛ̠͢ͅ ఱ̧̞౷֖ͅ CMP ਹ̷༹ࣣ͈ͬ͘͘ഐဥ̳̭̦ͥ͂ͅا ͉࿚ఴ̦̜ͥȅ ೒ુ CMP ਹࣣࢃ͉ͅȄ߹০͈̜ͥ฽ৣ࿂ͬୃ̱̞պ౾ ͅ࿗̳ζͼΈτȜΏοϋੜၑͬຈါ̳͂ͥȅζͼΈτȜ Ώοϋੜၑͤ͢ͅȄࡉ̥̫ષ͈฽ৣ࿂͈ਹٜ̈́ͤ̈́̓͜ક ါȅ൝८၄෨௢শެ஌ષ͒۷௶෨ࠁٽఱ̧̈́ા ଎ 2.2 ८၄ਹ༹ࣣ͈̦ڙȄྶၸ̈́ࢹ௮ࠁఠͬা̳ȅ฽ৣ࿂͈߹০̯ͦ ࣣ͞ະ޳ৗ͈೾ഽ̦ఱ̧̈́ાࣣ͉́ CMP ਹࣣͥ͢ͅ S/N ͈૦໙ͬ૦ͤ໦̫ͥȪऒȫȅ૦໙ͬ૦ͤ໦̫̹ࢃȄਹ ಺̯ͦͥȪֲȫȅޑࡉࣺ̞̹͛̈́͛Ȅड߃͉́ CMP ਹ̵ࣣͬ ࣣ̳̭ͥ͂ͤ͢ͅ८၄ത̦̦ض๤࢜ષ͈࢘ ̴̷͈͘͘ͅζͼΈτȜΏοϋ̳̞̹ͥ͂̽ਹࣣஜζͼ Fig. 2.2 Scheme of the Common Scatter-PointȪ CSPȫstacking ΈτȜΏοϋ̦৽ၠ̧̞͂̈́̽̀̀ͥȅਹࣣஜζͼΈτȜ method. Amplitudes are allocated on the isochrone of the ͈̜̦́ͥ͜Ḛ̏͛͘ scatter traveltimeȪleft*. The scatter point is emphasized̥̥̦ͥۼΏοϋ͈ࠗॳ͉ఱ་শ .*ෝ̹͂̈́̽ȅষ୯́ after the allocated amplitudes are stackedȪ rightخ଻ෝ͈࢜ષͤ͢ͅ৘ဥܥࠗॳ̞̱ ਹࣣஜζͼΈτȜΏοϋ͈̜֚̾́ͥ८၄ਹ༹ࣣ͈̭͉ ੆͓ͥȅ ͙̈́ͅȄ௸ഽ֚೰͈ાࣣḘ͈̏८၄෨൝௢শެ஌͉อૼ̞̀̾ͅ ८၄ਹ༹ࣣ ത͂਋૦തͬઙത̳͂ͥఔ׫Ȫ3 ষࡓ͈ાࣣ͉ٝഢఔ׫ఘȫ 2.3 2.3.1 ८၄ਹ༹ࣣࡔၑ ͂̈́ͥȅ̷͈൝௢শެ஌ષͅশ࣫ t=t0 ܱͅ჏̯̹ͦ૦໙౵