東北地域災害科学研究25第58巻（2022）୰ᑠᆅ㟈ࡢ◚ቯఏ᧛ᣦྥᛶ࡜ᛂຊ㝆ୗ㔞㸫 ᮾ໭Ἀᆅ㟈ᚋ࡟άⓎ໬ࡋࡓ⚟ᓥ-Ⲉᇛ┴ቃࡢᆅ㟈άືࡢゎᯒ 㸫 *ᮾ ໭኱Ꮫ ụ⏣㔛ዉ㸪ྜྷ⏣ᆂభ㸪ᯇ⃝ᬸࡣࡌࡵ࡟ᆅ㟈ࡣᆅẆෆ࡛ቑຍࡋࡓ೫ᕪᛂຊ࣭ṍ࢚ࢿࣝࢠ࣮ࢆゎᾘࡍࡿ⮬↛⌧㇟࡛࠶ࡿࠋᆅ㟈๓ᚋ࡛ࡢ᩿ᒙ㠃ୖࡢࡏࢇ᩿ᛂຊࡢῶᑡ㔞ࢆᛂຊ㝆ୗ㔞࡜࿧ࡪࠋᛂຊ㝆ୗ㔞ࡣ㸪ᆅ㟈◚ቯࢆグ㏙ࡍࡿࡓࡵࡢᇶ♏ⓗ࡞ࣃ࣓࣮ࣛࢱ࡜ࡋ࡚ᗈࡃ⏝࠸ࡽࢀࡿ࡜࡜ࡶ࡟㸪ᆅ㟈࡟ࡼࡿ㧗࿘Ἴᨺᑕ࢚ࢿࣝࢠ࣮ࡢ኱ࡁࡉࡢᣦᶆ࡜ࡋ࡚ࡶὀ┠ࡉࢀ࡚ࡁࡓ (e.g., Boore, 1983)ࠋ
㏻ᖖ㸪୰ᑠᆅ㟈ࡢᛂຊ㝆ୗ㔞ࡣ㸪෇ᙧ᩿ᒙࡢᑐ⛠◚ቯࢆ௬ᐃࡋࡓࣔࢹࣝ (௨㝆㸪ᑐ㇟◚ቯࣔࢹࣝࠋ౛࠼ࡤ㸪Brune 1970; Sato & Hirasawa, 1973) ࡟ᇶ࡙ࡁ㸪◚ቯ⥅⥆᫬㛫࡜ᆅ㟈࣮࣓ࣔࣥࢺ࠿ࡽ᥎ᐃࡉࢀ࡚࠸ࡿࠋᑐ⛠◚ቯࣔࢹ࡛ࣝࡣ㸪ほࡉࢀࡿ◚ቯ⥅⥆᫬㛫࡟ࡣᙉ࠸᪉ྥ౫Ꮡࡣ⏕ࡌ࡞࠸ࡇ࡜࡟࡞ࡿࠋ୍᪉㸪ᐇ㝿ࡢ◚ቯࡀ㠀ᑐ⛠࡛࠶ࡿሙྜ㸪ྛほⅬ࡛ほࡉࢀࡿࠕࡳ࠿ࡅࡢ◚ቯ⥅⥆᫬㛫ࠖࡣᙉ࠸᪉ྥ౫Ꮡᛶࢆᣢࡘࡇ࡜࡟࡞ࡿ (e.g., Ben-Menahem, 1962)ࠋ◚ቯఏ᧛ᣦྥᛶ
(rupture directivity) ࡣ㸪ࡳ࠿ࡅࡢ◚ቯ⥅⥆᫬㛫ࡔࡅ࡛ࡣ࡞ࡃᆅ㟈ືࡢ኱ࡁࡉ࡟ࡶᙳ㡪ࢆ୚࠼ࡿࠋࡑࡢຠᯝࡣ≉࡟ S Ἴ࡟ᑐࡋ࡚๻ⓗ࡛࠶ࡾ㸪◚ቯఏ᧛ᣦྥᛶࡣᆅ㟈ືࡢ⌮ゎࡢࡓࡵ࡟ᛂຊ㝆ୗ㔞࡜࡜ࡶ࡟㔜せ࡞㔞࡛࠶ࡿ࡜࠸࠼ࡿࠋࡇࢀࡲ࡛㸪୰ᑠᆅ㟈ࡢゎᯒ࡛ࡣ㸪◚ቯఏ᧛ᣦྥᛶࡢᏑᅾࢆ↓どࡋ㸪ᑐ⛠◚ቯࣔࢹࣝࢆ௬ᐃࡍࡿࡇ࡜ࡀṤ࡝࡛࠶ࡗࡓࡀ (Abercrombie, 2021)㸪ࡇࡢ௬ᐃࡀㄗࡗ࡚࠸ࡓሙྜ㸪ᛂຊ㝆ୗ㔞ࡢ᥎ᐃ್࡟ࡶ኱ࡁ࡞ㄗᕪࡀຍࢃࡿࡇ࡜࡟࡞ࡿࠋᮏ◊✲࡛ࡣ㸪୰ᑠᆅ㟈ࡢ◚ቯఏ᧛ᣦྥᛶࡢᵝ(a)  (b)Ꮚࢆㄪ࡭ࡿࠋ⚟ᓥ㸫Ⲉᇛ┴ቃ࿘㎶ࡢᆅ㟈άືࢆゎᯒᑐ㇟࡜ࡋࡓ (ᅗ 1)ࠋࡇࡢᆅᇦ࡛ࡣ㸪2011 ᖺ 3 ᭶ 11 ᪥ࡢᮾ໭ᆅ᪉ኴᖹὒἈᆅ㟈ᚋ࠿ࡽ㠀ᖖ࡟άⓎ࡟ṇ᩿ᒙᆅ㟈ࡀⓎ⏕ࡋ࡚࠾ࡾ㸪4 ᭶ 11 ᪥࡟ࡣ MJMA7.0 ࡢᆅ㟈ࡶⓎ⏕ࡋ࡚࠸ࡿ (ᅗ 1a ࡢᫍ༳)ࠋ
㸰. ࢹ࣮ࢱ࡜ᡭἲ⚟ᓥ㸫Ⲉᇛ┴ቃ࿘㎶࡛ 2011 ᖺ 3 ᭶ 11 ᪥࠿ࡽ 2018 ᖺ 10 ᭶ 31 ᪥ࡲ࡛࡟Ⓨ⏕ࡋࡓᆅ㟈ࡢ࠺ࡕ㸪F-net ࡟ࡼࡾ࣓࢝ࢽࢬ࣒ゎࡀ᥎ᐃࡉࢀ࡚࠸ࡿ 348 ಶࡢᆅ㟈ࡢゎᯒࢆ⾜ࡗࡓࠋ㟈※ࡢ῝ࡉࡣ 40 km ௨ὸ࡛࠶

ᅗ 1 (a) ゎᯒᑐ㇟ᇦ (㟷ᯟ)࡜ 2011 ᖺ⚟ᓥ┴὾㏻ࡾࡢ M7 ᆅ㟈ࡢ㟈ኸ (ᫍ༳)ࠋ (b) ᑐ㇟ᆅ㟈ࡢ㟈ኸ (㟷୸)࡜ほ Ⅼࡢ఩⨨ (㉥୕ゅ)*Simultaneous estimation of stress drop and rupture directivity of small earthquakes near the FukushimaIbaraki border by Rina Ikeda, Keisuke Yoshida, Toru Matsuzawa

26ࡾ㸪ᆅ㟈ࡢつᶍࡣ 3.3ӌMwӌ5.2 ࡛࠶ࡿࠋᅗ 2 ࡟ᑐ㇟ᆅ㟈ࡢ㟈ኸ (㟷୸) ࡜㸪౑⏝ࡋࡓほⅬࡢ఩⨨ (㉥୕ゅ) ࢆ♧ࡍࠋ
2.1 ᆅ㟈◚ቯࣔࢹࣝ㠀ᑐ⛠◚ቯࢆ⪃៖ࡋࡓࣔࢹࣝ࡜ࡋ࡚㸪Dong & Papageorgiou(2003) ࢆ⏝࠸ࡓ (௨㝆㸪୍⯡◚ቯࣔࢹࣝ)ࠋࡇࡢࣔࢹࣝࡣ㸪Sato& Hirasawa (1973) ࡢ෇ᙧᑐ⛠◚ቯࣔࢹࣝࢆᣑᙇࡋࡓࡶࡢ࡛㸪ᴃ෇ᙧ᩿ᒙࡸ㠀ᑐ⛠◚ቯࡶ⪃៖࡛ࡁࡿࠋ◚ቯࡣᴃ෇ୖࡢ௵ពࡢ
Ⅼ CN ࡛㛤ጞࡋ㸪ᴃ෇୰ᚰࡀ C0 ࡟ྥ࠿ࡗ୍࡚ᐃ㏿ᗘ࡛⛣ືࡋ࡚࠸ࡃࠋᴃ෇ᙧࡢ◚ቯࣇࣟࣥࢺࡶ୍ᐃ࣮ࣞࢺ࡛ᣑ኱ࡋ࡚࠸ࡃࠋࡇࡢࣔࢹࣝ࡟ᑐࡋ࡚ࡣ㸪௵ពࡢほᅗ 2 ୍⯡◚ቯࣔࢹࣝࡢᴫ␎ᅗࠋ
CN ࡣ◚ቯࡢ㛤ጞⅬ㸪C0 ࡣᴃ෇ࡢ୰ᚰⅬ࡛ࡢࡳ࠿ࡅࡢ㟈※᫬㛫㛵ᩘࡢゎᯒゎࡀᚓࡽࢀ࡚࠸ࡿࠋ௒ᅇࡣ (1) ◚ቯࡢ㛤ጞⅬ CN ࡀᴃ෇ࡢ↔Ⅼ࡟఩⨨ࡍࡿ(Savage, 1966)㸪(2) ᴃ෇ࣇࣟࣥࢺࡀ㛗㍈᪉ྥ࡟ᣑ኱ࡍࡿ㏿ࡉ ‫ݒ‬௥ ࡀ S Ἴ㏿ᗘ ‫ݒ‬௦ ࡜ ‫ݒ‬௥ Ȁ‫ݒ‬௦ ൌ ͲǤͻࡢ㛵ಀࢆ‶ࡓࡍ࡜࠸࠺ᣊ᮰᮲௳ࡶ୚࠼ࡓࠋ
2.2 㟈※᫬㛫㛵ᩘ࡜ࢥ࣮ࢼ࣮࿘Ἴᩘࡢ᥎ᐃ୰ᑠᆅ㟈ࡢ◚ቯఏ᧛ᣦྥᛶࢆㄪ࡭ࡿࡓࡵ࡟㸪ྛほⅬ࡛ࡳ࠿ࡅࡢ㟈※᫬㛫㛵ᩘࢆồࡵࡓࠋලయⓗ࡞᪉ἲࡣ㸪Yoshida (2019), Yoshida et al. (2019) ࡜ྠᵝ࡛࠶ࡾ㸪ᆅ㟈ࡢ S ἼἼᙧࢆ⏝࠸ࡓࠋᑐ㇟ᆅ㟈ࡢ㏆ഐ࡛Ⓨ⏕ࡋࡓᑠᆅ㟈ࡢἼᙧࢆ⤒㦂ⓗࢢ࣮ࣜࣥ㛵ᩘ࡜ࡋ࡚⏝࠸࡚㸪
deconvolution ࡟ࡼࡾ㸪ᑐ㇟ᆅ㟈ࡢࡳ࠿ࡅࡢ㟈※᫬㛫㛵ᩘࢆ᥎ᐃࡋࡓࠋDeconvolution ࡟ࡣ㸪Kikuchi & Kanamori (1982) ࡢᡭἲࢆ⏝࠸ࡓࠋᚓࡽࢀࡓࡳ࠿ࡅࡢ㟈※᫬㛫㛵ᩘ࡜⤒㦂ⓗࢢ࣮ࣜࣥ㛵ᩘࡢ convolution Ἴᙧ࡟ࡼࡾ㸪ᑐ㇟ᆅ㟈ࡢἼᙧࢆ᚟ඖ⋡ࡀ 80 %௨ୖ෌⌧࡛ࡁࡓࡶࡢࡢࡳࢆಙ㢗ᛶࡢ࠶ࡿ⤖ᯝ࡜ࡋ࡚᥇⏝ࡋ㸪ࡑࢀࡀ 15 ほⅬ௨ୖ࡛ᚓࡽࢀࡓᆅ㟈ࢆゎᯒᑐ㇟࡜ࡋࡓࠋᚓࡽࢀࡓࡳ࠿ࡅࡢ㟈※᫬㛫㛵ᩘࡢࡑࢀࡒࢀ࡟ᑐࡋ㸪 Andrews (1986) ࡟ࡼࡾᐃ⩏ࡉࢀࡓࢥ࣮ࢼ࣮࿘Ἴᩘࢆ᫬㛫㡿ᇦ࡛ồࡵࡓࠋ
2.3 ࣔࢹ࣭ࣝࣃ࣓࣮ࣛࢱࡢ᥎ᐃᚓࡽࢀࡓࢥ࣮ࢼ࣮࿘Ἴᩘ࡜ࡑࡢ᪉ྥ౫Ꮡᛶ࠿ࡽ㸪ࣔࢹ࣭ࣝࣃ࣓࣮ࣛࢱࡢ᥎ᐃࢆ⾜ࡗࡓࠋᴃ෇᩿ᒙࡢ㛗㍈ ܽ଴ 㸪ᴃ෇⋡ ܾ଴ Ȁܽ଴ ࠾ࡼࡧ◚ቯࡢ㐍ᒎ᪉ྥ߮଴ࢆࢢࣜࢵࢻࢧ࣮ࢳࡋ࡚ほࡉࢀࡓࢥ࣮ࢼ࣮࿘Ἴᩘࢆ᭱ࡶⰋࡃㄝ᫂ࡍࡿࣃ࣓࣮ࣛࢱࢆồࡵࡓࠋࣇ࢕ࢵࢸ࢕ࣥࢢࡢ㝿࡟ࡣ㸪ࢥ࣮ࢼ࣮࿘Ἴᩘࡢᖹᆒ஧஌ṧᕪ௡ଶ            ൌ ෍൫݂ୡ ୫୭ୢୣ୪ െ ݂ୡ ௜ ൯ ൗ݊             ሺͳሻ௜ୀଵࡀ᭱ᑠ࡜࡞ࡿࡼ࠺࡟ࡋࡓࠋࡇࡇ࡛ ݂ୡ ୫୭ୢୣ୪ࡣࢥ࣮ࢼ࣮࿘Ἴᩘࡢ⌮ㄽ್㸪݂ୡ ௜ ࡣྛほⅬࡢࢥ࣮ࢼ࣮࿘Ἴᩘ㸪݊ࡣࢹ࣮ࢱᩘ࡛࠶ࡿࠋᚓࡽࢀࡓṧᕪࢆ⏝࠸࡚㸪㉥ụ᝟ሗ㔞ᇶ‽ (AIC; Akaike, 1974)࡟ᇶ࡙ࡁ୍⯡◚ቯࣔࢹࣝ࡜ᑐ⛠◚ቯࣔࢹࣝ (ܽ଴ ൌ ܾ଴ ) ࡢẚ㍑ࢆ⾜ࡗࡓࠋ  ൌ ݊   െ݊൅ ʹ݉ ൅ ݊  ʹɎʹሺʹሻ

27݉ࡣࣔࢹࣝࡢ⮬⏤ᗘ࡛࠶ࡿࠋ☜⋡ศᕸࡀṇつศᕸ࡟ᚑ࠺ࡇ࡜ࢆ௬ᐃࡋࡓࠋAIC ࡣ㸪ࡑࡢ್ࡀᑠ
ࡉ࠸ࣔࢹࣝࡢ᪉ࡀඃ఩࡛࠶ࡿࡇ࡜ࢆ♧ࡍᣦᶆ࡜ࡋ࡚⏝࠸ࡿࡇ࡜ࡀ࡛ࡁࡿࠋᮏ◊✲࡛ࡣᑐ⛠◚ቯࣔࢹࣝࡢ AIC ࠿ࡽ୍⯡◚ቯࣔࢹࣝࡢ AIC ࢆᘬ࠸ࡓ್ǼAIC ࢆ⏝࠸࡚ࣔࢹࣝࡢẚ㍑ࢆ⾜ࡗࡓࠋゎᯒ⤖ᯝࡢ౛ࢆ♧ࡍࠋ1 ࡘ┠ࡢ౛ࡣ 2011 ᖺ 4 ᭶ 8 ᪥࡟Ⓨ⏕ࡋࡓ Mw 4.0 ࡢᆅ㟈࡛࠶ࡿࠋᅗ
3(a) ࡣࡳ࠿ࡅࡢ㟈※᫬㛫㛵ᩘࢆほⅬࡢ᪉఩࡟ᇶ࡙ࡁ୪࡭ࡓࡶࡢ࡛࠶ࡿࠋ180-270r(༡す᪉ྥ) ࡛ࣃࣝࢫࡢ⥅⥆᫬㛫ࡀ▷࠸ഴྥ࡟࠶ࡿࡇ࡜࠿ࡽ㸪◚ቯࡀ༡す᪉ྥ࡟ఏ᧛ࡋࡓࡇ࡜ࡀ♧၀ࡉࢀࡿࠋᅗ 3(b) ࡣ㸪ࢥ࣮ࢼ࣮࿘Ἴᩘࡢほ್࡜ࣔࢹࣝ࡟ࡼࡿ⌮ㄽ್ࢆẚ㍑ࡋ࡚࠸ࡿࠋほ್(㯮୸)ࡣ㸪ᑐ⛠◚ቯࣔࢹ࡛ࣝィ⟬ࡉࢀࡓ⌮ㄽ್ (⅊Ⰽ⥺) ࡼࡾࡶ㸪୍⯡◚ቯࣔࢹ࡛ࣝィ⟬ࡉࢀࡓ⌮ㄽ್ (㉥⥺) ࡟Ⰻࡃྜ࠺ഴྥࡀぢࡽࢀࡿࠋǼAIC ࡣ 82.8 ࡛㸪ᑐ⛠◚ቯࣔࢹࣝࡼࡾࡶ୍⯡◚ቯࣔࢹࣝࡢ᪉ࡀඃ఩࡛࠶ࡗࡓࠋ
(a)(b)

ᅗ 3 (a) ࡳ࠿ࡅࡢ㟈※᫬㛫㛵ᩘࡢ᪉఩౫Ꮡࡢ౛ࠋ(b) ⌮ㄽ࡜ほࡢࢥ࣮ࢼ࣮࿘Ἴᩘࡢẚ㍑ࠋ 㯮୸㸸ほ್㸪㉥⥺㸸୍⯡◚ቯࣔࢹࣝࡢ⌮ㄽ್㸪⅊Ⰽ⥺㸸ᑐ⛠◚ቯࡢሙྜࡢ⌮ㄽ್ࠋ

ᅗ 4 ࡟㸪ǼAIC ࡀప࠸ሙྜࡢ౛࡜ࡋ࡚㸪2011 ᖺ 5 ᭶ 5 ᪥࡟Ⓨ⏕ࡋࡓ Mw 4.4 ࡢᆅ㟈ࡢ⤖ᯝࢆ♧ࡍࠋࡳ࠿ࡅࡢ㟈※᫬㛫㛵ᩘ࡟㢧ⴭ࡞᪉ྥ౫Ꮡࡀぢࡽࢀ࡚࠸ࡿࡢ࡟ࡶᣊࢃࡽࡎ㸪ǼAIC ࡣ -4࡛㸪୍⯡◚ቯࣔࢹࣝࡼࡾࡶᑐ⛠◚ቯࣔࢹࣝࡢ᪉ࡀඃ఩࡜࡞ࡗ࡚࠸ࡿࠋࡇࡢᆅ㟈ࡢሙྜ࡟ࡣ㸪ࡳ࠿ࡅࡢ㟈※᫬㛫㛵ᩘ࡟ 2 ࡘࡢࣆ࣮ࢡࡀぢࡽࢀ㸪2 ࡘࡢ◚ቯࡀ㐃⥆ࡋ࡚Ⓨ⏕ࡋࡓ࡜⪃࠼ࡽࢀࡿ㸬ࡇࡢࡼ࠺࡞」㞧࡞㟈※᫬㛫㛵ᩘࢆᣢࡘᆅ㟈࡟ᑐࡋ࡚ࡣ㸪௒ᅇ㸪ࡳ࠿ࡅࡢ◚ቯ⥅⥆᫬㛫ࢆࡿᑻᗘ࡜ࡋࡓࢥ࣮ࢼ࣮࿘Ἴᩘࡸ㸪༢Ⓨᆅ㟈ࢆ௬ᐃࡋࡓࣔࢹࣝࡀ࠺ࡲࡃാ࠿࡞࠿ࡗࡓ࡜⪃࠼ࡽࢀࡿࠋ
(a)(b)

ᅗ 4 (a) ࡳ࠿ࡅࡢ㟈※᫬㛫㛵ᩘࡢ᪉఩౫Ꮡࡢ౛ࠋ(b) ⌮ㄽ࡜ほࡢࢥ࣮ࢼ࣮࿘Ἴᩘࡢẚ㍑ࠋ 㯮୸㸸ほ㉥⥺㸸୍⯡◚ቯࣔࢹࣝࡢ⌮ㄽ್㸪⅊Ⰽ⥺㸸ᑐ⛠◚ቯࣔࢹࣝࡢ⌮ㄽ್ࠋ್㸪28

㸱 . ⤖ᯝ࣭㆟ㄽ ᅗ 5 ࡟㸪ゎᯒᑐ㇟࡜ࡋࡓ 348 ಶࡢᆅ㟈࡟ᑐࡋ࡚ᚓࡽ
ṇࡢࢹ࣮ࢱᩘ㸸306

ࢀࡓǼAIC ࡢ㢖ᗘศᕸࢆ♧ࡍࠋ306 ಶࡢᆅ㟈࡛ǼAIC >㈇ࡢࢹ࣮ࢱᩘ㸸420 ࡛࠶ࡾ㸪ከࡃࡢᆅ㟈◚ቯࡀ᭷ព࡞◚ቯఏ᧛ᣦྥᛶࢆ᭷ࡋ࡚࠸ࡿࡇ࡜ࢆ♧ࡋ࡚࠸ࡿࠋࡇࡢ⤖ᯝࡣ㸪ᑠᆅ㟈ࡢሙྜ࡟ࡶ◚ቯఏ᧛ᣦྥᛶࡢᙳ㡪ࡀ↓ど࡛ࡁ࡞࠸ࡇ࡜ࢆ
♧၀ࡋ࡚࠸ࡿࠋᅗ 6 ࡟㸪᥎ᐃࡋࡓ᩿ᒙ㠃✚㸪ᛂຊ㝆ୗ㔞ǼȪ㸪ǼAIC ࡜࣐ࢢࢽࢳ࣮ࣗࢻࡢ㛵ಀࢆ♧ࡍࠋ᩿ᒙ㠃✚ࡀつᶍ࡜࡜ࡶ࡟ቑຍࡍࡿࡢ࡟ᑐࡋ㸪ᛂຊ㝆ୗ㔞ࡣつᶍ࡟࠶ࡲࡾ౫Ꮡࡋ࡚࠸࡞࠸ࠋࡇࡢഴྥࡣ㸪ᆅ㟈ࡢࢫࢣ࣮ࣜࣥࢢ๎࡜ㄪ࿴ⓗ࡛࠶ࡿ (Aki, 1967)ࠋǼAIC ࡶᙉ࠸つᶍ౫Ꮡᛶࢆ♧ࡉࡎ㸪◚ቯఏ᧛ᣦྥᛶࡢᙉࡉࡶつᶍ࡟኱ࡁᅗ 5. ǼAIC ࡢ㢖ᗘศᕸࡃ౫Ꮡࡋ࡞࠸ࡇ࡜ࢆ♧၀ࡍࡿࠋ(a)(b)(c)ᅗ 6 (a) ᩿ᒙ㠃✚㸪(b) ᛂຊ㝆ୗ㔞㸪(c) Ǽ AIC ࡜つᶍࡢ㛵ಀࠋ ㉥୸ࡣつᶍࡈ࡜ࡢᖹᆒ್ࢆ♧ࡍࠋᅗ 7(a) ࡟◚ቯࡢఏ᧛᪉ྥࡢ⤖ᯝࢆ♧ࡍࠋ◚ቯࡀ᪉఩ 50-180r࡟ఏ᧛ࡋࡓᆅ㟈ࡀከ࠸ࡼ࠺࡟
ࡳ࠼ࡿࠋඛ⾜◊✲࡟ࡼࡾ㸪ᆅ㟈◚ቯ࡟ఏ᧛ࡋࡸࡍ࠸᪉ྥࡀᏑᅾࡍࡿྍ⬟ᛶࡀᣦ᦬ࡉࢀ࡚࠸ࡿࡀ
(Kane et al., 2013; Calderoni et al., 2015; Yoshida et al., 2022)㸪௒ᅇࡢ⤖ᯝࡣࡑࢀࡽ࡜ㄪ࿴ⓗ࡛࠶ࡿࠋ(a)(b)

ᅗ 7 (a) ◚ቯࡢ㐍ᒎ᪉ྥࡢ㢖ᗘศᕸ, (b) ᛂຊ㝆ୗ㔞ࡢ㢖ᗘศᕸ

29ᚓࡽࢀࡓᛂຊ㝆ୗ㔞ࡢ್ࡣ 5-30 MPa ⛬ᗘࡢࡶࡢࡀከ࠿ࡗࡓ (ᅗ 7b)ࠋࡇࡢᆅᇦࢆྵࡴᮾ໭
᪥ᮏ࡛᥎ᐃࡉࢀ࡚࠸ࡿ᭱኱๧᩿ᛂຊࡢ್ࡣᩘ༑ MPa (Yoshida et al., 2015a and b)࡛࠶ࡾ㸪ᮏ◊✲࡛᥎ᐃࡉࢀࡓᛂຊ㝆ୗ㔞ࡢᖹᆒ್࡜ྠ⛬ᗘ࡛࠶ࡿࠋࡇࡢࡇ࡜ࡣ㸪᩿ᒙ㠃ୖࡢ๧᩿ᛂຊࡀᆅ㟈࡟ࡼࡾṤ࡝ゎᨺࡉࢀ࡚࠸ࡿࡇ࡜ࢆ♧ࡍࡢ࠿ࡶࡋࢀ࡞࠸ࠋ୍᪉㸪ᮏ◊✲ࡢゎᯒ࡟ࡼࡾ㸪୰ᑠᆅ㟈ࡢ◚ቯఏ᧛ࡢ」㞧ᛶࡶ᫂ࡽ࠿࡟࡞ࡗ࡚ࡁࡓࠋᅗ 4 ࡟♧ࡋࡓᆅ㟈ࡣ㸪」ᩘࡢ◚ቯ࠿ࡽ࡞ࡿᆅ㟈ࡢ౛࡛࠶ࡿࠋᮏ◊✲࡛ࡣ㸪ከࡃࡢඛ⾜◊✲࡛↓どࡉࢀ࡚ࡁࡓ◚ቯఏ᧛ᣦྥᛶࢆ⪃៖ࡋࡓ୍⯡◚ቯࣔࢹࣝࢆ⏝࠸࡚◚ቯఏ᧛ᣦྥᛶ࡜ᛂຊ㝆ୗ㔞ࢆ᥎ᐃࡋࡓ㸬ࡋ࠿ࡋ㸪ࡇࡢࣔࢹ࡛ࣝࡉ࠼㸪ᅗ 4 ࡢࡼ࠺࡞ᆅ㟈ࡢ」㞧ᛶࢆ༑ศ࡟ㄝ࡛᫂ࡁ࡞࠸ࠋࡇࡢࡼ࠺࡞」㞧࡞◚ቯࢆࣔࢹࣝ໬ࡍࡿࡓࡵ࡟ࡣ㸪኱ᆅ㟈 (M>6) ࡟ᑐࡋ࡚⾜ࢃࢀ࡚࠸ࡿ㟈※㐣⛬࢖ࣥࣂ࣮ࢪࣙࣥࡢࡼ࠺࡞ゎᯒࡀᚲせ࡛࠶ࡿࠋࡋ࠿ࡋ࡞ࡀࡽ㸪ࡑࡢࡼ࠺࡞ゎᯒ࡛ࡣ㸪ࢹ࣮ࢱࡢ㝈⏺࠿ࡽ⁥ࡾศᕸࡢ᫬㛫Ⓨᒎࡸᛂຊ㝆ୗ㔞ࢆ༑ศࡼࡃᣊ᮰࡛ࡁ࡞࠸ࡇ࡜ࡀከ࠸ࡔࢁ࠺ (Adams et al.,2016)ࠋ୍⯡࡟㸪◚ቯ⥅⥆᫬㛫࠿ࡽ᩿ᒙࢧ࢖ࢬࢆ㧗⢭ᗘ࡟ᣊ᮰ࡍࡿࡇ࡜ࡣ㞴ࡋࡃ㸪⿵ຓⓗ࡞௬ᐃࡀᚲせ࡛࠶ࡿ㸬ୖグࡢࡇ࡜ࢆ⪃࠼ࡿ࡜㸪ᑠᆅ㟈ࡢᛂຊ㝆ୗ㔞ࢆṇ☜࡟ぢ✚ࡶࡿࡇ࡜ࡣᐇ㝿ࡢ࡜ࡇࢁ㠀ᖖ࡟㞴ࡋ࠸ࡼ࠺࡟ᛮࢃࢀࡿࠋᑠᆅ㟈࡟ᑐࡋ࡚᥎ᐃࡉࢀ࡚࠸ࡿ͆ᛂຊ㝆ୗ㔞͆ࡣ㸪㧗࿘Ἴ࢚ࢿࣝࢠ࣮ᨺᑕࡢᑻᗘ࡜ࡋ࡚ࡣ᭷⏝࡛࠶ࡿࡶࡢࡢ㸪ࡑࡢᮏ᮶ࡢព࿡࡛࠶ࡿᆅ㟈᫬ࡢ᩿ᒙୖࡢᛂຊゎᨺ㔞࡜ࡣᚲࡎࡋࡶ⤖ࡧࡘ࠿ࡎ (e.g., Boore, 1983)㸪ヲ⣽࡞≀⌮ⓗゎ㔘ࢆ⾜࠺ࡇ࡜ࡣ㞴ࡋ࠸࠿ࡶࡋࢀ࡞࠸ࠋ୍᪉㸪ᑠᆅ㟈ࡢ◚ቯఏ᧛᪉ྥ➼ࡢࣃ࣓࣮ࣛࢱࡣ㸪ࡇࢀࡲ࡛࠶ࡲࡾὀ┠ࡉࢀ࡚ࡇ࡞࠿ࡗࡓࡶࡢࡢ㸪ከࡃࡢᆅ㟈࡟ࡘ࠸࡚᫂░࡟ࡳࡽࢀࡿࠋᑠᆅ㟈࡟ᑐࡋ࡚ࡶ robust ࡟᥎ᐃࡍࡿࡇ࡜ࡀྍ⬟࡞㔞࡜ࡋ࡚᭷⏝࡜࡞ࡿ࠿ࡶࡋࢀ࡞࠸ࠋ㸳 . ⤖ㄽ⚟ᓥ㸫Ⲉᇛ┴ቃ࿘㎶࡛Ⓨ⏕ࡋࡓ୰ᑠᆅ㟈ࡢ◚ቯఏ᧛ᣦྥᛶࡢ᥎ᐃࢆ⾜ࡗࡓࠋࡑࡢ⤖ᯝ㸪ከࡃࡢᑠᆅ㟈ࡀ㢧ⴭ࡞◚ቯఏ᧛ᣦྥᛶࢆ♧ࡋ࡚࠾ࡾ㸪ᚑ᮶ࡢᑐ⛠◚ቯࣔࢹࣝࢆ⏝࠸ࡓᛂຊ㝆ୗ㔞᥎ᐃࡢ㝿ࡢ௬ᐃࡀ࠶ࡲࡾࡼࡃᡂ❧ࡋ࡚࠸࡞࠸ࡇ࡜ࡀศ࠿ࡗࡓࠋ ௒ᅇࡣඛ⾜◊✲࡛↓どࡉࢀ࡚ࡁࡓ◚ቯఏ᧛ᣦྥᛶࢆ⪃៖ࡋ࡚◚ቯఏ᧛᪉ྥ࡜ᛂຊ㝆ୗ㔞ࢆྠ᫬࡟᥎ᐃࡋࡓࡀ㸪௒ᅇ⏝࠸ࡓࣔࢹ࡛ࣝࡉ࠼ᐇ㝿ࡢᆅ㟈◚ቯࡢ」㞧ᛶࢆ༑ศ࡟ㄝ࡛᫂ࡁ࡚࠸࡞࠸ሙྜࡀࡳࡽࢀࡓࠋࡑࢀࡽ࡟ࡘ࠸࡚ࡣᛂຊ㝆ୗ㔞ࢆ኱ᖜ࡟ㄗ᥎ᐃࡋ࡚࠸ࡿྍ⬟ᛶࡶ⪃࠼ࡽࢀࡿࠋᑠᆅ㟈ࡢ◚ቯఏ᧛ᣦྥᛶ࡟㛵ಀࡍࡿࣃ࣓࣮ࣛࢱࡣ㸪ࡇࢀࡲ࡛࠶ࡲࡾὀ┠ࡉࢀ࡚ࡇ࡞࠿ࡗࡓࡶࡢࡢ㸪௒ᅇ㸪ከࡃࡢᆅ㟈࡟ࡘ࠸࡚᫂░࡟☜ㄆࡉࢀࡓࠋᑠᆅ㟈ࡢ㟈※㐣⛬࡟㛵ࡋ࡚ robust ࡟᥎ᐃࡍࡿࡇ࡜ࡀྍ⬟࡞᝟ሗ࡜ࡋ࡚௒ᚋ᭷⏝࡟࡞ࡿ࠿ࡶࡋࢀ࡞࠸ࠋᘬ⏝ᩥ⊩
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