MoEFRwx - 東京大学

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腎腓腢腛腜腍腚腗腘腟腏腚腗腊腎腚腄腉腖腗腠腑腡腛腕 腙腐 ,**/ : 腌腀腋腒腝腇腔腣腈腅腃腆 臂腭腤膀 +*腷膙膈膲 ,腓腰膦膺 -腢膮膒膹 .腓膢 /膸膪 /腗膬 0腯膪 1膕腼膡膷 2腸膬膰膿膂 3腔膪膍腙 +*膎膪膝腾 ++膎膢膨腕 ++膌腖膋膐 ,腵腧膆 ,腧膌腱膾 ,膓膑膝膀 +,腼腻腳膞 +-膊膧膞臀 +.腎膘 +.+膫膴膠腚膠腚腒膽腚腫腣腘,膫膴膠腚膠腚腒膽腚腫腣腘-膫腤膠腚膠腚腒膽腚腪腫腣腘 腮腹: 膥腏 膥膯 腞腥 腫腣膉.膗膻膠腚膠腚腒膄膚腘腚腫腣腘/腠膅膠腚腲腚膱0腼膼膠腚腦腐膐腟 腘腚膱1腍膤腦腐膠腚腦腐腚膱2腽腨腡膇膜腶腫腣膉腛膣膛腫腣腊腌腋腀3膫腤膠腚膥膏腫腣 +*膫腤膠腚膠腚腒膽腚腪腫腣腘++腠膅膠腚膠腚腒腲腚腫腣腘+,膫膴膠腚膽腚膱+-腍膤腦腐膠 腚腦腐腚膱 腮腹: 膩膪腲腨腃腃+.腈腆腇腉 High-resolution seismic reflection profiling across the Shiraiwa fault, eastern margin of the Yokote basin fault zone, northeast Japan : data acquisition and processing Kyoko Kagohara +)* , Toshifumi Imaizumi ,, Tomoo Echigo -, Takahiro Miyauchi ., Shin Koshiya /, Masaru Noda /, Hajime Kato 0, Shigeru Toda 1, Tatsuya Ishiyama 2, Hiroshi Sato 3, Shinsuke Okada +*, Satoshi Kanda ++, Naoto Kamiya ++, Nobuto Morishita ,, Shuichi Takahashi ,, Kosuke Hashimori ,, Satoko Shimizu +,, Kota Yamazaki +-, Taro Koike +.and Takeshi Ikawa +.+Graduate School of Science, Tohoku University, ,Graduate School of Science, Tohoku University, -Graduate School of Science, the University of Tokyo (Now at Geo-Research Institute), .Graduate School of Science and Technology, Chiba University, /Faculty of Engineering, Iwate University, 0Faculty of Education and Human Sciences, Yamanashi University, 1Faculty of Education, Aichi University of Education, 2Active Fault Research Center, National Institute of Advanced Industrial Science and Technology, 3Earthquake Research Institute, the University of Tokyo, +*Graduate School of Science, the University of Tokyo, ++Graduate School of Engineering, Iwate University, +,Faculty of Science, Tohoku University, +-Faculty of Education, Aichi University of Education (Now at TSUDA INDUSTRIES CO., LTD.), +.Geosys Inc. Abstract The eastern margin of the Yokote basin fault zone extends about /0 km at the western foot of the Ou Backbone Range, northeast Japan. The Rikuu earthquake (M1.,) occurred in the Ou Backbone Range (Mahiru Range) on -+st August, +230. Associated with this earthquake, four thrust faults-Obonai, Shiraiwa, Ota, and Senya fault- appeared on the surface of the western foot of the Mahiru Range. These faults were highly sinuous with numerous gaps and en echelon steps. We conducted a high-resolution seismic reflection profiling survey across the Shiraiwa fault. The obtained seismic reflection data were processed by conventional common mid-point methods, post-stack migration, and depth conversion. The subsurface structure across the Shraiwa fault is characterized by branched low-angle reverse faults and conjugate back-thrust. The emergent thrust associated with the +230 earthquake is regarded to be a subsidiary reverse fault. Bull. Earthq. Res. Inst. Univ. Tokyo Vol. 2+ ,**0pp. +,3+-2 * e-mail : d*-*[email protected] 腂腅32*2/12 膖膟膁膔膻腩腴腝膃膔膻 0-129

Transcript of MoEFRwx - 東京大学

Page 1: MoEFRwx - 東京大学

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High-resolution seismic reflection profiling across the

Shiraiwa fault, eastern margin of the Yokote basin

fault zone, northeast Japan : data acquisition and

processing

Kyoko Kagohara+)*, Toshifumi Imaizumi,�, Tomoo Echigo-�, Takahiro Miyauchi.�, Shin

Koshiya/�, Masaru Noda/�, Hajime Kato0�, Shigeru Toda1�, Tatsuya Ishiyama2�, Hiroshi

Sato3�, Shinsuke Okada+*�, Satoshi Kanda++�, Naoto Kamiya++�, Nobuto Morishita,�, Shuichi

Takahashi,�, Kosuke Hashimori,�, Satoko Shimizu+,�, Kota Yamazaki+-�, Taro Koike+.� and

Takeshi Ikawa+.�

+�Graduate School of Science, Tohoku University, ,�Graduate School of Science, Tohoku University,-�Graduate School of Science, the University of Tokyo (Now at Geo-Research Institute), .�Graduate

School of Science and Technology, Chiba University, /�Faculty of Engineering, Iwate University,0�Faculty of Education and Human Sciences, Yamanashi University, 1�Faculty of Education, Aichi

University of Education, 2�Active Fault Research Center, National Institute of Advanced Industrial

Science and Technology, 3�Earthquake Research Institute, the University of Tokyo, +*�Graduate

School of Science, the University of Tokyo, ++�Graduate School of Engineering, Iwate University,+,�Faculty of Science, Tohoku University, +-�Faculty of Education, Aichi University of Education

(Now at TSUDA INDUSTRIES CO., LTD.), +.�Geosys Inc.

Abstract

The eastern margin of the Yokote basin fault zone extends about /0 km at the western foot of

the Ou Backbone Range, northeast Japan. The Rikuu earthquake (Mv1.,) occurred in the Ou

Backbone Range (Mahiru Range) on -+st August, +230. Associated with this earthquake, four thrust

faults-Obonai, Shiraiwa, Ota, and Senya fault- appeared on the surface of the western foot of the

Mahiru Range. These faults were highly sinuous with numerous gaps and en echelon steps.

We conducted a high-resolution seismic reflection profiling survey across the Shiraiwa fault.

The obtained seismic reflection data were processed by conventional common mid-point methods,

post-stack migration, and depth conversion. The subsurface structure across the Shraiwa fault is

characterized by branched low-angle reverse faults and conjugate back-thrust. The emergent

thrust associated with the +230 earthquake is regarded to be a subsidiary reverse fault.

M o E F R w xBull. Earthq. Res. Inst.

Univ. TokyoVol. 2+ I,**0� pp. +,3�+-2

* e-mail : d*-*[email protected] Iy32*�2/12 z{|}T~���}T 0�-�

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Key words : Riku-u earthquake, Shiraiwa fault, thrust fault, subsurface structure, high-resolution

seismic reflection profiling

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���������� ���������������� �� +*�2* Hz, +*�+** Hz, +*�+,* Hz

����� ���� / �!"#���� +2* ch$%&'�� ()� *�+�,-"�%&�� /** msec�AGC�.'��/� �����,-"�%&�01'�23$�� 456� *.-7*.28�9:+�/;<=>�?@ABCDE��/ +*�+** Hz��� ��F'� ��G� ,*8� HI!"#�� +* $J�'� KLM� �NOP��: 1 !"#�QRS� T+�/U��V�WX!Y�Z[�\�,�] GDAPS-

. KK^SU_`abcdefgS �h�� +2* ch$i&

'�� 23$� RP+**+-++,*� RP+-*2-+-02�jklmF'� RP++,+-+-*1�no 0* ch, po +,* ch�qrsVlm�t�Yutvwxy$i&'�� zh'�{|}� +* Hz K3~�S ${|�N�� +* mF'��-�, �����23W�!�� ;<�W�!@�h��� Super X-C

KK^SU_`abcdefgS�h���L��(��;<��c�$@�'� KFig. .S� W�!@�����[�!� Table ,��'� �����(��������/�

Fig. +. (A) Shaded relief map based on ,/* m DEM showing the locations of active thrusts in the Tohoku district.

Active faults are after Ikeda et al. (,**,) (B) Simplified geological map in and around the Yokote basin. Surface

geology is compiled from Usuda et al.(+310, +311, +32*), Osawa and Suda (+32*) and Osawa et al. (+322).

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� ������� �CMP Sorting������� ���� ������ �������� ������� �� CMP!"�#�$%�&' !"�#( Fig. ,)*+' � �#),-.���� /0�1-&' CMP 23( / m)4%�� CMP!"�#)5-&!"6(� 78 329 -&:Fig. /;'

� �� �Gain Recovery<=> ��� ?@ ABCDE�FG.� tnH�IJK9LM�IJK :AGC; �1G� �I NO�PQRS&'

tnH�IJK :n; : +.,, AGC Gate length : 0** msec

� ������ �First Break MuteCMP sortT)UVWM XYGZ��[\�&' F

G&ABCDE� Table -)*+'� ���������� �Deconvolution��]^_`�] ab6cde� bMfghi)^jklm ab6nop� qr�sDE��t%�\u�� �vw xGyz�{k&�� s|}~��D��}���1-&' ���(?@ ABCDE�FG&'

Operator length : +** msec, Gate length : +*** msec

White noise factor : /� Prediction length : , msec

� ����� �Static Correction�. ���>yz��UVWM�������� � �������)^jk Time-term�� ^_`����������69+k�}�D��} :��E��ED��; �1G� ��� ���&' v¡)(iRAS ::¢;£¤¥¦§"¨©ª«; �¬F�&' �}

Fig. ,. Location map of the Kotaki ,**/ seismic line and CMP stacking line.

Table +. Data acquisition parameters for the Kotaki

,**/ seismic line.

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Fig. -. Examples of shot gathers at di#erent sweep

frequency.

A. Sweep frequency +*�2* Hz.

B. Sweep frequency +*�+** Hz.

C. Sweep frequency +*�+,* Hz.

Fig. .. Flow chart of data processing.

Table ,. Processing parameters for the CMP of the Kotaki ,**/ seismic data.

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���������� �������� Time-

term�� ������������� Time-term�������� !��"�#$% Fig. 0&'() *+� ,�-./0�1234�� ��5 +�������67 0** m�sec%89�):����&�;<� ��5 +��=!�>?+@ABC>?&@D7EFGHI>?�JK L��MJKN %OD�)

� ���� �Velocity Analysis� �NMO� �Nor-

mal Move Out Correction�P��QRS LConstant Velocity StackN &@G��TU%OD�) TU�V ,* CMPW&XY� Z[ 3 CMP

�\�]�P��QR^_`%ab67OD�) ��QR��#$% Fig. 1&'() :���&�;c7def-.gh%ij/0%(k7 Normal Time&JK6�) JK&lmno�p2%qr(G�s&� no�tuvAw% ,.+x&ry6� :�%z9G{|VCMP gather%�&� }~�.%X�6��6�) �c�^���]% Table .&'()� ��� �Residual Static Correction�

NMOJK[�\�]&�67� ��MJK%Oc�MJK�VJK�<*�D���n�HI��j<%JK6�) JK������V 0 msec���6�)

Fig. 0. Surface structure determined by time-term analysis.

(A) Time-terms.

(B) Velocities of second layer.

(C) Topography and geometry of surface low velocity layer.

Fig. /. Distribution of number of folds along the CMP stacking line.

Table -. First break mute parameters for the CMP of

the Kotaki ,**/ seismic data.

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� ������� �CMP StackNMO��� CMP gather����� �� ���

CMP������ +������������ � ��� !"#$% *�2** m&'����()���� TV�� � �Time-Varying Filter*�+�,-.�/0�1&2� 3456789� :9;<�=>?@ABCDEF GHIJ� CMP� KL�M��� NO��PQR�89�ST3456�*�+�UV�3W'X��

Operator length : ,.* msec

Time Pass-band frequency

*� .** (msec) ,*/,2�+**/++* (Hz)

.**� 2/* (msec) +2/,.� 3*/+** (Hz)

2/*�-*** (msec) +*/+/� 2*/ 3* (Hz)

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Filter*�+�:9Y6�Z[\]^_`a GHIJ�NO�b)�\� cCdefgh�iP�� jkl� S�N�<mno�pq�rM��� )[�EcsJI�UV��t�

Operator length : - CMPs, Gate length : -* CMPs,

Time window length : /** msec

�� �������� �Migration� KL�uv��wx���yz{lA|����}~�� SW��A�V���������l��\��H��" 89�g��J��C�b)��� ��A�������-./0 �� ���+� ���;<������ 1*��F�J�C��M�����)[��

Fig. 1. Optimum stacking velocities determined by velocity analysis.

Table .. Post NMO mute parameters for the CMP of the Kotaki ,**/ seismic data.

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�� ���� �Depth Conversion����������� ������� �������������� ������� ��! � �"���#$%��&' +.* m()*!

.� ��� �������������+,���-�� Fig. 2-A, ���������-�� Fig. 2-B,��� -�� Fig. 3�./0/12!./0/�-�('� 345�� *.26� ������*.1 km7(�89:;<=>?/�! @�ABC�'D�%� ��=9EF��G� H��/�IJ(�,K�LMN� OPQRSTSU� +31.�WS-+.VPQRSTSU� +31/�WS-,* ; WX' Fig. +YZ[ �\]��^��_`abc�de�� ��� -�c�fg�� OFig. 3[! 9h� ij('� klmE O+310[ �_`�����no2*! p_q('�� ,** m7(=rst� �� ,**�/** m=�t� �� /** muvjW=wxytVz{|/*!

}~p_j OCMP+�,/*[ ('� �tE?� *.06 O�� .** m[ �E��� m���9:;�=����G?/*=� CMP+/*�,**('@/?�:;����� O,**

mi�[ =�! @/����� CMP-/*i� Owx�_q[ ('� :;�=-��()v� p_���2*��tV���=��()*! 7�� �_����'wxytE?9v� y�-ti�(' CMP-**��7(�t=����hv� ��� �j���e2*@V=�EF�! @��t' CMP,/*�-/*� ¡(�¢£¤���*�¥=��()v� CMP--*�./*('� @��t�¦§m���9:;��=�G?/*! @�:;��'� p_¨���2*©ª��|�:;���«¬��­��hv� rst��^|/*V®¯?/*!@�rst' CMP,**�--*�� Om� +** mi�[ ('�°o��t�¦F�±V���¢£¤2*!rst��²�³�?2-t'_��-t´ Oµ¶-t ; CMP

,**[ E?� �¢ ,/��£¤�³F� CMP.**���.** m��7(·¸|/*! |?�� :;-�(�t

Fig. 2. Filtered stacked section (A) and post stacked, migrated time section (B).

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����������� ���� �CMP-.*��� �� ������������� �Fig. ,�! "#� $%� CMP+/*�,**�&' +**�,** m���(���� �)��� �*+��,�� CMP+/*�&',** m��-� CMP-/*�&' /** m+./0�12���34 5�.67��! ���� CMP/**�0**�&' ,**�.** m��� 89:��;<= ��>?@A��� B>?@��� @����� C�C.-�A�����@DE��� F���1G�HI������J !

/� ���K�����<=�LMN�+�OPQR�-� C.QST.UV� WX�Y���Z.[�\]^�

�Q_� -.2 km�`�89a�YbcQdeU#!fg89hija�klmnop�kqV� &'�:QrsU#! ]^����� tuQvw/0���@�F�x#<=�\.DE��! yz�{|U#�:�} ~�����T���� ���������Q_��: ������� +332 ; ���-� ,**1 ; ���-� ,**1a, ,**1b� .����[�V�������E�\!

� �y��QMw�\#�� ��� ������ � ¡¢£Q���� }¤¥¦}��§¨©£��ª«¬�N­��� ®¯°Q�#±�#! 89a�Ybc²³�� �� ´µ��¶·.UV®¯°Q�#±�#! bc�\

Fig. 3. Depth converted seismic section (above) and its geologic interpretation (bottom). Black, heavy lines and thin

lines indicate main faults and subsidiary faults, respectively. The lines are dashed where inferred.

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����� �������� ���������������� � ���������� ������ �!�" #$��%�"�&��'��(��)�*+�� ,-"�&���.*/�01�23�4 5�65�7 �#��89:;�<3��$�� =�>?����� @��� =����A BC���!����D"E#���� �F� 5�65�7 #$G$HIJ%���& K'��L1:�()G3*��� �M N+OI�H�P,QL�RS 5�65�7 T-3*U�� .9P8/0V-W!O7

����"�X1� +3/.� YZ2�[3453<\67]^�_1`Ia8\� �39� 1� 0-�03.

:�;b� +32.� <c67d�ef=��gh3>?� 9�@A� /1� +1-�+2/.

Ikeda, Y., +32-, Thrust-front Migration and Its Mechanism

\Evolution of Intraplate Thrust Fault Systems\, Bull.Dept. Geogr., Univ. Tokyo, +/, +,/�+/3

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