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���������� !�>?@A�BC�� D E FGH������I� !AJ�KLA�BC�MNO�P+Q��� % R S T
Aftershock Distribution of the December 14, 2004 Rumoi-nanbu
Earthquake (M 6.1) in the Northern Part of Hokkaido, Japan
Masayoshi I8=>N6C6<>, Takahiro M6:96, Teruhiro Y6B6<J8=>,
Hiroaki T6@6=6H=> and Minoru K6H6=6G6
Institute of Seismology and Volcanology, Graduate School of Science, Hokkaido University,Kita 10, Nishi 8, Kita-ku, Sapporo 060�0810, Japan
Tsutomu S6H6I6C>
Department of Natural History Sciences, Faculty of Science, Hokkaido University,Kita 10, Nishi 8, Kita-ku, Sapporo 060�0810, Japan
Akihiko Y6B6BDID
Department of Earth’s Evolution and Environment, Division of Mathematics,Physics, and Earth Sciences, Graduate School of Science and Engineering,
Ehime University, Bunkyo-cho 2�5, Matsuyama 790�8577, Japan
(Received August 28, 2006; Accepted November 22, 2006)
On December 14, 2004, an M 6.1 earthquake occurred in the northwestern part of Hokkaido,Japan. We installed nine temporal seismic stations around the source area immediately after theoccurrence and had continued the observation for about two months after the main shock. Wedetermined 823 hypocenters of aftershocks and one dimensional P-wave velocity structure modelfrom the travel time data. It is found that aftershocks are clearly distributed on an eastward dippingplane with a dip angle of about 25 degrees. This plane agrees well with one of the nodal planes of thefocal mechanism determined by P-wave first motions in this study. Next, we investigated a positionof the main shock relative to the aftershock distribution. The station correction values for permanentstations were determined from the data during the period of the temporary observation. Estimatedmain shock hypocenter was confirmed to be situated on the aftershock plane. Finally, we estimatedthree-dimensional P-wave velocity structure based on the temporary travel time data. Relocatedaftershocks using the three dimensional velocity structure were mainly distributed along the bound-ary between the high and low velocity zones.
Key words : Aftershock distribution, P-wave velocity structure, Reverse fault
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Fig. 1. Location map showing seismic activity of earthquakes greater than M 2.0 in northern part ofHokkaido determined by Japan Meteorological Agency (JMA) from January 1, 1991 to December14, 2004 (date of the main shock). A solid star indicates the epicenter of main shock determined byJMA. The inset map shows the study area and epicenters of earthquakes with M 5.0 or greater.
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Fig. 2. (a) Permanent seismic stations used in this study. Open squares, triangles and circles arestations of Hokkaido University, JMA and Hi-net (National Research Institute for Earth Science andDisaster Prevention), respectively. (b) Temporary seismic stations (solid squares). Open squaresand circles indicate permanent stations. A solid star is the epicenter of the main shock determinedby JMA.
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Table 1. Station corrections used in the calcu-lation of hypocenters. The 4th columnshows the operation period.
Fig. 3. One dimendional (1-D) P-wave velocitystructure model inverted from the initialmodel by Crosson’s method (1976). We usethe smoothed inverted model for hypo-center determination. Also shown are themodels estimated by Moriya (1986) andTamura et al. (2003), and that routinelyused by ISV (Institute of Seismology andVolcanology, Hokkaido University).
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(1976)�������"#$%&'(I1J��*+��5�K��A���LM6�N���O#�P� "#?;���QRS�H�QRS�R6 0.001���SM��STU6V���S�?;.� W�� BCD�EFC�XY���;. Resolution
matrix��Z[6 1\]^_` a�U�bc6d�aS�e���.�I �fgI1 a���h@1\�@��hiUS��j�-.� 2����SISV��� k�*+��S�� � <=�>? 8
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Table 2. Diagonal elements of the resolutionmatrix.
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M"� Q&RST�H������j$��klm%�#"P]���no�&'()%Uq �������G\M�! &'D�% Fig. 5a�7$ � F � B�"�3&%67B���.q"8��=.� M3&��%�q"� M 2.512�3&�j$"���klm (Table 3)%�# ,-�W��.#,-�&'�45% Fig. 5b�7$ � Fig. 5b%8��� ���klm%�#��()$ &'�4�� ���klm%�#"()$ &'�� ���� ��j���=�F �h��#"# 3&�����OP !����.q � F � � Z[��¡��¢£¢�¤�>?$"#�� Fig. 5c������¥¦������OP$ &'OP¥¦%� ����%Uq H��M 2.012�C��/#"45$"7$ � ��6��� �������¥¦�� ������q"\M�! &'D��G�j��§=� ¨©¨�¤�ªª>?B�C��� �«��.Gz#D�%7B���.q ���D���������� ������ ¬�E��+�!��Q&�/#"C����%®�$"tOP%Uq"#��� ��l$#&'Z[%¯�� M�� 2�����&'OP$ C���|� ����H�h�RS$ 3&�h�� Q&�z#,��RS$ 3/�3&�/#"� Fig. 5d��������\M &'����������OP$ &'�°±�C�9���Z[%45$ � ��6��� #�!�3&C�����\M &'�2�����4�"� �¤��¢£¢�¤��§ �¤���#�¤�� 1 km>?$"#����D���$ �q"�0v,��RS$ Q&�/#"C�������Eq .�²0v���>?$ Z[�&'�E��+�!���� 3/��&� ³�>?´DnoQ&%>? _ �Fig. 5d��±�µ¶��°±�µ¶·�� F � \M�! &'Z[% Fig. 4a�������&D��h�µ¶�7B� Q&�� ¸�
Fig. 4. (a) Aftershock distribution with 1s error bars determined by using the 1-D smoothed P-wavevelocity structure (Fig. 3) from December 15, 2004 to February 9, 2005. Gray squares indicateseismic stations used for the location. A solid star is the main shock determined by this study.Solid lines indicate active faults; � Rikibiru and � Hirotomi active fault. A dashed line is ananticline axis [Ikeda et al. (2002)]. A focal mechanism of the main shock determined from P wavepolarities is also shown.(b) Comparison between hypocenters determined by the final 1-D velocity structure model (opencircles) and ISV velocity model (the tip of the bar connected to a open circle). Hypocenters ofevents with a magnitude greater than 2 are plotted.(c) Comparison between hypocenters determined from two datasets (December 22, 2004�January12, 2005); the first dataset includes two stations (HTM and SKB) and the second dataset does notinclude the two stations. Hypocenters for the first dataset are shown by open circles, and those forthe second dataset are shown by the tip of the bar connected to an open circle. Hypocenters ofevents with a magnitude greater than 2 are plotted.
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Fig. 5. (a) Relocated hypocenter distribution determined by using only permanent stations with thestation correction. A solid star is the main shock.(b) Comparison between hypocenters with station correction (open circles) and ISV hypocenterswithout station correction (tip of the bar connected to an open circle). These hypocenters areshown for events with Mc 2.5.(c) Comparison between hypocenters determined by using temporary stations (open circles) andpermanent stations with station correction (tip of the bar connected to an open circle). An openstar is the main shock corrected based on the shift of two aftershocks near the main shock (see (d)).(d) The same as (c), but only for the main shock and three aftershocks, A dashed star indicates themain shock corrected by the shift of two aftershocks (small open circles).
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Table 3. Station corrections for the permanentstations.
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Fig. 6. Results of checkerboard resolution test for three dimensional (3-D) P wave velocity structure.We assigned �5� velocity perturbations side by side to every grid nodes in each layer. Theresults of the test are shown for depths of 1 km, 3 km, 5 km, and 7 km. Open circles are grid pointsused in 3-D inversion. Gray squares are used stations. A red star is the main shock.
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Crosson, R. S., 1976, Crustal structure modeling ofearthquake data. 1. Simultaneous least squares es-timation of hypocenters and velocity parameters,J. Geophys. Res. 81, 23036�23046.
Heki, K., S. Miyazaki, H. Takahashi, F. Kimata, S.Miura, N. F. Vasilenko, and A. Ivashchenko, 1999,The Amurian plate motion and current plate kine-matics in East Asia, J. Geophys, Res., 104, 29147�29153.
Hirata, N. and M. Matsu’ura, 1987, Maximum-likelihod estimation of hypocenter with origintime eliminated using nonlinear inversion tech-nique, Phys. Earth Planet. Inter., 47, 50�61.
Humphreys, E. and R. W. Clayton, 1988, Adaptationof back projection tomography to seismic traveltime problem, J. Geophys. Res., 93, 1073�1085.0�m1nopq/n2�r3nstun@4v5nw678x 2002 9yVz:;{[8f 2|��}<~�
Inoue, H., Y. Fukao, K. Yanabe, and Y. Ogata, 1990,Whole mantle P-wave travel time tomography,Phys. Earth Planet. Inter., 59, 294�328.
Kato, A., E. Kurashimo, N, Hirata, S, Sakai, T, Iwasaki,and T. Kanazawa, 2005, Imaging the source regionof the 2004 mid-Niigata prefecture earthquake andthe evolution of a seismogenic thrust-related fold,Geophys. Res. Lett., 32, L07307, doi: 10. 1029/2005GL022366.�:;#$~ 1991 �'=�(�:; 2|��}<~ 437 pp.����� 1997 �����(��> �http: / /
www.gsi.go.jp� ��� 2006�8�18������� 2004, 12� 14= 14� 56?�(����@A(���B`��,C �http://www.gsi.go.jp/
WNEW/PRESS-RELEASE/2004/1215.html� ��� 2006�8�18��
Korenaga, M., S. Matsumoto, Y. Iio, T. Matsushima, K.Uehira, and T. Shibutani, 2005, A Three dimen-sional velocity structure around aftershock areaof the 2004 mid Niigata prefecture earthquake(M 6.8) by the Double-Di#erence tomography,Earth Planets Space, 57, 429�433.
Miyamachi, H., K. Iwakiri, H. Yakiwara, K. Goto, andT. Kakuta, 1999, Fine structure of aftershock dis-tribution of the 1997 Northwestern KagoshimaEarthquake with a three-dimensional velocitymodel, Earth Planets Space, 51, 233�246.����n�! DntE�Hn����n����n�E F 2005, 2004G����@A(���������H��#$I� 68, 243�253.�!JK 1983 ���(��iA�%�_ Vp/Vs(��� �������H��#$I� 42, 145�154.�!JK 1986 �;���C���>� ¡¢����(g£[¤£f �L#¥I 31, 475�485.�!JK 1999 ����¦(§M�%�_��(Y¨¤©9= ¡ª�«¬_��4A�® �¯��21, 557�564.
Okada, T., T, Matsuzawa, J. Nakajima, N. Uchida, T.Nakayama, S. Hirahara, T. Sato, S. Hori, T. Kono, Y.Yabe, K. Ariyoshi, S. Gamage, J. Shimizu, J. Suga-nomata, S. Kita, S. Yui, M. Arao, S. Hondo, T. Mizu-kami, H. Tsushima, T. Yaginuma, A. Hasegawa, H.Zang, and C. Thurber, 2005, Aftershock distribu-tion and 3D seismic velocity structure in andaround the focal area of the 2004 mid Niigataprefecture earthquake obtained by applying dou-ble-di#erence tomography to dense temporary seis-mic network data, Earth Planets Space, 57, 435�440.°�±I 2002 �9²Vh³(>T�N �O´Pn QRn��SW �'��=��2µ(�:;���g£[¤£f 2|��}<~ 111�121.
Sakai, S., T. Hirata, A. Kato, E. Kurashimo,T. Iwasaki,and T. Kanazawa, 2005, Multi-fault system of the2004 Mid-Niigata Prefecture Earthquake and itsaftershocks, Earth Planets Space, 57, 417�422.¶T·¸��U 2000 ���(���C �9 2<�
310 pp.¶T·¸��U 2005 ¹ 16G �2004G� 12� 14=����@A(��VQI� 29 pp.
Takahashi, H., M. Kasahara, F. Kimata, S. Miura, K.Heki, T. Seno, T. Kato, N. Vasilenko, A. Ivash-chenko, V. Bahtiarov, V. Levin, E. Gordeev, F. Kor-chagin, and M. Gerasimenko, 1999, Velocity fieldof around the Sea of Okhotsk and Sea of Japanregions determined from a new continuous GPSnetwork data, Geophys. Res. Lett., 26, 2533�2536.����n�E F 2005 ����º»A(���C�����A(g£[¤£f �������H��#$I� 68, 199�218.
tE�Hn����n����n����n�E Fn�! Dn��WR220
Tamaki, K. and E. Honza, 1985, Incipient subductionand deduction along the eastern margin of JapanSea, Tectonophysics, 119, 381�406.�� ���� ����� 2003� ���������������������� �!"#� ��2, 55, 337�350.�� ��$%&'(�)*+,�-./0�- 12� 2005,34 165 126 147�89:;<�=>?@A���B�CDEF��GHI�����JKL�MN�� ���O�GPQREF� 76, 113�128.
Thurber, C. H., 1983, A fast algorithm for two-pointseismic ray tracing, J. Geophys. Res., 88, 8226�
8236.Um, J. and C. H. Thurber, 1987, A fast algorithm for
two-point seismic ray tracing, Bull. Seism. Soc.Am., 77, 972�986.S� T�U�VW� 1991� XYZ[\Y]^_���������`abc�:d][\e� 7f��ghijklm� No. 1, 70.nopq� 2001� ��g� r 3s� tOus� 376 pp.Wessel, P. and W. H. F. Smith, 1995, New version of
the generic mapping tools released, EOS Trans.Am. Geophys. Union, 76, 329.
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