MeSO-net. Development of the Metropolitan Seismic Observation network (MeSO-net) for Detection of Mega-thrust beneath Tokyo Metropolitan Area

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1 Bull. Earthq. Res. Inst. Univ. Tokyo Vol. 2.,**3 pp MeSO-net * +,, Development of the Metropolitan Seismic Observation network (MeSO-net) for Detection of Mega-thrust beneath Tokyo Metropolitan Area Keiji Kasahara *, Shin ichi Sakai, Yuichi Morita, Naoshi Hirata, Hiroshi Tsuruoka, Shigeki Nakagawa, Kazuyoshi Z. Nanjo +, and Kazushige Obara + +, Earthquake Research Institute, the University of Tokyo National Research Institute for Earth Science and Disaster Prevention Abstract To better assess the seismic hazards produced by a magnitude 1 or greater ( M 1) earthquake in the Tokyo metropolitan area, we have launched the Special Project for Earthquake Disaster Mitigation in Tokyo Metropolitan area (,**1,*++ ). This requires establishing a highly dense seismicarray observation network in and around Tokyo to monitor ongoing micro-earthquakes with relatively high precision even if noise levels are generally high. We have started developing the Metropolitan Seismic Observation network (MeSO-net). Deployment of MeSO-net seismic stations is currently underway. The number of observatories at project termination will be.** with a, / km interval in space. In this paper, we summarize how we solved technically di$ cult and practical problems involved in MeSO-net construction. We start with a review of related work to better understand the technical di$ culties involved in deploying stations in metropolitan areas such as Tokyo. Next, we explain our approach to verifying a meaningful design of an observatory and its deployment at local sites. We further describe our decision-making process in practice for implementing station deployment. We hope that establishing the MeSO-net will support a new assessment of the seismic hazards produced by M 1 earthquakes in the Tokyo metropolitan area. Key words : Seismic instruments and networks, Seismic and tectonics, Subduction zones, Earthquake source observation, Tomography, Earthquake ground motion and engineering seismology +,**3 M 2 M1 * kkasa@eri.u-tokyo.ac.jp ++- **-,

2 SN +,,,**3,*** +30*,**3 SN MeSO-net: Metropolitan Seismic Observation network.** -*** m SN , m+* m,,+,* m +* m,**3,**3,* m / km.** SN +30* Hi-net Obara et al.,,**/ Hi- net 1** Bolt, +310 ; Lee et al.,,**, / LASA Large Hi-net Aperture Seismic Array Forbes et al., +30/ +/* m 1* m Hi-net LASA,** /,/,/,+ +30* 72

3 -2* m : + -,*** /* m +* +/ cm /* km +** km *0 m *,***; , +31* +302,- +32, -*** m /* m,*** m +32* +320 ; +32, /** m. 2, * km Hole Lock +32, / + -/** m 73

4 , km / km.**,**3,**3;,** MeSO-net + SN -/** m Fig. +. Seismographs on and around the P-wave arrival of the earthquake with magnitude -./ at ++ : *,,. March,**2 in southeastern Ibaraki prefecture. The traces are digital recordings made at the observatory in Earthquake Research Institute, at an epicentral distance of about /* km. The seismograms were made at depths of *, -, /, st nd rd th and,* m in the +,,, -, and. traces from the top, respectively. The numbers inside the figure are the maxiseismograph are normalized by the maximum amplitude mum amplitudes for the seismograms. Amplitudes in each for visualization purpose. + 1* km M m, / m SN P SN SN + +,* m - m, / m SN MeSO-net,* m -,**2 -,. ++ *, /* km M -./ P 2 - m Hz,* m P SN,* m +* -,,**2 -,- *- /2 +* Hz 74

5 +*** -*, MeSO-net Hz,* m +* Hz,* m Hz SN MeSO-net Fig.,. Same as Fig. + for an earthquake of magnitude --.,* m on *- : /2,- March,**2 in southeastern Ibaraki prefecture. The epicentral distance from the observatory in Earthquake Research Institute is about 1* km. Fig. -. Power spectral density of ground motion noise (UD component) at Earthquake Research Institute for di# erent depths : *, -, /, and,* m. Left panel: records under clear sky at night; right panel: records in heavy weather during daytime. 75

6 ,**1 MeSOnet Hi-net MeSO-net MeSO-net - MeSO-net.,* m MeSO-net / MeSO-net MeSO-net,**3 Fig... Schematic diagram of an observatory with structural drawing. Top left panel ( + ): overall structure ; top right panel (,): well structure ; and bottom left panel (-): case structure. 76

7 ,**-,**3 Hole Lock Hole Lock Obara et al.,,**/ Hi-net Hi-net Hi-net - MeSO-net Fig. /. Sensor part. First, second, and third panels from the top are conceptual drawings of the sensor, photo of component, and photo of internal component, respectively. 77

Fig. 0. Photos of fixing apparatus that utilizes the Hole lock. This apparatus is located at the top and bottom of the protective housing of a seismometer.

8 Fig. 0. Photos of fixing apparatus that utilizes the Hole lock. This apparatus is located at the top and bottom of the protective housing of a seismometer. Left panel: view of the inside; right panel: external view. Hole Lock,0 kg 0 /,1/. m STPG +,0. 0 mm / +0/. m SGP +-*. 2 mm. +0/. m 1 Fig. 1. Schematic diagram showing how to install a seismometer. See text. 78

9 -,.** Fig. 2. External view of the above-ground part of an observatory. From top left to bottom left: ISDN router, power source controller, and accumulator. From top right to bottom right : observation controller and arrester terminal block.,*+*,**3 -- GPS 2 / CAN GPS ISO CAN GPS GPS ms 1* Ah WIN +33. UDPIP /* ACK ACK SNMP 79

10 +332 ACROSS,**3 + Hz AKASHI -. V.*- Koketsu and Miyake,**2 JAE JA-/ QA-1** Honeywell International Inc. AKASHI V.*- JAE JA-/ DC +31, K-NET K-NET +32, JAE JA-/ JA-.*,**1 K-NET K-NET AD AD AKASHI V.*- 3 DC MeSO-net AD Hi-net KiK-net Obara et al.,,**/ JAE JAE JA JA-.* GA*, JAE JA-/ V JA-. Sundstrand -/ AD Data control Inc. QA-+.** Honeywell International TS+-2** Inc., +33* TS+-2/* TS+-2+* + +* *. +,* m IP01 mgal Fig. 3. Noise characteristics for the KIK-net (After Fujiwara et al.,,**2). 80

11 - +,/** gal, /** gal AD CAN AD DS DS Inose et al., +30, DS +-/ db DS AD AD AD AD DS AD AD AD +* mv +** Hz,** Hz.*,* +** Hz.* Hz +-/ db /* ms CAN AD AD /* ms +** m + AD +** Hz AD DS AD.* Hz, + RMS,* V -.- mv -./ mv +-/., db +-/. 0 db +-/ db 81

12 ,** Hz AD 2* Hz *,/ /* + DSAD +,* mv, - * +** mv,/ * mv, /* +/* mv -. mv AD AD,* m,* + Hz / mv,** Hz, 2* Hz AD,.* Hz, 0* Hz, 2* Hz *.***. *.***1 *.***1 1* m AD - AD SN 1* m 82

13 3 +* 1* m AD AD Hi-net Obara et al.,,**/ Hole Lock M./. ++ KiKdB SN +/,* net,** m, MeSO- net *,. Hz / MeSO-net *,. *2. Hz Hole Lock NHNM Peterson, +33- *.*/ Hz,*, SN K-NET,**1 Fig. +*. Power spectral density obtained from records of horizontal components obtained at the Tsukuba observatory. Set of dashed lines shows typical power spectral density of ground motion noise (NLNM and NHNM: USGS). 83

14 Fig. ++. Seismograms and power spectral density diagrams showing high-frequency observation and large amplitude observation for an earthquake of magnitude../ ( +3 :.3 ++ November,**1) under the MeSO-net. These observations were made at the Tsukuba observatory located in the area of the National Research Institute for Earth Science and Disaster Prevention (NIED), at an epicentral distance of about,0 km. WIN Matlab,**2 Matlab Power Spectrum Density; PSD M YYIM +, b,**2-3 YYIM 84

,. 2* Hz,**2-30 +- M... jma 2* Hz +, b -* Hz 3* Hz -* + * / +* +*, / Hz, +* +/ Hz,.2 /* Hz + ON-OFF. Fig. +,.,.-hour observation (UD component) on 3 March,**2 at the Yayoi observatory (YYIM).

15 ,. 2* Hz,** M... jma 2* Hz +, b -* Hz 3* Hz -* + * / +* +*, / Hz, +* +/ Hz,.2 /* Hz + ON-OFF. Fig. +,.,.-hour observation (UD component) on 3 March,**2 at the Yayoi observatory (YYIM). (a) Seismograph, (b) spectrogram, and (c) power spectral density for,.-hour observation. 85

16 AD /* Hz AD AD AD +, - cm, 0* cm,,** ,**3, ,,* / C :,**2-C-*, : MeSO-net + + m,*,,*./ m -*. 86

17 ,., + CP. - / SGP -* cm JIS G -./, +0./ m / STPG JIS G-./.,1/. m / SGP / STPG., / SOP-F-+,0A STPG STPG SUS-*. */. cm / SGP -* mm M+* SUS-*. / SGP / STPG / SGP / STPG / SGP +0/. m / STPG,1/. m,* m CP / SGP +0./ m / STPG,. 1/ m CP SGP STPG //. m, / -*. -*. SG : +2*. 87

18 / /* cm, -* cm /*/. Bolt, B.A., +310, Nuclear Explosions and Earthquakes : The Parted Veil, W.H. Freeman, -*3 pp.,**1 3* Forbes, C.B., R. Obenchain and R. J. Swain, +30/, The LASA sensing system design, installation, and operation, Proc. IEEE, /-, ,**1 K-NET: 1,, ,/.,*** ,.,** / ,---3. Inose, H., Y. Yasuda, and J. Marakami, +30,, A Telemetering System by Code Modulation : DS Modulation, IRE Trans. on Space Electronics Telemetry, SET-2,,*.,*3. +32*, * : 0/ Koketsu, K. and H. Miyake,,**2, A seismological overview of long-period ground motion, J. Seism., +,,, ACROSS, P 2*. Lee, W.H.K., H. Kanamori, P. Jennings, and C. Kisslinger (Editors),,**,, International Handbook of Earthquake & Engineering Seismology (International Geophysics Series) Part A, Academic Press, +,** pp.,**2 MeSO-net +. +-,,,**3 MeSO-net ACT protocol */.,**3 2. +* Obara, K., K. Kasahara, S. Hori and Y. Okada,,**/, A densely distributed high-sensitivity seismograph network in Japan: Hi-net by National Research Institute for Earth Science and Disaster Prevention, Rev. Sci. Instrum., 10, *,+-*+, doi: +*. +*0- / +. +2/.+31. Peterson, J., +33-, Observations and modeling of seismic back-ground noise, USGS Open File Report, 3--,,,,**3 2. / , /+1 /,0.,**-Hi-netKiK- net, / *.,**3 MeSO-net 2. ++/ +,/ :.. ++-/ , ,,2 + +* , P,.. Received November,*,,**3 Accepted January.,,*+* 88

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