Notice on using the OBS data
Seismic data obtained by using mobile and borehole ocean bottom seismometers (OBSs) are not
the same as those obtained at land stations due to various deployment conditions. Here, information,conditions and limitations of the OBS data to be opened for public use from this data center aredescribed. Users of the data should read this notice before downloading the data.
1. Available seismic data
Each OBS has its own time standard, such as a high precision digital crystal oscillator, and the timedifference of a mobile OBS to the UTC was measured before and after the observation. Because ofsmall change in temperature at the ocean floor and small drift of the OBS time, a linear interpolation
is applied to correct the OBS time. The overall time precision is less than 10 ms that is enough forusual analyses. In some OBSs, we could not measure the time difference after the observation causedby some trouble in a recorder. In such a case, we estimated the time drift using a method to measurea temporal change of ambient noise cross correlation function [1]. For borehole OBSs, we could not
apply a linear interpolation caused by the system limitation and the overall time precision is less than
1 second.
Another problem is a direction of horizontal components due to deployment ways for OBSs. For
mobile OBSs, an electric compass with an inclinometer is equipped on the seismic sensor. And, forborehole OBSs, circle shooting of the airgun was performed to determine the direction. The magnetic
azimuth of mobile OBS thus determined (from the north, clockwise in degree) for the H1 component
is indicated in the station list on the web page and in the data header. The coordinate system is theright-hand system, X: H2, Y: H1 and Z, those correspond to EW, NS and UD outputs from the seismicsensor. Azimuth of WP2, borehole OBS, determined by an airgun shooting [11], is also indicated in
the station list on the web page. However, we recommend users to determine the azimuth by analyzing
seismic waves (e.g., long-period P-waves, long-period Rayleigh wave) by themselves.
2. Difference in type of sensors and data IDs
There are three type of sensors used, the 1Hz (LE3D-lite) the PMD (WB2023LP) and the CMG (1T or -3T for OBS, 360 s) for the OBS. The 1Hz and CMG sensors are used with an active levelingmechanism, but the PMD sensor is operated under possible inclination. The horizontal componentsof the PMD sensors work correctly anyway, but the vertical component could be contaminated byhorizontal components. So that, the data of the inclinometer, within the electric compass, on the PMD
sensor is used to obtain the true vertical component after the instrumental response correction of threecomponents. The information about the inclination of PMD sensor is also indicated in the station list.
Pitch indicates an inclination of H1 axis in degree (up is positive) and roll indicates an inclination ofH2 axis in degree (down is positive). The data are not corrected to remove the instrumental response.
Some BBOBS were equipped with a differential pressure gauge (DPG) [17]. Sensor response of DPG

in a seed file is based on manufacture’s data sheet. Please note that the response of DPG on theseafloor may be different.
IDs of the mobile OBS data and the type of sensor are as following;
1Hz: CTJ
PMD: PHS, MAR, MRG
CMG: OHP, FP, SSP, TIARES, NOMan, OJP array, CTJ
All of borehole OBSs have the CMG-1T sensors. IDs of them are WP1 and WP2.
In the Normal Oceanic Mantle project (NOMan), we deployed a new type of a broadband ocean
bottom seismometer, namely the next-generation broadband ocean bottom seismometer (BBOBSNX)[2] using a special CMG-3T sensor can be operated correctly up to ±8° inclination. The BBOBSNX has no active leveling mechanism, so that vertical component could be contaminated byhorizontal components caused by a possible inclination. The information of the inclination measured
by the inclinometer in the sensor of the BBOBS-NX is shown in the station list on the web page. Pitch
indicates an inclination of H1 axis in degree (up is positive) and roll indicates an inclination of H2
axis in degree (down is positive). The data of the vertical component of BBOBS-NX are not corrected
to remove the contamination of horizontal components caused by a possible inclination.
3. Reference for the dataIt is preferable to refer one of these papers related to the OBS of each type and representative
analyses for each observation.
Project
Stations
PHS
PHS03,PHS04,PHS05,PHS08,PHS09,PHS11,PHS12,PHS13
MAR
MAR03,MAR04,MAR05,MAR06,MAR07,MAR08,MAR09
MRG
MRG03,MRG04,MRG16,MRG22,MRG40,MRG42,MRG58
OHP
NOT1,NWPAC1,NWPAC2,NWPAC3,SWSB1,SWSB2FP
FP2,FP3,FP4,FP5,FP6,FP7,FP8,S1,S2
OHP
WP1,WP2
SSP
T01, T02, T03, T05, T06, T07, T08, T09, T11, T12, T13, T14, T15,T16, T17, T18, T19, T21
TIARES
SOC1, SOC2, SOC3, SOC4, SOC5, SOC6, SOC7, SOC8, SOC9
NOMan
NM01, NM02, NM03, NM04, NM05, NM12, NM14, NM15,NM16, NM17, NM18, NM19, NM20, NM21, NM22, NM23,
NM24, NM25
OJP array OJ02*, OJ03, OJ04, OJ05, OJ06*, OJ08*, OJ09, OJ11*, OJ12, OJ13,OJ14*, OJ15, OJ16, OJ18, OJ19, OJ20, OJ22, CHUK, CHUK2,KOSR, KOSR2*: DPG data are available.
CTJ
LC1-5, CJ01-13

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T. Yamada, K. Mochizuki, Upper mantle and crustal seismic structure beneath the Northwestern
Pacific Basin using a seafloor borehole broadband seismometer and ocean bottom seismometers,
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[14] Matsuno, T., D. Suetsugu, K. Baba, N. Tada, H. Shimizu, H. Shiobara, T. Isse, H. Sugioka, A.
Ito, M. Obayashi, H. Utada. Mantle transition zone beneath a normal seafloor in the northwestern
Pacific: Electrical conductivity, seismic thickness, and water content. Earth and Planetary Science
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[15] Takeuchi, N., H. Kawakatsu, H. Shiobara, T. Isse, H. Sugioka, A. Ito, H. Utada, Determinationof intrinsic attenuation in the oceanic lithosphere-asthenosphere system. Science, 358, 1593–1596.
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Ishihara, S. Tanaka, M. Obayashi, T. Tonegawa, J. Yoshimitsu, T. Kobayashi, H. Utada, The OJP
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4. Caution and contact
We will not be responsible for any loss or damage caused by the data. If he/she has any question
about the data or request for the continuous data, please contact the data center.