5. Data Report: Broadband Seismic Observations at the Hawaii-2 Observatory, ODP Leg 2001

R.A. Stephen,2 F.K. Duennebier,3 D. Harris,3 J. Jolly,3 S.T. Bolmer,2 and P.D. Bromirski4

INTRODUCTION

Leg 200 was the first leg in deep sea and ocean drilling history to conduct operations in the vicinity of a continuously operating broadband seafloor seismometer (Stephen, Kasahara, Acton, et al., 2003). In September 1998, scientists from the University of Hawaii installed a broadband, shallow buried seismometer at the Hawaii-2 Observatory (H2O) site (Duennebier et al., 2002), and data continued to be acquired in real time in Oahu over the Hawaii-2 transoceanic cable until May 2003. Noise from the JOIDES Resolution as it approached and left the site as well as that from on-site operations was acquired continuously in Oahu in real time. In addition, shots from the 80-in3 water guns during single-channel seismic tests and the 1000-in3 gun during vertical seismic profile tests were also recorded. The purpose of this data report is to display in a variety of formats all of the seismic data acquired at H2O during Leg 200 (16 December 2001 [Julian day (JD)350/2001] to 27 January 2002 [JD27/2002]). Although this is an arbitrary time interval, it is long enough to record activities typical of the site, including events such as T-phases from distant earthquakes, local earthquakes, whales, shipping, and all of the JOIDES Resolution–related activities, including the water gun shots. Recorded activities at the beginning and end of this interval give some idea of background seismic activity when the drillship is not on site.

A complete description of drillship operations at Site 1224 is given in the "Operations" section of the site chapter (Shipboard Scientific Party, 2003). Operations for Site 1224 started at 0900 Universal Time Coordinated (UTC) on 26 December 2001 (JD360) when the drillship arrived at waypoint 1 (2732.787N, 14233.036W), ~36 nmi southwest of the H2O junction box (2752.916N, 14159.504W). (Note that all times in the Operations report are given in local ship time, which is UTC – 9 hr at Site 1224.) From waypoint 1, we approached H2O on a course of 56 at 6 kt while firing the water gun every 10 s as part of a seismic refraction survey (see "Seismic Results from Hawaii-2 Observatory" in the site chapter in Shipboard Scientific Party, 2003) (Fig. F1). The survey was completed at waypoint 2 (2754.426N, 14156.985W) at ~1645 UTC on 26 December, and the JOIDES Resolution returned and was positioned at Site 1224 (2753.363N, 14158.758W) at 1745 UTC on 26 December. At the site, drilling operations were interrupted six times, for a total of 6.11 days, while we waited on weather because of high seas (up to 7.7 m of heave) and strong winds (up to 44 kt). These storm periods correlate well with seismic noise in the microseism band as discussed by Bromirski et al. (2005). Site 1224 operations ended at 0930 UTC on 22 January 2002 (JD22), and the drillship departed the site on a bearing of 78.

Before presenting the actual data, this report summarizes the seismic data available and the transfer functions used to compute ground motion from the digital counts. The data for the complete interval are then displayed in two formats: spectrograms and root-mean-square (RMS) time series. The analysis and interpretation of features in the seismic data are discussed in a companion paper (Bromirski et al., 2005).

1Stephen, R.A., Duennebier, F.K., Harris, D., Jolly, J., Bolmer, S.T., and Bromirski, P.D., 2006. Data report: Broadband seismic observations at the Hawaii-2 observatory, ODP Leg 200. In Kasahara, J., Stephen, R.A., Acton, G.D., and Frey, F.A. (Eds.), Proc. ODP, Sci. Results, 200 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/200_SR/003/003.htm>. [Cited YYYY-MM-DD]

2Department of Geology and Geophysics, Woods Hole Oceanographic Institution, 360 Woods Hole Road, Woods Hole MA 02543-1542, USA. Correspondence author: rstephen@whoi.edu

3Department of Geology and Geophysics, University of Hawaii, 2525 Correa Road, Honolulu Hawaii 96822, USA.

4Center for Coastal Studies, Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla California, 92093-0209 USA.

Initial receipt: 21 May 2004
Acceptance: 13 December 2005
Web publication: 26 June 2006
Ms 200SR-003

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