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doi:10.2204/iodp.sp.332.2010

Cited by 2 publications

(3 citation statements)

References 31 publications

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“…A tuned airgun array system of 7,800 cubic inches was deployed as a seismic source fired along the circular lines, shown in Figure 6. Each of the circles in the figure encloses a seafloor seismometer of the DONET (Dense Oceanfloor Network System for Earthquake and Tsunamis) (Kawaguchi et al, 2015) cabled observatory, a borehole seismometer installed during the legs of the IODP (Integrated Ocean Drilling Program) (Kimura et al, 2013;Kopf et al, 2010), or both (Table S1). The seismometers of DONET are all telemetered in realtime to observe natural earthquake events such as regional microearthquakes, VLF (Very Low Frequency) events, and seismic microtremors in and around the seismogenic zone (NIED, 2019).…”

Section: Data Acquisitionmentioning

confidence: 99%

Stress Field Estimation From S‐Wave Anisotropy Observed in Multi‐Azimuth Seismic Survey With Cabled Seafloor Seismometers Above the Nankai Trough Megathrust Zone, Japan

et al. 2021

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The spatial variation of azimuthal S‐wave phase velocity anisotropies caused by differential horizontal stress along the Nankai Trough was analyzed to understand the stress state of the overhung block of the forearc region, off Kii Peninsula, Japan. We conducted controlled‐source seismic surveys along the circumference of a 3 km radius circle centered at each seismometer of a cabled seafloor observatory installed in the Nankai subduction zone. We applied an anisotropy semblance method to estimate the orientation of fast and slow S‐wave velocities of shallow sediments and deep accretionary prism using the multi‐azimuth seismic dataset acquired at each seismometer location. The estimated orientations of fast S‐wave velocity are parallel to the convergent direction of the subducting place beneath the Kumano basin in the deeper accretionary prism while perpendicular to the convergent direction in the shallow sediments inside the Kumano basin. These fast S‐wave polarization orientations in shallow sediments show good agreement with horizontal maximum stress orientations estimated in situ borehole measurements in the observation area. We estimated the differential horizontal stress field in the Nankai Trough region from obtained S‐wave anisotropy using a simple crack model. Using this method, we first suggest the convergent‐parallel horizontal maximum compression in the deeper part of the accretionary prism above the locked portion. Assuming obtained S‐wave anisotropy is attributed to the tectonic loading by the subducting plate, these results suggest that the S‐wave azimuthal anisotropy measurements can be used to monitor the subsurface stress field as a function of time.

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Section: Data Acquisitionmentioning

confidence: 99%

Stress Field Estimation From S‐Wave Anisotropy Observed in Multi‐Azimuth Seismic Survey With Cabled Seafloor Seismometers Above the Nankai Trough Megathrust Zone, Japan

et al. 2021

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“…During Expedition 332, acceleration measurements were recorded to monitor VIV on the drill pipe during the SmartPlug recovery at IODP Site C0010 and the LTBMS installation at IODP Site C0002 (Kopf et al, 2010). The BHA was made up and run in the hole while the Chikyu was in the low-current area (LCA) (current < ~1.5 kt), upstream and northwest (~30 miles away) of Site C0010.…”

Section: Viv Measurementsmentioning

confidence: 99%

“…VIV can be controlled by various passive methods (Blevins, 1990;Kwon et al, 2002) (e.g., streamlined fairings are one kind of effective device in general use for VIV suppression [Miyazaki et al, 2008]). Here we show acceleration data on drill pipe VIV collected during IODP Expedition 332 (Kopf et al, 2010). First, we evaluate the characteristics and causes of the vibration on drill pipe in order to suppress VIV.…”

Section: Introductionmentioning

confidence: 99%

Drill pipe monitoring of vortex-induced vibration during IODP Expedition 332 observatory installations

Kitada

Araki²,

Kojima³

et al. 2011

Proceedings of the IODP

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This study reports on vortex-induced vibration (VIV) suppression methods for long-term borehole monitoring system (LTBMS) installation in areas of strong ocean currents such as the Kuroshio Current. One of the primary challenges in installing the LTBMS was to deploy high-precision, sensitive sensors into the borehole without damaging them during their trip through the water column. Two field tests were performed using accelerometers attached to the instrument carrier and/or drill pipes to collect data on the characteristics and effects of drill pipe VIV. These tests demonstrated that vortex suppression can be achieved by using drill collars and attaching ropes to the drill pipe. Therefore, these methods were applied to the drill pipe (above the sensor assembly) for the actual recovery and installation of the observatory systems during the Integrated Ocean Drilling Program (IODP) Expedition 332. From the observations and data collected over a period of several days of VIV monitoring during the LTBMS installation and SmartPlug retrieval, the following three points can be made regarding VIV suppression: (1) the bottom-hole assembly should be lowered in the low-current area, with the relative current speed being as low as possible, (2) the drifting speed should be kept well below 1 kt, and (3) the drifting angle between drifting direction and sea current should be kept as small as possible (definitely <45°). The results of VIV monitoring during Expedition 332 attest that the amplitude was further reduced to <0.5 g, eventually contributing to the success of the first LTBMS installation at IODP Site C0002.

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Untitled

Cited by 2 publications

References 31 publications

Stress Field Estimation From S‐Wave Anisotropy Observed in Multi‐Azimuth Seismic Survey With Cabled Seafloor Seismometers Above the Nankai Trough Megathrust Zone, Japan

Stress Field Estimation From S‐Wave Anisotropy Observed in Multi‐Azimuth Seismic Survey With Cabled Seafloor Seismometers Above the Nankai Trough Megathrust Zone, Japan

Drill pipe monitoring of vortex-induced vibration during IODP Expedition 332 observatory installations

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