5:15 PM - 6:30 PM
[SCG45-P02] S wave velocity structure at the Kairei Hydrothermal Vent Field near the Rodriguez Triple Junction in the Indian Ocean
Keywords:S wave velocity structure, Vp/Vs ratio, Kairei hydrothermal vent field, serpentinization
1. Introduction
The Kairei Hydrothermal Vent Field (KHF) is located at eastern area of the first segment of the Central Indian Ridge which is extended from the Rodriguez Triple Junction. The KHF extrudes fluid with rich H2 content. Although the KHF itself exists above a basaltic rock massif (Hakuho Knoll), gabbro and mafic rocks such as peridotite were discovered on the seafloor around the KHF. These deep rocks may move upward, may be serpentinized by sea water, and may contribute to the high H2 concentration of the Kairei vent fluid. To investigate seismic structure, we conducted a seismic survey with ocean bottom seismometers and an air-gun in 2013. Takata et al. (JpGU, 2015) reported the P wave velocity structure. They revealed high velocity areas with more than 6.0 km/s of the P wave velocity under 1-2 km from the seafloor at the Hakuho Knoll and the Yokoniwa Rise which is located north of the Hakuho Knoll. This result indicated uplift of deep rocks. To investigate these rock’s properties, we determine the S wave structure using the air-gun.
2. Data acquisition and analysis methods
We conducted a seismic refraction/reflection survey from January 27 to March 19 in 2013 using S/V Yokosuka of Jamstec. In the experiment, we used 19 OBSs, an air-gun (G.I. gun) and a single channel steamer cable.
To make the S phase easer to see, we rotate the horizontal components of seismic sensors to the radial and transverse directions. We estimate horizontal direction of the sensors from trajectories of water waves. Using picking data of the S phase, we construct a 3D S wave velocity structure by the FAST program (Zelt and Barton, 1998).
3. Results
A provisional result is that the high P wave velocity areas under the Hakuho Knoll and the Yokoniwa Rise have high Vp/Vs ratio with about 2.0. This ratio is higher than those for gabbro (about 1.9) and peridotite (about 1.7). Since the Vp/Vs ratio of serpentine is about 1.8-2.2, this result may indicate serpentinization of these areas.
Acknowledgment
We thank the captain and crew of S/V Yokosuka of JAMSTEC for their support. This work was supported by Grant-in-Aid for Scientific Research on Innovative Areas of the Ministry of Education, Culture, Sports, Science and Technology (Grant Number 20109002, TAIGA project).
The Kairei Hydrothermal Vent Field (KHF) is located at eastern area of the first segment of the Central Indian Ridge which is extended from the Rodriguez Triple Junction. The KHF extrudes fluid with rich H2 content. Although the KHF itself exists above a basaltic rock massif (Hakuho Knoll), gabbro and mafic rocks such as peridotite were discovered on the seafloor around the KHF. These deep rocks may move upward, may be serpentinized by sea water, and may contribute to the high H2 concentration of the Kairei vent fluid. To investigate seismic structure, we conducted a seismic survey with ocean bottom seismometers and an air-gun in 2013. Takata et al. (JpGU, 2015) reported the P wave velocity structure. They revealed high velocity areas with more than 6.0 km/s of the P wave velocity under 1-2 km from the seafloor at the Hakuho Knoll and the Yokoniwa Rise which is located north of the Hakuho Knoll. This result indicated uplift of deep rocks. To investigate these rock’s properties, we determine the S wave structure using the air-gun.
2. Data acquisition and analysis methods
We conducted a seismic refraction/reflection survey from January 27 to March 19 in 2013 using S/V Yokosuka of Jamstec. In the experiment, we used 19 OBSs, an air-gun (G.I. gun) and a single channel steamer cable.
To make the S phase easer to see, we rotate the horizontal components of seismic sensors to the radial and transverse directions. We estimate horizontal direction of the sensors from trajectories of water waves. Using picking data of the S phase, we construct a 3D S wave velocity structure by the FAST program (Zelt and Barton, 1998).
3. Results
A provisional result is that the high P wave velocity areas under the Hakuho Knoll and the Yokoniwa Rise have high Vp/Vs ratio with about 2.0. This ratio is higher than those for gabbro (about 1.9) and peridotite (about 1.7). Since the Vp/Vs ratio of serpentine is about 1.8-2.2, this result may indicate serpentinization of these areas.
Acknowledgment
We thank the captain and crew of S/V Yokosuka of JAMSTEC for their support. This work was supported by Grant-in-Aid for Scientific Research on Innovative Areas of the Ministry of Education, Culture, Sports, Science and Technology (Grant Number 20109002, TAIGA project).