1:45 PM - 3:15 PM
[SCG52-P10] Seismic focal mechanisms near the Rodriguez Triple Junction in the Indian Ocean
Keywords:focal mechanism, Central Indian Ridge, Rodriguez Triple Junction, non-transform offset (NTO)
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. To investigate seismic structure, A seismic survey with ocean bottom seismometers and an air-gun was conducted in 2013. Takata et al. (JpGU, 2015) reported a P wave velocity structure, and Morii et al. (JpGU, 2021, SSJ, 2022), Sato et al. (JpGU, 2023) report P and S wave velocity structures. This study estimates focal mechanisms of earthquakes determined by Morii et al (SSJ, 2022), and discusses the tectonics of this region.
2. Data acquisition and analysis methods
Earthquake data are from the earthquake observation with ocean bottom seismometers from January 27 to March 19 in 2013 using S/V Yokosuka of Jamstec (YK13-01, YK13-03). We analyzed earthquakes determined by Morii et al. (SSJ, 2022) using the tomoDD program. The FPFIT program was used to determine the focal mechanisms.
3. results
Of about 1850 earthquakes, 423 focal mechanisms had precisely determined. In an earthquake cluster located a few km northwest of the KHF and earthquakes at the ridge axis, many of them have a normal fault type mechanism. About 70 % of earthquakes in the cluster and about 60 % in the ridge axis have the T axis that is closer to the direction of the plate motion than P axis. These indicate that the extensional stress in the direction of the plate motion is dominant in these regions. A non-transform offset (NTO) exists between the first and second segments of the ridge axis. This area has no terrains made from transform faults, and a rise is seen on the south side of the NTO. This rise is thought to be an NTO massif. Many of earthquakes in this area have strike-slip or normal fault type mechanisms. These results are consistent with the regional stress field and formation process of the NTO massif (rising by normal faults).
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. To investigate seismic structure, A seismic survey with ocean bottom seismometers and an air-gun was conducted in 2013. Takata et al. (JpGU, 2015) reported a P wave velocity structure, and Morii et al. (JpGU, 2021, SSJ, 2022), Sato et al. (JpGU, 2023) report P and S wave velocity structures. This study estimates focal mechanisms of earthquakes determined by Morii et al (SSJ, 2022), and discusses the tectonics of this region.
2. Data acquisition and analysis methods
Earthquake data are from the earthquake observation with ocean bottom seismometers from January 27 to March 19 in 2013 using S/V Yokosuka of Jamstec (YK13-01, YK13-03). We analyzed earthquakes determined by Morii et al. (SSJ, 2022) using the tomoDD program. The FPFIT program was used to determine the focal mechanisms.
3. results
Of about 1850 earthquakes, 423 focal mechanisms had precisely determined. In an earthquake cluster located a few km northwest of the KHF and earthquakes at the ridge axis, many of them have a normal fault type mechanism. About 70 % of earthquakes in the cluster and about 60 % in the ridge axis have the T axis that is closer to the direction of the plate motion than P axis. These indicate that the extensional stress in the direction of the plate motion is dominant in these regions. A non-transform offset (NTO) exists between the first and second segments of the ridge axis. This area has no terrains made from transform faults, and a rise is seen on the south side of the NTO. This rise is thought to be an NTO massif. Many of earthquakes in this area have strike-slip or normal fault type mechanisms. These results are consistent with the regional stress field and formation process of the NTO massif (rising by normal faults).
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).