Seismic evidence of continental margin influence on the NinetyEast Ridge in the Bay of Bengal

Abstract

The NinetyEast Ridge (NER), one of the most enigmatic features in the Indian Ocean, is covered by thick Bengal Fan sediment north of 9°N. We present seismic reflection data on the eastern flank of the NER, at 10°N, that show the presence of 4-5 km thick sediments beneath the Bengal Fan sediments. These sediments can be imaged up to 60 km beneath the Andaman fore-arc accretionary wedge, suggesting that the décollement lies above these sediments. The presence of thick sediments above the northernmost segment of the NER suggests that this segment was close to a continental margin during its emplacement. We propose that these sediments were deposited soon after the breakup of India and Antarctica, between 130 and 100 Ma, and might act as source rocks for oil and gas generation beneath recent Bengal Fan sediments. Furthermore, subducting thick sediments can significantly change the seismogenic behavior of the Andaman subduction zone.

Roughness Characteristics of Oceanic Seafloor Prior to Subduction in Relation to the Seismogenic Potential of Subduction Zones

“…The morphology is extremely smooth off Andaman Islands and northern Sumatra laterally over about 1,000 km of seafloor with both R SW and R LW < 100 m, mainly as the result of high sediment supply from the Bengal fan (70% of R LW < 250 m, R LW mode ≈ 40 m). Only the N-S-trending Ninety-East Ridge overhangs the abyssal plain at a distance from the trench with R LW up to 800 m, fringing the trench without being subducted yet (Moeremans & Singh, 2014).…”

Change of stress patterns during 2004 MW 9.3 off‐Sumatra mega‐event: Insights from ridge–trench interaction for plate margin deformation

“…The long rupture, extending for hundreds of kilometres along the strike of the trench, generated by these earthquakes, may redistribute the stress following the failure along this oblique convergence margin (Cattin et al, ; DeShon, Engdahl, Thurber, & Brudzinski, ; Sevilgen et al, ). Dynamic and static stress perturbations evolved sequentially, caused by the Sumatra mega‐shock and its aftershocks, and propagated along the entire margin between 2°S and 17°N (Khan, ; Moeremans & Singh, ; Nalbant et al, ). In line with the enormity of the 2004 off‐Sumatra mega‐shock, the well‐recorded 11 March 2011 M W 9.0 Japan earthquake off the eastern coast of Honshu with displacement of up to 40 m and a rupture duration of 150–160 s, and seismic moment of 3.9 × 10 22 N‐m created a large tsunami devastating the coastal communities in Japan (Ammon, Lay, Kanamori, & Cleveland, ; Imanishi, Ando, & Kuwahara, ; Kato, Sakai, & Obara, ; Lay, Duputel, Ye, & Kanamori, ).…”

“…The Andaman–Sumatra mega‐thrust event of the 26th December 2004 (M W 9.3) is one of the largest earthquakes ever recorded instrumentally (Ammon et al, ; Subarya et al, ; Vigny et al, ). This event was analysed critically for mission‐mode investigation under pre‐, co‐, and post‐seismic domains (Ammon et al, ; Gahalaut, Subrahmanyam, Kundu, Catherine, & Ambikapathy, ; Ishii, Shearer, Houston, & Vidale, ; Lay et al, ; Meltzner et al, ; Moeremans & Singh, ; Prawirodirdjo, McCaffrey, Chadwell, Bock, & Subarya, ; Sevilgen, Stein, & Pollitz, ; Stein & Okal, ). Another earthquake of M W 8.6 occurred on the 28th March 2005 with its epicentre located to the south‐west of the 2004 event (Nalbant, Steacy, Sieh, Natawidjaja, & McCloskey, ).…”

Nature of the Kergelen Plateau and Its Place in the Structural Plan of the Southern Sector of the Indian Ocean

“…According to plate tectonics, large geodynamic and tectonomagmatic events such as the breakup of East Gondwana and the Greater India northward flight took place in the southern Indian Ocean (Johnson et al, 1976). This so-called flight was associated with high spreading rate, the estimated value of which reached more than 20 cm/year (Moeremans and Singh, 2014). After that, the structural map of midoceanic ridges had changed and high spreading rates gave way to ultraslow growth of the ridges (Cande and Mutter, 1982).…”