Sedimentary fabric: A tool to delineate a high-velocity zone within a deep western Indian Ocean bottom current

1979 ◽  
Vol 33 (3-4) ◽  
pp. 51-55 ◽  
Author(s):  
Brooks B Ellwood ◽  
Michael T Ledbetter ◽  
David A Johnson
Keyword(s):  
Indian Ocean ◽  
High Velocity ◽  
Western Indian Ocean ◽  
Bottom Current ◽  
Ocean Bottom ◽  
Velocity Zone

scholarly journals Tomography of crust and lithosphere in the western Indian Ocean from noise cross-correlations of land and ocean bottom seismometers

2019 ◽  
Vol 219 (2) ◽  
pp. 924-944 ◽  
Author(s):  
Sarah Hable ◽  
Karin Sigloch ◽  
Eléonore Stutzmann ◽  
Sergey Kiselev ◽  
Guilhem Barruol
Keyword(s):  
Indian Ocean ◽  
Group Velocity ◽  
Western Indian Ocean ◽  
Spreading Ridge ◽  
Ocean Bottom ◽  
Depth Range ◽  
La Réunion ◽  
Velocity Measurements ◽  
Ocean Bottom Seismometers ◽  
Cross Correlations

SUMMARY We use seismic noise cross-correlations to obtain a 3-D tomography model of SV-wave velocities beneath the western Indian Ocean, in the depth range of the oceanic crust and uppermost mantle. The study area covers 2000 × 2000 km2 between Madagascar and the three spreading ridges of the Indian Ocean, centred on the volcanic hotspot of La Réunion. We use seismograms from 38 ocean bottom seismometers (OBSs) deployed by the RHUM-RUM project and 10 island stations on La Réunion, Madagascar, Mauritius, Rodrigues, and Tromelin. Phase cross-correlations are calculated for 1119 OBS-to-OBS, land-to-OBS, and land-to-land station pairs, and a phase-weighted stacking algorithm yields robust group velocity measurements in the period range of 3–50 s. We demonstrate that OBS correlations across large interstation distances of >2000 km are of sufficiently high quality for large-scale tomography of ocean basins. Many OBSs yielded similarly good group velocity measurements as land stations. Besides Rayleigh waves, the noise correlations contain a low-velocity wave type propagating at 0.8–1.5 km s−1 over distances exceeding 1000 km, presumably Scholte waves travelling through seafloor sediments. The 100 highest-quality group velocity curves are selected for tomographic inversion at crustal and lithospheric depths. The inversion is executed jointly with a data set of longer-period, Rayleigh-wave phase and group velocity measurements from earthquakes, which had previously yielded a 3-D model of Indian Ocean lithosphere and asthenosphere. Robust resolution tests and plausible structural findings in the upper 30 km validate the use of noise-derived OBS correlations for adding crustal structure to earthquake-derived tomography of the oceanic mantle. Relative to crustal reference model CRUST1.0, our new shear-velocity model tends to enhance both slow and fast anomalies. It reveals slow anomalies at 20 km depth beneath La Réunion, Mauritius, Rodrigues Ridge, Madagascar Rise, and beneath the Central Indian spreading ridge. These structures can clearly be associated with increased crustal thickness and/or volcanic activity. Locally thickened crust beneath La Réunion and Mauritius is probably related to magmatic underplating by the hotspot. In addition, these islands are characterized by a thickened lithosphere that may reflect the depleted, dehydrated mantle regions from which the crustal melts where sourced. Our tomography model is available as electronic supplement.

scholarly journals Velocity Structure Revealing a Likely Mud Volcano off the Dongsha Island, the Northern South China Sea

Energies ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 195
Author(s):  
Yuning Yan ◽  
Jianping Liao ◽  
Junhui Yu ◽  
Changliang Chen ◽  
Guangjian Zhong ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
High Velocity ◽  
Northern South China Sea ◽  
Mud Volcano ◽  
Ocean Bottom ◽  
Low Velocity ◽  
Low Velocity Zone ◽  
Mud Volcanism ◽  
Velocity Zone

The Dongsha Island (DS) is located in the mid-northern South China Sea continental margin. The waters around it are underlain by the Chaoshan Depression, a relict Mesozoic sedimentary basin, blanketed by thin Cenozoic sediments but populated with numerous submarine hills with yet less-known nature. A large hill, H110, 300 m high, 10 km wide, appearing in the southeast to the Dongsha Island, is crossed by an ocean bottom seismic and multiple channel seismic surveying lines. The first arrival tomography, using ocean bottom seismic data, showed two obvious phenomena below it: (1) a low-velocity (3.3 to 4 km/s) zone, with size of 20 × 3 km2, centering at ~4.5 km depth and (2) an underlying high-velocity (5.5 to 6.3 km/s) zone of comparable size at ~7 km depth. MCS profiles show much-fragmented Cenozoic sequences, covering a wide chaotic reflection zone within the Mesozoic strata below hill H110. The low-velocity zone corresponds to the chaotic reflection zone and can be interpreted as of highly-fractured and fluid-rich Mesozoic layers. Samples dredged from H110 comprised of illite-bearing authigenic carbonate nodules and rich, deep-water organisms are indicative of hydrocarbon seepage from deep source. Therefore, H110 can be inferred as a mud volcano. The high-velocity zone is interpreted as of magma intrusion, considering that young magmatism was found enhanced over the southern CSD. Furthermore, the origin of H110 can be speculated as thermodynamically driven, i.e., magma from the depths intrudes into the thick Mesozoic strata and promotes petroleum generation, thus, driving mud volcanism. Mud volcanism at H110 and the occurrence of a low-velocity zone below it likely indicates the existence of Mesozoic hydrocarbon reservoir, which is in favor of the petroleum exploration.

scholarly journals Performance report of the RHUM-RUM ocean bottom seismometer network around La Réunion, western Indian Ocean

2016 ◽  
Vol 41 ◽  
pp. 43-63 ◽  
Author(s):  
S. C. Stähler ◽  
K. Sigloch ◽  
K. Hosseini ◽  
W. C. Crawford ◽  
G. Barruol ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Network Performance ◽  
Western Indian Ocean ◽  
Primary Objective ◽  
Central Component ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
La Réunion ◽  
Ocean Bottom Seismometers ◽  
Performance Report

Abstract. RHUM-RUM is a German-French seismological experiment based on the sea floor surrounding the island of La Réunion, western Indian Ocean (Barruol and Sigloch, 2013). Its primary objective is to clarify the presence or absence of a mantle plume beneath the Reunion volcanic hotspot. RHUM-RUM's central component is a 13-month deployment (October 2012 to November 2013) of 57 broadband ocean bottom seismometers (OBS) and hydrophones over an area of 2000  ×  2000 km2 surrounding the hotspot. The array contained 48 wideband OBS from the German DEPAS pool and 9 broadband OBS from the French INSU pool. It is the largest deployment of DEPAS and INSU OBS so far, and the first joint experiment. This article reviews network performance and data quality: of the 57 stations, 46 and 53 yielded good seismometer and hydrophone recordings, respectively. The 19 751 total deployment days yielded 18 735 days of hydrophone recordings and 15 941 days of seismometer recordings, which are 94 and 80 % of the theoretically possible yields. The INSU seismic sensors stand away from their OBS frames, whereas the DEPAS sensors are integrated into their frames. At long periods (>  10 s), the DEPAS seismometers are affected by significantly stronger noise than the INSU seismometers. On the horizontal components, this can be explained by tilting of the frame and buoy assemblage, e.g. through the action of ocean-bottom currents, but in addition the DEPAS intruments are affected by significant self-noise at long periods, including on the vertical channels. By comparison, the INSU instruments are much quieter at periods >  30 s and hence better suited for long-period signals studies. The trade-off of the instrument design is that the integrated DEPAS setup is easier to deploy and recover, especially when large numbers of stations are involved. Additionally, the wideband sensor has only half the power consumption of the broadband INSU seismometers. For the first time, this article publishes response information of the DEPAS instruments, which is necessary for any project where true ground displacement is of interest. The data will become publicly available at the end of 2017.

Editorial Introduction

2020 ◽  
Vol 4 (1) ◽  
pp. 1
Author(s):  
Editors of the JIOWS
Keyword(s):  
Nineteenth Century ◽  
Indian Ocean ◽  
Western Indian Ocean ◽  
Late Nineteenth Century ◽  
Fourth Volume ◽  
History Of ◽  
The Indian Ocean ◽  
Complex Relationships ◽  
Indian Ocean World ◽  
Shed Light

The editors are proud to present the first issue of the fourth volume of the Journal of Indian Ocean World Studies. This issue contains three articles, by James Francis Warren (Murdoch University), Kelsey McFaul (University of California, Santa Cruz), and Marek Pawelczak (University of Warsaw), respectively. Warren’s and McFaul’s articles take different approaches to the growing body of work that discusses pirates in the Indian Ocean World, past and present. Warren’s article is historical, exploring the life and times of Julano Taupan in the nineteenth-century Philippines. He invites us to question the meaning of the word ‘pirate’ and the several ways in which Taupan’s life has been interpreted by different European colonists and by anti-colonial movements from the mid-nineteenth century to the present day. McFaul’s article, meanwhile, takes a literary approach to discuss the much more recent phenomenon of Somali Piracy, which reached its apex in the last decade. Its contribution is to analyse the works of authors based in the region, challenging paradigms that have mostly been developed from analysis of works written in the West. Finally, Pawelczak’s article is a legal history of British jurisdiction in mid-late nineteenth-century Zanzibar. It examines one of the facets that underpinned European influence in the western Indian Ocean World before the establishment of colonial rule. In sum, this issue uses two key threads to shed light on the complex relationships between European and other Western powers and the Indian Ocean World.

scholarly journals Factors influencing microbial mat composition, distribution and dinitrogen fixation in three western Indian Ocean coral reefs

2012 ◽  
Vol 47 (1) ◽  
pp. 51-66 ◽  
Author(s):  
Loïc Charpy ◽  
Katarzyna A. Palinska ◽  
Raeid M. M. Abed ◽  
Marie José Langlade ◽  
Stjepko Golubic
Keyword(s):  
Indian Ocean ◽  
Coral Reefs ◽  
Western Indian Ocean ◽  
Dinitrogen Fixation ◽  
Microbial Mat ◽  
Composition Distribution ◽  
Factors Influencing

scholarly journals Movement ecology of black marlin Istiompax indica in the Western Indian Ocean

2021 ◽  
Author(s):  
Christoph A. Rohner ◽  
Roy Bealey ◽  
Bernerd M. Fulanda ◽  
Jason D. Everett ◽  
Anthony J. Richardson ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Movement Ecology ◽  
Western Indian Ocean

scholarly journals Post-bleaching mortality of a remote coral reef community in Seychelles, Western Indian Ocean

2019 ◽  
Vol 18 (1) ◽  
pp. 11
Author(s):  
Elena Gadoutsis ◽  
Clare A.K. Daly ◽  
Julie P. Hawkins ◽  
Ryan Daly
Keyword(s):  
Coral Reef ◽  
Indian Ocean ◽  
Western Indian Ocean ◽  
Coral Reef Community ◽  
Reef Community

scholarly journals Variability in the Mozambique Channel Trough and Impacts on Southeast African Rainfall

2020 ◽  
Vol 33 (2) ◽  
pp. 749-765 ◽  
Author(s):  
Rondrotiana Barimalala ◽  
Ross C. Blamey ◽  
Fabien Desbiolles ◽  
Chris J. C. Reason
Keyword(s):  
Indian Ocean ◽  
Austral Summer ◽  
Western Indian Ocean ◽  
Strong Relationship ◽  
Ocean Basin ◽  
Moist Convection ◽  
South Indian Ocean ◽  
Mozambique Channel ◽  
Mascarene High ◽  
South Indian

AbstractThe Mozambique Channel trough (MCT) is a cyclonic region prominent in austral summer in the central and southern Mozambique Channel. It first becomes evident in December with a peak in strength in February when the Mozambique Channel is warmest and the Mascarene high (MH) is located farthest southeast in the Indian Ocean basin. The strength and the timing of the mean MCT are linked to that of the cross-equatorial northeasterly monsoon in the tropical western Indian Ocean, which curves as northwesterlies toward northern Madagascar. The interannual variability in the MCT is associated with moist convection over the Mozambique Channel and is modulated by the location of the warm sea surface temperatures in the south Indian Ocean. Variability of the MCT shows a strong relationship with the equatorial westerlies north of Madagascar and the latitudinal extension of the MH. Summers with strong MCT activity are characterized by a prominent cyclonic circulation over the Mozambique Channel, extending to the midlatitudes. These are favorable for the development of tropical–extratropical cloud bands over the southwestern Indian Ocean and trigger an increase in rainfall over the ocean but a decrease over the southern African mainland. Most years with a weak MCT are associated with strong positive south Indian Ocean subtropical dipole events, during which the subcontinent tends to receive more rainfall whereas Madagascar and northern Mozambique are anomalously dry.

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