scholarly journals Low-frequency earthquakes along the Ryukyu Islands triggered by teleseismic earthquakes

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Ayumi Kinjo ◽  
Mamoru Nakamura
Keyword(s):  
Low Frequency ◽  
Stress Transfer ◽  
Ryukyu Islands ◽  
Plate Interface ◽  
Okinawa Island ◽  
Slow Slip Events ◽  
Arrival Times ◽  
Short Period ◽  
Ryukyu Arc ◽  
The Ryukyu Islands

AbstractTremors and low-frequency earthquakes (LFEs), which occur in the plate interface, can provide useful information about the state of aseismic stress transfer in mega-earthquake fault zones. We estimated the distribution of triggered LFEs in the subducted plate interface. Specifically, we detected LFEs in the Ryukyu Trench triggered by the surface waves of large teleseismic earthquakes by using the waveform records of broadband and short-period seismometers installed in the Ryukyu Arc. We selected a total of 45 teleseismic earthquakes with magnitudes of more than 7.5, which occurred between 2004 and 2017, for the analysis. We could detect the triggered LFEs for five teleseismic earthquakes. Then, we determined the hypocenters of LFEs by using the relative arrival times of LFEs for each station. The LFEs were distributed in the south of Okinawa Island and the Yaeyama area. Moreover, they were distributed around the source fault of the slow slip events. These were almost the same as and concentrated near to the locations of the most active LFE clusters accompanying very low-frequency earthquakes, suggesting higher sensitivity of inducing LFEs near these clusters. This indicates that the LFEs accompanying VLFEs are activated by stress acceleration in the Yaeyama and Okinawa areas.

scholarly journals Low-Frequency Earthquakes along the Ryukyu Islands Triggered by Teleseismic Earthquakes

2021 ◽  
Author(s):  
Ayumi Kinjo ◽  
Mamoru Nakamura
Keyword(s):  
Surface Waves ◽  
Low Frequency ◽  
Stress Sensitivity ◽  
Peak Ground Velocity ◽  
Ryukyu Islands ◽  
Plate Interface ◽  
Okinawa Island ◽  
Short Period ◽  
Ryukyu Arc ◽  
The Ryukyu Islands

Abstract Tremors and low-frequency earthquakes (LFEs), which occur in the plate interface, can provide useful information about the state of aseismic stress transfer in mega-earthquake fault zones. We estimated the distribution of stress sensitivity in the subducted plate interface by using triggered LFEs. Specifically, we detected LFEs in the Ryukyu Trench triggered by the surface waves of large teleseismic earthquakes by using the waveform records of broadband and short-period seismometers installed in the Ryukyu Arc. We selected a total of 45 teleseismic earthquakes with magnitudes of more than 7.5, which occurred between 2004 and 2017, for the analysis. We could detect the triggered LFEs for five teleseismic earthquakes. Then, we determined the hypocenters of LFEs by using the relative arrival times of LFEs for each station. The LFEs were distributed in the south of Okinawa Island and the Yaeyama area. Moreover, they were distributed around the source fault of the slow slip events. These were almost the same as the position of LFEs accompanying very low-frequency earthquakes (VLFEs). However, the epicenters of the triggered LFEs were concentrated near the locations of the most active LFE clusters accompanying VLFEs. This suggests that the sensitivity for inducing LFEs was higher near the most active clusters of the LFEs accompanying the VLFEs. The amplitudes of the triggered LFEs were proportional to the peak ground velocity of the surface waves. This indicates that the LFEs accompanying VLFEs are activated by stress acceleration in the Yaeyama and Okinawa areas and the triggered LFEs observed in these areas can be a result of the activation of the ambient tremors due to increased stress.

Long-chain n-3 polyunsaturated fatty acids contained in liver and muscle tissues of Okinawan long-spine porcupinefish (Diodon holocanthus Linnaeus 1758)

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Yutaka Tashiro
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Polyunsaturated Fatty Acids ◽  
Ryukyu Islands ◽  
Okinawa Island ◽  
Content Type ◽  
Muscle Tissues ◽  
The Ryukyu Islands ◽  
Total Fatty Acids ◽  
Long Chain

Purpose This study aimed to analyze the lipid content and fatty acid composition in the liver and muscle of a porcupinefish species inhabiting waters around the Ryukyu Islands to investigate their potential as a source of long-chain n-3 polyunsaturated fatty acids (LC-PUFAs). Design/methodology/approach Porcupinefish were collected along the Okinawa Island coast. The composition of fatty acids and cholesterol in both liver and muscle were analyzed using a gas chromatograph mass spectrometer. Findings The liver of Okinawan long-spine porcupinefish was rich in lipids whose content correlated to the proportion of liver/body weight. Fatty acid compositions in their liver and muscles were similar to each other. LC-PUFAs occupied 44% of total fatty acids, with docosahexaenoic acid (DHA) being the dominant (42%), whereas eicosapentaenoic acid occupied 2.4%. The liver contained 1,690 mg of cholesterol and 14.8 g of DHA per 100 g, whose proportion decreased in summer compared to other seasons (p = 0.036). Originality/value The liver of Okinawan long-spine porcupinefish, which has not yet been commercially used although its non-toxicity is claimed, can be an excellent source of LC-PUFAs, especially DHA, accentuating its potential in food supplements’ production.

Redescription of a poorly known upogebiid mud shrimp Gebiacantha acanthochela (Sakai, 1967) and description of a new species of the genus from the Ryukyu Islands, Japan (Decapoda: Gebiidea)

Zootaxa ◽  
2020 ◽  
Vol 4881 (2) ◽  
pp. 307-322
Author(s):  
TOMOYUKI KOMAI
Keyword(s):  
New Species ◽  
New Caledonia ◽  
Original Description ◽  
Ryukyu Islands ◽  
Okinawa Island ◽  
The Ryukyu Islands ◽  
Female Holotype ◽  
Mud Shrimp ◽  
Japanese Waters ◽  
Amami Islands

Two species of the upogebiida mud shrimp genus Gebiacantha Ngoc-Ho, 1989, currently represented by 19 described species, are reported from the Ryukyu Islands, Japan. The first, G. acanthochela (Sakai, 1967), is redescribed in detail based on two female specimens from Amami Islands the second discovered since the original description, enabling better assessment of its diagnostic characters. The second, G. fortispinata n. sp., is described on the basis of a single female holotype from Okinawa Island. It appears closest to G. multispinosa Ngoc-Ho, 1994, known with certainty only from New Caledonia, but the proportionally narrower telson with a more deeply notched posterior margin and the distally unarmed pereopod 3 merus distinguish the new species from G. multispinosa. Three species of Gebiacantha, including G. sagamiensis Komai, 2017, are now known from Japanese waters.

A new hermit crab species of the genus Catapagurus (Crustacea: Decapoda: Anomura: Paguridae) from the Ryukyu Islands, southern Japan

Zootaxa ◽  
2009 ◽  
Vol 2211 (1) ◽  
pp. 57-68 ◽  
Author(s):  
TOMOYUKI KOMAI ◽  
MASAYUKI OSAWA
Keyword(s):  
New Species ◽  
Hermit Crab ◽  
Species Group ◽  
Shallow Waters ◽  
Ryukyu Islands ◽  
Crab Species ◽  
Okinawa Island ◽  
The Ryukyu Islands ◽  
The Family ◽  
A New Species

A new species of the pagurid hermit crab genus Catapagurus A. Milne-Edwards, 1880, C. insolitus, is described and illustrated based on specimens from shallow waters in Okinawa Island, the Ryukyus. It belongs to an informal species group characterized by the possession of blade-shaped ambulatory dactyli, and is morphologically most similar to C. kosugei (Asakura, 2001). However, the new species is unique within the genus in having a multispinose antennal acicle, rarely seen in species of the family Paguridae.

Founding of the Ming Dynasty and the Rise of the Ryukyu Kingdom

2016 ◽  
Author(s):  
Mamoru Akamine
Keyword(s):  
Ming Dynasty ◽  
East Asian ◽  
Trading Partner ◽  
Ryukyu Islands ◽  
Okinawa Island ◽  
Conventional View ◽  
The Ryukyu Islands ◽  
Tribute System ◽  
And Control ◽  
The Ming Dynasty

With the establishment of the Ming Dynasty, Emperor Hongwu announced a ban on sea travel to try and control wakō pirates. He established a tribute system whereby countries that accepted the Chinese emperor as sovereign could send tribute trade missions to and from China. Because the pirates frequented the Ryukyu Islands, Hongwu had a preference policy toward Ryukyu to obtain their help in controlling wakō pirates. Of the three domains dominating Okinawa Island, Chūzan emerged as China’s main trading partner, and this began the process of unifying the Ryukyu Kingdom. A number of Chinese merchants, traditionally known as “the Thirty-six Families” relocated to Ryukyu to facilitate tribute trade, though the author disputes the conventional view of this as a “gift” from China. By the end of the chapter, Ryukyu is poised to be a key player – a cornerstone – in the East Asian trade sphere.

Comanthus kumi, a new shallow-water comatulid (Echinodermata: Crinoidea: Comatulida: Comasteridae) from the Ryukyu Islands, Japan

Zootaxa ◽  
2012 ◽  
Vol 3367 (1) ◽  
pp. 261 ◽  
Author(s):  
YOSHIHISA FUJITA ◽  
MASAMI OBUCHI
Keyword(s):  
New Species ◽  
Coral Reefs ◽  
Shallow Water ◽  
Small Hole ◽  
Ryukyu Islands ◽  
Okinawa Island ◽  
The Ryukyu Islands ◽  
A New Species

A new species of the genus Comanthus A.H. Clark, 1908, is described on the basis of specimens collected from KumeIsland and Okinawa Island, the Ryukyu Islands, Japan. Comanthus kumi n. sp. is distinguished from all ten congeners byhaving extremely elongate arms exceeding 300 mm in length and the colouration in life. The new species concealed itswhole body in a crevice or small hole on coral reefs during the day and protruded only several elongate arms on the reef surface at night. This habit suggests that the new species is nocturnal.

scholarly journals Reconstruction of ocean environment time series since the late nineteenth century using sclerosponge geochemistry in the northwestern subtropical Pacific

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Ryuji Asami ◽  
Taketo Matsumori ◽  
Ryuichi Shinjo ◽  
Ryu Uemura ◽  
Yuki Miyaoka ◽  
...  
Keyword(s):  
Nineteenth Century ◽  
Time Series ◽  
Atmospheric Aerosols ◽  
Late Nineteenth Century ◽  
Ryukyu Islands ◽  
Okinawa Island ◽  
Carbon And Oxygen Isotope ◽  
The Ryukyu Islands ◽  
Decadal Variations ◽  
Late Nineteenth

AbstractThe geochemistry of calcifying marine organisms is an excellent proxy for reconstructing paleoceanographic history, but studies of hypercalcified demosponges (sclerosponges) are considerably fewer than those of corals, foraminifers, and bivalves. For this study, we first generated near-annual resolved stable carbon and oxygen isotope (δ13C and δ18O) and element/Ca ratios (Sr/Ca, Ba/Ca, Pb/Ca, U/Ca) time series for 1880–2015 from sclerosponge samples (Acanthochaetetes wellsi) collected at Miyako Island and Okinawa Island in the Ryukyu Islands of southwestern Japan. The δ13C records exhibited a typical variation of anthropogenically derived Suess effects, demonstrating that the rates of decrease of –0.0043‰/year before 1960 and – 0.024‰/year after 1960 in the northwestern subtropical Pacific were respectively similar to and about 1.4 times higher than those of the Caribbean Sea in the tropical Atlantic. Spectral analysis of the δ18O time series revealed significant periodicity of approximately 2, 3, 6.5, 7–10, and 20–30 year/cycle, indicating that sea surface conditions in the southern Ryukyu Islands had been dominated by interannual and decadal variations in temperature and seawater δ18O since the late nineteenth century. The Sr/Ca and U/Ca ratios for the species A. wellsi (high-Mg calcite) might not be a robust proxy for seawater temperatures, unlike Astrosclera willeyana and Ceratoporella nicholsoni sclerosponges (aragonite). An evident increasing Pb/Ca trend after 1950 found in the samples is probably attributable to Pb emissions from industrial activities and atmospheric aerosols in eastern Asian countries. The Ba/Ca variations differ greatly among sampling sites, which might be attributable to the respective local environments. This evidence demonstrates that more high-resolution age determinations and geochemical profilings enable delineation of secular variations in ocean environments on annual and interannual timescales. Results of our study suggest that if sclerosponges living in deeper ocean environments are collected, spatial and vertical oceanographic variations for the last several centuries will be reconstructed along with coral proxy records.

Phylogenetic relationships and divergence times of the genus Tokudaia within Murinae (Muridae; Rodentia) inferred from the nucleotide sequences encoding the Cytb gene, RAG 1, and IRBP

2004 ◽  
Vol 82 (8) ◽  
pp. 1343-1351 ◽  
Author(s):  
Jun J Sato ◽  
Hitoshi Suzuki
Keyword(s):  
Phylogenetic Relationships ◽  
Divergence Time ◽  
Nucleotide Sequences ◽  
Ryukyu Islands ◽  
Mitochondrial Cytochrome B ◽  
Short Period ◽  
The Ryukyu Islands ◽  
Codon Positions ◽  
Recombination Activating Gene ◽  
Rag 1

The phylogenetic relationships of six genera of Murinae (Apodemus, Diplothrix, Micromys, Mus, Rattus, and Tokudaia) were examined using the nucleotide sequences for the mitochondrial cytochrome b (Cytb), as well as the nuclear recombination activating gene 1 (RAG1) and interphotoreceptor retinoid-binding protein (IRBP), with special emphasis on the position of the genus Tokudaia, which is endemic to the Ryukyu Islands. Compared with Cytb at all codon positions, the first and second codon positions of Cytb, RAG1 (1002 base pairs (bp)), and IRBP (1586 bp) sequences were less prone to saturation. Close affinity between the genera Tokudaia and Apodemus was observed in the analyses using the IRBP (1586 bp) and combined nuclear (2588 bp; RAG1 + IRBP) sequences. The divergence time for the Tokudaia–Apodemus clade was estimated at approximately 6.5–8.0 Ma, which is more recent than previously reported, thereby indicating the recent colonization of the Ryukyu Islands by the genus Tokudaia. The other relationships among the main genera were highly ambiguous, owing either to saturation or insufficient phylogenetic information. The radiation of the main genera within a relatively short period of evolutionary time may explain the unresolved topologies, although molecular sources that are less subject to saturation are required to resolve the outstanding issues.

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