Absence of Near-Trench Early Triggering during the 2012 Mw 7.2 Indian Ocean Strike-Slip Earthquake: Evidence from One-Day Aftershocks

2021 ◽  
Author(s):  
Bo Jia ◽  
Han Yue ◽  
Muzli Muzli
Keyword(s):  
Indian Ocean ◽  
Dynamic Stress ◽  
Vital Role ◽  
Earthquake Triggering ◽  
Dynamic Triggering ◽  
Earthquake Interaction ◽  
Stress Triggering ◽  
Completeness Magnitude ◽  
Seismic Hazard Estimation ◽  
Dynamic Stress Triggering

Abstract Dynamic earthquake triggering is a widely accepted mechanism of earthquake interaction, which plays a vital role in seismic hazard estimation, although its efficacy at regional distances is under debate. The 2012 Mw 7.2 Indian Ocean event is one of the first reported events to produce dynamic stress triggering at regional distances using backprojection (BP) techniques. Alternatively, the coherent radiators in BP images can be interpreted as localized water reverberation phases. We present further evidence against near-trench triggering during this event. We collected 24 hr seismic recordings of two nearby stations located near the trench. We adopted a waveform denoising algorithm and detected 125 aftershocks using two regional seismic stations with a minimum magnitude of ML∼2.7 and completeness magnitude of ML∼3.6, whereas none of these aftershocks occurred near the trench. The absence of immediate (within one day) aftershocks near the trench suggest the absence of dynamic triggering during the offshore mainshock.

DynTriPy: A Python Package for Detecting Dynamic Earthquake Triggering Signals

2020 ◽  
Vol 92 (1) ◽  
pp. 543-554
Author(s):  
Naidan Yun ◽  
Hongfeng Yang ◽  
Shiyong Zhou
Keyword(s):  
Large Scale ◽  
Seismic Analysis ◽  
Parallel Architecture ◽  
Global Scale ◽  
Earthquake Triggering ◽  
Process Data ◽  
Dynamic Triggering ◽  
Earthquake Interaction ◽  
High Level ◽  
Python Package

Abstract Long-term and large-scale observations of dynamic earthquake triggering are urgently needed to understand the mechanism of earthquake interaction and assess seismic hazards. We developed a robust Python package termed DynTriPy to automatically detect dynamic triggering signals by distinguishing anomalous seismicity after the arrival of remote earthquakes. This package is an efficient implementation of the high-frequency power integral ratio algorithm, which is suitable for processing big data independent of earthquake catalogs or subjective judgments and can suppress the influence of noise and variations in the background seismicity. Finally, a confidence level of dynamic triggering (0–1) is statistically yielded. DynTriPy is designed to process data from multiple stations in parallel, taking advantage of rapidly expanding seismic arrays to monitor triggering on a global scale. Various data formats are supported, such as Seismic Analysis Code, mini Standard for Exchange of Earthquake Data (miniSEED), and SEED. To tune parameters more conveniently, we build a function to generate a database that stores power integrals in different time and frequency segments. All calculation functions possess a high-level parallel architecture, thoroughly capitalizing on available computational resources. We output and store the results of each function for continuous operation in the event of an unexpected interruption. The deployment of DynTriPy to data centers for real-time monitoring and investigating the sudden activation of any signal within a certain frequency scope has broad application prospects.

Systematic Investigation of Dynamic Earthquake Triggering in Japan

2021 ◽  
Author(s):  
Bogdan Enescu ◽  
Yuki Takeda
Keyword(s):  
Systematic Investigation ◽  
Earthquake Triggering ◽  
Significance Level ◽  
Dynamic Triggering ◽  
Stress Triggering ◽  
Remote Triggering ◽  
Pressure Changes ◽  
Large Earthquakes ◽  
Swarm Earthquakes ◽  
Triggering Threshold

<p><strong>Introduction. </strong>Previous studies (e.g., Harrington and Brodsky, 2006) documented a relative scarcity of remote triggering in Japan, compared to other seismic regions. For example, in California, dynamic triggering is reported to occur at levels of stress as small as 0.1 kPa, while in Japan it was reported that levels of 30 kPa or more are required to trigger detectable events (van der Elst and Brodsky, 2010). However, the threshold dynamic triggering level following the 2016 M7.3 Kumamoto earthquake was of just a few kPa (Enescu et al., 2016). Enescu et al. (2016) proposed that one of the possibilities to explain this observation is a change of stress triggering threshold that may have taken place after the 2011 M9.0 Tohoku-Oki earthquake.</p><p><strong>Motivation.</strong> Given the above observations, this study investigates 1) the occurrence of dynamically triggered earthquakes in Japan after some large earthquakes from 2004, and 2) whether the threshold of dynamic triggering may have changed due to the 2011 Tohoku-Oki earthquake and why this threshold might have changed.</p><p><strong>Analysis and Results.</strong> First, we investigated dynamic triggering throughout Japan, following some large earthquakes occurred after 2004. As a result, the  threshold appears to decrease following the 2011 Tohoku-Oki earthquake, however the number of earthquakes we have investigated was relatively small, so we could not draw statistically significant conclusions. In the second part of the study, we have focused on a few specific areas within Japan to systematically investigate dynamic triggering, which reduced significantly the computational costs. Thus, we focused on some areas in Tohoku and Hida, where swarm earthquakes occurred after the 2011 Tohoku-Oki earthquake. As a result, the change of the triggering level in an area close to the Yamagata-Fukushima border is considered to be statically significant at a 5% significance level. In other regions, the significance at a 5% level could not be established, however a decrease of this threshold is apparent, except for one region. We speculate that changes in the stress triggering threshold levels might be related to pore pressure changes in the crust following the 2011 Tohoku-Oki earthquake.</p>

Terminalia catappa (Singapore almond).

2021 ◽  
Author(s):  
Julissa Rojas-Sandoval
Keyword(s):  
Indian Ocean ◽  
Plant Communities ◽  
Western Indian Ocean ◽  
Agroforestry Systems ◽  
The Philippines ◽  
Vital Role ◽  
South East Asia ◽  
Edible Fruit ◽  
Tree Component ◽  
The Tropics

Abstract T. catappa is a hardy, fast-growing, deciduous multipurpose tree, reaching 25 (-40) m tall and producing an edible fruit. It plays a vital role in coastline stabilization as a tree component of strandline plant communities in the western Indian Ocean, South-East Asia and the South Pacific. Under suitable conditions it is a well-formed tree and has been widely planted throughout the tropics for shade, ornament and nuts, especially along sandy seashores (Heinsleigh and Holaway, 1988; Little and Skolmen, 1989). It is much used in agroforestry systems in the Philippines.

scholarly journals Climatology of the Mascarene High and Its Influence on Weather and Climate over Southern Africa

Climate ◽  
2020 ◽  
Vol 8 (7) ◽  
pp. 86 ◽  
Author(s):  
Nkosinathi G. Xulu ◽  
Hector Chikoore ◽  
Mary-Jane M. Bopape ◽  
Nthaduleni S. Nethengwe
Keyword(s):  
Indian Ocean ◽  
Southern Africa ◽  
Lower Troposphere ◽  
Western Indian Ocean ◽  
Vital Role ◽  
Tropical Cyclone Genesis ◽  
Trade Winds ◽  
Mascarene High ◽  
Weather And Climate ◽  
Cyclone Genesis

Globally, subtropical circulation in the lower troposphere is characterized by anticyclones over the oceans. Subtropical anticyclones locate over subtropical belts, modulating weather and climate patterns in those regions. The Mascarene High is an anticyclone located over the Southern Indian Ocean and has a vital role in weather and climate variability over Southern Africa. The warm Western Indian Ocean is a major source of moisture for the subcontinent also permitting tropical cyclone genesis. In this study, we review the dynamics of the Mascarene High, its interactions with the ocean, and its impact on weather and climate over Southern Africa. We also review studies on the evolution of subtropical anticyclones in a future warmer climate. The links between SST modes over the Indian Ocean and the strengthening and weakening of the Mascarene High have been demonstrated. One important aspect is atmospheric blocking due to the Mascarene High, which leads to anomalous rainfall and temperature events over the subcontinent. Blocking leads to landfall of tropical cyclones and slow propagation of cut-off lows resulting in severe weather and flooding over the subcontinent. Understanding how expansion of the Mascarene High due to warming will alter trade winds and storm tracks and change the mean climate of Southern Africa is crucial.

Changes in Subantartic Mode Water Properties and its Impact on Spiciness Variation in the Southern Indian Ocean

2020 ◽  
Author(s):  
Ying Zhang ◽  
Yan Du ◽  
Ming Feng
Keyword(s):  
Indian Ocean ◽  
Potential Temperature ◽  
Vital Role ◽  
Sea Surface ◽  
Southern Indian Ocean ◽  
Wind Stress Curl ◽  
Mode Water ◽  
Subantarctic Mode Water ◽  
The Indian Ocean ◽  
Global Oceans

<p><span>Subantarctic Mode Water (SAMW) is formed by deep mixing in winter in the Subantarctic Zone and transported into the adjacent subtropical gyres after subduction, which plays a vital role in heat, freshwater, carbon and nutrient budgets in the global oceans. The changes in SAMW properties and its impact on spiciness variation in the southern Indian Ocean have been investigated using the gridded Argo dataset in 2004-2018. Annual mean potential temperature and salinity of the SAMW have undergone significant variations during 2004-2018, with an increase (a decrease) trend for potential temperature (salinity). An analysis of decomposition shows that the heaving process contributes to warming and salinification while spiciness causes cooling and freshening, both of which modulate the SAMW properties. A strong deepening of the isopycnal surfaces </span>caused by positive wind stress curl anomalies over the subtropical southern Indian Ocean leads to warming/salinification heaving contribution to the changes in SAMW. The cooling/freshening contribution from spiciness process is due to a southward shift of sea surface potential density favoring colder and fresher water into the interior ocean, which is driven by an increase in wintertime sea surface temperature and salinity in the SAMW formation region. The colder and fresher water carried with the SAMW spreads along isopycnal surfaces via the Indian Ocean subtropical gyre, which results in cooling and freshening spiciness trends over the all basin of the subtropical southern Indian Ocean.</p><p> </p>

Contextualizing Complex Social Contact: Mauritius, a Microcosm of Global Diaspora

2016 ◽  
Vol 26 (2) ◽  
pp. 265-283 ◽  
Author(s):  
Krish Seetah
Keyword(s):  
Indian Ocean ◽  
Atlantic World ◽  
Group Interaction ◽  
Social Contact ◽  
Vital Role ◽  
Food Culture ◽  
Historical Processes ◽  
The Indian Ocean ◽  
Plural Societies ◽  
Development Of Language

This article supplements current dialogue on the archaeology of slavery, offering an Indian Ocean counterpoint to a topic that has largely focused on the Atlantic world. It also delves into the essentially uncharted domain of the archaeology of indentured labour. New plural societies, characterized by cultural hybridity, were created around the world as a consequence of labour diasporas in the late historic period. What do these societies look like during the process of nation building and after independence? Can we study this development through archaeology? Focusing on Mauritius, this paper discusses the complexities of the island, and how it can be representative of similar newly formed plural societies in the Indian Ocean. During French and British imperial rule, the island served as an important trading post for a range of European imperial powers. These varied groups initiated the movement and settlement of African, Indian and Chinese transplanted communities. By exploring the dynamic nature of inter-group interaction on Mauritius, this paper emphasizes the nuanced nature of how different peoples arrived and made the island their home. Mauritius played a vital role in the transportation of forced and free labour, both within and beyond this oceanic world, and offers an important viewpoint from which to survey the ways in which historical archaeology can improve our understanding of the broader archaeo-historical processes of which these diasporas were an integral feature. The paper focuses on the outcomes of settlement, as viewed through the complex practices that underpin local food culture, the use and development of language and the way materials are employed for the expression of identity. The article also traces the roots of contemporary cultural retention for indentured labourers to administrative decisions made by the British, and ultimately explores how heritage and language can provide a powerful lens on mechanisms of cultural expression. In addition to illustrating the nuanced and multifaceted nature of group interaction on Mauritius itself, this article raises an issue of broader relevance—the need for historical archaeologists to give greater consideration to the Indian Ocean, rather than focusing on the Atlantic world. This would allow us to achieve a more informed understanding of European slave trading and associated systems of labour migration within a more global framework.

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