Internal tides recorded at ocean bottom off the coast of Southeast Taiwan

Chang, En‐Chi; Chao, Benjamin F.; Chen, Guan-Yu; Liau, Jian-Ming

doi:10.1002/2015jc011370

Cited by 14 publications

(11 citation statements)

References 52 publications

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“…Long-lasting tremors and SDEs resembling ours were associated with bottom flow agitating the geophones induced by internal tides off Southeast Taiwan (Chang et al 2016). In that case, tremors were recorded at the natural frequency of the sensors and exhibited a non random periodicity, similar to the M2 tide.…”

Section: Nature Of the Sdes And Tremorssupporting

confidence: 57%

Spatial and temporal dynamics of gas-related processes in the Sea of Marmara monitored with ocean bottom seismometers

Tsang-Hin-Sun

Batsi

Klingelhoëfer

et al. 2018

Geophysical Journal International

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In the Sea of Marmara, areas of gas seepage or cold seeps are tightly related to the faults system and understanding the spatial and temporal dynamics in gas-related processes is crucial for geohazard mitigation. Although acoustic surveys proved to be efficient in detecting and locating cold seeps, temporal variability or trends in the gas-related processes are still poorly understood. Two arrays of 10 ocean bottom seismometers were deployed in the western part of the Sea of Marmara in 2011 and 2014, respectively. In addition to the local seismic events, the instruments recorded a large number of short duration events and long-lasting tremors. Short duration events are impulsive signals with duration <1 s, amplitude well above the noise level and a frequency spectrum with one or two narrow peaks. They are not correlated from one site to another, suggesting a very local source. Tremors consist of sequences of clustered impulsive signals lasting for minutes to more than an hour with a multipeak frequency spectrum. Based on evidence of known seepage and by analogy with volcanic and hydrothermal models, we suggest that short duration events and tremors are associated with gas migration and seepage. There is a relationship between tremors associated with gas emission and the local seismicity, although not systematic. Rather than triggering gas migration out of the seabed, locally strong earthquakes act as catalysts when gas is already present or gas emission is already initiated.

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Section: Nature Of the Sdes And Tremorssupporting

confidence: 57%

Spatial and temporal dynamics of gas-related processes in the Sea of Marmara monitored with ocean bottom seismometers

Tsang-Hin-Sun

Batsi

Klingelhoëfer

et al. 2018

Geophysical Journal International

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“…Tides and currents are able to generate SDEs and tremors resembling ours by agitating the sensors in their natural frequency of oscillation (Chang et al, ). Local turbulent flows might also be responsible for some background SDEs, as observed in Molène or in the Canary Channel (Ugalde et al, ).…”

Section: Sde Analysis Offshore Central Chilementioning

confidence: 97%

“…Tremors and SDEs were then associated with gas emissions out of the seabed, as they both occur during the same tidal phase and with comparable amplitudes. On the other hand, long‐lasting tremors were also attributed to bottom currents induced by internal tides off southeast Taiwan (Chang et al, ). Similarly, in the Canary Channel, harmonic tremors and SDEs were preferentially explained by environmental factors, such as sea life or transporting currents (Ugalde et al, ).…”

Section: Introductionmentioning

confidence: 99%

Nonseismic Signals in the Ocean: Indicators of Deep Sea and Seafloor Processes on Ocean‐Bottom Seismometer Data

Batsi¹,

Tsang-Hin-Sun²,

Klingelhoëfer³

et al. 2019

Geochem Geophys Geosyst

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Ocean‐bottom seismometers (OBSs) commonly record short‐duration events (SDEs) that could be described by all of these characteristics: (i) duration <1 s, (ii) one single‐wave train with no identified P nor S wave arrivals, and (iii) a dominant frequency usually between 4 and 30 Hz. In many areas, SDEs have been associated with gas‐ or fluid‐related processes near cold seeps or hydrothermal vents, although fish bumps, instrumental, or current‐generated noise have been proposed as possible sources. In order to address some remaining issues, this study presents results from in situ and laboratory experiments combined with observations from two contrasting areas, the Sea of Marmara (Turkey) and the Chilean subduction zone. The in situ experiment was conducted at the European Multidisciplinary Seafloor and water column Observatory‐Molène submarine observatory (near Brest, France) and consisted in continuously monitoring two OBSs with a camera. The images revealed that no fish regularly bumped into the instruments. Laboratory experiments aimed at reproducing SDEs' waveforms by injecting air or water in a tank filled by sand and seawater and monitored with an OBS. Injecting air in the sediments produced waveforms very similar to the observed SDEs, while injecting air in the water column did not, constraining the source of SDEs in the seafloor sediments. Finally, the systematic analysis of two real data sets revealed that it is possible to discriminate gas‐related SDEs from biological or sea state‐related noise from simple source parameters, such as the temporal mode of occurrence, the back azimuth, and the dominant frequency.

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“…Turbulences triggered by bottom water currents that exceed 22 cm/s at 1,319 m depth in this area could be the source of microshock clustering (Chang et al, 2016). Further study is required to better understand these possible processes.…”

Section: Short-duration Eventsmentioning

confidence: 99%

Seismicity and Noise Recorded by Passive Seismic Monitoring of Drilling Operations Offshore the Eastern Canary Islands

Ugalde

Gaite

Ruiz

et al. 2019

Seismological Research Letters

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In November 2014 a temporary land and marine seismic network was deployed to monitor the drilling of an exploratory well in the Canary Channel (Eastern Canary Islands). This region is characterized by low seismic activity; however, because of the increased awareness of the potential seismic hazard caused by hydrocarbon exploitation activities, the drilling operations were monitored with an unprecedented level of detail for an activity of this kind. According to the reported earthquakes, there was not a measurable increase in seismicity in the vicinity of the well. Overall seismic activity was low, which is consistent with the historical seismicity records. Harmonic tremor, explained here as resonances of the instrument-seafloor system generated by bottom water currents in the area, was commonly detected on the ocean bottom seismometer (OBS) recordings. The marine network data also revealed few dozens of non-seismic short-duration signals per day that appear similar to other events on OBS recorded throughout the world. We suggest that they may be caused by direct perturbations on the OBS, mostly induced by ocean currents in the Canary Channel.

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Internal tides recorded at ocean bottom off the coast of Southeast Taiwan

Cited by 14 publications

References 52 publications

Spatial and temporal dynamics of gas-related processes in the Sea of Marmara monitored with ocean bottom seismometers

Spatial and temporal dynamics of gas-related processes in the Sea of Marmara monitored with ocean bottom seismometers

Nonseismic Signals in the Ocean: Indicators of Deep Sea and Seafloor Processes on Ocean‐Bottom Seismometer Data

Seismicity and Noise Recorded by Passive Seismic Monitoring of Drilling Operations Offshore the Eastern Canary Islands

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