scholarly journals Very low frequency earthquakes along the Ryukyu subduction zone

2012 ◽  
Vol 39 (4) ◽  
pp. n/a-n/a ◽  
Author(s):  
Masataka Ando ◽  
Yoko Tu ◽  
Hiroyuki Kumagai ◽  
Yoshiko Yamanaka ◽  
Cheng-Horng Lin
Keyword(s):  
Subduction Zone ◽  
Low Frequency ◽  
Very Low Frequency

Spatial relationship between shallow very low frequency earthquakes and the subducted Kyushu-Palau Ridge in the Hyuga-nada region of the Nankai subduction zone

2020 ◽  
Vol 222 (3) ◽  
pp. 1542-1554
Author(s):  
Takashi Tonegawa ◽  
Yusuke Yamashita ◽  
Tsutomu Takahashi ◽  
Masanao Shinohara ◽  
Yasushi Ishihara ◽  
...  
Keyword(s):  
Rayleigh Wave ◽  
Subduction Zone ◽  
Group Velocity ◽  
Low Frequency ◽  
Horizontal Distance ◽  
Structural Factors ◽  
Very Low Frequency ◽  
Slow Earthquakes ◽  
Seismic Records ◽  
Nankai Subduction Zone

SUMMARY Shallow very low frequency earthquakes (sVLFEs) have occurred recurrently at the shallow plate interface of the Hyuga-nada region of the western Nankai subduction zone, Japan. Although the locations of sVLFE epicentres have been determined using land-based seismic records with moderate accuracy, it is necessary to determine their locations more precisely to explore the relationship between sVLFEs and other shallow slow earthquakes and examine the structural factors that may control sVLFE activity. Here, we identified sVLFE epicentres using seismic records obtained from temporarily deployed ocean bottom seismometers (OBSs) in the Hyuga-nada region. Seismic observations involved the deployment of 5–13 OBSs for approximately 1 yr, with deployments conducted three times during 2014–2016 each time with changing OBS numbers and array distribution. As a result, one sVLFE episode, containing successive Rayleigh wave pulses with slow velocities due to marine sediments, could be detected at a frequency band of 0.1–0.15 Hz per observation, resulting in a total of three episodes. Rayleigh wave amplitudes of ordinary earthquakes in the continuous records were suppressed using earthquake catalogues. We estimated the dispersion curve for the Rayleigh wave group velocity for each array, which represented the averaged group velocity within the array, using coda interferometry, and applied an envelope correlation method (ECM) using the group velocities to continuous records. These processing provided sVLFE epicentres with horizontal distance errors of <5 km. Our results showed that sVLFEs depths, which were inferred from the contour line of the top of the Phillipine Sea Plate, had increased from <10 km to 10–15 km in the region of the subducted Kyusyu-Palau Ridge (KPR). It was also apparent that migration of sVLFE epicentres occurred in 2015 from a depth of 15 km to shallower depths along the northern margin of the subducted KPR. These results identified the subducted KPR as a structural factor controlling the excitation conditions of sVLFE activities.

scholarly journals Shallow very-low-frequency earthquakes accompany slow slip events in the Nankai subduction zone

2018 ◽  
Vol 9 (1) ◽  
Author(s):  
Masaru Nakano ◽  
Takane Hori ◽  
Eiichiro Araki ◽  
Shuichi Kodaira ◽  
Satoshi Ide
Keyword(s):  
Subduction Zone ◽  
Low Frequency ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Very Low Frequency ◽  
Nankai Subduction Zone

Possible shallow slow slip events in Hyuga-nada, Nankai subduction zone, inferred from migration of very low frequency earthquakes

2015 ◽  
Vol 42 (2) ◽  
pp. 331-338 ◽  
Author(s):  
Youichi Asano ◽  
Kazushige Obara ◽  
Takanori Matsuzawa ◽  
Hitoshi Hirose ◽  
Yoshihiro Ito
Keyword(s):  
Subduction Zone ◽  
Low Frequency ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Very Low Frequency ◽  
Nankai Subduction Zone

The Attenuation of Very Low Frequency Brain Oscillations in Transitions from a Rest State to Active Attention

2009 ◽  
Vol 23 (4) ◽  
pp. 191-198 ◽  
Author(s):  
Suzannah K. Helps ◽  
Samantha J. Broyd ◽  
Christopher J. James ◽  
Anke Karl ◽  
Edmund J. S. Sonuga-Barke
Keyword(s):  
Brain Activity ◽  
Sampling Rate ◽  
Low Frequency ◽  
Future Research ◽  
Adhd Symptoms ◽  
Default Mode ◽  
Very Low Frequency ◽  
Wide Range ◽  
Interference Hypothesis ◽  
Mode Interference

Background: The default mode interference hypothesis ( Sonuga-Barke & Castellanos, 2007 ) predicts (1) the attenuation of very low frequency oscillations (VLFO; e.g., .05 Hz) in brain activity within the default mode network during the transition from rest to task, and (2) that failures to attenuate in this way will lead to an increased likelihood of periodic attention lapses that are synchronized to the VLFO pattern. Here, we tested these predictions using DC-EEG recordings within and outside of a previously identified network of electrode locations hypothesized to reflect DMN activity (i.e., S3 network; Helps et al., 2008 ). Method: 24 young adults (mean age 22.3 years; 8 male), sampled to include a wide range of ADHD symptoms, took part in a study of rest to task transitions. Two conditions were compared: 5 min of rest (eyes open) and a 10-min simple 2-choice RT task with a relatively high sampling rate (ISI 1 s). DC-EEG was recorded during both conditions, and the low-frequency spectrum was decomposed and measures of the power within specific bands extracted. Results: Shift from rest to task led to an attenuation of VLFO activity within the S3 network which was inversely associated with ADHD symptoms. RT during task also showed a VLFO signature. During task there was a small but significant degree of synchronization between EEG and RT in the VLFO band. Attenuators showed a lower degree of synchrony than nonattenuators. Discussion: The results provide some initial EEG-based support for the default mode interference hypothesis and suggest that failure to attenuate VLFO in the S3 network is associated with higher synchrony between low-frequency brain activity and RT fluctuations during a simple RT task. Although significant, the effects were small and future research should employ tasks with a higher sampling rate to increase the possibility of extracting robust and stable signals.

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