scholarly journals Very long period seismic signals observed before the caldera formation with the 2000 Miyake-jima volcanic activity, Japan

2009 ◽  
Vol 114 (B2) ◽  
Author(s):  
Tomokazu Kobayashi ◽  
Takao Ohminato ◽  
Yoshiaki Ida ◽  
Eisuke Fujita
Keyword(s):  
Volcanic Activity ◽  
Seismic Signals ◽  
Caldera Formation ◽  
Long Period

scholarly journals Very- and ultra-long-period seismic signals prior to and during caldera formation on La Réunion Island

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
F. R. Fontaine ◽  
G. Roult ◽  
B. Hejrani ◽  
L. Michon ◽  
V. Ferrazzini ◽  
...  
Keyword(s):  
Seismic Signals ◽  
Reunion Island ◽  
La Réunion ◽  
Caldera Formation ◽  
Long Period ◽  
Réunion Island ◽  
La Réunion Island

Observation of gliding tremors from the Gulf of Guinea might help solve over 50 year old mystery

2021 ◽  
Author(s):  
Charlotte Bruland ◽  
Sarah Mader ◽  
Céline Hadziioannou
Keyword(s):  
Spectral Analysis ◽  
Volcanic Activity ◽  
Rayleigh Waves ◽  
Spectral Characteristics ◽  
Gulf Of Guinea ◽  
Seismic Amplitude ◽  
Long Period ◽  
Amplitude Spectra ◽  
Using Data ◽  
Over Time

<p>In the 1960's a peak in the seismic amplitude spectra around 26 s was discovered and detected on stations worldwide. The source was located in the Gulf of Guinea, with approximate coordinates (0,0), and was believed to be generated continuously. A source with similar spectral characteristics was discovered near the Vanuatu Islands, at nearly the antipodal location of the Gulf of Guinea source. Since it was located close to the volcanoes in Vanuatu, this source is commonly attributed to magmatic processes. The physical cause of the 26 s microseism, however, remains unclear.</p><p>We investigate the source location and evolution of the 26 s microseim using data from permanent broadband stations in Germany, France and Algeria and temporary arrays in Morocco, Cameroon and Botswana for spectral analysis and 3-C beamforming to get closer to resolving the source mechanism responsible for this enigmatic signal. We find that the signal modulates over time and is not always detectable, but occasionally it becomes so energetic it can be observed on stations worldwide. Such a burst can last for hours or days. The signal is visible on stations globally approximately 30 percent of the time. Our beamforming analysis confirms that the source is located in the Gulf of Guinea, as shown in previous studies, and that the location is temporally stable. Whenever the signal is detectable, both Love and Rayleigh waves are generated. We discover a spectral glide effect associated with the bursts, that so far has not been reported in the literature. </p><p>The spectral glides last for about two days and are observed on stations globally. Although at higher frequencies, very long period tremors and gliding tremors are also observed on volcanoes as Redoubt in Alaska and Arenal in Costa Rica, suggesting that the origin of the 26 s tremor is also volcanic. However, there is no reported volcanic activity in the area where the source appears to be located.</p><p> </p>

scholarly journals Variation patterns of landslide basal friction revealed from long-period seismic waveform inversion

2019 ◽  
Vol 100 (1) ◽  
pp. 313-327
Author(s):  
Dan Yu ◽  
Xinghui Huang ◽  
Zhengyuan Li
Keyword(s):  
Steady State ◽  
Friction Coefficient ◽  
Water Waves ◽  
Waveform Inversion ◽  
Time History ◽  
Seismic Signals ◽  
Long Period ◽  
Basal Friction ◽  
Seismic Waveform ◽  
Variation Patterns

Abstract A catastrophic landslide struck the Xiaoba village in Fuquan, Guizhou, southwestern China at about 8:30 p.m. (Beijing Time, UTC + 8) on August 27, 2014. The landslide and induced impulse water waves destroyed two villages and killed 23 persons. By reprocessing seismic signals from a seismic network deployed in the surrounding area of the landslide, we recognized the event from low-frequency seismic signals and subsequently performed a long-period seismic waveform inversion to obtain its force–time history. The inversion results reveal that the maximum force for the landslide is 5 × 109 N, and the duration of the landslide is 38.4 s. The landslide reached its maximum velocity of 12.4 m/s at 13.2 s after its initiation, and the mass center plugged into the quarry at 24.2 s. Based on the inversion results, we estimated basal friction of the landslide. We found the friction coefficient rapidly reduces to a relatively steady-state value of ~ 0.4 at a steady-state distance of 35 m and subsequently reduces in a near-linear manner that satisfies the empirical formula $$ \mu = - 1.4d + 0.44 $$μ=-1.4d+0.44, where $$ d $$d is sliding distance in km. The reduction in friction revealed by the formula is compatible with the finding of previous studies for landslides of similar volume in landslide acceleration stage. However, our result does not make it possible for the friction coefficient to increase again in landslide deceleration stage that a velocity-dependent friction law would allow. The friction variation patterns can be used to constrain input parameters in numerical landslide simulation, which can predicate runout distance and deposit areas for massive landslides to carry out landslide hazard assessment.

Sign in / Sign up

Export Citation Format

Share Document