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  • 1
    Publication Date: 2019-11-04
    Description: During the Proyecto de Investigaciòn Sismològica de la Cordillera Occidental (PISCO '94) in the Atacama desert of Northern Chile, a continuously recording broadband seismic station was installed to the NW of the currently active volcano, Lascar. For the month of April, 1994, an additional network of three, short period, three-component stations was deployed around the volcano to help discriminate its seismic signals from other local seismicity. During the deployment, the volcanic activity at Lascar appeared to be limited mainly to the emission of steam and SO2. Tremor from Lascar is a random, «rapid-fire» series of events with a wide range of amplitudes and a quasi-fractal structure. The tremor is generated by an ensemble of independent elementary sources clustered in the volcanic edifice. In the short-term, the excitation of the sources fluctuates strongly, while the long-term power spectrum is very stationary.
    Description: JCR Journal
    Description: open
    Keywords: volcano seismology ; volcanic tremor ; rapid-fire events ; Lascar volcano ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 2523390 bytes
    Format: application/pdf
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  • 2
    Publication Date: 2019-11-04
    Description: Many of the recent ash eruptions of Galeras volcano (Colombia) have been preceded by tornillos. These unusual seismic events of unknown origin have screw-like profiles on seismograms and can last up to several minutes. In March, 1996, a broadband, three-component seismometer station was installed 1.6 km south of Cono, Galeras' active vent. With high quality recordings acquired by this system, and methods which work well with narrow band signals, we investigate the frequency content and polarization properties of two tornillos. They have slighty different predominant frequencies, 3.0420 Hz and 3.0595 Hz which remain highly stable for the entire tornillo duration. The polarization analysis shows that the polarization for the two events also differs slightly but remains constant. Most of their energy is linearly polarized and lies in the horizontal plane. If these waves are taken to be SH waves, the remaining energy is confined to the beginning of the tornillo during its initiation or excitation. The remainder of the tornillo is characterized by exponential decay. These observations provide parameters for the classification of tornillos and constraints for source models.
    Description: JCR Journal
    Description: open
    Keywords: Galeras ; tornillo ; polarizations ; analytic function ; parametrization ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 2807037 bytes
    Format: application/pdf
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