Dataset Information

Spatial and temporal seismic velocity changes on Kyushu Island during the 2016 Kumamoto earthquake.

ABSTRACT: Monitoring of earthquake faults and volcanoes contributes to our understanding of their dynamic mechanisms and to our ability to predict future earthquakes and volcanic activity. We report here on spatial and temporal variations of seismic velocity around the seismogenic fault of the 2016 Kumamoto earthquake [moment magnitude (Mw) 7.0] based on ambient seismic noise. Seismic velocity near the rupture faults and Aso volcano decreased during the earthquake. The velocity reduction near the faults may have been due to formation damage, a change in stress state, and an increase in pore pressure. Further, we mapped the post-earthquake fault-healing process. The largest seismic velocity reduction observed at Aso volcano during the earthquake was likely caused by pressurized volcanic fluids, and the large increase in seismic velocity at the volcano's magma body observed ~3 months after the earthquake may have been a response to depressurization caused by the eruption. This study demonstrates the usefulness of continuous monitoring of faults and volcanoes.

SUBMITTER: Nimiya H

PROVIDER: S-EPMC5706751 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature

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Spatial and temporal seismic velocity changes on Kyushu Island during the 2016 Kumamoto earthquake.

Nimiya Hiro H Ikeda Tatsunori T Tsuji Takeshi T

Science advances 20171124 11

Monitoring of earthquake faults and volcanoes contributes to our understanding of their dynamic mechanisms and to our ability to predict future earthquakes and volcanic activity. We report here on spatial and temporal variations of seismic velocity around the seismogenic fault of the 2016 Kumamoto earthquake [moment magnitude (<i>M</i><sub>w</sub>) 7.0] based on ambient seismic noise. Seismic velocity near the rupture faults and Aso volcano decreased during the earthquake. The velocity reduction ...[more]

PMID: 29202026

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Project description:In this paper, the seismic assessments of two footbridges, i.e., a single-span steel frame footbridge and a three-span cable-stayed structure, to the spatial variation of earthquake ground motion (SVEGM) are presented. A model of nonuniform kinematic excitation was used for the dynamic analyses of the footbridges. The influence of SVEGM on the dynamic performance of structures was assessed on both experimental and numerical ways. The comprehensive tests were planned and carried out on both structures. The investigation was divided into two parts: in situ experiment and numerical analyses. The first experimental part served for the validation of both the finite element (FE) modal models of structures and the theoretical model of nonuniform excitation as well as the appropriateness of the FE procedures used for dynamic analyses. First, the modal properties were validated. The differences between the numerical and the experimental natural frequencies, obtained using the operational modal analysis, were less than 10%. The comparison of the experimental and numerical mode shapes also proved a good agreement since the modal assurance criterion values were satisfactory for both structures. Secondly, nonuniform kinematic excitation was experimentally imposed using vibroseis tests. The apparent wave velocities, evaluated from the cross-correlation functions of the acceleration-time histories registered at two consecutive structures supports, equaled 203 and 214 m/s for both structures, respectively. Also, the coherence functions proved the similarity of the signals, especially for the frequency range 5 to 15 Hz. Then, artificial kinematic excitation was generated on the basis of the adopted model of nonuniform excitation. The obtained power spectral density functions of acceleration-time histories registered at all supports as well as the cross-spectral density functions between registered and artificial acceleration-time histories confirmed the strong similarity of the measured and artificial signals. Finally, the experimental and numerical assessments of the footbridges performance under the known dynamic excitation generated by the vibroseis were carried out. The FE models and procedures were positively validated by linking full-scale tests and numerical calculations. In the numerical part of the research, seismic analyses of the footbridges were conducted. The dynamic responses of structures to a representative seismic shock were calculated. Both the uniform and nonuniform models of excitation were applied to demonstrate and quantify the influence of SVEGM on the seismic assessment of footbridges. It occurred that SVEGM may generate non-conservative results in comparison with classic uniform seismic excitation. For the stiff steel frame footbridge the maximum dynamic response was obtained for the model of nonuniform excitation with the lowest wave velocity. Especially zones located closely to stiff frame nodes were significantly more disturbed. For the flexible cable-stayed footbridge, in case of nonuniform excitation, the dynamic response was enhanced only at the points located in the extreme spans and in the midspan closely to the pillars.

Dataset Information

Spatial and temporal seismic velocity changes on Kyushu Island during the 2016 Kumamoto earthquake.

Publications

Spatial and temporal seismic velocity changes on Kyushu Island during the 2016 Kumamoto earthquake.

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