5:15 PM - 6:45 PM
[SVC26-P07] Three-dimensional VSV and VSH structures beneath Asama volcano inferred from seismic interferometry
Recent studies report the existence of the discrepancy between VSV and VSH beneath volcanoes with large calderas such as Toba caldera (Jaxybulatov et al., 2014) and Yellow Stone caldera (Jiang et al., 2018) or volcanoes at the rim of large calderas such as Kirishima volcanoes. Such discrepancies imply the radial anisotropy generated by a sill complex in the magma reservoir. However, it is not clear whether this feature is common only among volcanoes related to large calderas. In this poster, we will present whether there is the same feature beneath a volcano without a large caldera taking an example of Asama volcano for comparison.
The technique we employed is seismic wave interferometry, which extracts the seismic wave propagation between two seismic stations by taking cross correlations of random wavefields, such as the ambient seismic noise or the seismic coda wave. The cross correlations of random wavefields recorded at two stations can be represented as if the source is at one station and the recorder is at the other. This technique is suitable for exploring local structure since the extracted wave is sensitive to the internal structure between the two stations.
We applied this technique to the ambient seismic noise data recorded at 46 seismic stations on and around Asama volcano between July 2005 and July 2007. Rayleigh and Love waves are extracted by taking cross correlations (Rayleigh waves from cross correlation functions of pairs of vertical components, and Love waves from transverse components). We derived the reference dispersion curves of Rayleigh and Love waves, respectively, using all possible pairs of stations, then measured phase velocity anomalies of all possible pairs with respect to the reference in multiple frequency bands (0.1-0.2 Hz, 0.15-0.3 Hz, 0.2-0.4 Hz, and 0.25-0.5 Hz).
The two-dimensional phase velocity maps of Rayleigh and Love waves were obtained by the surface wave tomography at frequencies, and three-dimensional VSV and VSH structures were constructed from a collection of local one-dimensional velocity profiles derived by inverting phase velocities of Rayleigh and Love waves, respectively, at each grid point.
Both VSV and VSH structures show low velocity regions around the summit at depth of about 2 km and in the western part of the volcano at depths of 5-10 km. The low velocity region in the western part of the volcano, located beneath the pressure source associated with the eruption of Asama volcano, is interpreted as a magma reservoir. The result shows the discrepancy between VSVand VSH in the magma reservoir is little, and implies the radial anisotropy is not remarkable.
The technique we employed is seismic wave interferometry, which extracts the seismic wave propagation between two seismic stations by taking cross correlations of random wavefields, such as the ambient seismic noise or the seismic coda wave. The cross correlations of random wavefields recorded at two stations can be represented as if the source is at one station and the recorder is at the other. This technique is suitable for exploring local structure since the extracted wave is sensitive to the internal structure between the two stations.
We applied this technique to the ambient seismic noise data recorded at 46 seismic stations on and around Asama volcano between July 2005 and July 2007. Rayleigh and Love waves are extracted by taking cross correlations (Rayleigh waves from cross correlation functions of pairs of vertical components, and Love waves from transverse components). We derived the reference dispersion curves of Rayleigh and Love waves, respectively, using all possible pairs of stations, then measured phase velocity anomalies of all possible pairs with respect to the reference in multiple frequency bands (0.1-0.2 Hz, 0.15-0.3 Hz, 0.2-0.4 Hz, and 0.25-0.5 Hz).
The two-dimensional phase velocity maps of Rayleigh and Love waves were obtained by the surface wave tomography at frequencies, and three-dimensional VSV and VSH structures were constructed from a collection of local one-dimensional velocity profiles derived by inverting phase velocities of Rayleigh and Love waves, respectively, at each grid point.
Both VSV and VSH structures show low velocity regions around the summit at depth of about 2 km and in the western part of the volcano at depths of 5-10 km. The low velocity region in the western part of the volcano, located beneath the pressure source associated with the eruption of Asama volcano, is interpreted as a magma reservoir. The result shows the discrepancy between VSVand VSH in the magma reservoir is little, and implies the radial anisotropy is not remarkable.