First evidence from anisotropy change of a porosity wave at Mount Fuji following the 2011 Tohoku earthquake
Abstract
The monitoring of the stress field is fundamental for understanding active processes in volcanic and seismogenic zones. Seismic velocity measurements revealed that the Tohoku-Oki earthquake affected the velocity structure of volcanic zones, such as Mount Fuji. By using the ambient noise data covering the year 2011 in which the Tohoku-Oki earthquake (M_{W}=9.0) occurred, we monitor the horizontal polarisation anomalies (HPA) of surface waves. HPA are derived from off-diagonal terms of the noise cross-correlation tensor and are mainly related to stress-induced anisotropy. A co-seismic change of seismic anisotropy is observed and explained by a change in the alignment of cracks or fluid inclusions due to the stress perturbation. Two large scale (≈2 20 km) areas with strong static anisotropy are found eastward (in the WNW-ESE direction) and westward (in the NS direction) of Mount Fuji . This indicates that the regional stress field in this zone may be controlled by both subduction of the Pacific plate and the Philippine Sea plate.
Another unexpected very strong change of HPA with an opposite sign, is also observed one month later around the Hakone hydrothermal-volcanic area. It is interpreted as the propagation of a porosity wave triggered by the Tohoku-Oki earthquake, initiated at ≈ 3km depth and associated with its arrival at the surface.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S12A..06M
- Keywords:
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- 7203 Body waves;
- SEISMOLOGYDE: 7255 Surface waves and free oscillations;
- SEISMOLOGYDE: 7260 Theory;
- SEISMOLOGYDE: 7270 Tomography;
- SEISMOLOGY