11:15 〜 11:30
[SSS11-09] スロースリップの準備過程としてのスラブ内脱水とプレート境界への水の供給
キーワード：スロースリップ、減衰、水
Slow slip (SSE) is a phenomenon in which a fault slowly slides and releases the strain, unlike a normal earthquake that releases the strain instantly by seismic rupture, and its relationship with a large earthquake has been discussed. Although the detailed mechanism of SSE generation has not been clarified, it is known that the presence of high pore-fluid pressure plays an important role. Therefore, it is very important to investigate the behavior of water around the SSE generation area.
To dates, there are many studies conducted to investigate the behavior of water around the SSE generation area using various methods, but there are still few studies investigating the behavior of water from attenuation structure of seismic waves. Examining the attenuation of seismic waves is suitable for investigating inhomogeneous structures such as temperature, cracks, and fluids in the target area, and in particular, investigating time changes of the attenuation shows the behavior of substances that are constantly moving underground, such as water.
Nakajima and Uchida (2018) investigated the temporal change of the P wave attenuation structure around the SSE generation area (depth 40-50 km) at the subducting Philippine Sea plate boundary in the southwestern part of Ibaraki prefecture, and revealed the repeated drainage to the upper plate by SSE in an about one-year cycle. However, the behavior of water before the occurrence of SSE remains unclear by observation using the attenuation of seismic waves.
In this study, motivated by Nakajima and Uchida (2018), we investigated the time change of the attenuation structure in the slab around the SSE generation area in the southwestern part of Ibaraki prefecture from 2009 to 2015 using the waveform data of MeSO-net, and the time change of the seismic activity in the slab from 2004 to 2015. As a result, it was found that the attenuation and seismic activity in the slab remarkably increased 0.2 to 0.4 years before the occurrence of SSE along the plate boundary. This result suggests a process by which the water in the slab is drained to the plate boundary prior to SSE.
Also, we compared the attenuation structure of the S wave in the upper plate with that of the P wave, and it was found that the P wave was attenuated more than the S wave. Similar results have been reported in Southern California observations and laboratory experiments, which may lead to a better understanding of the wave attenuation in partially saturated clacks.
To dates, there are many studies conducted to investigate the behavior of water around the SSE generation area using various methods, but there are still few studies investigating the behavior of water from attenuation structure of seismic waves. Examining the attenuation of seismic waves is suitable for investigating inhomogeneous structures such as temperature, cracks, and fluids in the target area, and in particular, investigating time changes of the attenuation shows the behavior of substances that are constantly moving underground, such as water.
Nakajima and Uchida (2018) investigated the temporal change of the P wave attenuation structure around the SSE generation area (depth 40-50 km) at the subducting Philippine Sea plate boundary in the southwestern part of Ibaraki prefecture, and revealed the repeated drainage to the upper plate by SSE in an about one-year cycle. However, the behavior of water before the occurrence of SSE remains unclear by observation using the attenuation of seismic waves.
In this study, motivated by Nakajima and Uchida (2018), we investigated the time change of the attenuation structure in the slab around the SSE generation area in the southwestern part of Ibaraki prefecture from 2009 to 2015 using the waveform data of MeSO-net, and the time change of the seismic activity in the slab from 2004 to 2015. As a result, it was found that the attenuation and seismic activity in the slab remarkably increased 0.2 to 0.4 years before the occurrence of SSE along the plate boundary. This result suggests a process by which the water in the slab is drained to the plate boundary prior to SSE.
Also, we compared the attenuation structure of the S wave in the upper plate with that of the P wave, and it was found that the P wave was attenuated more than the S wave. Similar results have been reported in Southern California observations and laboratory experiments, which may lead to a better understanding of the wave attenuation in partially saturated clacks.