地殻変動論ゼミの予定をお知らせします。
Zoomによるオンラインでの開催となります。

科目：地殻変動論ゼミナール（修士・博士）
日時：2020年5月21日（木）10時00分~
場所：オンライン(Zoom)
発表者：西川友章

内容：最近の研究紹介

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Here is information about the next seminar on the Crustal Deformation. ​​

Date: May 21, 2020 AM 10:00~
Place: Zoom Meetings
発表者 (Presenter): Tomoaki Nishikawa

タイトル (Title)：
Detection of Earthquake Swarms along the Hikurangi Trench: Insights into the Relationship between Seismicity and Slow Slip Events

アブストラクト (Abstract)：
Earthquake swarms, which are anomalous increases in seismicity rate without a distinguishable mainshock, often accompanies aseismic transients such as fluid migrations and episodic aseismic slips on faults. Investigating earthquake swarm activity provides insights into the causal relationship between aseismic processes and seismicity. In the Hikurangi Trench, New Zealand, slow slip events (SSEs) on the plate interface are often accompanied by intensive earthquake swarms. However, the detailed spatiotemporal distribution of earthquake swarms along the Hikurangi Trench is still unclear. Here we used the Epidemic-Type Aftershock-Sequence (ETAS) model to detect earthquake swarms (M >= 3) and created a new earthquake swarm catalog covering 1997 to 2015 along the Hikurangi Trench. We compared the earthquake swarm catalog with Global Navigation Satellite System (GNSS) time series data and existing catalogs of SSEs and tectonic tremors. Most of the detected 119 earthquake swarm sequences are intraplate events, and their epicenters are concentrated mainly along the eastern coast of the North Island, while epicenters of tectonic tremors are located inland. The earthquake swarms often occurred temporally close to transient eastward GNSS displacements associated with known and newly detected SSEs. We found that earthquake swarms sometimes preceded the displacements by more than several days. The stress loading due to SSEs are not plausible as the triggering mechanism of these pre-SSE earthquake swarms. We instead suggest that high fluid pressure within the slab, accumulated before SSEs, might have caused intraplate fluid migrations, which in turn triggered the pre-SSE earthquake swarms.