14:45 〜 15:00
[SCG40-35] Association between regular small earthquakes and tectonic tremors along the northern Japan Trench
キーワード：浅部テクトニック微動、微小地震、日本海溝
Interaction between slow and regular earthquakes in subduction zones has been reported in recent studies with various styles. In the northern Japan Trench, it has been revealed that regular earthquakes occur nearby and simultaneously with slow earthquakes, making the region an important environment for studies to understand the interaction. This study clarifies the spatiotemporal correlation between tectonic tremors, a type of slow earthquake, and regular earthquakes by relocating many micro-earthquakes occurring around shallow tremors in the northern Japan Trench.
The periods of the study were October 2007 to June 2008 (Period I) and August 2016 to July 2022 (Period II). We analyzed the seismograms obtained by a temporal OBS deployment in Period I and the S-net data in period II. The event identification was made by the envelope correlation method. The detected events were classified into tremors and earthquakes, based on durations and spatiotemporal clustering patterns. Although the tremor locations were estimated by the envelope correlating, the hypocenters of earthquakes were located by using P- and S-readings obtained by auto-picking methods.
The earthquakes around the tremors were concentrated along the plate boundary and their activations were often spatiotemporally correlated with the tremor activations. In some tremor-earthquake association events, tremors and earthquakes followed an identical migration pattern. Such tremor-earthquake associating activities were found to have occurred repeatedly at almost the same locations both in Period I and Period II, although some events were newly identified in Period II. The increases in seismicity associated with tremors tended to involve swarms of small regular earthquakes and the occurrences of Very Low-Frequency Earthquakes (VLFEs), suggesting that Slow Slip Events (SSEs) occurred around the locations of the simultaneous tremor-earthquake activation events. Therefore, the tremor-earthquake associating event would be a proxy of an SSE occurrence, which is difficult to detect by on- and offshore geodetic monitoring along the Japan Trench. The tremor-earthquake association events occurred in several specific small areas during our observation, and the locations of the small areas were unchanged throughout Period I and Period II. This nature suggests that the condition required to host the tremor-earthquake associations was persistent before and after the 2011 Tohoku Earthquake. Large-scaled association events involve multiple small areas, but the combination was found to be different from one activation event to another. This characteristic may reflect the fact that recurring SSEs responsible for the tremor-earthquake associations were diverse in size and location.
The periods of the study were October 2007 to June 2008 (Period I) and August 2016 to July 2022 (Period II). We analyzed the seismograms obtained by a temporal OBS deployment in Period I and the S-net data in period II. The event identification was made by the envelope correlation method. The detected events were classified into tremors and earthquakes, based on durations and spatiotemporal clustering patterns. Although the tremor locations were estimated by the envelope correlating, the hypocenters of earthquakes were located by using P- and S-readings obtained by auto-picking methods.
The earthquakes around the tremors were concentrated along the plate boundary and their activations were often spatiotemporally correlated with the tremor activations. In some tremor-earthquake association events, tremors and earthquakes followed an identical migration pattern. Such tremor-earthquake associating activities were found to have occurred repeatedly at almost the same locations both in Period I and Period II, although some events were newly identified in Period II. The increases in seismicity associated with tremors tended to involve swarms of small regular earthquakes and the occurrences of Very Low-Frequency Earthquakes (VLFEs), suggesting that Slow Slip Events (SSEs) occurred around the locations of the simultaneous tremor-earthquake activation events. Therefore, the tremor-earthquake associating event would be a proxy of an SSE occurrence, which is difficult to detect by on- and offshore geodetic monitoring along the Japan Trench. The tremor-earthquake association events occurred in several specific small areas during our observation, and the locations of the small areas were unchanged throughout Period I and Period II. This nature suggests that the condition required to host the tremor-earthquake associations was persistent before and after the 2011 Tohoku Earthquake. Large-scaled association events involve multiple small areas, but the combination was found to be different from one activation event to another. This characteristic may reflect the fact that recurring SSEs responsible for the tremor-earthquake associations were diverse in size and location.