In the southwest Japan subduction zone, short‐term slow slip events (SSEs) accompanying nonvolcanic tremor (ETS: episodic tremor and slip) occur repeatedly with recurrence intervals of several months. It is important to know the detailed slip areas of the SSEs because short‐term SSEs occur at the downdip extension of a megathrust earthquake rupture zone, and hence the SSEs play a key role in the stress buildup processes of the megathrust earthquakes. Although most of the previous studies model a SSE fault motion with uniform slip on a rectangular fault, this may lead to a bias in estimating the slip area. In this study we estimate a spatial slip distribution for each of the short‐term SSEs from tilt offset measurements. In total, the slip distributions of 61 SSEs in Shikoku from January 2001 to March 2019 are obtained. The ETS zone in Shikoku is divided into three segments in terms of slip history of the SSEs. Before 2011, the slip areas of most of the SSEs are limited in any one of the three segments. After 2012, however, the number of SSEs having a slip area that extends to multiple segments increases. The slip histories at each position in the ETS zone suggest that the short‐term SSE activity is affected by the occurrence of nearby long‐term SSEs. The average slip rate over 18 years suggests that an estimated slip‐deficit in the ETS zone in western Shikoku could be released by long‐term SSEs, or coseismic slip or afterslip of the megathrust earthquakes.

中文翻译：

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基于倾斜度变化量测的2001年至2019年日本西南部四国地区短期慢滑事件的滑动分布

在日本西南俯冲带中，伴随非火山性震颤（ETS：偶发性震颤和滑坡）的短期慢滑事件（SSE）反复发生，复发间隔数月。重要的是要了解SSE的详细滑动区域，因为短期SSE发生在大推力地震破裂带的下倾延伸处，因此SSE在大推力地震的应力建立过程中起着关键作用。尽管以前的大多数研究都对矩形断层上具有均匀滑动的SSE断层运动进行了建模，但是这可能会导致估算滑动区域时出现偏差。在这项研究中，我们通过倾斜偏移量的测量来估算每个短期SSE的空间滑动分布。总共获得了2001年1月至2019年3月四国61家上交所的单据分布。根据SSE的滑移历史，四国的ETS区分为三个部分。在2011年之前，大多数上交所的滑点面积仅限于三个细分市场中的任何一个。但是，2012年之后，具有滑移区域扩展到多个段的SSE数量增加。ETS区每个位置的滑动历史表明，短期SSE活动受附近长期SSE的影响。18年的平均滑移率表明，四国西部ETS地区的估计滑坡赤字可能会因长期的SSE，同震滑移或特大推力地震的后滑而释放。具有滑移区域延伸到多个段的SSE数量增加。ETS区每个位置的滑动历史表明，短期SSE活动受附近长期SSE的影响。18年的平均滑移率表明，四国西部ETS地区的估计滑坡赤字可能会因长期的SSE，同震滑移或特大推力地震的后滑而释放。具有滑移区域延伸到多个段的SSE数量增加。ETS区每个位置的滑动历史表明，短期SSE活动受附近长期SSE的影响。18年的平均滑移率表明，四国西部ETS地区的估计滑坡赤字可能会因长期的SSE，同震滑移或特大推力地震的后滑而释放。