[S-GD02] Crustal Deformation

[SGD02-P03] Slow-slip events of one-hour duration (3)

*Akio Katsumata¹, Kazuki Miyaoka², Takahiro Tsuyuki³, Satoshi Itaba⁴, Masayuki Tanaka³, Takeo Ito⁶, Akiteru Takamori⁵, Akito Araya⁵ (1.University of Toyama, 2.JMA, 3.MRI, JMA, 4.AIST, 5.ERI, Univ. of Tokyo, 6.Nagoya Univ.)

Keywords:slow earthquake, slow-slip event, laser strainmeter, borehole strainmeter

We are investigating slow-slop events of one-hour duration (1H-SSE) with data from laser strainmeters at Inuyama (Nagoya Univ. and ERI) and Tenryu-Funagira (MRI and ERI), and borehole strainmeters installed by Japan Meteorological Agency, The National Institute of Advanced Industrial Science and Technology, and Shizuoka Prefecture. 1H-SSEs were recognized as slip-speed increase during short-term slow-slip events (S-SSE). Three 1H-SSEs were recognized during a S-SSE in Feb. 2019 (Figure). We identify strain steps as 1H-SSEs based on the observations of simultaneous activation of tectonic tremors and overlapped source locations of 1H-SSE and tectonic tremor. There are some strain steps that do not meet these criteria. We searched for 1H-SSEs in strain data from 2016 to 2019. Only a limited number of 1H-SSEs were identified. It is considered that some special conditions are necessary for 1H-SSEs to occur.

Because magnitude of 1H-SSEs were around Mw 5.0, the background S-SSE should be large enough to include some Mw 5.0 events. The magnitude of the S-SSE in Feb. 2019 was Mw 5.9.

The S-SSE in Feb. 2019 which included three 1H-SSEs was one of three successive S-SSEs. It is not often for such successive S-SSEs to occur. Similar successive occurrence of S-SSEs were observed in November 2017 (Figure). Two strain steps were recognized in a S-SSE in November 2017. Source location could be estimated for one of the two strain steps. Successive occurrence of S-SSEs might be related to the conditions necessary for 1H-SSEs to occur.