Japan Geoscience Union Meeting 2018

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-CG Complex & General

[S-CG53] Science of slow earthquakes: Toward unified understandings of whole earthquake process

Wed. May 23, 2018 10:45 AM - 12:15 PM Convention Hall B (CH-B) (2F International Conference Hall, Makuhari Messe)

convener:Satoshi Ide(Department of Earth an Planetary Science, University of Tokyo), Hitoshi Hirose(Research Center for Urban Safety and Security, Kobe University), Kohtaro Ujiie(筑波大学生命環境系, 共同), Takahiro Hatano(Earthquake Research Institute, University of Tokyo), Chairperson:Hirose Hitoshi, Takagi Ryota(東北大学)

11:30 AM - 11:45 AM

[SCG53-10] Along-strike variation of long-term slow slip event activity in the Nankai subduction zone

*Ryota Takagi1, Naoki Uchida1, Kazushige Obara2 (1.Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 2.Earthquake Research Institute, The University of Tokyo)

Keywords:Slow Slip Event, Nankai subduction zone, GNSS

We systematically searched long-term slow slip events (SSEs) in the Nankai subduction zone using GNSS data. We fit observed GNSS time series by modeled displacements that used a single rectangle fault and a ramp function with 300-day-long duration for expressing long-term SSE. A grid maximizing variance reduction was selected as a candidate of long-term SSE. We searched onset of the ramp function based on the grid search. By applying the method to GNSS data, we found 24 long-term SSEs with Mw6.1-6.9 in southern Miyazaki, northern Miyazaki, Bungo channel, and western Shikoku in southwest Japan from 1996 to 2016, which include unreported events. The long-term SSEs are segmented along strike and quasi periodic in each segment. The average recurrence interval and moment magnitude are 2.14±0.73 years and Mw6.6±0.2 in southern Miyazaki, 5.53±0.69 years and Mw6.7±0.2 in northern Miyazaki, 3.07±0.98 years and Mw6.5±0.3 in Bungo Channel, and 5.76±1.00 years and Mw6.3±0.1 in western Shikoku. In the Bungo channel, large SSEs (Mw6.5-6.9) and small SSEs (Mw6.1-6.3) occur alternately. The total slip amounts within the 20 years are approximately 58% of the plate convergence (6.5 cm/yr x 20 years) in southern Miyazaki, 21% in northern Miyazaki, 53% in Bungo Channel, and 12% in western Shikoku. There are M7.5 and M8-class locked asperities in the updip regions of the northern Miyazaki and western Shikoku SSEs, whereas the updip region of the Bungo Channel SSE is between the two asperities and the updip region of the southern Miyazaki SSE is creeping. The recurrence intervals and total slip amounts may be related to the strength of the updip interplate coupling.