The 2018 Hokkaido Eastern Iburi Earthquake: Fault Model(preliminary)

An earthquake (Mj6.7) struck eastern Iburi subprefecture in Hokkaido in Japan on September 6, 2018. A fault model was constructed from the crustal deformation data observed by InSAR (ALOS-2) and GNSS.

1) The estimated rectangular fault model with a uniform slip shows a high-angle reverse fault motion with the strike of N – S direction.
2) The upper edge of the fault is at a depth of ~16 km.
3) The moment magnitude (Mw) is estimated to be 6.56 (seismic moment: 8.68× 10¹⁸Nm).

Fig.1 Observed and model-calculated coseismic displacements by GNSS data (red: observation / blue: calculation). (a) Horizontal component. (b) Vertical component. Star and gray dots indicate the epicenter of the main shock and the aftershock, respectively. The frame indicate surface projections of the fault plane and the thick line represents the upper edge. Red lines on the map stand for active faults.[PNG: 205KB]



Fig.2 InSAR-derived LOS displacement field. Observation (Left). Model Calculation (Middle). Residual (Right).[PNG: 2.4MB]

Table1.Fault parameters for the fault model

Lon. (°)	Lat. (°)	Depth (km)	Length (km)	Width (km)	Strike (°)	Dip (°)	Rake (°）	Slip (m)	Mw
141.976 (0.021)	42.586 (0.017)	16.2 (1.7)	14.0 (3.9)	15.9 (3.5)	358 (3.5)	74 (4.4)	113 (7.2)	1.3 (0.4)	6.56

Fig.3 Schematic view of the 2018 Hokkaido eastern Iburi earthquake.[PNG: 1.1MB]


Analysis by GSI from ALOS-2data of JAXA.
These results were obtained through the activity of the SAR analysis working group of the Coordinating Committee for Earthquake Prediction.

Date-Time	September 6, 2018, 03:07(local time) September 5, 2018, 18:07(UTC)
Hypocenter Location	42.690°N、142.007°E、Depth:37 km (JMA, as of September 12, 2018)
Magnitude	Mj=6.7(JMA, as of September 12, 2018)

  

ALOS-2 (Advanced Land Observing Satellite 2) launched by Japan Aerospace Exploration Agency on May 24, 2014

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YARAI Hiroshi : Head of Division
KOBAYASHI Tomokazu : Chief Researcher
YAMADA Shinya : Researcher