EGU2020-18393 Fault stressing in the overriding plate due to ......Okinawa Trough 1946 M8.0 Active...
Transcript of EGU2020-18393 Fault stressing in the overriding plate due to ......Okinawa Trough 1946 M8.0 Active...
Hashima, A.1, H. Sato 1, T. Ishiyama 1,A.M. Freed 2, T.W. Becker 3
1Earthquake Research Institute, University of Tokyo, 2Purdue University, 3University of Texas at Austin
EGU2020-18393Fault stressing in the overriding plate due to megathrust coupling along the Nankai trough, Japan
TS5.1Seismic analysis and geodetic modelling:multi-disciplinary approach to problem-solving
EGU 2020 Online4 May 2020, 16:15-18:00
Recent inland earthquakes around SW Japan
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Tectonics around Philippine Sea (Wu et al., 2016, JGR) 126˚ 128˚ 130˚ 132˚ 134˚ 136˚
28˚
30˚
32˚
34˚
36˚
2016 Mw7.1
1995
2000
2005
2015
Korea
Kyushu
Ryuk
yu
Trenc
h
Nankai Trough
Okinawa Trough
1946 M8.0
Active seismic activity of ~M7, especially around Kyushu since 1995
Inland earthquakes due to Nankai megathrust
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6.5
7.0
7.5
8.0
8.5
1700 1800 1900 2000
Nankai Yr−M
1707M8.6
1854M8.4
1944 M7.91946 M8.0Megathrust
Inland
Nankai Map
M<78>M>=7M>=8
128˚ 132˚ 136˚ 140˚
32˚
36˚
128˚ 132˚ 136˚ 140˚
32˚
36˚1605 ~ 1707
1620 1650 1680
M<78>M>=7M>=8
128˚ 132˚ 136˚ 140˚
32˚
36˚
128˚ 132˚ 136˚ 140˚
32˚
36˚1707 ~ 1854
1710 1740 1770 1800 1830
M<78>M>=7M>=8
128˚ 132˚ 136˚ 140˚
32˚
36˚
128˚ 132˚ 136˚ 140˚
32˚
36˚1854 ~ 1946
1860 1890 1920
M<78>M>=7M>=8
128˚ 132˚ 136˚ 140˚
32˚
36˚
128˚ 132˚ 136˚ 140˚
32˚
36˚1946 ~ 2020
1950 1980 2010Year
Nankai Map
M<78>M>=7M>=8
128˚ 132˚ 136˚ 140˚
32˚
36˚
128˚ 132˚ 136˚ 140˚
32˚
36˚1605 ~ 1707
1620 1650 1680
M<78>M>=7M>=8
128˚ 132˚ 136˚ 140˚
32˚
36˚
128˚ 132˚ 136˚ 140˚
32˚
36˚1707 ~ 1854
1710 1740 1770 1800 1830
M<78>M>=7M>=8
128˚ 132˚ 136˚ 140˚
32˚
36˚
128˚ 132˚ 136˚ 140˚
32˚
36˚1854 ~ 1946
1860 1890 1920
M<78>M>=7M>=8
128˚ 132˚ 136˚ 140˚
32˚
36˚
128˚ 132˚ 136˚ 140˚
32˚
36˚1946 ~ 2020
1950 1980 2010Year
Inland earthquakes tend to occur before megathrust earthquakes
1944, 1946 ???
Data from historical documents (Utsu, 1990, 2002, 2004) http://iisee.kenken.go.jp/utsu/index_eng.html
2016 Mw7.1
M-T diagram
Map View
Time in earthquake cycle
Motivation of this study
• Inland source faults are activated by the Nankai megathrust coupling? How the Ryukyu trench contributes?
Methods– Calculate the stressing rate on source faults by the
interplate coupling using 3-D finite element model
– interplate coupling under the Ryukyu-Nankai trenches is constrained by the GPS data
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This method can be used to determine the inland fault going close to rupture
4700 km
4600 km
700 km
PAC PHSEUR
PHSPAC
Tohoku-okiNankai
3D FEM around the Japanese islands
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(Hashima et al., 2016, EPS; Freed et al., 2017, EPSL)
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View from NWEU removed
• Plate interface geometry based on Nakajima & Hasegawa (2006), Hayes et al. (2012), etc.
• 1000,000 Elements with the size of 5–100 km
Viscoelastic effect of asthenosphere (Li et al., 2015, 2018; Noda et al., 2018)
1019 Pa s 1019 Pa s
70 kmTe
*We use solution at t = 100 yr (perfectly relaxed)
Elastic thickness Te is critical to deformationWe examine cases of Te = 30, 50, and 80 km
(Flat layer)
125˚ 130˚ 135˚
25˚
30˚
35˚
5 cm/yr
data/disp_oct.dat
1998/1/1-2010/12/31, 404 stations
Reference
GPS Data and inland fault model
6
• Plate interface divided into 8×27 Patches• Slip response is computed for each patch for inversion
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Source fault modelGPS data (from GSI of Japan)
Slip angle is estimated to be the optimum direction by regional stress field (Terakawa & Matsu’ura, 2010)
Landward
Trenchward
Rotation
Results of slip-rate inversion for Te = 30 km
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Figure 4
120˚
125˚
125˚
130˚
130˚
135˚
135˚
140˚
25˚
35˚
40˚
Observed
Calculated
5 cm/yr
−10 −5 0 5 10
Slip (cm/yr)
Figure 4
120˚
125˚
125˚
130˚
130˚
135˚
135˚
140˚
25˚
35˚
40˚
Residual
2 cm/yr
−10 −5 0 5 10
Slip (cm/yr)
Te = 30 km (Comparison)
Te = 30 km (Residual)
(obs. - cal.)
Widespread residuals
Deficit Excess
Deficit Excess
5 cm/yr (Slip rates)
Results of slip-rate inversion for Te = 50 & 80 km
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Figure 4
120˚
125˚
125˚
130˚
130˚
135˚
135˚
140˚
25˚
35˚
40˚
Residual
2 cm/yr
−10 −5 0 5 10
Slip (cm/yr)
Figure 4
120˚
125˚
125˚
130˚
130˚
135˚
135˚
140˚
25˚
35˚
40˚
Residual
2 cm/yr
−10 −5 0 5 10
Slip (cm/yr)
Fitting too much!
Te = 50 km (Residual)
Te = 80 km (Residual)
Deficit Excess
Deficit Excess
Opposite slip at depth
5 cm/yr (Slip rates)
5 cm/yr (Slip rates)
The optimum model (Te = 50 km)
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Figure 4
120˚
125˚
125˚
130˚
130˚
135˚
135˚
140˚
25˚
35˚
40˚
Residual
2 cm/yr
−10 −5 0 5 10
Slip (cm/yr)
Residuals might be due to structural anomalies
Edge effect
Slip-rate deficit ~ 8 cm/yr(Interplate locking)
Consistent with previous studies (e.g. Ito et al., 1999; Yokota et al., 2016; Noda et al., 2018)
Slip-rate excess 3~ 6 cm/yr
Direction of slip-rate excess is deviated from the EUR-PHS relative motion, which represents different characteristics from relative plate motion
Related to slab rollback?
Te = 50 km (Residual)
Deficit Excess
5 cm/yr (Slip rates)
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(extension)(contraction)(σ11+ σ22 +σ33)/3
NS extension
NW-SE compression
Te = 50 km
Intra-plate stressing rate for optimum modelStress at depth of 10 km
Coulomb stress rates on inland faults
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promotionsuppression
2005 Mw6.6
2015 Mw6.7
2016 Mw7.1
Coulomb StressΔCFS = σn+ µσs (µ = 0.4)
Three recent ~M7 earthquakes occurred on the faults of positive ΔCFF
Summary
• Using 3-D FEM, we inverted GPS data in the Ryukyu-SW Japan arcs to obtain slip-rate excess/deficit under the Ryukyu-Nankai trenches– Slip-rate excess under the Ryukyu trench might be due to
slab rollback– Slip rates under the Ryukyu trench is critical to the
deformation on the Kyushu island, junction of the Ryukyu-SW Japan arcs
• Using slip-rate distribution, we computed stressing rate on the inland faults. In particular, source faults of the recent ~M7 earthquakes shows positive Coulomb stressing rates
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