Seismic coupling, down-dip limit of the seismogenic zone, and dehydration of the
slab
Tetsuzo Seno
( Earthquake Res Inst, Univ of Tokyo )
Along-arc variation of Seismic coupling & Down-dip limit of the seismogenic zone near Japan
in relation to
Dehydration from the subducted crust (Low-frequency tremor)
A
B
C
D
Kanto
NorthernHonshu
Tokai
KiiPen.
Shikoku
Japan Sea
Pacifiic Plate
Philippine Sea Plate
SagamiTrough
Fig. 1
Hyuganada
80
79
59
27
42
49
13
130° E 135° 140° 145°
30°
35°
N
500 km
Seismic coupling along the Nankai - Sagami Troughs
Eurasian plate
Okhotsk plate
Pacific plate
Philippine Sea plate
Seno et al. (1996)
Seno et al. (1993)
Yagi (2002)
Occurrence of smaller earthquakes in Hyuganada
1703 Genroku
1923 Taisho Tokai, 1707, 1854
~150 yrs
~400
~1500
~1500 ∞
∞
Central Honshu
Recurrence intervals of great earthquakes
Izu
Kanto
Nankai Trough
~50%
Sagami Trough
・ Vc = 3 cm/yr
・ U = 6 m
~100 %
・ Vc = 4 - 6 cm/yr
・ U = 4 - 6 m
Seismic coupling coefficient
・ T = 90 - 150 yrs ・ T = ~400 yrs
Taisho Kanto
(Seismic slip/plate motion)
Oleskevich et al. (1999)
Down-dip limit of the seismogenic zone
Seno & Pongsawat (1982),Seno et al. (1980)
1978 Miyagi-oki earthquake (M7.5)
50 km
Miyagi-oki,n. Honshu
Kawakatsu & Seno (1983)
Northern Honshu: three types of events
Thrust
Down-dip compression Down-dip tension
Kawakatsu & Seno (1983)
Whole section: three types of events
Thrust
Down-dip compression
Down-dip tension
A
B
C
D
Kanto
NorthernHonshu
Tokai
KiiPen.
Shikoku
Japan Sea
Pacifiic Plate
Philippine Sea Plate
SagamiTrough
Fig. 1
Hyuganada
80
79
59
27
42
49
13
130° E 135° 140° 145°
30°
35°
N
500 km
Hori (1997)
Philippine Sea slab beneath Kanto
●●●
●●
● thrust
Goto (2001)
S. Kyushu P-axes
●
Seismic coupling Down-dip limit of the seismogenic zone
in relation to
Dehydration from the subducted crust (Low-frequency tremor)
Basic assumptions
100 MPa 1 GPA
3 km
30 km
Lithostatic pressure
Depth
Tectonic stress
Weakening
Fault strength
Interplate earthquakes
Elevated pore fluid pressure
Slab earthquakes (intermediate-depth)
Dehydration instability
Weakening mechanisms
Dehydration instability: Serpentinite
Raleigh & Paterson (1965)
(a) Cold slab type (b) Hot slab type
Dehydration from crust
Dehydration from crust
Dehydration from serpentine
Dehydration from serpentine
Dehydration loci for slab seismicity
Yamasaki & Seno (2003)
Obara (2002)
Low-frequency Tremor in the upper plate wedge
Low freq. tremorFreq. great earthquakes
Subduction ofNormal oceanic crust Island-arc crust subduction
No dehydrationDehydration from crust
No low freq. tremor
No great earthquakes
No dehydration
Hot slab type: Nankai Trough
N. of Izu
Crust Upper plate
Tokai district:easternmost Nankai Trough
Seismicity: Matsumura (1997)
350°C
Low frequency tremor (Obara, 2002)
Dehydration From crust
Piosson’s ratio (Kamiya & Kobayashi, in prep.)
Temperature: Seno & Yamasaki , in prep.
Obara(2002)
震震
Low-frequency earthquakes & tremor: Upper plate
Okino et al. (1999)
Low-frequency tremor ~ Moho depth (Obara, 2002)
KantoE. Shikoku
S.Kyushu
No tremor region
Okino et al. (1994)
Kinan seamount chain
Subducted continental or island-arc crust is mainly composed of granite, then does not involve dehydration.
No low-frequency tremor
No earthquake within the subducted crust
Hypothesis:
Later crustal phaseSerpentine dehydration loci
Serpenine dehydration loci
a) Event in the oceanic crust b) Event in the mantle
Generally along the Nankai Trough
Discrimination of crustal events
No later crustal phase
Hori (1997)
PHS slab beneath Kanto(no tremor)
No later phase(Hori, 1990)
Kurashimo et al. (2002)
E. Shikoku (no tremor)
Hayashimoto et al. (2001)
110 km
200 km
DDC
DDT
DDT, i.e., lower plane seismicity in the mantle
S. Kyushu (no tremor)
Goto et al. (2001) DDT Thrust
mantle
thrust
S. Kyushu
Areas without earthquakes within the subducted crust
Kanto
E. Shikoku
S. Kyushu (?)
Areas without low-frequency tremor
Noguchi & Sekiguchi (2001)Obara (2002)
High Vp
Top of slab seismicityIzu
KantoSlab
Ni & Barazangi (1986)
Mature collision zones: Zagros and Himalaya
Low freq. tremorFreq. great earthquakes
Normal oceanic crust subduction Island-arc crust or continental crust subduction
No dehydrationDehydration from crust
No low freq. tremor
No great earthquakes
No dehydration
NankaiTrough N. of Izu, Zagros, Himalaya
Crust Upper plate
Areas with island-arc or continental crust subducted
Kanto, E. Shikoku, S. Kyushu Infrequent large interplate earthquakes
vs.
N. Izu, Zagros, Himalaya No or very rare large interplate earthquakes
Hori (1997)
Philippine Sea slab beneath Kanto
Shikoku Basin
Izu-Bonin Arc
Trench Axis
Serpentine stable
V. F.
Origin of the double seismic zone in Kanto
Seno et al. (2001); Seno & Yamasaki, in prep.
No dehydration from crust
No low freq. tremor
Infreq. great earthquakes& deep thrusts
Kanto
Dehydration from serpentine
Kawakatsu & Seno (1983)
Northern Honshu: three types of events
Thrust
Down-dip compression Down-dip tension
Kawakatsu & Seno (1983)
1994 aftershocks (Hino et al., 2000)
Yamanaka et al. (2001))EpicenterAsperity
Larger events
(a)
(a)
(b)(b)
Vp in northen part of n. Honshu
S. Ito et al. (2000)
Depth = 40 km
W E
No serpentine
Fractured zone
Dehydration
Ductile shear zone + hydrofracturing
Repeated earthquakes Plastic flow
Dehydration
Cold mantle wedge
N. Honshu, Kanto, S. Kyushu Iwate-oki, Bonin, Tonga
Serpentine
350°C350°C
Anisotropicpermeability
Plastic flow
Dehydration
Hot mantle wedge
Nankai, Ryukyu, Cascadia, Mexico
Ductile shear zone + hydrofracturing
Serpentine 350°C
No serpentine
Stable sliding with very high shear stress
No dehydration
Collision zone
N. Izu, Himalaya, Zagros
No serpentine
No dehydration
or delamination
Conclusions
・ Sudbduction of island-arc or continental crust does not involve dehydration of subducted crust, then does not induce low- frequency tremor in the wedge, or large interplate earthquake.
・ If sudbduction of island-arc crust accompanies dehydration of the serpentinized mantle, it produces large interplate earthquakes infrequently. ・ Thrust zone in the manle part may evolve into either of the two branches: earthquake-no serpentinized wedge or no earthquake-serpentinized wedge. This determines the down-dip limit of the seismogenic zone.
・ Earthquake occurrence in Kanto may be a result of no earthquake occurrence in Bonin; if Bonin generated great earthquakes, Kanto would have turned into a mountain belt.