The 6th Joint Meeting of the UJNR Panel on Earthquake Research, 2006/11/9-10 Deep slow earthquake families in the Nankai Trough subduction zone: non-volcanic tremor, slow slip event and very low frequency earthquake Kazushige Obara,Yoshihiro Ito, Shutaro Sekine, Hitoshi Hirose and Katsuhiko Shiomi (NIED)
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Deep slow earthquake families in the Nankai Trough ...non-volcanic tremor, slow slip event and very low frequency earthquake ... Deep VLF earthquakes with tremor and slip of episode
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The 6th Joint Meeting of the UJNR Panel on Earthquake Research, 2006/11/9-10
Deep slow earthquake families in the Nankai Trough subduction zone:
non-volcanic tremor, slow slip event and very low frequency earthquake
Deep Very Low Frequency Eq (D-VLFE) Seismic slip of small patch on S-SSE fault plane
Slow Earthquake Families in Nankai Zone
Micro crack failurearound S-SSE
Source time duration (or predominant time period) of slow earthquakes in Nankai subduction zone
Shallow Ito, P014VLFE
1000s 100s 10s 1s 0.1s1000d 100d 10d 1d 0.1d
Deep
Long-termSSE
Short-termSSE
VLFE LF Tremor
(LF Earthquake)included(0.5~5years) (2~5days)
Tremor
Slow Slip
High-quality dense seismic network
with Tiltmeter
NIED Hi-net(800stations)
Epicentral distribution of tremor
Deep tremorNIED Hi-net stations
Iso-depth contour of intra-slab seismicity
Nankai
Tonankai
Tokai
anticipated seismogenic zone
Tremor activity in Shikoku
East
Center
West
Three major segments
2001 2002 2003 2004 2005 2006
3mon.
3mon.
6mon.
(SW)
(NE)
Tremor and Tilt change in the western part of Shikoku
(Time window:14days)
5days 5days 5days 6days
0 50 100 150 200[km]
Tilt change and Tremor migration in W. Shikoku HIYH
(SW) (NE)
(SW)
(NE)
(SW)
(NE)
9
Short-term SSE & Tremor, 2002 AugustAugust 6-8 August 9-12
Cross sectional view of the tremor
Based on JMA catalog
TremorRegular Earthquake
Cross sectional view of the tremor
Based on JMA catalog
TremorRegular Earthquake
plate boundary from reflection survey (Baba, 2002)Short-term SSE
Oceanic Moho from receiver function analysis(Shiomi et al.,2004)
Tremor energy release in the active stageTremor energy release in the active stagewith shortwith short--term slow slip in west of Shikokuterm slow slip in west of Shikoku
Aug.-Sep. 2003
The periodicity of 12 hours == effect of earth tideThe periodicity of 12 hours == effect of earth tide
Tremor triggered by M7.6 Indonesia earthquakeTremor triggered by M7.6 Indonesia earthquake
P T-phase
Surface wave
TremorsTremors
Observational result of short-term slow slip・Occur and migrate with active tremor・recur with a period of 6 months (W. Shikoku, Kii, Tokai)・slip duration of 2~5 days・Reverse faulting at the depth of the plate boundary
Stick-slip on plate boundary
Scenario of short-term slow slip1.Locked for 6 months at the transition zone2.Strain accumulation due to the slab descending3.Weakening of frictional strength by fluid from dehydration4.Slip event occurs periodically as a stable process(Control factor:plate motion velocity, fluid generation rate,
segment size, overriding structure, etc)
Observational result of tremor・Activated by slow slip( affected by earth tide)・migrate with slow slip ・Isolated tremor with large amplitude occurs at plate boundary
(Shelly et al.,2006),with thrust type focal mechanism (Ide et al.,2006)・Minor tremor frequently occurs・Triggered by teleseismic wave(Miyazawa et al.,2006)
Chain-like crack failure in inhomogeneous layer around plate boundary generated by underplating
Scenario of tremor1.Micro crack failure triggered by sudden increasing of fluid pressure by occurrence of slow slip2.Minor tremor triggered by small fluctuation of fluid pressure by teleseismic wave
Migrating tremor and slow-slip eventin Tokai and Kii area, January 2006
Total Mw ~ 6.2
Vel.=10km/dayJanuary, 2006
Kii TokaiIseBay
(SW)
(NE)
Tremor activity in Kii and Tokai area
(NE)
Tokai
Kii
Ise Bay
6mon.
3mon.
6mon.
?(SW)
Migration of tremor in Kii area
(NE)
Tokai
Kii
Ise Bay
(SW)Start point of tremor activity with short-term slow slip detected by NIED tiltmeter
Interpretation of the episode 2006 in Tokai ・Small ridge structure of Philippine Sea plate at Ise Bay・The ridge acts as a barrier.・Usually, tremor and SSE occur on both sides of ridge independently.・ In the Kii segment, tremor usually starts from the Ise Bay.・ Episode 2006 started from the south end of the Kii segment,
Deep VLF earthquakes with tremor and slip of episode 2006 in Tokai and Kii area
VLF earthquake Tremor Tilt
Deep VLF earthquakes with tremor and slip of episode 2006 in W. Shikoku
VLF earthquake Tremor Tilt
Observational result of deep VLF earthquake・Occur and migrate with active tremor and short-term SSE・Predominant in 20 seconds and radial component・Apparent velocity ~ 6km/s・Thrust type focal mechanism near plate boundary
Seismic slow slip of small patch surrounded by short-term slow slip fault plane
Scenario of deep VLF earthquake1.strain accumulation at small patch due to slow slip on surrounded area2.seismic slow slip with high fluid pressure 3. No VLF without SSE period
●Three types of slow earthquakes in transition zone
○Short-term slow slip = Stick slip on the plate boundaryDeep VLF earthquake = seismic slow slip at small patchDeep LF tremor = chain-like crack failure
○reflecting inhomogeneous structure in transition zone
OneOne--hour record chart at the station IKTHhour record chart at the station IKTHin Shikoku Island, Southwest Japanin Shikoku Island, Southwest Japan
(2(2001/8/17 4 a.m.)001/8/17 4 a.m.)
Time (s)
Tim
e (m
in)
Clustering of tremor activity
Shikoku
Kii Tokaieastwestcenter
IKTH HIYHHIYH
KWBH YNDH
1 hour continuous seismograms observed at 1 hour continuous seismograms observed at 3 stations in the western part of Shikoku3 stations in the western part of Shikoku
4 am, 17 August 20014 am, 17 August 2001
Time [sec] Time [sec]
Time [sec]
Tim
e [m
in]
Tim
e [m
in]
3 days envelope traces in Shikoku
Outline
- Tremor & Short-term slow slip
- 2006 episode in Tokai
- Very low frequency earthquake
- Summary
Migration of tremor in W.ShikokuRupture process of short-term SSE
Long-term slow slip
Start point of tremor activity with short-term slow slip detected by NIED tiltmeter