Upper mantle seismic anisotropy around the plate edge beneath northern taiwan
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Upper Mantle Seismic Anisotropy around the Plate Edge beneath northern Taiwan. Wen-Tzong Liang 1 Yih-Zhen Hsu 2 Bor-Shouh Huang 1 Char-Shine Liu 3. Institute of Earth Sciences, Academia Sinica, Taiwan Institute of Geophysics, National Central University, Taiwan

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Upper Mantle Seismic Anisotropy around the Plate Edge beneath northern Taiwan

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Upper mantle seismic anisotropy around the plate edge beneath northern taiwan

Upper Mantle Seismic Anisotropy around the Plate Edge beneath northern Taiwan

Wen-Tzong Liang1 Yih-Zhen Hsu2 Bor-Shouh Huang1 Char-Shine Liu3

  • Institute of Earth Sciences, Academia Sinica, Taiwan

  • Institute of Geophysics, National Central University, Taiwan

  • Institute of Oceanography, National Taiwan University, Taiwan


Outline

Outline

  • Taiwan Tectonics

  • Upper Mantle Anisotropy in the Taiwan Region

  • New Measurements

  • Implications

  • Conclusions


Taiwan tectonic setting

Taiwan Tectonic Setting

CWB ML 3.5

WEP

80 mm/yr

South China Sea

Manila Trench

Kuo, 2003

IES DMC


Tectonic evolution of the northern taiwan mountain belt

Tectonic Evolution of the Northern Taiwan Mountain Belt

NW

SE

  • Southwest-propagating arc-continent collision

  • Westward extended Ryukyu subduction and caused flipping of subduction in the northern part of the collision orogen

  • Lithospheric stretching induced by the trench suction

  • Collision orogen collapsed as a result of crustal thinning

Teng, 1996


Upper mantle anisotropy in the taiwan region i

Upper Mantle Anisotropy in the Taiwan Region (I)

  • Splitting in regional and teleseismic shear waves (ScS, S) ignoring source side anisotropy

  • Mountain-parallel anisotropy

  • Taiwan Orogen

Rau et al., 2000


Upper mantle anisotropy in the taiwan region ii

Upper Mantle Anisotropy in the Taiwan Region (II)

T32A-01 10:20 MCS 302Seismic anisotropy beneath an active collision orogen of Taiwan from dense array observationsHuang et al. GRL (2006)


Upper mantle anisotropy in the vicinity of northern taiwan sks

Upper Mantle Anisotropy in the vicinity of Northern Taiwan (SKS)

  • SKS phases radiated from the 2006/02/22 Mozambique Earthquake (Mw=7.0) occurred ~97 away from N. Taiwan

  • Seismic Stations of BATS/ MT/ YM/ HC/ F-Net Networks

  • Mountain-parallel (on land) vs. Trench-parallel fast direction (in agreement with Long et al. 2005, 2006)

  • t = 0.2 ~ 1.5 s

WFSB

ANPB

Okinawa Trough

YNG

IGK


Upper mantle anisotropy beneath northern taiwan sks

50 km

Upper Mantle Anisotropy beneath Northern Taiwan (SKS)

One Backbone Network

  • Broadband Array in Taiwan for Seismology (BATS)

    3 Portable BB Netowroks

  • Metropolitan Taipei BB Network (MT)

  • Yangmingshan National Park Network (YM)

  • Hsinchu (HC) BB Network

    Contours of Wadati-Benioff zone are adopted from Chou et al. (2006)

Tatun Volcanic Area

Taipei

150 km

100 km

Hsinchu

Central Range


Mantle wedge anisotropy beneath northern taiwan local s

74 < d < 154 km

ANPB

60 < d < 192 km

WFSB

Crustal anisotropy

Mantle Wedge Anisotropy beneath Northern Taiwan (local S)

Trench-parallel anisotropy in the mantle wedge derived from local deep events


Mantle wedge anisotropy beneath northern taiwan tele s

Mantle Wedge Anisotropy beneath Northern Taiwan (tele. S)

  • Waveforms generated from deep earthquakes in the Tonga-Kermedec region

  •  = 74

  • Incidence angle= 20

  • T0 = 12-15 s

Trench direction

210 km

S

tele. S

SKS

410 km


Possible origins of upper mantle anisotropy in the northern taiwan

Possible Origins of Upper Mantle Anisotropy in the Northern Taiwan

  • Edge mantle flow?

  • Melt preferred orientation

  • Collision induced mantle deformation beyond the mantle wedge

  • B-type olivine fabric vs. corner flow


Seismic anisotropy around the slab edges in the western pacific

Seismic Anisotropy around the Slab Edges in the Western Pacific

  • Similar anisotropy pattern observed in the Kamchatka region (Peyton, et al., 2001; Levin et al., 2004)

    • Trench-parallel in the mantle wedge

    • Trench-normal beyond the slab edge

    • Suggesting mantle flow at the slab edge driven by the slab retreat

  • Slab edge subjected to an oblique subduction in the Taiwan region

?

Kamchatka

76 mm/yr

Eurasian Plate

Pacific Plate

?

Taiwan

Philippine Sea Plate

80 mm/yr


Possible origins of upper mantle anisotropy in the northern taiwan1

Possible Origins of Upper Mantle Anisotropy in the Northern Taiwan

  • Edge mantle flow

  • Melt preferred orientation?

  • Collision induced mantle deformation beyond the mantle wedge

  • B-type olivine fabric vs. corner flow


3d vp and vs structural models

3D Vp and Vs Structural Models

  • A low velocity layer attached on the slab surface

N

S

100

A’

Offshore

Mantle wedge

100

*Note the color scale is not the conventional one

CWB dataset

Kim et al., 2005


Subduction beneath north taiwan

Subduction beneath North Taiwan

Vp %

Vs %

A

A’

A

N

S

N

S

A’

N

S

Vp/Vs %

checkerboard test

CWB+JMA datasets

Chou et al., 2006b


Possible origins of upper mantle anisotropy in the northern taiwan2

Possible Origins of Upper Mantle Anisotropy in the Northern Taiwan

  • Edge mantle flow

  • Melt preferred orientation

  • Collision induced mantle deformation beyond the mantle wedge

  • B-type olivine fabric


Slab collision and folding

Slab Collision and Folding

S

N

Slab folding

N

Lateral compression along slab at 50~100 km depth range

S

Chou et al., 2006a


Possible origins of upper mantle anisotropy in the northern taiwan3

Possible Origins of Upper Mantle Anisotropy in the Northern Taiwan

  • Edge mantle flow

  • Melt preferred orientation

  • Collision induced mantle deformation beyond the mantle wedge

  • B-type olivine fabric


B type olivine fabric

B-type Olivine Fabric

Nakajima & Hasegawa, 2004

Jung and Karato, 2001 Katayama et al., 2004

Kneller et al., 2005


3d geodynamic structure in the taiwan region

N

?

3D Geodynamic Structure in the Taiwan Region

Eurosian Plate

Philippine Sea Plate

N

Lin et al., 2004 Kim et al., 2005 Chou et al., 2006 Wang et al., 2006

S


Conclusions

Conclusions

  • Mountain-parallel anisotropy beyond the mantle wedge implies mantle deformation due to the collision tectonics

  • Trench-parallel anisotropy exists in the mantle wedge beneath Northern Taiwan

  • Significant spatial variation of anisotropy beneath ANPB indicates different origins of anisotropy – weak coupling between mantle wedge and continental lithosphere?

  • Preserved upper mantle deformation /B-type olivine fabric/ Edge mantle flow/ melt preferred orientation

  • Deployment of Broadband OBS is necessary to study the subduction process in the Taiwan region – ongoing!


Ies broadband obs experiment

IES Broadband OBS Experiment

The 1st deployment of BB OBS experiment in the eastern offshore region

Kuo and Chi, Sep. 2006

http://obs.earth.sinica.edu.tw


Thank you

Syueshan, Taiwan

- Thank you -


Flow fields for the obliquely subducted slab

Flow Fields for the Obliquely Subducted Slab

3D perspective plots of the particle paths of different scenarios : (a) rotating Euler vectors onto the slab surface

(b) Flow field minimizing the integrated in-plane deformation rate of the subducted slab

(c) Flow field minimizing the overall in-plane deformation rate in the entire modeling region

Chiao, et al., 2001


Melting features along the western ryukyu slab edge

Melting Features along the Western Ryukyu Slab Edge

N

Lin et al., 2004


Measurement examples

Measurement Examples


Crustal deformation in the central and southern ryukyu arc

Crustal Deformation in the Central and Southern Ryukyu Arc

  • Trench-parallel extensional strain

  • Southward migration of Ryukyu Arc

  • Bending/retreat of Philippine Sea slab

Interaction between the Taiwan-Luzon Arc Collision and the bending of Ryukyu Arc.

Nakamura, 2004


Subduction beneath south taiwan

Subduction beneath South Taiwan

Local/Regional/Teleseismic events joint inversion

Prescribed slab

Wang et al., 2006


Upper mantle seismic anisotropy around the plate edge beneath northern taiwan

Wang et al., 2004


Seismic anisotropy and mantle creep in young orogens

Seismic anisotropy and mantle creep in young orogens

Fast LPOof olivine in the direction of mantle creep that is responsible for the Lithospheric Collision

Meissner et al., 2002


Effect of water and stress on lpo of olivine

Effect of Water and Stress on LPO of Olivine

Jung and Karato, 2001 Katayama et al., 2004 Jung et al., 2006


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