Participants

1. From Subduction to Collision : Taiwan Participants At Caltech Bruce Shyu (Grad) Martine Simoes (Grad) Ya-Ju Hsu(Postdoc) Olivier Beyssac (Visitor) Jing Yang (Grad Taiwanese partners Yue-Gau Chen Shui-Beih Yu Yu-Chang Chang, Kuo-Fong Ma, Shiann-Jong Lee, How-Wei Chen, Yi-Min Wu Cheng-Horng Lin Other partners O. Beyssac B. Goffe A. Singhvi J.P Avouac K. Farley K. Sieh M. Simons D. Helmberger J. Tromp T. Heaton J. Galeztka

2. A Mature Collision : the Nepal Himalaya Participants Nepali partners S. Rajaure S. Sapkota C. Chitrakar J.P Avouac K. Farley D. Helmberger J. Galeztka Pierre Bettilleni (Grad) Aron Meltzner (Grad) Gweltaz Maheo (PostDoc) … French partners L. Bollinger M. Flouzat

3. Objectives of this research • Provide physically sound guidelines on how to take into account Geodetic, Geophysical and Geological data in Seismic Hazard assessment. • Reconciling our understanding of recent deformation with long-term geological processes associated with mountain building in a collisional context.

4. We need to establish rheological laws describing the mechanical behavior of the lithosphere. • This requires some idea of • the state of stress • temporal evolution of strain • the controlling factors (T, lithology, fH2O…) Friction Law t/s=m=m*+a ln(V/V*)+b ln(q/q*) dq/dt=1-Vq /Dc Ductile Flow laws dε/dt = A fH2Omσn ℮-Q/RT

5. Active faults Map (Bruce,Kerry, Yue-Gau), 91mm/yr Shyu et al, 2005

6. Malaveille A B C (Shyu et al, 2005) Malavielle et al, 2000

7. (Malavielle et al, 2000)

8. Malaveille (Malavielle et al, 2000)

9. Ground displacements as measured by GPS • Before the Chichi EQ (black arrows) • Effects of the Chichi EQ (red arrows)

10. The critical wedge model (J. Suppe, 1981)

11. Motivations for a TO project on Taiwan • Transition from subduction to collision : Lateral variation may reveal the time evolution of the mountain belt since the “end” of the subduction) • Archetype of active mountain belt : Revisiting “the critical taper model”; an opportunity to understand better interplay between crustal deformation, evolution of thermal structure and denudation. • Toward a physical model of the seismic cycle : A unique area where we can put together information about large EQ, crustal strain in the interseismic period, intense background seismicity, structural geology,

12. Some Geology, Geophysics and Mechanical Modeling • Task 1 : Kinematics of geological crustal deformation • Task 2 : Geodetic measurements and modeling of the current pattern, and test consistency with seismicity distribution and possible rate changes. • Task 3 : Determination of peak metamorphic temperatures and denudation along transects across Taiwan. Model the thermal structure based on these data the the kinematic results from task 1. • Task 4 : Seismology. Deep structure of the range form seismological investigations. Analysis of local and regional seismic waveforms from the Taiwan networks to determine the crust and upper-most-mantle structure (slabs, intracrustal thrust faults) and their relationship with seismic events and seismicity. Re-examination of prior events with the globally calibrated paths (using the ChiChi EQ). • Task 5 : Mechanical modeling. Lithospheric deformation associated with the transition from subduction to collision. Modeling of the seismic cycle with proper account for faults geometry, thermal structure, stress distribution.

13. Task 1: Kinematic of deformation along the Longitudinal valley See Bruce’s Poster

14. from foreland sedimentation: 39-45mm/yr Task 1 :Kinematic of deformation along the western foothills ? 15mm/yr Interseismic velocities 16mm/yr See Martine’s Posters

15. Co-seismic deformation From SPOT images and Air photos (S. Leprince, F, Ayoub, Y.T. Kuo) From SAR images (Florence Levy) Task 3 :Geodesy and seismic cycle model

16. Co-seismic deformation Model based on a realistic fault geometry and layered earth strusture (Yaru Hsu) Task 3 :Geodesy and seismic cycle model

17. Task 3 :Geodesy and seismic cycle model (Ya-Ju Hsu et al, in prep)

18. Displacement at station I007 postseismic deformation over the first year following the Chi-Chi EQ added about 10-20% to the co-seismic moment Time evolution of afterslip obeys frictional sliding (Perfettini and Avouac, JGR,2004) Task 3 :Geodesy and seismic cycle model

19. Tcycle/TM 1.7 hence TM  50 yr From Yaru Over the first year postseismic displacements show a logarithmic decay consistent with frictional afterslip but require require some viscous relaxation over the longer term. Task 3 :Geodesy and seismic cycle model

20. Task 2: Metamorphic petrology and Thermochronology

21. Beyssac et al in prep Task 2: Metamorphic petrology and Thermochronology

22. See Martine’s Posters Task 2: Metamorphic petrology and Thermochronology

23. Thermo Kinematic Model See Martine’s Posters Task 2: Metamorphic petrology and Thermochronology

24. Thermo Kinematic Model See Martine’s Posters Task 2: Metamorphic petrology and Thermochronology

25. Thermo Kinematic Model See Martine’s Posters Task 2: Metamorphic petrology and Thermochronology

26. Thermo Kinematic Model See Martine’s Posters Task 2: Metamorphic petrology and Thermochronology

27. Downdip limit of Locked Fault Zone, Transition to stable sliding? Transition to Ductile Flow? Effect of temperature on the mechanics ofcrustal deformation?What is the mechanics deteemining the observed Kinematics?

28. 1934 Bihar-Nepal EQ Mw= 8.2 Geodetic deformation across the Nepal Himalaya

29. cGPS Time series-ITRF2000 See Sudhir’s Posters

30. Modeling interseismic deformation from a creeping dislocation -cGPS data indicate 17.5+/1 1.5mm/yr of shortening - Holocene shortening rate: 21+/-1.5mm/yr (Pierre Bettilleni) See Sudhir’s Poster

31. Velocities relative to India measured from GPS (1995-2000) (Bollinger et al, JGR, 2004)

32. Interseismic deformation can be modelled from a fully Locked Fault Zone rooting into a creeping zone Locked Fault Zone (Laurent Bollinger) See Sudhir’s Poster

33. The locked fault zone can be delineated from background seismicity. (Bollinger et al, JGR, 2004)

34. Evidence for a strong topographic control on the seismicity pattern and on the state of stress. Seismicity cut-off (thrust events) occurs for a ‘critical’ elevation of 3500m. See Sudhir’s Poster

35. The effect of topography on CFS due to interseismic strain implies low deviatoric stresses at seismogenic depth (less than 35 Mpa) and hence a low friction on the MHT (around 0.1) See Sudhir’s Poster

36. He zircon ages

37. Modeling of the age elevation relationship Exhumation rate of ~ 1mm/yr

38. Compatibility with thermo-mechanical models

40. Comparing interseismic and co-seismic ground displacement (T=250yr) Downdip limit of Locked Fault Zone, width  60km (Dominguez et al, 2002) Task 3 :Geodesy and seismic cycle model