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Taiwan has resulted from on-going collision between the Luzon volcanic arc, the continental margin of south China, 5 to 7 Myr ago, and intervening continental fragments. In the north, the island is submitted to horizontal extension as the orogen transfers to the hanging wall of the Ryukyu subduction system. To the south, subduction is still going on along the Manilla trench. Taiwan is an exceptional active orogen, due to its extremely rapid rates of deformation and high erosion rates. A dense array of survey-mode and continuous GPS stations monitor tectonic deformation across the entire island and landforms and stratigraphy provide an exceptional source of information on ongoing lithospheric deformation. In addition, neotectonic deformation was illuminated by the Mw 7.6 Chichi earthquake of 1999, which ruptured the Chelungpu thrust fault under the Western Foothills.

Taiwan is therefore an exceptional area to investigate mountain building processes over time scales ranging from the seconds of an earthquake to millions of years of an orogeny. It is also a ultimate place to investigate both the transition from subduction to collision and from collision to collapse.

 Among the key scientific questions to be addressed :

click to go to read more How is the 80 cm/yr convergence rate across Taiwan accommodated by crustal and lithospheric deformation? (in other terms, what is the partitioning of deformation from the western foothills of the central range to the Longitudinal valley?)  and what are the physical factors controlling this partitioning?
click to go to read more What proportion of the deformation is absorbed by large recurring earthquakes or aseismic deformation (ductile flow or possibly slow events)? and what are the physical factors controlling?
click to go to read more Is the interseismic deformation stationary or does it vary with time? (lateral variations may actually reveal temporal changes during the seismic cycle) ?
click to go to read more Does the critical brittle taper model really apply to explain the mechanics of mountain building in Taiwan?
click to go to read more What is the role played by deep seated upper mantle  processes?

The TO effort will first focus on the determination of the kinematics of the deformation across the range and how it varies along strike in relation to the different stage of development of the collision, or different stage in the seismic cycle. We will also work out the thermal structure taking advantage of recent technical advances (Carbonaceaous Matter Graphitisation as a quantitative tool to estimate peak metamorphic temperatures). Indeed the thermal structure is probably controlling the mechanics of the deformation on the long term as well and seismic behavior. Also we would need better constraints on the geometry of the faults at depth. By combining with geodetic information on crustal deformation during the interseismic phase, or related to Chichi co-seismic and post seismic deformation, we should be able to develop a well constrained physical model of the seismic cycle.



Funding provided in part by the National Science Foundation

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