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
||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?
||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
||Is the interseismic deformation
stationary or does it vary with time? (lateral variations may actually
reveal temporal changes during the seismic cycle) ?
||Does the critical brittle taper
model really apply to explain the mechanics of mountain building
||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.