Structural, geodetic and seismological evidence for tectonic escape in SW Taiwan

Recent structural, geodetic and seismological data in SW Taiwan are analyse d and discussed in terms of present-day tectonic escape occurring in respon se to the active N100 degrees collisional shortening. The escaping area cor responds to the onland extension of the Manila accretionary wedge; this reg ion comprises a theologically weak, thick muddy cover which is decoupled fr om the underlying basement by a decollement and which deforms mainly by ase ismic creep. It is separated from the northern actual collisional area by a major WNW- to NW-trending structural and kinematic transition zone oblique to the structural grain of the belt, the Chishan Transfer Fault Zone. Geod etic data are further used to define several poorly deforming blocks underg oing nearly uniform displacement velocities and bounded by kinematic discon tinuities that fit the major faults, and to determine the present-day acros s-strike and along-strike motions on these major faults. Although direct on land structural evidence of tectonic escape is poor, reconstruction of Quat ernary paleostress patterns demonstrate that this escape probably began dur ing the late Pleistocene, later than in northeastern Taiwan as a result of the southward migration of the collision through time. Offshore structural data help to constrain the geometry and the southern extension of the escap ing blocks. Finally, a tentative model of lateral extrusion in SW Taiwan is proposed. (C) 2001 Elsevier Science B.V. All rights reserved.