Elements of Lithospheric Structure Beneath Taiwan from Seismic Reflection and Teleseismic Conversion Recordings during Project TAIGER

Recordings of explosive sources collected during both the test phase and main phase of land seismic surveying during Project TAIGER exhibit near-vertical reflections from intracrustal interfaces as well as the Moho beneath western Taiwan. A least some of the intracrustal events may correspond to basal decollements into which foreland thrusting is rooted; however these markers cannot be traced with any confidence beneath the central range. The Moho reflections correspond with converters mapped by sP and Ps receiver functions computed from TAIGER broadband stations. sP receiver functions were also used to estimate lithospheric thickness, but the results are ambiguous due largely to the short deployment period for these instruments. The most prominent observation from the land source recording is an anomalously strong reflector observed on two distinct shots in NE Taiwan. This "bright spot" is similar to amplitude anomalies encountered by deep seismic surveys elsewhere and usually associated with fluids at mid-crustal depths (in this case ca 20 km). Either magma, water or both may be involved. The location of the bright spot beneath the Central Range adjacent to the Lian plain suggest that it may result from partial melting triggered by exhumation, or alternatively to melting associated with propagation of the Okinawa trough at depth into NE Taiwan proper.