地震及活斷層研究-(孕震帶構造)─台灣西南海域活斷層的調查與孕震構造研究

This 2-year research project intends to
investigate the active fault systems and their
seismogenic properties in the area offshore
southwestern Taiwan. The preliminary
results from the first year study are reported
here.
In the active fault investigation,
high-resolution bathymetry map of the study
area has been compiled which reveal
detailed fault systems distribution. Unique
structural pattern has been observed that
shows the effect of the continental margin
crust to the development of the accretionary
wedge near Taiwan. Many topographic
lineaments have been developed on the
frontal portion of the accretionary wedge off
southwestern Taiwan. These lineaments
could be developed due to the tectonic
escape of the southwestern Taiwan block
during the arc-continent collision processes.
The different nature of the continental
margin crust (from oceanic crust in the south
to continental crust in the north) also
contributes to the unique structural pattern
observed.
Two coring cruises have been
conducted to collect pore waters of the sea
floor sediments in the hope to find chemical
evidence of fluid seepages from deep along
active fault planes. However, probably due
to inadequate penetration depths of the core
samples, or due to the deviation of the
coring sites from the active fault outcrops,
geochemical signatures of the pore fluid
samples are similar to that of seawater.
Seismic reflection profiles running across a
major out-of-sequence thrust, however,
show strong fault-plane reflections that
usually indicate the existence of fluid along
fault planes. Further investigation of this
major out-of-sequence thrust is planned in
the 2nd year study of this project. An IODP
drilling proposal or letter of intend will be
submitted to IODP in the 2nd year also for
drilling consideration.