We present on- and offshore structural data from the Nazca-Panama plate boundary zone in the Gulf of Chiriquí and surrounding onshore areas of southwest Panama. Major offshore structures interpreted on multichannel seismic profiles from the Gulf of Chiriquí include Cébaco basin complex, a series of northeast-striking, Plio-Pleistocene half-grabens, and Montuosa basin, an asymmetric Plio-Pleistocene sag basin associated with a major strike-slip fault. We interpret Cébaco basin complex as a pull-apart basin between two major, left-lateral strike-slip faults that accommodate oblique motion between the Nazca plate and the mainland of southwestern Panama. Interpretation of regional seismic stratigraphic data indicates that the...