Seismic identification of basement reflectors: The Bagdad Reflection Sequence in the Basin and Range Province—Colorado Plateau Transition Zone, Arizona

Although seismic reflection profiling has contributed greatly to our knowledge of the crust and upper mantle, it is often difficult to unambiguously identify the geologic origin of reflections. This is particularly true of intrabasement reflectors whose geometry and origin we need to know in order to understand tectonic processes operating in the crust. We present synthetic seismogram modeling of recently collected P and S wave seismic reflection data which suggests that the intrabasement Bagdad reflectors in west central Arizona are intrusive mafic sheets. The identification is based on the determination of the phase (positive polarity) and amplitudes of the reflected arrivals. If the Bagdad reflectors are Cenozoic age mafic sheets, they may be the product of rapid intrusion into an area of weak extension where the principal stresses are approximately equal.