Seismic Reflection Imaging of the Tucson Basin and Subsurface Relations Between the Catalina Detachment System and the Santa Rita Fault, SE Arizona

Industry seismic reflection data collected in SE Arizona in the 1970's imaged the structure of the Tucson basin, the low-angle Catalina detachment fault, and the Santa Rita fault. Recent reprocessing of these data, including detailed near-surface statics compensation and modern event-migration techniques, have served to better focus the subsurface images. The Tucson basin occupies an area of approximately 2600 km² and is bounded to the northeast by the Catalina-Rincon metamorphic core complex and to the south by the Santa Rita Mountains. The basin is characterized by an apparent half-graben structure down dropped along the eastern side and filled with up to 3700 m of Oligocene to recent volcanic and sedimentary rocks. In the northern portion of the basin, the gently-dipping ( ∼30 degrees) Catalina detachment fault is imaged from the western flank of the core complex dipping to the southwest beneath the Tucson basin. The detachment surface is evident to several seconds two-way-time in the seismic data and is characterized by broad corrugations parallel to extension with wavelengths of tens of kilometers. In the southern portion of the basin, the Santa Rita fault is imaged at the northwest side of the Santa Rita Mountains and dips ∼20 degrees to the northwest beneath the Tucson basin. Large, rotated hanging-wall blocks are also imaged above both the Catalina detachment and Santa Rita faults. While the Catalina detachment fault is no longer active, geomorphic analysis of fault scarps along the western flank of the Santa Rita Mountains supports recent (60-100 ka) movement on the Santa Rita fault. Preliminary results indicate that the Santa Rita fault terminates against the Catalina detachment fault beneath the central basin, suggesting that the recent movement observed on this fault may be, in part, a reactivation of the older fault surface.