ANALYZING SHALLOW FAULTING AT A SITE IN THE WASATCH FAULT ZONE, UTAH,USA, BY INTEGRATING SEISMIC, GRAVITY, MAGNETIC, AND TRENCH DATA

Gravity, magnetic, and seismic surveys were conducted across the Wasat ch fault zone east of Springville, Utah, near the mouth of Hobble Cree k Canyon. The geophysical data were acquired, processed, and interpret ed to determine possible locations of larger [total offset greater tha n 6 ft (1.8 m)], shallow normal faults within the fault zone. Interpre tations of the individual data sets were integrated to help eliminate spurious readings and to strengthen the interpretations. Visual method s of integration, along with computer modeling, were chosen for this s tudy. Furthermore, the geophysical data were correlated and integrated with available trench data and surface data. In addition to verifying locations of known faults, the geophysical surveys detected numerous possible additional faults not previously mapped. Of particular intere st is a newly discovered graben structure near the southern end of the site, where building of new homes has recently been proposed. New str uctural information about fault densities and styles was also determin ed from the surveys. The fault concentration for this site is 1.3 faul ts/100 ft (30.5 m), or one fault per 77 ft (23.5 m). Interpreted antit hetic faults at the Hobble Creek site account for 65% of the total, wh ile synthetic faults account for 35% with respect to the main fault st rand. Information derived from this study should be useful during plan ning and development of areas within the Wasatch fault zone. The chara cteristics of subsurface deformation can be used to gain a better unde rstanding of the potential for surface rupture at a given site. This i s also useful in planning appropriate site development and remedial me asures to help mitigate hazards associated with large-magnitude earthq uakes.