A Case Study in Developing a 3-D Map of the Shallow Faulting and Structures Beneath Springville, Utah-An Aid to Future Building, Zoning Ordinances, and Emergency Planning

摘要

A west-dipping normal fault known as the Springville Fault branches off from the Wasatch Fault and runs through Springville, Utah, 65 km south of Salt Lake City. Parts of this fault can be mapped from surface expression, but due to erosion and/or cultural activity, other portions are concealed. There are also other unmapped concealed faults associated with the Springville Fault that need to be mapped from geophysical data. Future seismic activity along the Springville Fault could result in extensive property damage and loss of human life. The subsurface expression of the Springville Fault, other associated concealed faults, and flexures were mapped using dose-order gravity and magnetic surveys. The associated subsurface map provides a better understanding of potential earthquake hazards, as well as possible sources of numerous springs in the study area. The gravity data were used as the primary data set, but magnetic data provided supporting information in areas where cultural noise was minimal. The residual gravity and reduced magnetic data were used to generate models of the subsurface. Ambiguities in the models were reduced by (l)using data from surface observations; (2)incorporating data from previous geophysical surveys; (3)integrating the gravity and magnetic data wherever feasible; and (4)correlating the models along numerous profiles. The modeled traverses and 3-D interpretation of the data indicate that the Springville Fault extends a considerable distance to the north and to the south of any existing surface expression. In addition, the data indicate the presence of three or more other concealed faults associated with the Springville Fault All of these faults represent potential earthquake threats, most likely producing surface rupture. The 3-D map of shallow subsurface structures provides additional understanding about the structure of the Springville fault system and associated potential earthquake hazards.