GEOLOGIC MAPPING: THE FOUNDATION TO GREATER GEOLOGIC UNDERSTANDING, AN EXAMPLE FROM SUNSHINE VALLEY, NEW MEXICO

Geologic mapping provides a four-dimensional data set that is the foundation for credible geologic interpretations and the development of site-specific topical research. Within Sunshine Valley, New Mexico, regional geologic mapping documented geomorphic relationships that more precisely defined and quantified tectonic activity rates that had been derived previously from morpho-metric analyses (e.g., fault-scarp regression lines, valley floor vs. valley height ratios, mountain-front sinuosity, and mountain-front faceted spur analyses). The range-front is characterized by relict features created by higher tectonic activity rates during previous tectonic cycles, leading to misinterpretation in previous seismic hazard analyses. In addition, geologic mapping coupled with regional geomorphic activity rates show relationships that discredit localized morpho-metric analyses. Within this basin, geologic mapping provided a more accurately defined paleoseismic record than fault trench investigations and explained both long-term (>100 k.y.) temporal and spatial faulting migration patterns. Due to localized erosion rates and processes, fault scarps and amount of surface offset can be misleading when the age of the deposit and/or landform is not properly defined. Only detailed, regional mapping can accomplish this. Lastly, geologic mapping discovered and illuminated structural fabrics that enabled a more geologically sound interpretation of geophysical data and the kinematic evolution of the basin. Acquired aeromagnetic data displayed a chaotic distribution of anomalies. By drapping the mapped regional structural fabric expressed at the surface over the aeromagnetic data, the anomalies in the subsurface could be more accurately recognized and defined.