ADVANCES IN DATA-RICH BALANCING FOR DEEP INSIGHT, WITH EXAMPLES OF RAPIDLY GROWING STRUCTURES IN WESTERN TAIWAN

The classical balancing measurements of area of relief and bed-length that were pioneered by Chamberlin, Laubscher and Epard & Groshong provide a straightforward route to rich structural insight when they are combined with new concepts and rich data from seismic imaging, velocity analysis, well logs and, in the case of active structures, geodesy. These new methods (Gonzalez-Mieres & Suppe 2006, 2010) yield reflector-by-reflector measurements of total shortening, shortening history, and components of shortening, including flexural, pure shear, simple shear and horizontal compaction. The potential sources of error include distortions of imperfect seismic imaging, such as incorrect migration, and failure to properly distinguish stratigraphic and structural thickness variations, but new methods and better data overcome these issues. We illustrate the application of these methods and concepts with two actively growing examples from western Taiwan: [1] Tungshih anticline which is a complex detachment fold that grew by ~10-12 m in the 1999 M=7.6 Chi-Chi earthquake by a combination of kink-band migration and limb rotation and [2] Tainan anticline which is shear fault-bend fold growing in creep by limb rotation above the frontal backthrust of SW Taiwan, currently shortening at ~15 mm/y.