FEASIBILITY OF IMAGING PALEOSEISMOLOGICAL FEATURES WITH HIGH RESOLUTION SEISMIC REFLECTION PROFILING: A MODELING STUDY

Cross sections of trenches dug across active faults for paleoseismicity studies were digitized to provide models for computation of synthetic, high-resolution seismic reflection responses to determine which of the salient features could be imaged and recognized. The sample trenches, approximately 15 meters wide by 5 meters deep, were selected from extensional, compressional, and strike-slip environments. Relevant soil properties were drawn from published laboratory and field studies of analogous materials. Seismic acquisition parameters were chosen to represent both current and plausible future capabilities. Under favorable geological conditions and near the limits of present instrumental capabilities, the location and geometry of typical trench-scale faults are identifiable from the synthetics. Related features, such as colluvial wedges associated with both normal and thrust faults, are also evident on the synthetics, suggesting that seismic reflection profiling could guide borehole placement for dating. Other representative paleoseismic features recognizable on these synthetic seismic sections include a channel offset of 2.5 meters at a strike-slip fault, 0.2-meter wide liquified sand dykes, and a 0.2-m thick horizontal intrusion of liquefied sand. Although seismic reflection techniques are unlikely to replace paleoseismic trenching methods, the modeling presented here suggests that seismic imaging can significantly guide or augment a trenching program by non-invasively imaging relevant subsurface features.