Integration of the NEES T-Rex Vibrator and PASSCAL Texan Recorders for Seismic Profiling of Shallow and Deep Crustal Targets

Abstract

In September 2004, Stanford University and the University of Texas (UT) at Austin collected crustal reflection and refraction data with the Network for Earthquake Engineering Simulation (NEES) tri-axial (T-Rex) vibrator in two separate surveys: (1) a 40-km “crustal-scale” profile in the Black Rock Desert and Black Rock Range, NV; and (2) a 16-km “high-resolution” basin imaging profile in Surprise Valley, CA (figure 1). Both experiments were completed at the northwestern margin of the Basin and Range Province, embedded in a larger, 300-km wide-angle refraction line recorded by an Incorporated Research Institutions for Seismology (IRIS) PASSCAL transportable array (Lerch et al. 2007). Our broad goals were to test the feasibility of the T-Rex in crustal-scale applications with existing IRIS-PASSCAL equipment and to augment our refraction data with structural information. T-Rex (figure 1, inset A), acquired by NEES-UT Austin in 2002, is a 29,000-kg buggy-mounted vibrator with a tri-axial mass, capable of generating P , SV , and SH waves (for details on T-Rex, see Stokoe et al. 2004). Given its relatively large mass, and hence its high peak force output of 267 kN for frequencies between 12 and 180 Hz, T-Rex is a potentially viable source for single-vibrator crustal profiling compared to COCORP (Consortium for Continental Reflection Profiling) profiling with five vibrators, each producing ≤ 120 kN (Allmendinger et al. 1987). Additionally, T-Rex's ability to produce shear waves may open the door to a variety of exciting research avenues, from Vs velocity modeling of basin sediments for earthquake hazard analysis to the ability to record mid- and lower-crustal shear-wave anisotropy resulting from regional tectonic deformation. The integration of T-Rex into our crustal-scale and high-res profiles revealed its strengths and limitations as well as the logistic and quality-control problems associated with recording continuous vibrator data with PASSCAL's transportable instrumentation. Our attempts …