RECEIVER STRUCTURE BENEATH THE SOUTHERN MOJAVE BLOCK, CALIFORNIA

An inversion of a receiver function recorded at Lawrence Livermore National Laboratory Nevada Test Site Network Station LAC reveals a range of 1-D velocity structures that are consistent the observed waveform. The shear-velocity structure southeast of LAC is relatively simple, consisting of an approximately 30 to 34 km thick crust. All models contain relatively sharp crust-mantle boundaries with a change in velocity from about 3.5 km / sec to approximately 4.6 km / sec over a depth range of 4 to 6 kilometers. The range of models can be roughly divided into two groups that differ mostly in the mid-to-lower crust. The first model of the earth structure contains a large low-velocity zone in the middle and lower crust (shear-wave velocities as low as 2.8 km/sec), the second model contains nearly constant velocities (approximately 3.5 km/sec) through the middle-to-lower crust. In contrast with the simplicity of the southeast receiver function, the receiver functions corresponding to the northwest and southwest show the influence of lateral velocity heterogeneity and can at best be discussed qualitatively.