Global survey of frequency dependent attenuation

We analyze frequency-dependent attenuation of Lg waves, 1/Q(f), for numerous tectonic environments. Tectonic environments studied include: south Pacific oceanic subduction zone near Samoa, the oblique subduction zone off Hispaniola, two continental-oceanic subduction zones in Chile and Alaska, the continental-continental collision zone of the Tibetan Plateau, stable continental interior regions of the central US and Colorado Plateau, the eastern US passive margin and the active margins of the western US. Lg propagates with a group velocity of about 3.5 km/s, the average crustal shear wave velocity. This wave is commonly observed as the dominant phase on high-frequency seismograms at regional distances and is generated by a superposition of higher-mode surface waves or multiply-reflected shear energy in a crustal waveguide. Consequently, Lg provides a good measure of path-averaged crustal properties, such as shear-wave velocity and attenuation. Lg is particularly useful since its amplitude is sensitive to lateral heterogeneity in the crust due to varying tectonic environment. In this global survey we observe that Lg attenuation is generally higher for tectonically active regions than for stable continental interiors. Q(f) is an important physical parameter and is required for a variety of USGS research projects such as the simulation of strong ground motion and seismic network magnitude detection threshold modeling.