An estimate of shear-wave Q of the mantle wedge in Mexico

Abstract

We utilize earthquake recordings at two broadband seismographs located on the coast of the Gulf of Mexico to estimate Q of the mantle wedge. From the data at a station situated in the Laguna Verde nuclear power plant (LVIG), about 100 km northwest of Veracruz, and at the eastern edge of the Mexican Volcanic Belt, we estimate an upper bound of shear-wave Q of the mantle wedge, Q(f) similar to 120f(0.75) (0.1 <= f <= 10 Hz), as compared with Q(f) = 251 f(0.58) for the average path through subducted slab and continental lithosphere. Curiously, the estimated Q of the mantle wedge at station SCIG, which is located on the Yucatan Block, is about the same as the average Q in southern Mexico. There are several possible explanations for the difference: (1) very few recordings at SCIG, (2) a site effect at SCIG masking the effect of low Q of the mantle wedge, and (3) relatively high-mantle Q beneath the Yucatan Block. The third possibility is supported by surface-wave tomography that reveals a thick, cold, mantle lithosphere below the Yucatan Block and near absence of mantle lithosphere in the backarc region of central Mexico. A higher density of seismographs along the gulf coast is needed to resolve these issues. Our study predicts diminished ground motions at the Laguna Verde nuclear power plant if the seismic waves pass through the mantle wedge or traverse below the Popocatepetl or Orizaba volcanoes.