Lg wave Q tomography in Central America

Abstract

The lateral variation of Lg wave spectral attenuation in Central America was studied through tomographic inversion at various frequencies between 0.5 and 5 Hz, separately for each frequency. The input data set consisted of 558 travel paths recorded on short-period and broadband seismic stations in the region. The size and quality of the data set were sufficient to resolve significant lateral variation in the Lg wave quality factor QLg. The average dependence of QLg with frequency was found to be QLg (f) = 182f0.84, corresponding to high attenuation. Low QLg values in the Nicaraguan Depression presented the most significant variation from the average. The strong attenuation of Lg waves in the Nicaraguan depression was also observed in the visual analysis of the seismograms. This observation is possibly explained by the near-surface low-velocity layers in the depression. Low QLg values were also found along the chain of volcanos due to increased scattering and partial melting beneath the volcanic belt. This study is the first attempt to determine QLg for Central America and to provide knowledge on attenuation of Lg waves needed for the prediction of ground motion during future earthquakes.