Propagation modeling of T-phase time series via RDOASES

Abstract

Properly situated earthquakes and explosive sources often radiate acoustic energy into the oceanic waveguide and are thereby detectable at long ranges. Details of how this energy actually couples into the ocean remain elusive. Recent development of a range-dependent version of OASES has made it possible to model acoustic propagation in range-varying, elastic environments. It has been very successful in investigating the effect of epicenter depth for T-phase excitation on a sloping bottom. The present study extends earlier work to consider time-domain characteristics of the arrival and their dependence upon properties of the source and its surrounding region. The general environment considered here is a Munk sound-speed profile and sloping bottom out to a range of 30 km, after which the bottom depth is constant. The seismoacoustic field is computed using RDOASES, and then projected onto the local mode shapes. The complex mode coefficients are propagated to a distant receiving array, where the time-domain signal is synthesized. Understanding the source excitation in terms of mode and frequency content is critical to interpreting the arrival structure. At teleseismic ranges, the dependence of group delays on mode number and frequency leads to significant time spreading of the various signal components.