Local seismo-acoustic waves, but from the other side of the world

Abstract

It is well understood that shallow seismic events near the Earth surface couple readily to the atmosphere where they can be observed as infrasonic waves. Typically, the observed sequence of infrasound arrivals includes a first arrival (i.e., “local infrasound”), which corresponds to the coupling of seismic body and surface waves to atmospheric infrasound, near an infrasound array. Under favorable atmospheric ducting conditions, additional coupled arrivals arrive later in time, having propagated throughout the (slower) atmosphere for part of the propagation path. In this presentation, we show that seismo-acoustic waves can couple from very deep earthquakes that occur on the other side of the world. This is demonstrated using seismo-acoustic observations from a M8.2 earthquake in Fiji that generated infrasound throughout Europe. Our analysis shows that various phases that reflected off the inner core boundary (ICB) were detected as pressure waves. This suggests that signals that are detectable on microbarometer arrays may have a surprising origin.