Improving seismic resolution of outermost core structure by multichannel analysis and deconvolution of broadband SmKS phases

The presence of a thin (≤12 km) layer atop the outermost core has important implications for the geodynamic and geomagnetic nature of the Earth, but detecting such a layer is difficult. SmKS seismic phases, which traverse the mantle as an S-wave and reflect m − 1 times from the underside of the core–mantle boundary (CMB), offer a means to test proposed models since they are extremely sensitive to the velocity structure of the outermost core. To improve seismic resolution in this region, we have developed and validated a modified vespagram (slant stack) technique that makes use of phase-independent amplitude-envelope traces. Confidence limits on arrival-time and slowness estimates are obtained by bootstrap resampling. In order to mitigate the effects of waveform complexity and facilitate comparison between observed and modeled waveforms, we have used a simple deconvolution method similar to techniques used in exploration seismology. We have applied these methods to high-quality broadband recordings of three deep-focus earthquakes recorded by seismic arrays in Canada. Some of our measurements have turning depths