The nature of Earth's correlation wavefield: late coda of large earthquakes

• Published in: Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
• Main Authors: Kennett, Brian, Pham, Thanh-Son
• Format: Article in Journal/Newspaper
• Language: English
• Published: Royal Society of London
• Subjects: seismology; correlation wavefield; earthquake coda; body waves; Seismological Facilities for the Advancement of Geoscience and EarthScope
• Online Access: http://hdl.handle.net/1885/255800; https://doi.org/10.1098/rspa.2018.0082; https://openresearch-repository.anu.edu.au/bitstream/1885/255800/3/01_Kennett_The_nature_of_Earth%2527s_2018.pdf.jpg

The seismic correlation wavefield constructed from the stacked cross-correlograms of the late coda of earthquake signals at stations across the globe provides a wealth of observed pulses as a function of inter-station distance. The interval from 3 to 10 h after the onset of major earthquakes is employed for the period range from 15 to 50 s. The observations can be well matched by synthetic seismograms for a radially stratified Earth. Many of the correlation phases have similar time behaviour to those in the regular wavefield, but others have no correspondence. All such correlation phases can be explained by the interaction of arrivals with a common slowness at the each of the stations being correlated. Using a generalized ray description of the seismic wavefield, the time-distance behaviour of these correlation phases arises from differences in accumulated phase on different propagation paths through the Earth. Distinct arrivals emerge from the correlation field when there are many ways in which combinations of seismic phases can arise with the same difference in propagation legs. The constituents of the late coda are dominated by steeply travelling waves, and in consequence features associated with multiple passages through the whole Earth emerge distinctly, such as high-order multiples of PKIKP. IRIS Data Services are funded through the Seismological Facilities for the Advancement of Geoscience and EarthScope (SAGE) Proposal of the National Science Foundation under Cooperative Agreement No. EAR1261681. T.S.P. is supported by an ANU PhD Scholarship