Passive seismic imaging of a craton edge – Central Australia

Abstract

Passive seismic recordings of teleseismic P wave arrivals and their immediate coda along a dense profile of stations can be used to image the reflection structure beneath the profile. The process exploits the autocorrelation of the seismic signals that extracts the reflection response from the transmitted signals recorded at the surface, which can be migrated to provide a depth image. This common reflection point (CRP) imaging exploits the same portion of the seismic record used in receiver function studies, but is much less influenced by multiple problems in the presence of sediments. This style of passive seismic imaging is applied to a dense line of 68 stations at 3.5 km spacing at the northern edge of the Gawler Craton in South Australia in the MAL experiment. With nine months of passive seismic monitoring it has been possible to image fine-scale structural variations throughout the lithosphere. There is a strong variation in crustal thickness as the MAL profile crosses the inferred location of the craton edge under sedimentary cover. A transitional zone between crust and mantle can be identified that extends beneath the receiver function Moho, pinching out gently at the craton edge. The CRP imaging reveals distinct reflectivity in the lithospheric mantle with horizontal scales of 10–30 km, and vertical scales of no more than a few kilometres. The character of this reflectivity appears to change across the craton edge. There are indications of a semi-continuous mid-lithosphere discontinuity at around 90 km depth.