b'Education matters Theses in geophysics completed in 2022PhD theses uncovers an inverse correlation betweenSeismic coda waves are the late part the subducting slab depth and the upperof the seismic energy generated by Mohd Zuhair, Monash University: Sundaplate shortening and thickening in theearthquakes. Global coda correlograms convergent margin deformation acrossSumatra subduction zone. In contrast withare constructed by cross-correlating and timescales the NW nearby Andaman domain, wherestacking seismic event late coda records a short slab explains backarc extensionthat are noisy and seemingly useless, but and a thin upper plate, and also comparingthey exhibit many prominent features with the SE Java subduction, where asensitive to the Earths internal structure. long and deep slab explains a thickenedThus, the coda correlation rises as a upper plate, in Sumatra, a short slabnew paradigm in global observational interestingly correlates with compressionseismology. As a new category of and thickening of the upper plate. Afterobservation, the correlation features, extensively inspecting the geophysicalif interpreted correctly, can provide data supporting such an inverse correlationnew information about the Earths and in Sumatra, we use 3D numerical modellingplanetary interiors.to evaluate the effect of a slab-step on the strong interplate coupling and thickeningHow to accurately utilise seismic event in the Sumatran upper plate. We concludecoda correlations, for instance, in that trench parallel slab-pull exerted by theglobal coda correlation tomography, long slab in the Java subduction can forcehas been controversial and unresolved. convergence along the Sumatra segment,Some attempts treat coda correlations explaining the strong coupling and upperas reconstructed seismic waves, which plate deformation and are well-matchedis on a par with methods developed in with present-day observational data, i.e.ambient-noise correlations, for they share seismicity. similar data processing and computation Major earthquakes occur along theroutines. However, that introduces interface between the down going andThe signature of the forced convergenceerroneous interpretation because upper plates, known as megathrust.is also investigated in the subductingtheoretical analyses have demonstrated Previous studies highlighted the roleslab deformation along the Sumatrafundamental differences in the formation of several subduction parameters inmargin. The time-series earthquakemechanisms of coda correlations and controlling such seismicity. Most of theseanalyses show increased compressiveambient noise correlations. Therefore, studies tested the subduction parametersdeformation in the subducting slab atwe need a solution, a correct approach, in a two-dimensional framework.shallow depths ( 70 km) and the upperto allow us to use a massive amount of Such approaches fail to reconcileplate after the 2004 great earthquakecoda correlation observables to increase the megathrust seismicity with thein the Sumatra domain. Strikingly, aconstraints on the Earths interior.deformation observed along subductioncumulative increase in the Java slab margins, invoking the role of large-scale,deformation at deeper depths ( 70My PhD study consists of theoretical three-dimensional subduction dynamicskm) correlates with and precedes largeanalyses, method developments, in understanding seismotectonics of theSumatra megathrust earthquakesand applications for utilising seismic subduction margins. This thesis aims(M w 7.0) in the period coveringevent coda correlations to image to provide a new 3D seismotectonicboth pre-and post-great earthquakes.the Earths and planetary interiors. model for the Sunda subduction margin,The forced tectonic coupling by theWe first conduct comprehensive reconciling the link between the large- neighbouring deep slabs on the shallowanalyses to quantitatively dissect scale subduction dynamics, interplatesubduction margins may play a criticalcoda correlations for their formation coupling and margin deformation acrossrole in defining stress conditions alongmechanism. The analyses reveal the timescales, and speculating on thethe high seismic potential segments. mathematical relationship between inferences of the megathrust seismicity. coda correlations and the Earths Sheng Wang, Australian Nationalinternal structure. Based on that, we We study the Sunda subductionUniversity: Seismic-event coda correlationbuild a novel framework toward global margin by incorporating geophysicalimaging of the Earths and planetarycoda correlation tomography. We verify observables, numerical modelling results,interiors the new framework in experiments and earthquake catalogues. The oceanicand compare it with the method based Indo-Australian plate subducts beneathon the assumption of seismic wave the Sunda upper plate, causing marginreconstruction. We illustrate significant deformation across timescales and majorinaccuracy in tomographic images can earthquakes. We show consistency in slabarise if coda correlations are treated as geometry and upper plate deformationreconstructed seismic waves. Then, in an since Cenozoic by integrating gravityapplication, we provide a new class of modelling, global strain rate andobservation for inner-core shear-wave crustal thicknesses model analysis, andanisotropy utilizing coda correlations in tomography driven subduction historythe new framework. We find that inner-with plate reconstruction. The studycore shear waves travel faster by at least 29 PREVIEW DECEMBER 2022'