15:00 〜 15:15
[SSS08-06] Investigating shallow structures beneath the Kalahari craton and surrounding tectonic regions by inversion of receiver functions harmonic components.
キーワード：Shallow structure, Kalahari craton, Dipping and anisotropic structures, Southern Africa
The Kalahari craton, which makes up the majority of the southern African crust, consists of Archean cratons bifurcated and surrounded by deformational zones. The nature of its seismic structure at shallow depths can reveal associated tectonic and depositional processes and provide insights into the crustal evolution of the region. However, a lot of aspects of the nature of shallow structure in and around the Kalahari craton remain largely unknown.
We attempt to define the nature of the shallow seismic structure beneath the Kalahari craton and around it by analyzing Ps receiver functions from shallow interfaces. In particular, we study the back-azimuthal variation of amplitude and delay time of the converted phases, which has been proven to be a perfect tool for detecting the presence of dipping and anisotropic structures (e.g. Shiomi & Park, 2008; Bianchi et al., 2010; Park & Levin, 2016), expected to occur in regions of tectonic deformation. By applying harmonic decomposition to the receiver functions, we constrain the presence of dipping and anisotropic structures and then apply an inversion of the harmonic components. We first demonstrate that such a technique can resolve the causative dipping and or anisotropic structure, in a theoretical case, before applying the technique to recover the shallow structure beneath the Kalahari craton region.
The resulting harmonic stacks suggest that the basement layer in the region of the Kaapvaal craton bordering the Limpopo belt dips towards the N-to-NW, while crystalline metamorphic basement beneath the Limpopo belt is uneven, with some likely plunging anisotropy in the overlying metasedimentary sequences, as well as in the metamorphosed clastic sediments and basalts of the Kheis belt. Parts of the other regions of the Kalahari craton seem to exhibit near surface scattered energy, likely due to strong heterogeneity in the overlying unconsolidated sediments at the near-surface, but a possible plunging anisotropy exists in some part of the Okavango rift zone. By performing inversion of the harmonic stacks, we can quantify the crustal velocities, the magnitudes and orientations of dip and anisotropy in the shallow crust beneath the Kalahari craton.
We attempt to define the nature of the shallow seismic structure beneath the Kalahari craton and around it by analyzing Ps receiver functions from shallow interfaces. In particular, we study the back-azimuthal variation of amplitude and delay time of the converted phases, which has been proven to be a perfect tool for detecting the presence of dipping and anisotropic structures (e.g. Shiomi & Park, 2008; Bianchi et al., 2010; Park & Levin, 2016), expected to occur in regions of tectonic deformation. By applying harmonic decomposition to the receiver functions, we constrain the presence of dipping and anisotropic structures and then apply an inversion of the harmonic components. We first demonstrate that such a technique can resolve the causative dipping and or anisotropic structure, in a theoretical case, before applying the technique to recover the shallow structure beneath the Kalahari craton region.
The resulting harmonic stacks suggest that the basement layer in the region of the Kaapvaal craton bordering the Limpopo belt dips towards the N-to-NW, while crystalline metamorphic basement beneath the Limpopo belt is uneven, with some likely plunging anisotropy in the overlying metasedimentary sequences, as well as in the metamorphosed clastic sediments and basalts of the Kheis belt. Parts of the other regions of the Kalahari craton seem to exhibit near surface scattered energy, likely due to strong heterogeneity in the overlying unconsolidated sediments at the near-surface, but a possible plunging anisotropy exists in some part of the Okavango rift zone. By performing inversion of the harmonic stacks, we can quantify the crustal velocities, the magnitudes and orientations of dip and anisotropy in the shallow crust beneath the Kalahari craton.