A SEISMIC INVESTIGATION OF CRUST AND UPPER MANTLE STRUCTURE BENEATH THE ZAGROS MOUNTAINS AND THE SOUTHERN AND EAST AFRICAN PLATEAUS

Open Access
Author:
Adams, Aubreya Nicole
Graduate Program:
Geoscience
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
April 02, 2010
Committee Members:
  • Andrew Arnold Nyblade, Dissertation Advisor
  • Andrew Arnold Nyblade, Committee Chair
  • Charles James Ammon, Committee Member
  • Sridhar Anandakrishnan, Committee Member
  • Derek Elsworth, Committee Member
Keywords:
  • Zagros Mountains
  • tomography
  • surface waves
  • plume
  • African Superplume
  • Africa
  • seismology
  • southern Africa
  • East Africa
Abstract:
This thesis addresses crustal and upper mantle structure in three regions in and around the African Superswell: the Zagros Mountains, southern Africa, and the East African Plateau, each representing a different tectonic regime. In the Zagros Mountains of southwestern Iran, source mechanisms for six moderate-sized earthquakes are investigated using a combination of moment tensor inversion and depth phase analysis. The six earthquakes that are studied were reported in global earthquake catalogs as having lower crustal or upper mantle source depths, but upon further study, it was found that all six nucleated within the upper crust. This finding contributes to a growing number of studies indicating that seismicity in the Zagros Mountains is limited to the upper crust. In both southern and eastern Africa, upper mantle structure was investigated to evaluate the thermal state of the upper mantle and implications for the source of uplift in each area. Rayleigh wave phase velocities were measured for these regions using a two plane wave approximation method and were then inverted for a quasi-three dimensional shear wave velocity model. In southern Africa, it was found that the lithospheric lid structure and the sublithospheric velocity reduction for the Kaapvaal Craton is comparable to the upper mantle structure beneath other Archean Cratons. Thus, little seismic evidence was found of an upper mantle thermal anomaly sufficient to support high elevations in that area. In East Africa, evidence was found for a broad thermal anomaly across the study region that extends from the base of the lithosphere into the transition zone. This anomaly is larger than previous studies have indicated and its presence and size imply a possible connection to the African Superplume.