Influence of Inherited Structures on Segmentation and Linkages of Two Subparallel Faults in Southern Malawi Rift

Abstract

Important questions remain about the role preexisting structures play on the development of magma poor rifts. The influence of preexisting pervasive upper crustal fabrics on the development and evolution of faults is poorly understood. In Malawi two large (>100 km) synthetic normal faults the Chirobwe-Ncheu and Bilila-Mtakataka faults, were analyzed for the effect of pervasive fabrics on fault segment and linkage. We used Shuttle RADAR Topography Mission Digital Elevation Models (SRTM DEM) and high resolution aeromagnetic data to determine fault segmentation from both topographic displacement profiles and Source Parameter Imaging (SPI) depths. Moreover, the combination of SRTM DEM and aeromagnetic data allowed for the delineation of the upper crustal pervasive fabrics. Our results show that each fault is broadly composed of three segments. The location and orientation of the fault segments are affected by the gneissic fabrics where the foliations are perpendicular to extension direction. Furthermore the combination of the regional joints and the gneissic fabrics control the geometry of the linkage zones. The lengths and segmentation for each of these faults established by this study have an important relationship to the seismic hazard for the region. Finally, our research shows that the faults exhibit characteristics of two models of fault growth where the type of growth is modulated by the pervasive upper crustal inherited fabrics. Therefore, our work demonstrates the effects that preexisting pervasive fabrics may exert on the development, evolution, and linkage of segments in two large faults in a magma poor rift.