The Malawi Active Fault Database: An Onshore-Offshore Database for Regional Assessment of Seismic Hazard and Tectonic Evolution

Abstract

We present the Malawi Active Fault Database (MAFD), an open-access (https://doi.org/10.5281/zenodo.5507190) geospatial database of 113 fault traces in Malawi and neighboring Tanzania and Mozambique. Malawi is located within the East African Rift's (EAR) Western Branch where active fault identification is challenging because chronostratigraphic data are rare, and/or faults are buried and so do not have a surface expression. The MAFD therefore includes any fault that has evidence for displacement during Cenozoic East African rifting or is buried beneath the rift valley and is favorably oriented to the regional stresses. To identify such faults, we consider a multidisciplinary data set: high-resolution digital elevation models, previous geological mapping, field observations, seismic reflection surveys from offshore Lake Malawi, and aeromagnetic and gravity data. The MAFD includes faults throughout Malawi, where seismic risk is increasing because of population growth and its seismically vulnerable building stock. We also investigate the database as a sample of the normal fault population in an incipient continental rift. We cannot reject the null hypothesis that the distribution of fault lengths in the MAFD is described by a power law, which is consistent with Malawi's relatively thick seismogenic layer (30–40 km), low (<8%) regional extensional strain, and regional deformation localization (50%–75%) across relatively long hard-linked border faults. Cumulatively, we highlight the importance of integrating onshore and offshore geological and geophysical data to develop active fault databases along the EAR and similar continental settings both to understand the regional seismic hazard and tectonic evolution.