This project is to analyze earthquake data collected after a large earthquake sequence occurred in the Malawi section of the East African Rift zone. InSAR data from the area will also be analyzed to determine how the region was affected by the earthquakes. The goal of the proposed work is to obtain a better understanding of the deformation associated with the inception and early stages of rifting of a continent.
Broader Impacts This project has a large component of international collaboration. The PIs have a strong relationship with the Malawi Geological Survey department and will host Malawi colleagues in the U.S. so they can learn earthquake relocation techniques. The PIs will also travel to Malawi to speak with various groups, and help to install the software needed for seismic analysis.
In November and December, 2009, a rare sequence of earthquakes occurred in northern Malawi’s Karonga province that is part of the Western Branch of the East African Rift system where the continent of Africa is splitting apart. The earthquakes studied in this project had devastating consequences for the population around Karonga (population about 45,000). They caused four deaths, 300 injuries and the displacement of >5000 people. The fact that the earthquakes continued for several months and grew in magnitude from November to December means that there was growing concern and anxiety among the population during the sequence. To provide insight into what faults were active during this earthquake sequence, we combine observations of seismic waves from the global seismometer network and a temporary (4 month) local network along with satellite radar images of the ground displacements. The ground deformation modeling suggests that the bulk of the deformation can be explained by a previously unknown single west-dipping normal fault beneath Karonga, with peak slip of ~1 m localized within the upper 5 km. There is no evidence for magmatic or aseismic deformation during the earthquake sequence near Karonga or the Rungwe volcanic province 70 km to the north. The locations of over 2000 aftershocks recorded between Jan-May 2010 are largely consistent with the ground deformation results. Event depths are quite shallow (generally <6 km), and show evidence of multiple fault structures. The majority of events are consistent with a west-dipping normal fault directly beneath Karonga. However, a substantial number of epicenters cluster in a east-dipping geometry in the northern extent of the active region, and additional west-dipping clusters can be discerned beneath the Lake. Given the extensive network of hanging wall faults mapped in the Karonga region, the distribution of events is strongly suggestive of multiple faults interacting, which could have implications for future earthquake hazard in the area.
