Evidence From High‐Resolution Topography for Multiple Earthquakes on High Slip‐to‐Length Fault Scarps: The Bilila‐Mtakataka Fault, Malawi

Abstract

AbstractGeomorphological features such as fault scarps and stream knickpoints are indicators of recent fault activity. Determining whether these features formed during a single earthquake or over multiple earthquakes cycles has important implications for the interpretation of the size and frequency of past events. Here, we focus on the Bilila‐Mtakataka fault, Malawi, where the 20 m high fault scarps exceed the height expected from a single earthquake rupture. We use a high‐resolution digital elevation model ( 1 m) to identify complexity in the fault scarp and knickpoints in river profiles. Of 39 selected scarp profiles, 20 showed evidence of either multiscarps or composite scarps, and of the seven selected river and stream profiles, five showed evidence for multiple knickpoints. A near‐uniform distribution of vertical offsets on the subscarps suggests they were formed by separate earthquakes. These independent methods agree that at least two earthquakes have occurred with an average vertical offset per event of 10 and 12 m. This contrasts earlier studies which proposed that this scarp formed during a single event and demonstrates the importance of high‐resolution topographic data for understanding tectonic geomorphology. We use a one‐dimensional diffusion model of scarp degradation to demonstrate how fault splays form multiscarps and estimate the diffusion age of the Bilila‐Mtakataka fault scarp to be m , corresponding to years since formation. We calculate that a continuous rupture would equate to a M earthquake, greater than the largest seismic event previously recorded in East Africa.