Cosmogenic exposure data can be used to calculate time-varying fault slip rates on normal faults with exposed bedrock scarps. However, the method relies on assumptions related to how the scarp is preserved, which should be consistent at multiple locations along the same fault. Previous work commonly relied on cosmogenic data from a single sample locality to determine the slip rate of a fault. Here we show that by applying strict sampling criteria and using geologically informed modelling parameters in a Bayesian-inference Markov chain Monte Carlo method, similar patterns of slip rate changes can be modelled at multiple sites on the same fault. Consequently, cosmogenic data can be used to resolve along-strike fault activity. We present cosmogenic 36Cl concentrations from seven sites on two faults in the Italian Apennines. The average slip rate varies between sites on the Campo Felice Fault (0.84 0.23 to 1.61 0.27 mm yr ^-1), and all sites experienced a period of higher than average slip rate between 0.5 and 2 ky and a period of lower than average slip rate before 3 ky. On the Roccapreturo fault, slip rate in the centre of the fault is 0.550.11 and 0.350.05 mm yr ^-1 at the fault tip near a relay. The estimated time since the last earthquake is the same at each site along the same fault. These results highlight the potential for cosmogenic exposure data to reveal the detailed millennial history of earthquake slip on active normal faults.

Fracturing and gouge formation absorb ≥50% of earthquake energy on low displacement (<1-2 km) faults in isotropic crust. To assess how these processes absorb earthquake energy in anisotropic crust, we performed field and microstructural investigations on the 110 km long, 0.4-1.2 km displacement, Bilila-Mtakataka Fault (BMF), Malawi. Where the fault is parallel to surface metamorphic fabrics, macroscale fractures define a 5-20 m wide damage zone. This is narrow relative to where the BMF is foliation-oblique (20-80 m), and to faults with comparable displacement in isotropic crust (~40-120 m). There is minimal evidence for cataclasis and microfracturing along the BMF; therefore, despite its 110 km length and geomorphic evidence for MW 7-8 earthquakes, widespread fault zone fracturing has not occurred. We attribute lack of damage to fault growth along shallow and deep-seated pre-existing weaknesses. This conclusion implies that earthquake energy dissipates differently along incipient faults in isotropic and anisotropic crust.

We present the Malawi Active Fault Database (MAFD), a geospatial database of 114 active fault traces in Malawi, and in neighboring Tanzania and Mozambique. The MAFD has been developed from a multidisciplinary dataset: high resolution digital elevation models, field observations, aeromagnetic and gravity data, and seismic reflection surveys from offshore Lake Malawi. Active faults longer than 50 km are found throughout Malawi, where seismic risk is increasing due to its rapidly growing population and its seismically vulnerable building stock. The MAFD also provides an opportunity to investigate the population of normal faults in an incipient continental rift. We find that the null hypothesis that the distribution of fault lengths in the MAFD is described by a power law cannot be rejected. Furthermore, a power-law distribution of faults in Malawi is consistent with its thick seismogenic crust (~35 km), and low (<8%) regional extensional strain that is predominantly (50-75%) accommodated across relatively long hard-linked border faults. Cumulatively, the data and inferences drawn from the MAFD highlight the importance of integrating onshore and offshore geological and geophysical data to develop active fault databases along the East African Rift and similar continental settings, both to understand the regional seismic hazard and tectonic evolution.