A strike slip fault dynamic and seismic hazard implications on the future big event: insights from the Mw 5.5 Rukwa earthquake of 21 March 2019

Abstract

The moderate-sized M_w 5.5 Rukwa earthquake of 21 March 2019 in southwestern Tanzania caused strong shaking in the vicinity of towns. Results from the relocation suggest the earthquake is associated with the Chisi shear zone and the fault plane solution reveals dextral strike-slip motion. The association of the event with shear zone and dextral strike-slip faulting likely represents reactivation of the Paleoproterozoic dextral shear faults caused by transfer of strain energy accommodated in the previously north-eastern active Lupa border fault into the previously less-active south-western Ufipa border fault. The orientations of lineaments around the epicenter and the macroseismic intensity distribution indicate the ruptured plane of the event propagated along SE direction. The intensity map shows significant ground shaking extending further southwest, up to ~ 450 km, affecting buildings in towns along the Western Rift. The notable strong vibration is associated with the amplification of the ground movement caused by soil effects. Most of the buildings in towns along the Western Rift cannot withstand strong shaking when a big event occurs. This implies that a future, bigger event in the Western Rift would result in large casualties and destruction of properties. The occurrence of a big event can also result in major volcanic hazards by triggering an eruption within the Rungwe Volcanic Province. The event provides the most useful first-hand input data for the estimation of hazards and also assists in better planning against earthquake hazards in near-field cities and towns along the Western rift.