Daudi, I'm not privy to the exact info you may be looking for. My wild guess would be:

- Seismic adjustments are most prone along some identified zones. 

- Our dear Rift valley happens to have been formed through seismic activities ->Indicates that this belt was once seismologically active.

This gives it a marginal propensity to behave likewise should an outside chance present itself.

- Now with Nakuru being the most built up and inhabited area within this belt, the casualty/damage risk factor therein increases.

Tony.