The amount of damage an earthquake depends on multiple factors. Of course, its strength is one of the biggest factors, but very often it is not the decisive factor. If an earthquake strikes at an area where there's higher density of population, than the chances are that there will be more dead and injured people. If the earthquake strikes a place where there's little to no people doesn't matter its strength, there will be no dead or injured people, or only very few. If there's a lot of infrastructure in the area where the earthquake appeared, there will be lot of damage, but if there's very little infrastructure, than there will be very little damage done. The warning of the population on time can also be crucial for avoiding casualties, and if it is done on time and the people are evacuated, there will be very few or no victims, but if there isn't any warning, or it is too late, than there will be much more casualties. All these things were also the difference in the earthquakes in Haiti and Chile. The one in Haiti was in densely populated area, with lot of infrastructure, and there was not warning on time, while in Chile it was in an area where there's small population density, less infrastructure, and the warning was on time so the people were evacuated.
