Earthquakes in Uganda, July 3, 2013

On July 3, two M>5 earthquakes occurred in the Lake Albert region of Uganda, on the border with the Democratic Republic of Congo. The largest of the events had a magnitude M5.7, the other was M5.4

These events occurred in one of the more active areas of the East African rift valley. Events of this magnitude can cause damage and injuries if building construction is not seismically resistant. 

The focal mechanisms of the earthquakes indicated NW-SE tension, or in other terms, these were normal faulting earthquakes typical of a rift valley where the continent is splitting apart.

The screenshot at left shows the geographic region, with the Open Hazards global forecast superposed on the area.  Screenshot was taken from the Hazard Viewer page. 

As can be seen, the epicenters are in Lake Albert.  Lakes such as this often form in rift valleys. Other examples are the Salton Sea in California, and the Dead Sea on the boundary of Israel and Jordan.  The blue circle was drawn with the circle select tool from the left menu. 

The table of forecast probability in the circle area appears in the lower left of the figure and is reproduced at right.  As can be seen, the current probability of another M>5 earthquake within the blue selection circle during the next year is currently about 27%.  

This region of Africa is seismically active.  One of the largest earthquakes of recent history was the destructive 1966 Toro (Ruwenzori) earthquake that occurred on March 20, 1966. [1]

With a magnitude of M6.8, this event led to the deaths of 157 persons, with another 90 deaths occurring as a result of the aftershocks, the largest of which occurred on May 18.

104 of the deaths were in Uganda, with the remaining deaths in the DRC.  The event was also felt in Ruwanda, Burundi, Tanzania, and Kenya. 

Below we show a screenshot of the time variation of the computed earthquake probabilities for M>5 during the next 1 year.  It can be seen that calculated probabilities had been increasing since about mid 2010, if the data in the catalog are complete (often not the case in some parts of the world). 

The last data point at the extreme right hand side represents the probability computed last night, just after the two M>5 earthquakes occurred.

[1] Source: http://en.wikipedia.org/wiki/1966_Toro_earthquake