An earthquake was felt in Kigali on Thursday mid-morning, November 5, with residents in Mwanza, Tanzania, as well as Kampala, Nairobi and other parts of the region also reporting tremors. The Rwanda Mines, Petroleum and Gas Board (RMB), which monitors seismic activity, confirmed that the earthquake occurred at 11:22 am and had a magnitude of 6.4. The quake’s epicentre was reportedly in Tanzania’s north-western region, about 292 kilometres from Kigali, in the less seismically active Eastern Branch of the Rift Valley. What to know about seismic activity in Rwanda Rwanda lies in the Western Rift of the African Rift Valley, which is considered more seismically active than the Eastern Branch. According to the Rwanda Environment Management Authority (REMA), Rwanda and its surrounding areas straddle Africa’s Kibaran and Western Rift zones. REMA identifies the Western Rift system as the main source of seismic activity in Rwanda, with the Western Province being the area most affected by earthquakes. How earthquakes happen According to the United States Geological Survey (USGS), a scientific agency of the United States, an earthquake occurs when two blocks of the earth suddenly slip past each other. The surface along which they slip is called a fault or fault plane. “The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicentre,” reads an explainer on the USGS website. ALSO READ: New ocean forming, to split Africa into two, scientists say The USGS explains that when the edges of faults are stuck together while the rest of the blocks continue moving, energy builds up. This energy would normally cause the blocks to slide past each other, but friction between the jagged edges of the fault prevents them from moving. When the force of the moving blocks finally overcomes the friction, the fault unsticks, releasing the stored energy. The energy radiates outward from the fault in all directions in the form of seismic waves, similar to ripples spreading across a pond. As the waves travel through the earth, they cause it to shake. When they reach the surface, they shake the ground and everything on it, including buildings and people. The USGS also explains that some earthquakes are preceded by foreshocks, which are smaller earthquakes that occur before a larger one. However, scientists can only identify an earthquake as a foreshock after a larger earthquake has occurred. The largest earthquake in a sequence is called the mainshock. ALSO READ: Volcanic earthquakes damage 40 houses, road in Rubavu Mainshocks are always followed by aftershocks, which are smaller earthquakes that occur in the same area. Depending on the magnitude of the mainshock, aftershocks can continue for weeks, months or even years. How earthquakes are measured Earthquakes are recorded using instruments called seismographs. A seismograph has a base that is firmly fixed to the ground and a heavy weight that hangs freely. When an earthquake causes the ground to shake, the base of the seismograph moves with it, but the hanging weight remains relatively still. The spring or string supporting the weight absorbs the movement. The difference in position between the moving base and the relatively stationary weight is what the instrument records. The size of an earthquake is expressed as its magnitude. Can scientists predict earthquakes? According to the USGS, scientists have tried various methods of predicting earthquakes, but none has been successful. Scientists know that another earthquake will eventually occur along any particular fault, but they cannot tell exactly when it will happen. The USGS says it is unlikely that scientists will ever be able to predict earthquakes accurately.
