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'Small earthquake measured 4.2 on the Richter scale - Ghana Geological Survey Authority

BY: Kweku Zurek

Mr Nicholas Opoku, a Seismologist at the Ghana Geological Survey Authority (GGSA) has disclosed that the minor earthquake which rocked parts of Accra yesterday measured a magnitude of 4.2 on the Richter scale.

Mr Opoku confirmed that the incident which he described as a  "small earthquake" occurred three times and was felt in the whole of Accra and its environs.

Data from the USGS (United States Geological Survey) had indicated that the earthquake was recorded at a magnitude of 4.0 but Mr Opoku says the GGSA recorded it at 4.2 on the Richter scale. 

"It happened three times. The first one which is the foreshock, the magnitude was 3.7, then the mainshock which was the second one the magnitude was 4.2 and then the third one was 3.5 all on the Richter Scale," Mr Opoku said in an interview on Citi FM.

READ ALSO: Earth tremor measuring Magnitude 4.0 hits Accra and environs

Different magnitudes of earthquake on the Richter scale

Measuring earthquakes

Earthquakes, until recently, have been measured on the Richter scale. The Richter scale measures the magnitude of an earthquake (how powerful it is).

It is measured using a machine called a seismometer which produces a seismograph. A Richter scale is normally numbered 1-10, though there is no upper limit. It is logarithmic which means, for example, that an earthquake measuring magnitude 5 is ten times more powerful than an earthquake measuring 4.

Earthquakes measuring 1-2 on the scale happen regularly, and they are so small that people cannot feel them. Earthquakes measuring upwards of 7 are less frequent but very powerful, and can cause a lot of destruction. 

The largest earthquake ever recorded was in Chile in 1960, which measured 9.5 on the Richter scale. The Richter scale is not very accurate in measuring these larger earthquakes and today scientists use the Moment Magnitude Scale which uses the same logarithmic scale but which more accurately measures the strength of larger earthquakes.