Complex sentence: On 7 January 2007, Unst was rocked by an earthquake measuring 4.9 on the Richter scale, which is believed to have been one of the most powerful earthquakes in the Norwegian Sea area in the past 10 years.
Split into simpler sentences: On 7 January 2007, Unst was rocked by an earthquake measuring 4.9 on the Richter scale. This is believed to be one of the most powerful earthquakes in the Norwegian Sea area in the past 10 years.