Better earthquake-detection instruments revealed that there is a whole range of slip speeds in between. These are known as slow earthquakes and can last days, months or sometimes even years.
Dr. Ake Fagereng, a geologist at Cardiff University in the UK said “there are still many questions to be answered about slow earthquakes though. How they happen, for example, still isn’t clear, as well as what the repercussions might be.”
For more info, please read the original article by Phys.org: