Given the following passage  "Official figures (as of July 21, 2008 12:00 CST) stated that 69,197 were confirmed dead, including 68,636 in Sichuan province, and 374,176 injured, with 18,222 listed as missing. The earthquake left about 4.8 million people homeless, though the number could be as high as 11 million. Approximately 15 million people lived in the affected area. It was the deadliest earthquake to hit China since the 1976 Tangshan earthquake, which killed at least 240,000 people, and the strongest in the country since the 1950 Chayu earthquake, which registered at 8.5 on the Richter magnitude scale. It is the 21st deadliest earthquake of all time. On November 6, 2008, the central government announced that it would spend 1 trillion RMB (about US $146.5 billion) over the next three years to rebuild areas ravaged by the earthquake, as part of the Chinese economic stimulus program.",  answer the following question. Note that the answer is present within the text.  Question: How strong was the Chayu earthquake?
8.5 on the Richter magnitude scale