Firstly,earthquake situations are described,including shocked degree by people, distribution of intensity, disaster loss,and macroscopic and microscopic phenomena appeared before and after the earthquake.
According to the historical data provided by literatures,the parameters such as time,sensing range,intensity and magnitude of the strong foreshocks and aftershocks of the 1605 Qiongshan macroquake are studied in the paper.
This demand is approximately met by inquiries for sources covering an area greater than the expected felt area of the historical earthquake.The Friuli event of 25 January 1348 is presented as an example.
This result throws a light on the possible error in determining the felt area of historical events.
Finally macroseismic analysis related to the felt area is shown with isoseismals map.
Analysis shows that the felt area of the earthquake was probably only about 200 km2; however, heavy damage occurred in the village of Rampside and the maximum intensity is assessed at 8.
A Magnitude-Felt Area Relation in the Evaluation of the Magnitude of Historical Earthquakes