1884年云南宁洱6 3/4地震补充考证与发震构造讨论

Supplement Textual Research on Historical Data of the 1884 Ninger Earthquake in Yunnan Province and Discussion on its Seismogenic Structure

摘要:

对1884年11月14日云南宁洱地震参数进行了重新核定。这次地震的震中位置位于普洱府（今宁洱）周围，即23.1°N、101.0°E，精度为1类，误差≤10 km，震级6 3/4级，震中烈度Ⅷ度。等震线破坏区呈NE走向，而有感区长轴呈NE向，二者之间有一定差异。1884年宁洱地震区位于滇西南地区的龙陵—澜沧江断裂与红河断裂之间思茅次级地块内的普洱断裂带附近，其极震区长轴方向与断裂走向一致，应为本次地震的发震构造。

Abstract:

Based on the historical earthquake reports of the Ninger earthquake in the Yunnan province on November 14，1884，and a site inspection，new information has been obtained about this historical earthquake，providing credible evidence for the improvement of the isoseismal line.This paper thus reevaluates the Ninger earthquake parameters.The historical earthquake material is primarily from Guangxu Memoir and the memorial to the throne of the Palace，as well as the historical material of local chronicles.The results show that the epicenter was located near Puer mansion （presently Ninger）， which is 23.1°N，101.0°E.The accuracy is class 1，with an average error less than or equal to 10 km；the earthquake magnitude was 6.75；the epicentral intensity was Ⅷ.The most damaged area in this earthquake was Puer mansion.The damage scope was limited，and the epicenter zone can be delineated within 30 km from Puer mansion.The aftershocks were frequent and lasted for almost one month.It was a typical mainshock-aftershock earthquake.The early frequent seismic activity and continued aftershocks，as well as the relief activity of the local government and the Qing court，reveal that the magnitude of this earthquake was high and the damage was severe.The isoseismal line damage area of this earthquake pointed northwest，and the long axis of the earthquake-sensitive area pointed northeast.There is a marked difference between those two areas. Yunnan is located on the east edge of the continental border of the Indian and Eurasian plates.There are two force components acting on the Yunnan region.One is the strong lateral pressing of the Indian plate，and the other is the SSE squeezing force related to the plate activity.The east fault activity of the Yunnan region is closely related to the squeezing force.Analysis of seismogenic structures shows that the Puer fault is a seismogenic structure of this Ninger earthquake.The geometric position of the Ninger earthquake in year 1884 overlaps with the position of the Puer fault，and it is located among the checkerboard made of the NNW-trending Puer fault and a series of NEE-trending faults.Because the lateral offset of the Puer fault and the left offset of the NEE-trending faults，the earthquake of MS6.75 happened in 1884 in Ninger.The Puer fault belongs to the Simao secondary block，which is located between the Longling-Lancang River fault and the Red River fault.The trend of the long axis of the meizoseismal damage area runs parallel to that of the causative fault.Between the NNW-trending Puer fault and the Mohei fault，there exist multiple NEE-trending parallel fracture belts，which are small-scale，have poor continuity，and form in groups with a left-lateral dislocation.These grouped parallel faults formed a checkerboard fault block.An MS6.4 earthquake occurred approximately 3 km south of Ninger on June 3，2007. Studies of this earthquake showed that main characteristics of the northwest nodal plane were a right-lateral thrusting slide and those of the northeast nodal plane were left slip. Thus， the right-lateral slide of the NNW-trending Puer fault and the left-lateral dislocation led to this earthquake.Because of the fragmentized crustal structure，the region is MS6.2~6.8 earthquake-prone，and this is why there are no bigger earthquakes in this region.Due to the complicated fault structure and fragmentation，as well as the landscape and geomorphic influences，there are still uncertainties.A further detail study of the Puer fault and seismogenic structures should be carried out so as to obtain more reliable results.