Abstract: On March 1, 138 AD, a great earthquake of magnitude about 6³/4 occurred in Jincheng-Longxi area. This event had caused "surface ruptures, serious damages of towns and houses, death of people, collapse of hills and river banks, and sink of land" in Jingcheng-Longxi area. It is worthy of noting that this earthquake is the only earthquake that had been recorded by seismograph invented by Zhang Heng, the famous Chinese ancient scientist, and it is also the earliest earthquake that was recorded by seismograph in the world. According to the detailed textual research of the historical earthquake records and the ancient town chronicles, it can be concluded that the Qianya town,the capital of the Jincheng state in the Eastern Han Dynasty, which was damaged during this earthquake,is situated in present-day Xiachuankou of Machangyuan village,Minhe Hui and Tu Autonomous County of Qinghai Province. At present, the ancient town site is located on the second level terrace of the south bank of the Huangshui River about 700m to the northwest of the Xiachuankou village. We found the remnants of pottery pots and animal bones from the rammed earth of the ancient town walls. The ages of these remnant pottery pots was dated by themoluminescent method to be about 2.77?0.24ka BP, which is consistent with the epoch of the Eastern Han Dynasty. The ancient Didao town, the capital of ancient Longxi state, is located in the present-day Lintao County, Gansu Province. The epicentral area of the 138 AD earthquake, therefore, can be located in the intersection area of the Yellow River and Huangshui River to the northwest of Yongjin County, Gansu Province. The intersection area of the Yellow River and Huangshui River is also a region where loess landslides are densely distributed, among which the largest ones might be produced by earthquake. Tectonically, this area is located on the frontier of the northern marginal arcuate thrust fault zone of the Lajishan Mountains. This fault zone is a late Pleistocene active fault zone, but some segments of the fault have been reactivated since Holocene. The low-angle reverse faulting toward the Minhe basin along NE direction had caused the intense compressive deformation of Neogene mudstone and early Pleistocene conglomerate on the northern side of the fault, resulting in compressive thrust fold zone. This may indicate that the frontier of the northern marginal arcuate fault zone of the Lajishan Mountains is probably a buried active compressive reverse fault-fold zone. This recognition has been supported by the recent data of petroleum prospecting. It is concluded, therefore, that it was the new activity of the reverse fault-fold zone on the frontier of the Lajishan Mountains that caused the 138 AD Jincheng-Longxi M6³/4 earthquake.

Key words: Jincheng-Longxi, historical earthquake, textual research of historical data, loess landslide, sesimogenic structure

摘要： 对138年金城-陇西6³/4级地震的历史资料考证、黄土滑坡分布及活动构造的综合研究表明:在138年地震中遭破坏的东汉金城郡郡治允吾县应在今青海省民和县马场垣乡下川口附近;陇西郡治狄道县在今甘肃省临洮县城.由此确定138年地震的极震区位置大致在今甘肃省永靖县西北的湟水、黄河交汇地带.该区也是黄土滑坡密集分布区,其中的大型滑坡应为地震滑坡.在构造上该区位于拉脊山北缘弧形逆冲断裂带的前缘.拉脊山北缘断裂带为一条晚更新世活动断裂,部分地段为全新世活动,其向NE方向的逆冲推覆致使古近系泥岩和早更新世砾岩等发生了明显的挤压褶皱变形.石油勘探资料也证实拉脊山北缘弧形构造带前缘在深部存在隐伏的挤压逆冲断褶带.由此推断138年金城-陇西6³/4级地震的发生很可能与该逆断裂-褶皱带的新活动有关.

关键词: 历史地震, 史料考证, 黄土滑坡, 发震构造, 金城, 陇西