四川北部地区三次中强历史地震补充考证

Additional Textual Criticism of Three Moderate-strong Historical Earthquakes in the Northern Region of Sichuan Province

四川北部地区位于南北强震构造带的中北段,区内活动断裂众多、构造关系复杂、历史及现今地震活动频繁。其中,早期历史地震因时间久远、史料记载简略等原因,其地震基本参数确定和发震构造分析难度较大,存在较大的不确定性。通过对地震史料的系统梳理和实地考证,对该区1900年以前的3次中强破坏性地震(公元638年松潘地震、1738年南坪地震和1748年松潘北地震)进行补充考证,对其震中位置、震级和烈度等基本参数进行重新核定,并综合分析其发震构造特征。研究结果对分析该区地震活动特征及判定未来强震危险区等均具有重要参考意义。

The northern region of Sichuan province in China is located at the central and northern segment of the north-south seismic belt.A series of active faults are developed in this region;they have a complex distribution and have been historically responsible for a series of strong （large） earthquakes,extending to the present-day.However,it is difficult to confirm the basic parameters and causative structures relating to earthquakes that occurred many years ago.Therefore,this study verifies the basic parameters and discusses the causative structures of three moderate-strong earthquakes that occurred before 1900 A.D.in the northern region of Sichuan province （the Song-pan earthquake in 638 A.D.,Nanping earthquake in 1738 A.D.,and an earthquake in the north of Songpan in 1748 A.D.）,based on detailed textual research using historical earthquake records and field investigations.The results indicate that：（1）the magnitude of the Songpan earthquake in 638 A.D.should be amended from a magnitude of 5 to that of about 6.In addition,the epicenter in-tensity was about 8,and the heavily-damaged area of this earthquake was located in （Gonggangling） and Hulugou,near the boundary of Songpan county and Nanping county （now Jiuzhaigou coun-ty）.The long axis direction of the isoseismal line had an approximate N-S orientation,which is consistent with the strike of the northern segment of the Minjiang active fault zone.（2）The mag-nitude of the Nanping earthquake in 1738 A.D.should be amended from a magnitude of 5 to one of about 6;the epicenter intensity was approximately 7~8,and the heavily-damaged area of this earthquake was located northwest of Huilongbu.The long axis direction of the isoseismal line has an approximate NW orientation,which is consistent with the strike of the southeastern seg-ment of the Tazang active fault zone.（3）The intensity of northern Songpan earthquake in 1748 A. D.should be amended to 8,and the heavily-damaged area relating to this earthquake was located near Huangshengguan.The long axis direction of the isoseismal line had an approximate N-S ori-entation,which is consistent with the strike of the northern segment of the Minjiang active fault zone.These results can be used as an important reference to analyze features of seismic activity and to j udge areas at risk from strong earthquakes in the future.