在科学研究的实践中学习和进步——纪念海原大地震90周年,为地震预测和防震减灾事业而努力

1920年12月16日20时06分09秒发生于中国宁夏海原地区的8.5级大地震是中国3个最大的8.5级地震之一,死亡人数当时估计为23万余人,最近重新估计达27万余人,其灾难之重,惨绝人寰.海原地震研究开辟了中国首次地震实地科学调查、利用现代科学方法观测地震的先河.20世纪中叶海原地震研究获得了突破性进展,发现了长达2...     

沉积速率摇摆匹配法限定古地震事件日历年龄

尝试运用沉积速率摇摆匹配方法来获得淤泥质泥炭系列样品的日历年龄,并与单个<‘14>C年代、时序已知系列<‘14>C年代的日历年龄进行对比.结果表明:在采样厚度较小的情况下,沉积速率摇摆匹配方法可以获得较小的日历年龄区间,具有一定的优越性;在采样数量足够多的情况下,系列<‘14>C年代贝叶斯校正也可以获得理想的日历年龄区...     

PALEOSEISMIC RECORDS OF LARGE EARTHQUAKES ON THE CROSS-BASIN FAULT IN THE SALT LAKE PULL-APART BASIN AND CASCADE RUPTURE EVENTS ON THE HAIYUAN FAULT

Cascade rupture events often occur along large strike-slip fault zone.The 1920 AD M 8¹/₂ earthquake ruptured all 3 segments of the Haiyuan Fault,and the Salt Lake pull-apart basin is the boundary between the west and middle segment of the fault.The data of trenching and drilling reveal 7 events occurring since last stage of late Pleistocene,and the two youngest events are associated with the historical records of 1092 AD (possibly) and 1920 AD respectively.These events are all large earthquakes with magnitude M>8,and the recurrence of them is characterized by earthquake clusters alternating with a single event.Now it is in the latest cluster which may last about 1000 years.Comparison of the paleoseismic sequence of this study and previous results reveals that the cross-basin fault in the Salt Lake pull-apart basin does not always rupture when cascade rupture events occur along the Haiyuan Fault,and likely ruptures only when the magnitude of the events is large (maybe M>8).Though there are many advantages in paleoseismic study in pull-apart basin,we should avoid getting the paleoseismic history of major strike-slip fault zones only depending on the rupture records of inner faults in pull-apart basins with large scale (maybe a width more than 3km).     

龙陵-瑞丽断裂带附近的构造地貌与断裂活动性

利用ALOS全色、ASTER多光谱遥感影像和SRTM数字高程模型数据解译,并结合野外地质调查和实时差分GPS测量,对龙陵-瑞丽断裂带晚第四纪活动的构造地貌和地质特征进行了研究。综合遥感解译、构造地貌和地震地质调查的结果认为,龙陵-瑞丽断裂带是一条以左旋走滑作用为主的断裂,在晚第四纪具有一定的活动性;并确定了龙陵-瑞丽断裂带各活动段落的空间分布情况。选取朱家寨一带开展了探槽挖掘工作。探槽很好地揭露了基岩中发育的新鲜断层面和晚第四纪冲洪积层,但是未发现断层错动晚第四纪沉积物的迹象。采集了冲洪积层底部的植物化石进行了14C测年,结果为（1150±30）a BP。据此推测,从距今1150年以来,龙陵-瑞丽断裂带活动断层在北段未再发生过破坏性古地震事件。综合分析1976年龙陵地震的发震特点,认为1976年发生在龙陵的大地震未发生在龙陵-瑞丽断裂带上,其震源机制解和余震分布特征表明地震活动与NNW向展布的新生断裂带活动有关,这很有可能造成了NE向龙陵-瑞丽断裂带晚第四纪构造活动性减弱。     

青藏高原中部温泉盆地西缘的晚新生代正断层作用

在青藏高原中部的温泉盆地西侧发育了1条倾向东的强烈活动的近SN正断层——温泉盆地西缘断裂。它是在印度板块与欧亚板块强烈碰撞的背景下,青藏高原中北部地区自晚新生代以来发生近EW向伸展变形的产物。晚新生代以来,该断裂上的最大垂直错动量不会<21km,错动中生代褶皱地层所暗示的最大垂直位移量为(60±22)km。第四纪期间,该断裂发生了多期活动,形成了山前的多套断层三角面和多级断层陡坎地貌。根据断裂垂直错动晚第四纪期间不同时代的地层和地貌体所形成的断层崖高度估算,其晚第四纪以来的最大活动速率不超过12mm/a,平均活动速率为045mm/a。初步的探槽分析表明,晚更新世末期以来沿该断裂至少发生了3次震级不同的古地震事件。综合该断裂的全新世活动特点推断,它是在未来具有较大可能发生6～7级地震的一条重要控震断裂     

Millennium‐scale recurrent uplift inferred from beach deposits bordering the eastern Nankai Trough,Omaezaki area,central Japan

A flight of Holocene marine terraces on the southwestern coast of Cape Omaezaki of central Japan provides evidence of recurrent millennium‐scale uplift events. We reconstructed the uplift history of these terraces by using facies analysis of drill core and geoslicer samples, environmental analysis of trace fossils, and ¹⁴C age determinations. Coastal uplift can be identified by the displacement of beach deposits such as foreshore deposits, which represent the intertidal swash zone of a wave‐dominated sandy coast. Three levels of former beach deposits facing the Nankai Trough were identified near the coast in the Omaezaki area. The highest of these, dated at about 3020–2880 BC, records a maximum of 2.2–2.7 m of emergence. The middle beach surface, of minimum age 370–190 BC, shows 1.6–2.8 m of emergence. The lowest beach surface, which is older than 1300–1370 AD, records 0.4–1.6 m of emergence. Our analysis of vertical crustal deformation data during the Holocene in this region suggests that rapid and strong uplift was restricted to the southwestern coast of the Omaezaki area and was probably caused by high‐angle thrusting on subsidiary faults branching from the underlying plate boundary megathrust.     

焉耆盆地北缘和静逆断裂-褶皱带古地震破裂方式和时间序列

古地震研究是构造地质基础研究工作之一,获得较为精细的古地震结果有利于提高对断层构造变形的样式、强度以及时间的认识。焉耆盆地是南天山东段的山间盆地,现今的构造应力场特征以挤压兼有走滑为主。盆地南北缘断裂均为全新世活动断裂,南缘开都河断裂以走滑运动为主。盆地北缘断裂向盆内扩展的新生和静逆断裂-褶皱带以逆冲运动为主,且具备发生7级以上大地震的能力。因此,对于焉耆盆地北缘和静逆断裂-褶皱带的古地震破裂方式和发生时间的研究具有重要意义。调查发现,其中的哈尔莫敦背斜南翼主逆断裂以30°左右向盆内逆冲,在河漫滩和T1阶地上形成了3排断层陡坎。在3条断层陡坎上开挖的5个探槽中,通过标志地层建立的时间序列可以确定6次古地震事件的先后关系。利用14C和光释光(OSL)测年手段获得了探槽中相关地层和坎前堆积物的沉积时代,利用逐次限定法得到了各次古地震事件的发生时间和全新世以来2ka左右的古地震复发间隔。结果显示F1断层在所有的古地震事件中都发生了破裂,F2断层只在事件E时产生了破裂,F3断层只在事件D和事件E中发生过破裂。从古地震事件上分析,事件D是一次3条断层同时破裂的事件,事件E是一次F1和F32条断层同时破裂的事件,其他事件都只在F1断层上破裂。和静逆断裂的古地震破裂同时存在必然性和不确定性。     

Using borehole core analysis to reveal Late Quaternary paleoearthquakes along the Nankou-Sunhe Fault,Beijing

The Nankou-Sunhe Fault is a buried active normal fault that traverses the urban area of Beijing.Its seismic risks have caused considerable concerns.This paper studies paleoearthquakes along this fault by analyzing and correlating bore-hole cores obtained from triple-tube coring,incorporating experience acquired from trenching.As a result,a model for identifying earthquake-derived colluvium by sediment-core analysis is proposed.Triple-tube coring technique is useful to collect continuous undis-turbed soil core near the Nankou-Sunhe Fault.By identifying fault-scarp colluviums,determining cumulative displacement,and analysing stratum thickening on the hanging wall,we are able to establish a preliminary paleoearthquake sequence consisting of 13 surface-rupturing events since 60 ka.The seismic history can be divided into three periods based on different recurrence intervals.Between 60 and 40 ka,three earthquakes occurred with recurrence interval of ～10 ka.From 40 to 25 ka,there were six earthquakes with the recurrence interval of about 2.5 ka.In the last 25 ka,four earthquakes have taken place with the recurrence interval varying considerably.The recurrence interval between the last three events is ～5 ka.Smaller recurrence intervals correspond to stages of faster fault slip.The coseismic displacement of a single event is 0.8 to 2.2 m,average 1.4 m,largely equivalent to moment magnitudes 6.7-7.1.This study demonstrates the feasibility of bore-hole drilling in investigating paleoearthquakes along normal faults.It also suggests that closely spaced boreholes with continuous undisturbed cores are essential for reconstructing the complete paleoearthquake sequence.     

Late Quaternary surface deformation and rupture behavior of strong earthquake on the segment north of Mianning of the Anninghe fault

The Anninghe fault is an important active fault along the eastern boundary of Sichuan-Yunnan active tectonic block, and the study of its surface deformation and rupture behavior during strong earthquake in the late Quaternary is of fundamental importance for understanding the future seismic risk of the fault zone or even the entire western Sichuan region. Using the methods of detailed geomorphic and geological survey, digital image analysis, total station instrument survey, excavation of combined trench and dating, we analyze the geomorphologic sequences of the offset strata at several sites where the late Quaternary deformation remnants are fairly well preserved and obtain some new results as follows: Strong earthquake events with left-lateral displacements of about 3 m occurred at the two sites of Zimakua and Yejitong at 1634-1811, 1030-1050 and 280-550 a BP, respectively, and the recurrence interval is 520-660 a; The youngest event in the area of Dahaizi-Ganhaizi should be the earthquake of 1536, other events are at 1768-1826, 2755-4108 and 4108-6593 a BP, respectively, with a recurrence interval of 1300-1900 a. The strong earthquake activity shows a clustering character. The possibility of occurrence of a strong earthquake exists on the north segment of the Anninghe fault sometime in the future.     

临泽断裂新活动特征初步研究

临泽断裂在地貌上可见3条断层陡坎,总体走向NNW,最长约8 km,东侧和中间陡坎主体倾向E,西侧陡坎倾向W。①利用差分GPS对3条断层陡坎进行了详细的测量,发现临泽断层陡坎较低,局部发育多级断层陡坎,坡角较缓,高度几十厘米至1米多;②在临泽断裂上选取4个探槽剖面进行古地震分析、样品采集和年代测试,发现东侧和中间的断层陡坎为正断层所控制,西侧的断层陡坎为逆断层所控制;③探槽开挖揭露出晚更新世晚期以来,临泽断裂上发生过4次古地震事件,时间分别为(8 895±125)a B.P.之前、(7 245±75)a B.P.～(6 190±20)a B.P.、(5120±20)a B.P.～(4.8±0.5)ka和(2 550±50)a B.P.～(2 326±64)a;④全新世以来可以确定3次事件,较早一次事件与榆木山北缘断裂上较早一次古地震事件时间比较吻合,说明临泽断裂可能是榆木山断裂向河西走廊内部继续活动的延伸;最后一次古地震事件的离逝时间约为2 500 a,表明临泽断裂全新世活动一直比较强烈。