罗云山山前断裂中段土门-贾朱村晚第四纪断错地貌特征

罗云山山前断裂位于山西临汾盆地西侧,控制着盆地的西界。通过对该断裂1∶ 5万地质填图、对河流冲沟阶地及山前断错地貌的调查,介绍了罗云山山前断裂中段土门-贾朱村晚第四纪断错地貌特征。罗云山山前发育D1、D2、D3 等3 级洪积扇,罗云山山前断裂上升盘冲沟发育T1 ～ T5 等5 级阶地。D1 洪积扇与T1、T2 阶地形成于全新世早中期;D2 洪积扇与T3 阶地形成于晚更新世中晚期;D3 洪积扇与T4、T5 阶地形成于中更新世中晚期。罗云山山前断裂中段不同部位断错地貌特征差异较大,D1 洪积扇的断错在席坊沟一带断距约2. 9m;在金殿镇峪口村南西山前断错约3m。D2 洪积扇的断错在土门镇南西堡子村约2. 5m;在杨家庄村西山前断错约4m;在景村西山前断错约6m;在襄陵镇浪泉沟南西侧山前断错约7. 7m。罗云山山前断裂中段山前断错地貌明显,其最新活动时代为全新世。其中,土门段最新活动时代为全新世早期,龙祠段最新活动时代为全新世中晚期。罗云山山前断裂中段晚更新世中晚期以来活动速率为0. 18～ 0. 54mm / a,由北向南活动呈增强趋势;全新世早中期以来活动速率为0. 4 ～ 0. 9mm / a,断裂活动主要集中于席坊沟-峪口一带。罗云山山前断裂中段从晚更新世中晚期到全新世活动速率有增大的趋势,这与该断裂上升盘冲沟阶地从晚更新世中晚期到全新世抬升速率有增大的趋势以及临汾盆地从晚更新世晚期到全新世沉降速率也有增大的趋势具有较好的一致性。     

华山山前断裂断错地貌及晚第四纪活动性

基于华山山前断裂1︰5万活动断层填图成果,对断裂沿线地层地貌、断层三角面、河流阶地、陡坎地貌以及典型断错剖面等进行了详细的研究。研究表明:1)华山山前断裂按几何结构、断错地貌表现分西段(蓝田—华县段)、中段(华县—华阴段)及东段(华阴—灵宝段)3段;2)西段及东段断裂错断了T_2阶地及马兰黄土,T_1阶地跨断裂连续,测年结果表明,T_2阶地形成于晚更新世中期,T_1阶地形成于全新世早期,由此得出西段及东段断裂在晚更新世有过活动,全新世以来活动弱或不活动;3)中段断错地貌显著,河谷两侧发育Ⅲ级阶地,跨断裂阶地均被错断,测年结果表明:T_1阶地形成于2~3kaBP,T_2阶地形成于6~7kaBP,T_3阶地形成于60~70kaBP,结合阶地陡坎高度,得出不同时段的平均垂直滑动速率:T_3—T_2时期0.4mm/a;T_2—T_1时期1.1mm/a;T_1以来1.6mm/a;4)中段在晚更新世晚期以来发生过多次活动,在石堤峪、沟峪等地见漫滩陡坎,结合文化层及炭样年龄,可知漫滩形成于距今400~600a,对比历史地震资料,漫滩陡坎应为华县1556年地震的遗迹;5)结合前人研究认为,公元1556年华县81/2级地震的发震构造为华山山前断裂及渭南塬前断裂,其它断裂是否参与有待进一步研究。     

西南天山柯坪塔格前缘断裂带东段晚第四纪活动特征

柯坪塔格前缘断裂东段是柯坪推覆构造系前缘的一条活动断裂,野外调查获得了其晚第四纪错断洪积扇、冲沟阶地面的证据,实测了变形地貌面上的断层陡坎,分析了断层的形变量,通过采样测年估算了断层的缩短速率。由7个观测点的断层陡坎剖面测量,计算了观测点处断层的水平缩短速率,结果表明,断裂弧顶部位的五道班、三间房以西及其大山口道班附近,断层错断了Ⅰ级和Ⅱ级洪积扇(阶地)。断层在这些地点最新活动强烈,水平缩短平均速率全新世以来为0·35~0·44mm/a,更新世晚期末以来为0·16~0·30mm/a,而在非弧顶部位的巴楚磷矿、三岔口以北及大山口北断层只错断了更新世晚期Ⅲ级洪积扇,且水平缩短速率较小,断层水平缩短平均速率更新世晚期以来为0·05~0·07mm/a     

柯坪塔格山前层状地貌面与晚第四纪逆断层变形——以三岔口北西山前断错地貌为例

柯坪塔格山前三岔口北西发育了5级不同期次的冲洪积扇面,其中较年轻的3期完整地保留了断裂最新活动形成的陡坎.依据断错地貌面上砾石混合样品的10Be暴露年龄及差分GPS地形实测结果,计算出(20.22± 1.91) ka以来T1、T2、T3级冲洪积扇上记录的断裂垂直滑动速率分别为(0.16±0.02)、(0.17±0.02...     

青海热水-日月山断裂带的新活动特征

热水 -日月山断裂带是发育在青藏高原东北缘柴达木 -祁连活动地块内部的 1条重要的NNW向逆 -右旋走滑活动断裂带 ,长约 183km。断裂由 4条不连续的次级断裂段右阶羽列而成 ,阶距 2～ 3km左右 ,在不连续部位形成拉分区。主断裂两端则形成帚状分叉。断裂活动形成了一系列山脊、冲沟和阶地等右旋断错微地貌 ,其中Ⅰ级阶地右旋断错约 8～ 11m ,Ⅱ级阶地右旋断错约 35m。同时沿断裂带还形成了许多断层陡坎 ,Ⅰ级阶地或洪积台地上断层陡坎高约 0 .5～ 1m ,最高达 2 .8m ,Ⅱ级阶地或台地上的断层陡坎高约 2 .5～ 3m ,最高达 4～ 5m。根据相应的阶地年代 ,计算得到断裂带全新世以来的平均水平滑动速率为 3 16mm/a ,垂直滑动速率为 0 .83mm/a     

榆木山北缘断裂的构造地貌特征与断层活动性

构造地貌能反映断裂的结构变形特征和断层的活动强度。便如断层陡坎的高度、长度和坡度以及断层陡坎的连续程度。在这篇文章中，讨论了断层段内每个段落断层陡坎的F（C），F（D），F（LR），F（SR）值的特征。在这篇文章结尾，还讨论了冲洪积扇特征对以活动强度的反映。从地貌统计结果来看，发现在榆木山断裂的中间部位冲洪积扇体坡度最大，从中间向两侧中洪积扇扇体坡度呈减弱趋势。文中还给出了断层陡无坎变形的测量结果，冲洪积扇扇顶热释光年龄和断层滑动速度。从分析结果来看，榆木山北缘断裂可以细分为三段，东段（梨园小口子－排路口）、中段（排路口－芦泉河）和西段（芦泉河－李家山子）。     

博罗可努-阿齐克库都克断裂精河段晚更新世以来的断错地貌和走滑速率

博罗可努-阿齐克库都克断裂(博-阿断裂)是中天山与北天山的板块会聚边界,它NW向斜切天山山脉,是一条继承性的右旋走滑活动断层。研究其活动性质、限定其滑动速率有助于理解天山地区晚第四纪构造变形模式、应变速率分配情况及评估区域地震危险性。文中通过卫星遥感影像解译及野外考察,基于地貌面高程、水系密度和切割深度等,将精河东南的冲洪积扇分为4期,由老到新分别命名为Fan1、Fan2、Fan3和Fan4。利用无人机航拍获取断裂附近的高精度影像,并对冲洪积扇上发育的冲沟、阶地陡坎等进行构造地貌解译,发现Fan1、Fan2和Fan3 3期冲洪积扇上发育右旋位错冲沟及断层陡坎。其中,Fan2b、Fan3a和Fan3b上的冲沟最小右旋位错约6m,最大位错分别为(414±10) m、(91±5) m和(39±1) m; Fan2b与Fan3a分界的地貌陡坎被右旋位错(212±11) m。结合前人在天山北麓得到的阶地或冲洪积扇的堆积年龄,并与古里雅冰芯气候曲线进行对比,推测Fan2b、Fan3a和Fan3b 3期冲洪积扇的下切年龄分别为56～64ka、35～41ka和10～14ka。博-阿断裂自冲洪积扇Fan2b、Fan3a和Fan3b形成以来的滑动速率分别为3. 3～3. 7mm/a、2. 2～2. 6mm/a和2. 7～3. 9mm/a,利用蒙特卡洛模拟方法拟合得到晚更新世以来其平均右旋走滑速率为(3. 1±0. 3) mm/a。     

博—阿断裂带中东段晚第四纪以来滑动速率

通过对新疆博—阿断裂带中东段的实地调查,发现断裂在吐鲁番盆地西南山前冲洪积扇上形成了冲沟右旋错动、断层陡坎、挤压隆起等与断裂活动相关的典型断错地貌。对比区域地貌面的分布和年龄,并结合测年结果,认为研究区内主要分布了3期冲洪积扇,并对应3级河流阶地。实测Fan3冲洪积扇上冲沟的最大右旋位错达40.8 m,其余分布在22～27 m区间内,Fan2冲洪积扇上冲沟的右旋位错达26.5 m,结合光释光年代样品的测试结果,得到1.8万年以来断裂平均右旋走滑速率为(1.42±0.18)mm/a。     

华山山前断裂中段全新世垂直活动速率的重新厘定

全新世以来,距今越近,华山山前断裂中段的垂直活动速率越大,甚至出现跳跃式的增长。重新梳理该断裂带40多处断层陡坎测量结果,发现这种不合理应与1556年华县8级地震有关。通过减掉1556年华县大地震的同震位移量,消除了这次大震的同震位移对活动速率计算值的放大作用,而且不同时期地貌陡坎的计算结果均表现出了很好的稳定性,说明这种处理是必要和有效的。最后,应用上述处理方法得到了华山山前断裂中段全新世以来较为可靠的平均垂直活动速率为(1.56±0.2)mm/a。     

天山内部博罗可努断裂精河—阿拉山口段晚更新世以来的活动特征

通过对博罗可努断裂精河—阿拉山口段微地貌的实地调查 ,发现该断裂错断精河东南到阿拉山口之间的晚更新世冲洪积扇 ,地表留下了冲沟和山脊同步右旋位错、断层陡坎、断层鼓包、拉分盆地等与断层活动有关的微地貌。精河东南冲洪积扇上大冲沟的最大右旋位移为 50 0m ,平均4 0 0m。断层陡坎上的纹沟右旋位移为 2 6～ 4 0m ,较大级别的纹沟位移可分为 5 7m ,8 3m和 15 3m3组。它们大致为 3的整数倍。实测断层陡坎的高度分别为 1 2m ,2 51m和 3 6 3m ,大致是 1 2的整数倍 ,阿拉山口西南断层的水平位移为 1～ 1 7m ;垂直位移可分为两组 ,一组为 0 55m ,另一组为 1 2～ 1 5m。这些数据可能揭示了该断裂段的特征地震水平位移为 3m ,垂直位移为 1 2m。区域地貌对比和年代学分析得出 ,精河东南冲洪积扇的最后形成时代为距今 7万a左右 ,右旋滑动速率为4 7mm/a。     

LATE QUATERNARY FAULTED LANDFORMS AND FAULT ACTIVITY OF THE HUASHAN PIEDMONT FAULT

Based on the 1︰50000 active fault geological mapping, combining with high-precision remote imaging, field geological investigation and dating technique, the paper investigates the stratum, topography and faulted landforms of the Huashan Piedmont Fault. Research shows that the Huashan Piedmont Fault can be divided into Lantian to Huaxian section (the west section), Huaxian to Huayin section (the middle section) and Huayin to Lingbao section (the east section) according to the respective different fault activity. The fault in Lantian to Huaxian section is mainly contacted by loess and bedrock. Bedrock fault plane has already become unsmooth and mirror surfaces or striations can not be seen due to the erosion of running water and wind. 10~20m high fault scarps can be seen ahead of mountain in the north section near Mayu gully and Qiaoyu gully, and we can see Malan loess faulted profiles in some gully walls. In this section terraces are mainly composed of T₁ and T₂ which formed in the early stage of Holocene and late Pleistocene respectively. Field investigation shows that T₁ is continuous and T₂ is dislocated across the fault. These indicate that in this section the fault has been active in the late Pleistocene and its activity becomes weaker or no longer active after that. In the section between Huaxian and Huayin, neotectonics is very obvious, fault triangular facets are clearly visible and fault scarps are in linear distribution. Terrace T₁, T₂ and T₃ develop well on both sides of most gullies. Dating data shows that T₁ forms in 2~3ka BP, T₂ forms in 6~7ka BP, and T₃ forms in 60~70ka BP. All terraces are faulted in this section, combing with average ages and scarp heights of terraces, we calculate the average vertical slip rates during the period of T₃ to T₂, T₂ to T₁ and since the formation of T₁, which are 0.4mm/a, 1.1mm/a and 1.6mm/a, and among them, 1.1mm/a can roughly represent as the average vertical slip rate since the middle stage of Holocene. Fault has been active several times since the late period of late Pleistocene according to fault profiles, in addition, Tanyu west trench also reveals the dislocation of the culture layer of(0.31~0.27)a BP. 1~2m high scarps of floodplains which formed in(400~600)a BP can be seen at Shidiyu gully and Gouyu gully. In contrast with historical earthquake data, we consider that the faulted culture layer exposed by Tanyu west trench and the scarps of floodplains are the remains of Huanxian M_S8½ earthquake. The fault in Huayin to Lingbao section is also mainly contacted by loess and mountain bedrock. Malan loess faulted profiles can be seen at many river outlets of mountains. Terrace geomorphic feature is similar with that in the west section, T₁ is covered by thin incompact Holocene sand loam, and T₂ is covered by Malan loess. OSL dating shows that T₂ formed in the early to middle stage of late Pleistocene. Field investigation shows that T₁ is continuous and T₂ is dislocated across the fault. These also indicate that in this section fault was active in the late Pleistocene and its activity becomes weaker or no longer active since Holocene. According to this study combined with former researches, we incline to the view that the seismogenic structure of Huanxian M_S8½ earthquake is the Huashan Piedmont Fault and the Northern Margin Fault of Weinan Loess, as for whether there are other faults or not awaits further study.     

THE STUDY OF LATE QUATERNARY ACTIVITY OF HANCHENG FAULT

Based on the 1︰50000 geological and geomorphologic mapping of active fault, the structural geomorphic features and activity of Hancheng Fault are investigated in detail. In the study, we divide the fault into three sections from north to south: the section between Xiweikou and Panhe River, the section between Panhe River and Xingjiabao and the section between Xingjiabao and Yijing, the three sections show different characters of tectonic landform. The section between Xiweikou and Panhe River is a kind of typical basin-mountain landform, where diluvial fans spread widely. In the north of Yumenkou, the fault deforms the diluvial fans, forming scarps, along which the fault extends. In the south of Yumenkou, the fault extends along the rear edge of the diluvial fans. In the section between Panhe River and Xingjiabao the fault extends along the front of the loess mesa. In the section between Xingjiabao and Yijing the fault forms scarp in the loess and extends as an arc shaped zone, and the landform is formed by the accumulative deformation of the fault. The activity of the fault becomes weak gradually from northeast to southwest. The fault activity of the section between Xiweikou and Panhe River is the strongest, and the latest age of activity is Holocene. The slip rate since the mid-Holocene is bigger than 0.8mm/a at Yumenkou. The fault activity of the section between Panhe River and Xingjiabao is weaker than the north part, the fault's latest active age is identified as the later period of Late Pleistocene and the activity becomes weak gradually from northeast to southwest. At the estuary of the Jushui River the slip rate of the fault is about 0.49mm/a since late Late Pleistocene. The fault activity of the section between Xingjiabao and Yijing is the weakest. There is no evidence of paleosol S1 deformed in fault profiles, and only some phenomena of fracture and sand liquefaction in the earlier Late Pleistocene loess. The activity of the fault is in line with the fault landform feature. At macro level, the relationship between the uplifted side and the thrown side of the fault switches gradually from the Ordos uplifting region and the rifted basin to the interior blocks of the rifted basin, which maybe is the regional reason why the activity of the Hancheng Fault becomes weak from the northeast to the southwest.     

青藏高原中部五道梁-曲麻莱断裂系西段晚第四纪滑动速率厘定

五道梁-曲麻莱断裂系位于青藏高原中部，关于其晚第四纪活动性迄今鲜有介绍。由高分辨率卫星影像解译和野外地质考察可知，断裂系西段由五道梁南山北缘断裂和五道梁南山南缘断裂组成，二者分别断错了五道梁南山两侧的各级洪积扇。通过洪积扇上的断错地貌分析和光释光测年方法得到南缘断裂缩短速率为（0.25±0.11）mm/a，北缘断裂缩短速率为（0.50±0.05）mm/a。基于经验公式和最新洪积扇上陡坎高度，推测南、北缘断裂可能曾发生7.2～7.4级地震，大震复发周期长达8 000余年；如果陡坎高度由2次古地震事件叠加形成，则可能发生6.9～7.1级地震，全新世中期以来大震复发周期可能为2 000～3 000年。     

THE SLIP RATE AND PALEOEARTHQUAKES OF THE YUMEN FAULT IN THE NORTHERN QILIAN MOUNTAINS SINCE THE LATE PLEISTOCENE

The Yumen Fault lies on the west segment of the north Qilian Fault belt and adjacent to the Altyn-Tagh Fault,in the north margin of the Tibet Plateau.The tectonic location of the Yumen fault is special,and the fault is the evidence of recent activity of the northward growth of Tibetan plateau.In recent twenty years,many researches show the activity of the Yumen Fault became stronger from the early Pleistocene to the Holocene.Because the Yumen Fault is a new active fault and fold belt in the Qilian orogenic belt in the north margin of the Tibet Plateau,it is important to ascertain its slip rate and the recurrence interval of paleoearthquakes since the Late Pleistocene.Using the satellite image interpretation of the Beida river terrace,the GPS measurement of alluvial fans in front of the Yumen Fault and the trench excavation on the fault scarps,two conclusions are obtained in this paper.(1) The vertical slip rate of the Yumen Fault is about 0.41~0.48mm/a in the Holocene and about 0.24~0.30mm/a in the last stage of the late Pleistocene.(2) Since the Holocene epoch,four paleoearthquakes,which happened respectively in 6.12~10.53ka,3.6~5.38ka,1.64~1.93ka and 0.63~1.64ka,ruptured the surface scarps of the Yumen Fault.Overall,the recurrence interval of the paleoseismic events shortens gradually and the activity of the Yumen Fault becomes stronger since the Holocene.Anther characteristic is that every paleoearthquake probably ruptured multiple fault scarps at the same time.     

新疆阜康—吉木萨尔断层晚第四纪活动与变形特征的新认识

阜康—吉木萨尔断层是博格达山体与山前冲洪积平原的分界断层，全新世以来仍在活动，山前的冲洪积平原和河流低级阶地均发生了不同程度的拱曲变形，断层剖面揭示了该断层晚更新世末期有3次古地震事件。断层近地表后倾角变缓，地表的陡坎地形主要是由地层的拱曲变形形成的，反映了断层近地表位错的消减和分配规律。     

FAULTED LANDFORM AND SLIP RATE OF THE JINGHE SECTION OF THE BOLOKENU-AQIKEKUDUKE FAULT SINCE THE LATE PLEISTOCENE

The Bolokonu-Aqikekuduke fault zone(Bo-A Fault)is the plate convergence boundary between the middle and the northern Tianshan. Bo-A Fault is an inherited right-lateral strike-slip active fault and obliquely cuts the Tianshan Mountains to the northwest. Accurately constrained fault activity and slip rate is crucial for understanding the tectonic deformation mechanism, strain rate distribution and regional seismic hazard. Based on the interpretation of satellite remote sensing images and topographic surveys, this paper divides the alluvial fans in the southeast of Jinghe River into four phases, Fan1, Fan2, Fan3 and Fan4 by geomorphological elevation, water density, depth of cut, etc. This paper interprets gullies and terrace scarps by high-resolution LiDAR topographic data. Right-laterally offset gullies, fault scarps and terrace scarps are distributed in Fan1, Fan2b and Fan3. We have identified a total of 30 right-laterally offset gullies and terrace scarps. Minimum right-lateral displacement is about 6m and the maximum right-lateral displacements are(414±10)m, (91±5)m and(39±1)m on Fan2b, Fan3a and Fan3b. The landform scarp dividing Fan2b and Fan3a is offset right-laterally by (212±11)m. Combining the work done by the predecessors in the northern foothills of the Tianshan Mountains with Guliya ice core climate curve, this paper concludes that the undercut age of alluvial fan are 56~64ka, 35~41ka, 10~14ka in the Tianshan Mountains. The slip rate of Bo-A Fault since the formation of the Fan2b, Fan3a and Fan3b of the alluvial-proluvial fan is 3.3~3.7mm/a, 2.2~2.6mm/a and 2.7~3.9mm/a. The right-lateral strike-slip rate since the late Pleistocene is obtained to be 3.1±0.3mm/a based on high-resolution LiDAR topographic data and Monte Carlo analysis.     

甘加盆地西缘断裂带发现新活动证据

甘加盆地位于西秦岭北缘断裂带西端,盆地西缘发育了三条近南北向的断层（东支、中支、西支）,表现为西高东低的弧形地貌阶梯带。基于高分辨率卫星遥感影像解译、地质地貌调查、UAV航拍测量、剖面清理与¹⁴C测年等工作,对甘加盆地西缘断裂带进行综合研究,发现该断裂带第四纪晚期有新活动。断层新活动在地貌上表现为不同级别的断层陡坎、阶地与洪积台地断错以及冲沟与阶地右旋等特征。断层剖面与擦痕揭示,该断裂带具右旋逆冲性质,断层断错最新地层为全新统。根据测量与测年数据,初步估算甘加盆地西缘断裂带西支全新世中期以来的平均水平右旋滑动速率为0.89 mm/a,平均垂直滑动速率为0.30 mm/a。     

ANALYSIS OF EVOLUTION OF THE RIYUESHAN FAULT SINCE LATE PLEISTOCENE USING STRUCTURAL GEOMORPHOLOGY

The northeastern margin of Tibetan plateau is an active block controlled by the eastern Kunlun fault zone, the Qilian Shan-Haiyuan fault zone, and the Altyn Tagh fault zone. It is the frontier and the sensitive area of neotectonic activity since the Cenozoic. There are widespread folds, thrust faults and stike-slip faults in the northeastern Tibetan plateau produced by the intensive tectonic deformation, indicating that this area is suffering the crustal shortening, left-lateral shear and vertical uplift. The Riyueshan Fault is one of the major faults in the dextral strike-slip faults systems, which lies between the two major large-scale left-lateral strike-slip faults, the Qilian-Haiyuan Fault and the eastern Kunlun Fault. In the process of growing and expanding of the entire Tibetan plateau, the dextral strike-slip faults play an important role in regulating the deformation and transformation between the secondary blocks. In the early Quaternary, because of the northeastward expansion of the northeastern Tibetan plateau, tectonic deformations such as NE-direction extrusion shortening, clockwise rotation, and SEE-direction extrusion occurred in the northeastern margin of the Tibetan plateau, which lead to the left-lateral slip movement of the NWW-trending major regional boundary faults. As the result, the NNW-trending faults which lie between these NWW direction faults are developed. The main geomorphic units developed within the research area are controlled by the Riyueshan Fault, formed due to the northeastward motion of the Tibet block. These geomorphic units could be classified as:Qinghai Lake Basin, Haiyan Basin, Datonghe Basin, Dezhou Basin, and the mountains developed between the basins such as the Datongshan and the Riyueshan. Paleo basins, alluvial fans, multiple levels of terraces are developed at mountain fronts. The climate variation caused the formation of the geomorphic units during the expansion period of the lakes within the northeastern Tibetan plateau. There are two levels of alluvial fans and three levels of fluvial terrace developed in the study area, the sediments of the alluvial fans and fluvial terraces formed by different sources are developed in the same period. The Riyueshan Fault connects with the NNW-trending left-lateral strike-slip north marginal Tuoleshan fault in the north, and obliquely connects with the Lajishan thrust fault in the south. The fault extends for about 180km from north to south, passing through Datonghe, Reshui coal mine, Chaka River, Tuole, Ketu and Xicha, and connecting with the Lajishan thrusts near the Kesuer Basin. The Riyueshan Fault consists of five discontinuous right-step en-echelon sub-fault segments, with a spacing of 2~3km, and pull-apart basins are formed in the stepovers. The Riyueshan Fault is a secondary fault located in the Qaidam-Qilian active block which is controlled by the major boundary faults, such as the East Kunlun Fault and the Qilian-Haiyuan Fault. Its activity characteristics provide information of the outward expansion of the northeastern margin of Tibet. Tectonic landforms are developed along the Riyueshan Fault. Focusing on the distinct geomorphic deformation since late Pleistocene, the paper obtains the vertical displacement along the fault strike by RTK measurement method. Based on the fault growth-linkage theory, the evolution of the Riyueshan Fault and the related kinetic background are discussed. The following three conclusions are obtained:1)According to the characteristics of development of the three-stage 200km-long steep fault scarp developed in the landforms of the late Pleistocene alluvial fans and terraces, the Riyueshan Fault is divided into five segments, with the most important segment located in the third stepover(CD-3); 2)The three-stage displacement distribution pattern of the Riyueshan Fault reveals that the fault was formed by the growths and connections of multiple secondary faults and is in the second stage of fault growth and connection. With CD-3 as the boundary, the faults on the NW side continue to grow and connect; the fault activity time on the SE side is shorter, and the activity intensity is weaker; 3)The extreme value of the fault displacement distribution curve indicates the location of strain concentration and stress accumulation. With the stepover CD-3 as the boundary, the stress and strain on NW side are mainly concentrated in the middle and fault stepovers. The long-term accumulation range of stress on the SE side is relatively dispersed. The stress state may be related to the counterclockwise rotation inside the block under the compression of regional tectonic stress.     

SLIP RATES OF THE RIYUE MT. FAULT AT DEZHOU SEGMENT SINCE LATE PLEISTOCENE

The Riyue Mt. Fault is a secondary fault controlled by the major regional boundary faults (East Kunlun Fault and Qilian-Haiyuan Fault). It lies in the interior of Qaidam-Qilianshan block and between the major regional boundary faults. The Riyue Mt. fault zone locates in the special tectonic setting which can provide some evidences for recent activity of outward extension of NE Tibetan plateau, so it is of significance to determine the activity of Riyue Mt. Fault since late Pleistocene to Holocene. In this paper, we have obtained some findings along the Dezhou segment of Riyue Mt. Fault by interpreting the piedmont alluvial fans, measuring fault scarps, and excavating trenches across the fault scarp. The findings are as follows:(1) Since the late Pleistocene, there are an alluvial fan f_p and three river terraces T₁-T₃ formed on the Dezhou segment. The abandonment age of f_p is approximately (21.2±0.6) ka, and that of the river terrace T₂ is (12.4±0.11) ka. (2) Since the late Pleistocene, the dextral strike-slip rate of the Riyue Mt. Fault is (2.41±0.25) mm/a. In the Holocene, the dextral strike-slip rate of the fault is (2.18±0.40) mm/a, and its vertical displacement rate is (0.24±0.16) mm/a. This result indicates that the dextral strike-slip rate of the Riyue Mt. Fault has not changed since the late Pleistocene. It is believed that, as one of the dextral strikeslip faults, sandwiched between the the regional big left-lateral strike-slip faults, the Riyue Mt. Fault didn't cut the boundary zone of the large block. What's more, the dextral strike-slip faults play an important role in the coordination of deformation between the sub-blocks during the long term growth and expansion of the northeast Tibetan plateau.     

中甸-大具断裂南东段晚第四纪活动的地质地貌证据

中甸-大具断裂南东段位于哈巴和玉龙雪山北麓,属于川西北次级块体西南边界,断裂总体走向310°~320°,是一条重要的边界断裂。了解该断裂的活动性质、活动时代和滑动速率等对分析川西北次级块体运动,研究该断裂与玉龙雪山东麓断裂的交切关系等问题具有重要意义。文中基于1︰5万活动断层地质填图,对断裂沿线地层地貌、陡坎地貌、地表破裂、典型断层剖面以及河流阶地等进行了详细的研究。研究表明:1)中甸-大具断裂南东段按几何结构、断错地貌表现、断裂活动性可分为马家村—大具次级段和大具—大东次级段。2)通过野外地质调查发现,马家村—大具次级段断错了全新世冲洪积扇,形成了地表破裂,为全新世活动段;而大具—大东次级段虽然也断错了晚更新—全新世地层,但其断错规模及滑动速率均较小,由此认为其全新世以来活动较弱。3)通过分析断裂沿线断层陡坎、水平位错及地表破裂等地质地貌问题,认为马家村—大具次级段的活动性质为右旋走滑兼正断,其晚更新世以来的垂直滑动速率为0.4~0.8mm/a,水平滑动速率为1.5~2.4mm/a;大具—大东次级段以右旋走滑为主、正断为辅,其晚更新世晚期以来的垂直滑动速率为0.1mm/a。4)在大具盆地内发现的NW向地表破裂带的形成时代很年轻,不排除是1966年中甸6.4级地震或1996年丽江7.0级地震造成的地表破裂。