青藏高原东北缘断层泥的研究

本文对青藏高原东北缘一些主要断裂（包括阿尔金、昌马、毛毛山等断裂）的断层泥首次进行了研究。在对断裂带的内部结构、围岩成分、断层泥的厚度及石英颗粒表面特征等综合分析的基础上对断裂的活动年代、活动方式及断层泥形成的深度进行了讨论。石英颗粒表面上溶蚀程度（颗粒表面的光滑程度、凹凸现象及孔洞发育情况）可划分为６种类型并且每种类型都有相应的年代。根据断裂的粘滑、蠕滑特征，对该区的各活动断裂进行了粘滑段与蠕滑段的划分。用红外光谱与稀土元素的分析结果，算得断层泥形成的深度在地壳１０ｋｍ范围内。     

Cambrian trace fossils and worm like impressions from the Tal Group, Gopi-Chand-Ka Mahal section, Mussoorie syncline, Lesser Himalaya

Cambrian trace fossils and worm like impressions are described herein from the three stratigraphic units of Tal Group of rocks exposed along the track from Maldeota to Dhaulagiri in Gopi-Chand-Ka Mahal sec-tion, Mussoorie syncline. The upper 10 m thick sand-stone succession (Arenaceous Member) of Deo-Ka- Tibba Formation (lower Tal Group) contains high den-sity and low diversity Skolithos pipe rock. The Sko-lithos pipe rock in sandstone succession of Arenaceous Member (Deo-Ka-Tibba Formation) indicates shallow marine condition under sand shifting environment of deposition. Higher in the succession, in calcareous Member (Deo-Ka-Tibba Formation), Cruziana ichno-facies occurs in association with Monomorphichnus, Planolites and Paleophycus.     

北祁连山-河西走廊大震危险区预测

以青藏块体北部的北祁连山-河西走廊地震构造带为研究对象,在系统收集整理该区主干活动断裂新活动性特征、断裂滑动速率、历史地震及古地震资料的基础上,结合现今地震活动性,采用地震空区、空段识别方法和地震活动b值空间图像扫描方法,分析了研究区内历史地震及b值的分布特征.结果显示,该区的榆木山北缘断裂离逝时间较长,应力积累程度较...     

Fractal size and spatial distributions of fault zones: An investigation into the seismic Chelungpu Fault, Taiwan

Abstract   The fractality of fault zones of thickness T for the 248-m-long core from a borehole penetrating the northern segment of the seismic Chelungpu Fault, Taiwan, was analyzed. The frequency curve of T shows that the fractal dimension is normal when T is smaller than a characteristic thickness T _c, and it becomes abnormally large when T exceeds T _c. The fractal dimensions of size and spatial distributions of T increase as the mean distribution density of T increases, which is inconsistent with the evolution laws for ordinary brittle faults. This discrepancy implies that the thickening rate of T when T is more than T _c is not constant, but a decreasing function of fault displacement. The slow thickening rate is related to the elastohydrodynamic lubrication which was effective on the fault when T exceeds T _c. This slip instability mechanism can explain the large, fast and smooth slip on the northern segment of the Chelungpu Fault during the 1999 Chi-Chi earthquake.     

STUDY ON PALEOEARTHQUKES ALONG THE FODONGMIAO-HONGYAZI FAULT,GANSU PROVINCE

The Fodongmiao-Hongyazi Fault is a Holocene active thrust fault, belonging to the middle segment of northern Qilianshan overthrust fault zone, located in the northeastern edge of the Tibet plateau. The Hongyapu M7(1/4) earthquake in 1609 AD occurred on it. A few paleo-seismology studies were carried out on this fault zone. It was considered that four paleoearthquakes occurred on the Fodongmiao-Hongyazi Fault between(6.3±0.6) ka BP and(7.4±0.4) ka BP, in(4.3±0.3) ka BP, in(2.1±0.1) ka BP and in 1609 AD. The occurrences of the earthquakes suggested the quasi-periodic characteristic with a quasi-periodic recurrence interval between 1 600~2 500a(Institute of Geology, State Seismological Bureau, Lanzhou Institute of Seismology, State Seismological Bureau. 1993; Liu et al., 2014). There was no direct evidence for the Hongyapu M7(1/4) earthquake in 1609 AD from trench research in the previous studies. Great uncertainty exists because of the small number of the chronology data, as a few TL and OSL measurement data and several¹⁴ C data, and it was insufficient to deduce the exact recurrence interval for the paleoearthquakes. Five trenches were excavated and cleared up respectively in the eastern segment, middle segment and western segment along the Fodongmiao-Hongyazi Fault. After detail study on the trench profiles, the sedimentary characteristics, sequence relationship of the stratigraphical units, and fault-cuts in different stratigraphical units were revealed in these five trenches. Four paleoearthquakes in Holocene were distinguished from the five trenches, and geology evidences of the Hongyapu M7(1/4) earthquake in 1609 AD were also found. More accurate constraint of the occurring time of the paleo-earthquakes since Holocene on the Fodongmiao-Hongyazi Fault is provided by the progressive constraining method(Mao and Zhang, 1995), according to amounts of ¹⁴ C measurement data and OLS measurement data of the chronology samples from different stratigraphical units in the trenches. The first paleoevent, E4 occurred 10.6ka BP. The next event, E3 occurred about 7.1ka BP. The E2 occurred about 3.4ka BP. The last event, E1 is the Hongyapu M7(1/4) earthquake in 1609 AD. Abounds of proofs for the occurrences of the events of E1, E2 and E3 were found in the trench Tc1, trench Tc2, trench Tc4 and trench Tc3, located in the eastern, middle and western segments of the Fodongmiao-Hongyazi Fault accordingly. It's considered that the events E1, E2 and E3 may cause whole segment rupturing according to the proofs for these three events found together in individual trenches. The event E4 was only found in the trench Tc5 profile in the west of the Xiaoquan village in the eastern segment of the Fodongmiao-Hongyazi Fault. The earthquake rupture characteristics of this event can't be revealed before more detailed subsequent research. The time intervals among the four paleoearthquakes are ca 3.5ka, ca 3.7ka, and ca 3.0ka. The four events are characterized by ca 3.4ka quasi-periodic recurrence interval.     

利用InSAR资料反演缅甸Mw6.8地震断层滑动分布

2011年3月24日缅甸东北部发生M_w6.8级地震.本文利用覆盖该地区的升降轨ALOS PALSAR数据,获取了该次地震的同震形变场,并采用灰度配准技术获取了其地表破裂位移.针对影像中因轨道不精确造成的非线性长波长误差,本文采用二次多项式曲面法予以去除,获取了更为精确的同震形变场.最后,基于弹性半空间形变模型反演了该地震的断层滑动分布.结果表明,该地震断层滑动以左旋走滑为主,兼具少许的倾滑运动分量,断层滑动主要集中分布在断层面0~10 km深度范围,最大滑动量达5 m,位于地表以下5 km深处.反演获得的地震标量矩为2.49×10¹⁹N·m,震级约为M_w6.8级.     

The Quaternary Tectonic Stress Field of the Kunming Basin and Its Surrounding Areas

The Kunming basin is a Cenozoic faulted basin controlled by N-S trending active faults. there are totally 8 main active faults in and around the Kunming basin area. Inversion of fault slip data suggests that the stress field of the Kunming basin has experienced two major stages. In the first stage (from the late-Pliocene to mid-Pleistocene), the regional tectonic stress field was characterized by near E-W compression and near N-S extension. In the second stage (from the late-Pleistocene to the present), the tectonic stress field has been mainly characterized by NNW-SSE compression and NEE-SWW extension. Under such a stress field, the near N-S trending faults in the region mainly show a lateral slip.     

P-wave velocity structure in the crust and the uppermost mantle of Chao Lake region of the Tan-Lu Fault inferred from teleseismic arrival time tomography

Chao Lake is a Geoheritage site on the active Tan-Lu Fault between the Yangtze craton, the North China craton, and the Dabie orogenic belt in the southeast. This segment of the fault is not well constrained at depth partly due to the overprinting of the fault zone by intrusive materials and its relatively low seismic activity and sparse seismic station coverage. This study took advantage of a dense seismic array deployed around Chao Lake to delineate the P-wave velocity variations in the crust and uppermost mantle using teleseismic earthquake arrival time tomography. The station-pair double-difference with waveform cross-correlation technique was employed. We used a multiscale resolution 3-D initial model derived from the combination of high-resolution 3-D v_S models within the region of interest to account for the lateral heterogeneity in the upper crust. The results revealed that the velocity of the upper crust is segmented with structures trending in the direction of the strike of the fault. Sedimentary basins are delineated on both sides of the fault with slow velocities, while the fault zone is characterized by high velocity in the crust and uppermost mantle. The high-velocity structure in the fault zone shows characteristics of magma intrusion that may be connected to the Mesozoic magmatism in and around the Middle and Lower Yangtze River Metallogenic Belt (MLYMB), implying that the Tan-Lu fault might have formed a channel for magma intrusion. Magmatic material in Chao Lake is likely connected to the partial melting, assimilation, storage, and homogenization of the uppermost mantle and the lower crustal rocks. The intrusions, however, seem to have suffered severe regional extension along the Tan-Lu fault driven by the eastward Paleo-Pacific plate subduction, thereby losing its deep trail due to extensional erosion.     

川西喜马拉雅期碰撞造山带岩浆碳酸岩的地幔源区特征——Pb-Sr-Nd同位素证据

对形成于大陆碰撞带内的川西碳酸岩进行了详细的Pb-Sr-Nd同位素分析.结果表明,川西碳酸岩具有非常负的εNd值（-3.2～-18.7）和高的（^87Sr/^86Sr）i值（0.706020～0.707923）,以及较宽的^207Pb/^204Pb值（15.362～15.679）和^208Pb/^204Pb值（38.083～39.202）的特征,明显不同于世界上由非造山作用形成的碳酸岩.它们的Sr-Nd、Pb-Pb、Sr-Pb和Nd-Pb同位素特征表明大多数碳酸岩来源于EM Ⅰ与EMⅡ之间的一种混合地幔,与元古宙不同质量比的深海/陆源沉积物和下覆的似MORB由俯冲作用引起的洋壳的再循环有关,而少数碳酸岩则受到地壳物质混染的结果.此外,通过动力学背景分析可以得出,富集地幔EM Ⅰ与EMⅡ之间的熔融产生了川西碳酸岩以及同时代的富钾岩浆岩,这种熔融可能是由于印度大陆板片与扬子大陆板片俯冲引起的新生代软流圈物质的上涌产生的,并发生于青藏高原东缘始新世-渐新世分界线的从转换压扭变形向转换张扭变形的转变过渡的构造背景下.     

Cosmogenic Be dating of a sackung and its faulted rock glaciers, in the Alps of Savoy (France)

Sackungs are the largest gravitational deformation observed in mountains. They are characterized by the long-term slowness of the movements, but their mechanism is still not well understood. Nowadays cosmic ray exposure (CRE) dating methods allow dating the morphologic structures involved in sackung and can contribute at the understanding of their origin. In the Alps, the 5.3 km long Arcs sackung initiated during the activity of rock glaciers. Three samples from these faulted rock glaciers provide their first CRE ages and show that at 2000 m elevation these block accumulations moved during the Younger Dryas and stopped in early Holocene. Six ¹⁰Be ages of fault scarps show that the Arcs sackung lasted only a few thousand years and stopped at about 8462 ± 432 ¹⁰Be yr. They also reveal that deformation migrated upslope in agreement with a mechanism of flexural toppling of vertical layers. This unique and long gravitational event, characterized by migration of the deformation, does not support earthquake shaking as triggering mechanism for individual faults. It shows that, in the upper Isère valley, slope deformation was delayed of several thousand years after glacial debuttressing, and is not anymore active despite its fresh morphology.