2022年9月17日中国台湾地震序列的触发机制及其动力学成因

2022年9月17—18日, 中国台湾先后发生台东县MS6.5和花莲县MS6.9两次强震及多次余震。两次强震均为逆走滑型地震, 且震中都位于台湾纵谷断裂带, 该地区构造复杂, 为晚中生代古太平洋板块朝东亚陆缘的消减带, 具有逆冲型构造应力背景。对纵谷断裂带周围地区历史上发生过的地震进行统计发现, 大部分地震为逆断型。为探究该地区此次发生逆走滑型地震的原因及其与构造应力场的关系, 首先通过搜集研究区相关的地震震源机制, 反演该地区的构造应力场, 明确其是以走向为北西西向的压应力为主的应力场; 然后将应力场投影到走向、倾角不同的断层面上, 发现一些节面上表现出较大的相对剪应力和较小的相对正应力, 说明这些节面上具有较强的剪切作用和较小的摩擦力, 容易发生错动而产生逆断型、逆走滑型和走滑型的地震。同时, 为明确短时间内两次强震间的触发关系, 通过计算MS6.5地震在MS6.9地震破裂面和滑动方向上产生的库伦破裂应力变化发现, MS6.9地震约在0.02MPa的库伦破裂应力触发下发生。相关结论对研究台湾纵谷带地震的发震机理和地球动力学具有一定的指导意义。     

Frequency–magnitude statistics and spatial correlation dimensions of earthquakes at Long Valley caldera, California

Intense earthquake swarms at Long Valley caldera in late 1997 and early 1998 occurred on two contrasting structures. The first is defined by the intersection of a north-northwesterly array of faults with the southern margin of the resurgent dome, and is a zone of hydrothermal upwelling. Seismic activity there was characterized by high b -values and relatively low values of D , the spatial fractal dimension of hypocentres. The second structure is the pre-existing South Moat fault, which has generated large-magnitude seismic activity in the past. Seismicity on this structure was characterized by low b -values and relatively high D . These observations are consistent with low-magnitude, clustered earthquakes on the first structure, and higher-magnitude, diffuse earthquakes on the second structure. The first structure is probably an immature fault zone, fractured on a small scale and lacking a well-developed fault plane. The second zone represents a mature fault with an extensive, coherent fault plane.     

西辽河流域全新世以来的农业垦殖活动(英文)

The agricultural reclamations in the Xiliao River Valley since the Holocene have led to a huge landscape change from grassland to farmland. In this paper we reconsider the man-land relationship in the Xiliao River Valley by analyzing three major agricultural reclamations in prehistory, the Liao-Jin Dynasty and the period since the Qing Dynasty. We argue that when the demographic pressure appears in this area, especially during the last reclamation, the intraregional migration (second migration) is the major response to relieve such pressure, which also distinguishes two different settlement locations: "the initial area" and "the secondary area". Due to the environmental differences between these two areas, the cultivation on the latter one has caused more serious disturbance to the local environment. Thus the secondary area has become the key region which needs environmental management seri-ously.     

Sediment budget and tectonic evolution of the Meuse catchment in the Ardennes and the Roer Valley Rift System

The Meuse river system is located in the northeastern part of the Paris Basin, the Ardennes, and the Roer Valley Rift System (RVRS). The Meuse river system developed during the uplift of the Ardennes since the Eocene and it was affected by renewed rifting of the RVRS starting in the Late Oligocene. In response to the uplift of the Ardennes, the river system incised and a terrace sequence developed during the Plio–Pleistocene. The sediments generated by erosion in the catchment were transported into the RVRS and further to the north, into the Zuiderzee Basin and the North Sea Basin. Using a digital terrain model, the amount of eroded rock volume versus time for the Meuse catchment has been computed using the Paleogene and older planation surfaces and the fluvial terraces. Comparison of the amount of eroded material with the volume of sediment preserved in the RVRS for the early Middle Pleistocene shows that about 17.5% of the sediment volume transported into the RVRS remained there, the rest being transported further into the Zuiderzee Basin and the North Sea Basin. The Quaternary tectonic uplift of the Ardennes inferred from the incision history of the Meuse river system is characterized by a long-term uplift, on which a Middle Pleistocene acceleration is superimposed. The accelerated uplift is contemporaneous with an uplift event in the RVRS and in the neighbouring Eifel area, and with the onset of the youngest phase of volcanism in the Eifel area. The areal distribution of this uplift is characterized by a dome shape centered around the Eifel area.     

下扬子区三叠纪古生物和古地理变迁及其主要原因

根据下扬子区三叠系生物化石和沉积相的研究，该区三叠纪古地理环境先后经历陆表海，萨布哈潮坪－泻湖，下三角洲平原滨海河口湾及三角洲平原河，湖和沼泽一系列变迁，其主要原因是由于扬子板块从赤道以南附近持续向北进行跨气候带漂移抵达北回归线以北附近的结果。     

峡谷高坝蓄水诱发近坝库盆及岸坡微变形机理研究现状

峡谷高坝蓄水诱发的库盆及岸坡微变形,多指由于高坝蓄水导致两岸山体应力状态调整而产生的非失稳变形,一般数厘米到数十厘米,有的研究亦称谷幅变形（水平向）、库盆变形（竖向）、河谷变形（库区内）等。目前仅在我国少数特高坝工程中开展过监测分析,如锦屏一级、小湾、溪洛渡等,其中谷幅变形是研究的重点。然而,目前关于这一变形的系统研究和定量分析较少,基于不同工程监测数据得到的变形规律有所差异,很难用单一的理论进行解释,所提出的机理尚不完备。特别地,由于可借鉴的工程经验不足,在设计中缺乏相应技术标准,高坝蓄水导致的岸坡微变形对坝体长期影响不得而知。此外,正在建设的白鹤滩（289m）、双江口（314m）等水电站,都需要面临峡谷高坝谷幅变形的问题。因此,本文综述了这一问题的研究现状,探讨了库盆及岸坡微变形可能的机理并进行了展望。     

美国田纳西流域开发及其对我国流域经济发展的启示

本文在分析了美国田纳西河流域开发的历史背景和主要特点基础上 ,借鉴其成功经验 ,提出了我国流域经济发展的方向和途径。     

Surface-wave propagation across the Mexican Volcanic Belt and the origin of the long-period seismic-wave amplification in the Valley of Mexico

A network of nine broad-band seismographs was operated from March to May 1994 to study the propagation of seismic waves across the Mexican Volcanic Belt (MVB) in the region of the Valley of Mexico. Analysis of the data from the network reveals an amplification of seismic waves in a wide period band al the stations situated in the southern part of the MVB.
The group velocities of the fundamental mode of the Rayleigh wave in the period range 2–13 s are found to be lower in the southern part of the MVB than in its northern part and in the region south of the MVB. The inversion of dispersion curves shows that the difference in group velocities is due to the presence of a superficial low-velocity layer (with an average S -wave velocity of 1.7 km s^-1 and an average thickness of 2 km) beneath the southern part of the MVB. This low-velocity zone is associated with the region of active volcanism.
Numerical simulations show that this superficial low-velocity layer causes a regional amplification of 8–10 s period signals, which is of the same order as the amplification measured from the data. This layer also increases the signal duration significantly because of the dispersion of the surface waves. These results confirm the hypothesis of Singh et al. (1995), who suggested that the regional amplification observed in the Valley of Mexico is due to the anomalously low shear-wave velocity of the shallow volcanic rocks in the southern MVB     

区域经济空间分异机制研究——一个理论分析模型及其在黄河流域的应用

区域经济空间分异机制是区域经济研究的一个重要问题。目前对此问题的研究有多个视角,但各个视角的研究成果都只是从某个方面阐释区域经济空间分异的机制。本文从区域经济空间分异机制的内涵出发,以经济增长因素的相关理论和分工理论为基础,将各个视角的研究成果贯穿起来,构建了一个解释区域经济空间分异机制的理论分析模型,并运用这个模型对黄河流域经济空间分异机制进行了实证分析。结果表明,黄河流域综合要素禀赋、分工与集聚的耦合互动关系明显存在,黄河流域经济空间分异受要素禀赋决定作用机制、分工传导作用机制和循环累积因果机制的支配。     

清代青藏高原东北部河湟谷地林草地覆盖变化

河湟谷地是青藏高原东北缘典型的农牧交错区,清代以来耕地的扩张导致林草地覆盖发生明显变化。本文在现代植被图的基础上,选取土壤、地形因素,并依据历史文献数据,重建河湟谷地潜在林地草地格局,在此基础上结合清代耕地变化的重建结果,推算出清代河湟谷地林草地覆盖的变化状况。结果显示：①清代耕地扩张之前,其林、草地分布与现今各类植被类型的空间分布格局基本一致,林地分布范围比现代略大,灌木林地在空间上连续性更强,草地分布区域更广;②估算出河湟谷地潜在林地、灌木林地、草地面积分别约为0.28×10⁴、0.93×10⁴、2.1618×10⁴ km²,由于耕地开垦,至清代末期,河湟谷地草地、灌木林地、林地面积分别累计减少5180.41、1330.35、441.31 km²,其中草地被垦殖占用的面积最大,程度最深,减少的区域主要集中在湟水谷地中游的乐都盆地、西宁盆地以及黄河谷地的尖扎盆地、化隆盆地等;③清代河湟谷地中人类垦殖原始覆盖类型的差异性不仅受自然环境的限制,同样受到社会政策因素的影响。