东北地震区地震活动趋势数学建模分析

本文按照活动地块边界带和地震区的划分方案,使用Mapsis软件选取了东北地震区1900年以来Ms4.7级以上地震资料,这样得到的地震资料可能具有一个完整的地质系统性。使用数学中19阶多项式模型,对地震资料进行最佳逼近拟合,并递推未来1～2年时间尺度预测,模型中的参数用最小二乘法求取,引用了一种数学方法来描述东北地震区的地震趋势规律。     

新疆地震活动区的地磁观测与研究

新疆地区是中国最活跃的地震区之一.为了监测新疆地区潜在的强烈地震,2003年在该地区建立了N和S两个地磁测网并进行了地磁三分量测量.在N和S两个测网所选建的51个测点周围环境良好,地磁梯度小,适宜地磁测量.在野外测量中,使用性能稳定可靠的G-856磁力仪、DI磁力仪与GPS仪器,应用GPS测定方位角,DI磁力仪测量地磁偏角D与倾角I,G-856磁力仪测量总强度F.应用新疆地区乌鲁木齐与喀什地磁台站的资料,分别通化了N和S两个测网的地磁测量资料.该地磁通化值的平均标准偏差σ为:F的σf=0.20 nT;D的σd=0.06′;I的σI=0.03′,表明地磁测量资料准确可靠.根据上述地磁测量资料,应用精度高的spline方法,得到了N与S测网地磁场及其异常场的分布.结果表明,该地磁场及其异常场的分布,可以准确地描述N与S测网的地磁场及其地磁异常场.该地磁分布为今后在新疆地区的震磁研究与地震监测提供了良好的地磁参考场.     

Velocity structure and active fault of Yanyuan-Mabian seismic zone―The result of high-resolution seismic refraction experiment

The authors processed the seismic refraction Pg-wave travel time data with finite difference tomography method and revealed velocity structure of the upper crust on active block boundaries and deep features of the active faults in western Sichuan Province. The following are the results of our investigation. The upper crust of Yanyuan basin and the Houlong Mountains consists of the superficial low-velocity layer and the deep uniform high-velocity layer, and between the two layers, there is a distinct, and gently west-dipping structural plane. Between model coordinates 180-240 km, P-wave velocity distribution features steeply inclined strip-like structure with strongly non-uniform high and low velocities alternately. Xichang Mesozoic basin between 240 and 300 km consists of a thick low-velocity upper layer and a high-velocity lower layer, where lateral and vertical velocity variations are very strong and the interface between the two layers fluctuates a lot. The Daliang Mountains to the east of the 300 km coordinate is a non-uniform high-velocity zone, with a superficial velocity of approximately 5 km/s. From 130 to 150 km and from 280 to 310 km, there are extremely distinct deep anomalous high-velocity bodies, which are supposed to be related with Permian magmatic activity. The Yanyuan nappe structure is composed of the superficial low-velocity nappe, the gently west-dipping detachment surface and the deep high-velocity basement, with Jinhe-Qinghe fault zone as the nappe front. Mopanshan fault is a west-dipping low-velocity zone, which extends to the top surface of the basement. Anninghe fault and Zemuhe fault are east-dipping, tabular-like, and low-velocity zones, which extend deep into the base-ment. At a great depth, Daliangshan fault separates into two segments, which are represented by drastic variation of velocity structures in a narrow strip: the west segment dips westward and the east segment dips eastward, both stretching into the basement. The east margin fault of Xichang Mesozoic basin features a strong velocity gradient zone, dipping southwestward and stretching to the top surface of the basement. The west-dipping, tabular-like, and low-velocity zone at the easternmost segment of the profile is a branch of Mabian fault, but the reliability of the supposition still needs to be confirmed by further study. Anninghe, Zemuhe and Daliangshan faults are large active faults stretching deep into the basement, which dominate strong seismic activities of the area.     

Ductile deformation and development of andalusite microstructures in the Hongusan area: Constraints on the metamorphism and tectonics of the Ryoke Belt

Abstract   The main mesoscopic features of the ductile deformation in the Hongusan region of the Ryoke Belt can be explained in terms of a single deformation phase, Dm . The associated stretching lineation is roughly east–west and has an associated top-to-the-west sense of shear. This information fills an important gap in our knowledge about the deformational history of the Ryoke metamorphic belt. Andalusite porphyroblasts are well-developed in the Hongusan area and their microstructure can be used to link the deformational history with the metamorphism. However, the andalusite porphyroblasts show both intertectonic and post-tectonic microstructures. Some porphyroblasts have an intertectonic core and post-tectonic rim. Analysis of associated metamorphic minerals and bulk-rock chemistry suggests that the distinct types of microstructure can be explained in terms of distinct formation reactions related to regional and contact metamorphism. The intertectonic microstructure shows the presence of a deformation pre-dating Dm , referred to as Dc . These two deformation stages are sufficient to account for all the main deformation features. The distribution of post-tectonic andalusite growth shows a very broad thermal effect around an intrusion in the area. This can help place constraints on the thermal history of the Ryoke metamorphic belt.     

刚性挡土墙主动土压力颗粒流模拟

将土体离散为具有滑动连接模型的刚性条块,用颗粒流PFC2D程序数值从细观力学角度模拟了墙体平移(T)、绕墙底转动(RB)和绕墙顶转动(RT)位移模式下不同位移大小时刚性挡土主动土压力分布。模拟结果表明：刚性挡墙主动土压力非线性分布、墙土间外摩擦角和土体剪切角或内摩擦角对土压力有很大影响;墙体绕顶部转动时,大约0.3倍墙高以上的主动土压力大于静止土压力产生土拱效应;模拟计算值与模型试验实测数据吻合比较好,具有一定的理论价值。     

华北燕山带东部三叠纪和侏罗纪大地构造演化：来自备受争议的邓杖子组及相邻地层的线索

位于辽西凌源市南部的牛营子-邓杖子地区侏罗系地质问题多年来困扰着地质学家。争论最多的构造形迹是一套平面上呈狭长矩形,以断层为界的近直立中元古界常州沟组石英岩,及局部长城系顶部地层。这套地层绵延35 km,呈北北东展布。其西界为近直立的大齐子断层（新命名断层）和大部分向东倒转的陡倾下侏罗统邓杖子组;东界为近直立的朱杖子断层（新命名断层）和西倾的中侏罗统郭家店组。前人的构造解释倾向于大齐子断层为邓杖子组一侧下降的陡倾正断层,朱杖子断层为郭家店组一侧下降的陡倾逆断层。文中不同意这样的解释,并发现有证据表明上述两个断层都形成于之前尚未识别出的侏罗纪构造事件时期。将大齐子断层解释为早侏罗世晚期-中侏罗世早期形成的一条向西逆冲的断层,沿着它使长城系推覆于邓杖子组之上,然后,该逆冲断层上、下盘地层共同卷入后期褶皱变形当中。朱杖子断层原本为正断层,形成于原来未识别出的中侏罗世伸展变形阶段,并构成了郭家店半地堑边界断层。朱杖子断层沿着向东倾斜的常州沟组石英岩与串岭沟组页岩的界面发育。随着断层的发育,位于常州沟组石英岩之上的串岭沟组及长城系上部地层发生拆离沉降并被埋藏在半地堑之下。随后,发生在中侏罗世晚期或晚侏罗世早期收缩构造变形,改造了邓杖子-常州沟-郭家店组构造组合的几何形态。本期改造导致以下结果：（1）朱杖子正断层发生反转成为逆断层;（2）蓟县系沿着杨杖子-瓦房店逆冲断层向东掩覆于断层围限的长城系地层及相邻侏罗系之上。同时,邓杖子组倾角加大并向东倒转。研究表明,辽西地区的侏罗纪构造演化过程远比原先所认为的要复杂。     

Soil fertility evolution and landscape dynamics in a Mediterranean area: a case study in the Sant Llorenç Natural Park (Barcelona, NE Spain)

The cartography of land covers was used to study fertility and soil evolution in a mountainous Mediterranean area during the anthropocene period ( Crutzen P J 2002 Geology of mankind Nature 415 23). The aim was to determine changes in fertility as agricultural lands were abandoned in the 14 000 hectare area that constitutes Sant Llorenç del Munt Natural Park in a pre-coastal Catalan mountain range (north-eastern Iberian Peninsula). The analysis of land covers using vegetation maps, orthorectified images and aerial photography has allowed us to differentiate six vegetation groups: holm-oak wood, pine grove, oak wood, scrub, active agricultural fields and abandoned agricultural fields. The anthropic covers over the past 100 years were subdivided into five categories: active fields and those abandoned over four time periods. Study variables include field shape (concave, convex, flat), orientation (north, south) and slope (ranging from 12º to 24º). The parameters used for the physical-chemical soil analysis included organic material, phosphorous and potassium; fertility was classified based on groups, types and classes. The results indicate that even when the visual appearance of certain landscapes is similar, the edaphic characteristics may be very different. Changes induced by human disturbance share this phenomenon. Therefore, land management should be considered globally, taking into account vegetation, soils and water as interdependent factors, since it is their interaction that produces landscape and most affects its evolution over time.     

Late Quaternary deformation on the island on Pantelleria: New constraints for the recent tectonic evolution of the Sicily Channel Rift (southern Italy)

Structural observations carried out on the volcanic Island of Pantelleria show that the tectonic setting is dominated by NNE trending normal faults and by NW-striking right-lateral strike-slip faults with normal component of motion controlled by a ≈N 100°E oriented extension. This mode of deformation also controls the development of the eruptive fissures, dykes and eruptive centres along NNE–SSW belts that may thus represent the surface response to crustal cracking with associated magma intrusions. Magmatic intrusions are also responsible for the impressive vertical deformations that affect during the Late Quaternary the south-eastern segment of the island and producing a large dome within the Pantelleria caldera complex. The results of the structural analysis carried out on the Island of Pantelleria also improves the general knowledge on the Late Quaternary tectonics of the entire Sicily Channel. ESE–WNW directed extension, responsible for both the tectonic and volcano-tectonic features of the Pantelleria Island, also characterizes, at a greater scale, the entire channel as shown by available geodetic and seismological data. This mode of extension reactivates the older NW–SE trending fault segments bounding the tectonic troughs of the Channel as right-lateral strike-slip faults and produces new NNE trending pure extensional features (normal faulting and cracking) that preferentially develop at the tip of the major strike-slip fault zones. We thus relate the Late Quaternary volcanism of the Pelagian Block magmatism to dilatational strain on the NNE-striking extensional features that develop on the pre-existing stretched area and propagate throughout the entire continental crust linking the already up-welled mantle with the surface.     

A Review on Researches of Active Tectonics——History, Progress and Suggestions1

This paper reviews the history and progress of research on active tectonics in China and overseas. By giving a brief introduction on the history of active tectonic research in China and other countries, the paper sums up the process and development of quantitative investigation of active tectonics since the 1980s. The focus is on the main efforts and progress made in China on certain aspects of research, such as basic surveys and applied investigation of active tectonics, the study of theories related to regional active tectonics and their kinematics and geodynamics, surveys on coupling relations between deep and shallow structures, active fault surveys and prospecting and seismic hazard assessment in urban areas, as well as the efforts made using Quaternary geochronology. Furthermore, the paper looks back on Chinese quantitative investigation of active tectonics in China and sums up cognitions derived from studies on the determination of several basic and measurable parameters of active tectonics. These parameters include the length of fault and fault segmentation, coseismic slip and cumulative slip, fault slip rate, the sequence of paleoearthquake events and the time elapsed since the most recent event. At the same time, efforts and progress made in China on assessing the long-term seismic potential for active faults and evaluating the risk from potential active fault movement have been reviewed by summarizing research on developing theories, models, methods and the application of time-dependent seismic potential to prohabilistic assessment, magnitude estimation for potential earthquakes on active faults, and the forecast of potential risk caused by active fault movement. Finally, in consideration of the realities and problems in the research of active tectonics in China, the authors put forward several suggestions for issues worthy of more attention for further investigation in the future.