巴姆地震变形场和应力场：Ⅱ．用FEPG有限元方法求解

本文利用 FEPG 有限元程序对2003年12月的巴姆地震变形场和应力场进行了模拟计算。2003年12月26日,巴姆地区发生6.6级地震。Nakamura、Suzuki 等人利用余震资料和地震破坏程度的分布图分析了余震震中的统计分布形式,得到了此次地震的发震断层是巴姆断层以西大约5km 的 Arg-e-Bam 隐伏断层的结论。凌勇等人从差分干涉雷达(D-InSAR)出发,得到了此次地震的同震干涉条纹和雷达视线方向的位移场,并从雷达干涉的相干图上确定了发震断层的痕迹。他们还利用 Okada 程序模拟计算了此次地震的位移场,模拟计算的结果与 D-InSAR 测量的位移场比较符合。Okada 程序从断层的位错为出发点进行计算,从运动学角度对此次地震变形场和应力场进行研究;本文从动力学的角度出发,研究远场区域边界的应力状态以及断层的物性参数的变化对巴姆地震形变场的影响,将各种计算结果进行对比的同时也和前人的结果相比较。本文计算中采用了凌勇等人的断层参数,即 Arg-e-Bam 隐伏断层为近南北走向,向东倾斜,近直立的倾角,右旋走滑,其(Strike,dip,slip)为(175°,80°,173°)。断层未延伸到地表,自地面以下1km 处往下延伸16km 的宽度,断层长度为20km。对断层的杨氏模量、泊松比、断层附近区域的边界受力大小、两个主应力的比例以及主应力的方向的改变对计算结果的影响做了讨论。最后通过上述几组计算结果建立了一个与前人结果较为符合的巴姆地震参数模型。通过计算,一方面揭示了应力状态和物性参数的影响,另一方面也说明 Arg-e-Bam 隐伏断层是此次地震的发震断层这一结论是可信的。     

中部天山地壳活动的GPS初步分析

通过对天山中部地区连续多年的GPS观测分析,得到了该监测区相对欧亚板块的运动速度场及应变场分布情况。计算表明天山中部地区内部断裂两盘的运动方向以婆罗科努断裂为界,北部各断层表现为拉张特征,南部总体表现为聚合特征。     

NUMERICAL ANALYSIS OF THE MECHANICS OF SOIL REINFORCEMENT

1 INTRODUCTION China is rich in mountains. The mountainous area occupies 69% of the total land of the country. Thus, landslides frequently occur in the mountain areas of China. Landslides originating in subsurface soils are typical, and constitute approxi…     

Study on determination of stress level by seismic stress drops and the stress axis deflections before and after large earthquakes

Introduction The study of tectonic stress field, a major branch of the Earth science, plays an important role in geodynamics. The world stress map plan started from 1980s and was leaded by Zoback. Lots of scientists from many countries participated this plan. The plan collected global tectonic stress measurements and research results and established global stress database. The world stress map was edited based on the global stress database. The world stress map reflected feature of global li…     

巴姆地震变形场和应力场：Ⅰ．用差分干涉雷达和Okada方法求解

本文对2003年12月26日伊朗东南部克尔曼省巴姆地区发生的6.6级地震产生的位移场、应变场和应力降分布进行了定量研究。首先从差分干涉雷达(D～InSAR)出发,求解出此次地震的同震干涉条纹和雷达视线方向的位移场,并从雷达干涉的相干图上清楚的观察到了发震断层的痕迹,得出此次地震的发震断层是巴姆断层以西的隐伏断层的结论。然后结合 Harvard 的 CMT(震源机制解)结果、Nakamura 的断层结果(Arg-e-Bam 隐伏断层)以及本文 D-InSAR 求解出的发震断层结果,利用 Okada 程序,计算出此次地震的北、东、垂向三个位移分量,投影得到雷达视线方向的位移,将投影结果与由 D-InSAR得到的位移场比较,看到我们所讨论的断层模式可以很好的解释差分干涉雷达的观测结果,可以合理的解释 Arg-e-Bam 隐伏断层为此次地震的发震破裂断层,通过分析地震的破坏程度分布图,隐伏断层为发震断层的解释可以很好的符合巴姆地震的等震分布图。最后,本文利用 Okada 程序计算得到了此次地震所产生的应变场和应力降场。     

1997-1998年伽师强震群震源区应力场特征

利用1997-1998年伽师强震群中强地震震源机制系统聚类及震源区应力场反演,得到以下主要结果:(1)伽师强震群中强地震主要以走滑和正断层为主,伽师震源区主压应力方向为NNE或近NS向,与相邻的柯坪块体区域构造应力场方向不一致;伽师强震群的破裂面沿NEE方向,属左旋破裂;(2)4~5级中强地震应力场反演得到最大主压应力轴为NNE向,最小主压应力轴为NWW向,中等主应力轴倾角为65°,比较直立;(3)伽师强震群震源区应力场在强震前后经历了一系列变化。最后对所得结果进行了一定的讨论。     

由多个震源机制解分析民乐Ms6.1级地震前后应力场演化

2003年10月25日在甘肃省民乐县和山丹县境内发生了Ms6．1与Ms5．8级地震，对震区200km范围、震前2年内发生的地震，及对震后部分余震矩张量反演得到它们的震源机制解，并对其进行统计分析得到该区的背景应力场及应力轴的整体特征，根据发震区地质构造背景和对平均应力场变化分析，寻求民乐地震的发震机制。     

Source parameters of intermediate-depth Vrancea (Romania) earthquakes from empirical Green's functions modeling

Several source parameters (source dimensions, slip, particle velocity, static and dynamic stress drop) are determined for the moderate-size October 27th, 2004 (M_W = 5.8), and the large August 30th, 1986 (M_W = 7.1) and March 4th, 1977 (M_W = 7.4) Vrancea (Romania) intermediate-depth earthquakes. For this purpose, the empirical Green's functions method of Irikura [e.g. Irikura, K. (1983). Semi-Empirical Estimation of Strong Ground Motions during Large Earthquakes. Bull. Dis. Prev. Res. Inst., Kyoto Univ., 33, Part 2, No. 298, 63–104., Irikura, K. (1986). Prediction of strong acceleration motions using empirical Green's function, in Proceedings of the 7th Japan earthquake engineering symposium, 151–156., Irikura, K. (1999). Techniques for the simulation of strong ground motion and deterministic seismic hazard analysis, in Proceedings of the advanced study course seismotectonic and microzonation techniques in earthquake engineering: integrated training in earthquake risk reduction practices, Kefallinia, 453–554.] is used to generate synthetic time series from recordings of smaller events (with 4 ≤ M_W ≤ 5) in order to estimate several parameters characterizing the so-called strong motion generation area, which is defined as an extended area with homogeneous slip and rise time and, for crustal earthquakes, corresponds to an asperity of about 100 bar stress release [Miyake, H., T. Iwata and K. Irikura (2003). Source characterization for broadband ground-motion simulation: Kinematic heterogeneous source model and strong motion generation area. Bull. Seism. Soc. Am., 93, 2531–2545.] The parameters are obtained by acceleration envelope and displacement waveform inversion for the 2004 and 1986 events and MSK intensity pattern inversion for the 1977 event using a genetic algorithm. The strong motion recordings of the analyzed Vrancea earthquakes as well as the MSK intensity pattern of the 1977 earthquake can be well reproduced using relatively small strong motion generation areas, which corresponds to small asperities with high stress drops (300–1200 bar) and high particle velocities (3–5 m/s). These results imply a very efficient high-frequency radiation, which has to be taken into account for strong ground motion prediction, and indicate that the intermediate-depth Vrancea earthquakes are inherently different from crustal events.     

Relocation of aftershocks, focal mechanisms and stress inversion: Implications toward the seismo-tectonics of the causative fault zone of Mw7.6 2001 Bhuj earthquake (India)

The HYPODD relocation of 1172 aftershocks, recorded on 8–17 three-component digital seismographs, delineate a distinct south dipping E–W trending aftershock zone extending up to 35 km depth, which involves a crustal volume of 40 km × 60 km × 35 km. The relocated focal depths delineate the presence of three fault segments and variation in the brittle–ductile transition depths amongst the individual faults as the earthquake foci in the both western and eastern ends are confined up to 28 km depth whilst in the central aftershock zone they are limited up to 35 km depth. The FPFIT focal mechanism solutions of 444 aftershocks (using 8–12 first motions) suggest that the focal mechanisms ranged between pure reverse and pure strike slip except some pure dip slip solutions. Stress inversion performed using the P and T axes of the selected focal mechanisms reveals an N181°E oriented maximum principal stress with a very shallow dip (= 14°). The stress inversions of different depth bins of the P and T axes of selected aftershocks suggest a heterogeneous stress regime at 0–30 km depth range with a dominant consistent N–S orientation of the P-axes over the aftershock zone, which could be attributed to the existence of varied nature and orientation of fractures and faults as revealed by the relocated aftershocks.     

利用地基土应力分布原理确定砂垫层厚度

软弱土层场地若采用天然地基不能满足建筑物所需强度与沉降要求,采用换土撼砂法就可以提高地基的承载力。运用应力分布原理合理确定撼砂层厚度不仅可保证工程稳固性,并可节约投资和缩短工期。