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通过分析１９９５年５月２日新疆乌苏５．８级地震前北天山部分跟踪台站地震波参数异常特征，特别是石场台视孕震区内地震直达波振幅比的空间分布和时序变化规律，及时发现了异常并大致判断出潜在孕震区的范围，为预报决策和动态跟踪提供了依据。 相似文献
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本文对1975年2月4日辽宁省海城7.3级地震和1976年7月28日河北省唐山7.8级地震,广大孕震区内震前三年多时间地震波振幅比的变化,进行了系统的测量。地震前二—三年期间在震中区出现振幅比的相对高值区,而其外围则出现相对的低值区。随着孕震态势的发展,不同时期的地震波振幅比,其高值区逐渐缩小,低值区逐渐加大,即高值区和低值区都是自孕震区外围向震中区收缩移动,形成有规律的空间变化图象。本文用孕震区形成地壳波浪状形变的模型,解释地震波振幅比移动变化图象的成因。孕震期间,由于地壳波浪状形变的性质,导致孕震地壳受力状态各异,形成广大的非均匀介质区。从一般非均匀、各向同性的弹性体内位移的运动方程出发,划分出受扰介质和非受扰介质。按着相应的波动方程,解出“原生波”和“散射波”的位移,给地震波振幅比异常以物理上的解释。本文同时讨论地震波振幅比异常对地震予报的意义。 相似文献
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本文利用1978～1985年菏泽地震巢内发生的地震,分析研究了1983年11月7日菏泽5.9级地震前后的地震波特性。发现在菏泽5.9级地震前出现26个月的波速比和振幅比低值异常,两者同步变化,震后恢复正常。这种现象,为观测地震波特性的前兆异常给予了启示。 相似文献
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正地震发生前后孕震区的应力状态和介质属性会发生变化,监测地球内部介质变化,为研究地震的发生过程并发现地震前的异常变化提供了可能。由于难以直接深入地球内部进行测量,只能通过地震波分析来研究地球内部介质的变化,而地震波速变化能直接反映地下介质的应力状态和物质组成等物性参数。远震P波接收函数是,用远震P波波形的垂直分量,对径向分量或切向分量作反褶积得到时间序列,主要由直达波、 相似文献
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从高波速比试论云南丽江7级地震的孕震模式 总被引：4，自引：1，他引：3
利用震中周围多台地震波资料计算平均波速比, 并对计算误差作了统计和分析, 提出了在介质存在横向不均匀的情况下数据处理方法。在资料有相当可信度的基础上, 动态追踪了１９９６ 年２ 月３ 日云南丽江７ 级地震前滇西北地区波速比的十余年时空演化图象。显示出： 丽江地震孕震区的高波速比异常图象经历了由小到大、由大到小并再次扩大的过程;而低波速比的异常图象则由大到小、由小到大并再次缩小的过程; 地震发生在低波速比异常区包围的高波速比异常区的交汇部位。其时间进程的演化显示丽江地震的孕震区在１９８８年耿马—澜沧７６ 、７２ 级地震后进入非线性阶段, １９９５ 年孟连西中缅边境７３ 级地震前进入失稳阶段。结合滇西北地区地震垂直分布图象和对照含硬包体试样在破裂孕育过程中波速场的演化图象, 表明丽江地震的孕震区具备了坚固体孕震模式的高波速特征 相似文献
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丽江,宁蒗强震的波速比时人演化图象和数值分析 总被引：6，自引：0，他引：6
通过对１９９６年２月３日滇西北丽江７．０级地震前波速比时空演化图象的动态追踪,同时对比了相距９０ｋｍ的１９７６年１１月７日,１２月１３日宁蒗６．７,６．４级地震。发现不同作者在不同时间研究的滇西北地区这两次重复发生的强震在孕育过程中波速比的时空演化图象十分相似：强震前５－７年,强震孕震区出现波速比高值异常区;强震前３－４年,孕震区的波速比大面积低值异常;强震前１－２年左右,孕震区再次出现范围略小的 相似文献
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介绍了2007年7月20日新疆特克斯5.9级地震的基本参数、震源机制解、地震序列特征、震源参数、发震构造和局部构造应力场等;分析了震前周围台站地震波参数的变化和部分地震学前兆异常特征。研究认为,特克斯5.9级地震发生在伊犁盆地南缘具有强构造运动背景的高应力少震区,是那拉提断裂发生左旋走滑错动所致,为一次孤立型的地震事件。震前观察到震中附近P波与S波振幅比的变化。震前震中周围地区曾出现4级地震围空、2级地震带状图像,震前5个月内北天山震群活跃,震前2个月地震窗出现异常。 相似文献
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本文首先清理了近年来我国一些中强地震前后波速比异常概况。在21个震例中,有7次震前提出过不同程度的预报意见,12次是震后总结发现异常的,2次震后总结未发现异常。其次,讨论了利用天然地震资料探索地震波速度异常的几个问题:(1)现有较密的区域电信传输台网需提高观测精度,使得较大的前兆异常量不致于被误差所掩盖;(2)使用多台和达法探索波速比异常时必须注意其方向性效应,而且,若能把单台波速比法与多台波速比法平行对照使用,效果可能更好些;(3)要注意远台与近台出现异常的早晚与反应的程度;(4)高值点反映地震前兆的信息较小,而低值却可能携带某些前兆信息;(5)不会有固定不变的异常区,应该考虑到异常区的变迁。 相似文献
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选取１０３°～１１３°Ｅ,３１°～３９°Ｎ范围内陕西、山西、河南、湖北、甘肃、宁夏等省（区）共７９个地震观测台站１９８４—１９９３年的观测资料,对于被４个以上台站所记录到的地震,根据其直达横波与纵波的到时差,采用鲍威尔（Ｐｏｗｅｌ）搜索法重新进行了定位,测定了震源深度,共得到２０５１个可定震中的地震的震源深度数据．作出了渭河断陷及邻近地区现代地震的震中分布图、震源空间分布图、震源深度的平均等值线分布图、震源深度的经向剖面图和纬向剖面图．根据这些资料对震源空间分布规律进行了初步探讨．结果表明,渭河断陷及邻近地区震源的空间分布是不均匀的,与该地区大地构造的差异性及地壳速度结构的非均匀性密切相关． 相似文献
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本文对新疆库车—库尔勒地区4次中强震前后地震波的振幅比特性进行了初步分析,着重分析了震前的短临异常特性。得出的初步结果是:(1)中强震前后,、波垂直向最大振幅比值A/A明显减小;(2)震前4个月内距震中较近的台相继观测到 A/A突跳位,出现 A/A值突跳的小震震中在平面上有成带分布的特点;(3)震前10天内,A/A的时空分布最为集中;(4)A/A异常与波速比、振动持续时间比异常大致同步出现。最后,提出了利用振幅比异常预报地震的可能的途径。 相似文献
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湖泊沉积物有机碳埋藏是陆地碳循环中重要的环节,对全球碳平衡起着重要的作用.洱海是云贵高原第二大淡水湖,目前对洱海生态环境变化、重金属与营养盐污染等已展开了较为深入的研究,但对近百年来沉积物有机碳埋藏时空变化与驱动因素缺乏系统的分析.本文通过对洱海北部湖区典型岩芯（编号EH2012）以及其他湖区13个沉积岩芯中有机碳（OC）含量的分析,结合湖泊生态环境与气候因子变化,研究了近百年来沉积物有机碳埋藏时空变化特征与影响因素.C/N摩尔比值表明洱海沉积物中OC以湖泊内源为主,不同湖区岩芯中OC含量变化趋势基本相似.以EH2012岩芯为例,OC含量历史变化可分为3个阶段：1970年以前,表现出较稳定的低值;1970-2000年,OC含量逐渐增加;2000年以来,OC含量增加更加明显并达到近百年来的最大值.近百年来,EH2012岩芯有机碳累积速率（OCAR）呈逐渐增加趋势,变化范围为7.9~87.2 g/（m2·a）,平均OCAR（OCAR）为24.1 g/（m2·a）;OCAR变化与OC含量和区域气温呈显著正相关,全球变暖与营养驱动下的湖泊生产力提高可能是近年来OCAR增加的主要原因之一.基于重金属Cd污染初始时间建立的时标,1982年以来不同湖区OCAR为17.1~44.7 g/（m2·a）,采用克里金插值得到的全湖OCAR均值为31.4 g/（m2·a）;不同湖区OCAR与磷累积速率呈显著正相关,指示了湖泊营养水平对有机碳埋藏空间变化的重要影响. 相似文献
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论确定地震震源深度的地震宏观方法及其解答 总被引：1，自引：0，他引：1
作者基于在近场震源不能视作点源的认识,分析导出了相当于线、面源幅射场的深度公式,进而对源的类型不予作假定,将源指标的几何扩散率n作为待定参数,导出了一个物理意义明确且普遍化的震源深度公式。该公式的诸种解法中,以计算方法较准确,精度高;作图求解有较直观的优点,但准确性差,精度低;图算法仅作为获取粗略值和考察数据的均匀性用。用该公式对我国发生的一些不同震级的地震的震源深度进行了计算,经对比,效果很好。利用计算所得震源类型,初步研究了这些地震的震源几何学,并且首次给出了宏观地震震源深度测定值的标准误差。 相似文献
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The earthquake occurred in Lushan County on 20 April, 2013 caused heavy casualty and economic loss. In order to understand how the seismic energy propagates during this earthquake and how it causes the seismic hazard, we simulated the strong ground motions from a representative kinematic source model by Zhang et al. (Chin J Geophys 56(4):1408–1411, 2013) for this earthquake. To include the topographic effects, we used the curved grids finite difference method by Zhang and Chen (Geophys J Int 167(1):337–353, 2006), Zhang et al. (Geophys J Int 190(1):358–378, 2012) to implement the simulations. Our results indicated that the majority of seismic energy concentrated in the epicentral area and the vicinal Sichuan Basin, causing the XI and VII degree intensity. Due to the strong topographic effects of the mountain, the seismic intensity in the border area across the northeastern of Boxing County to the Lushan County also reached IX degree. Moreover, the strong influence of topography caused the amplifications of ground shaking at the mountain ridge, which is easy to cause landslides. These results are quite similar to those observed in the Wenchuan earthquake of 2008 occurred also in a strong topographic mountain area. 相似文献
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We applied the maximum likelihood method produced by Kijko and Sellevoll (Bull Seismol Soc Am 79:645–654, 1989; Bull Seismol Soc Am 82:120–134, 1992) to study the spatial distributions of seismicity and earthquake hazard parameters for the different regions in western Anatolia (WA). Since the historical earthquake data are very important for examining regional earthquake hazard parameters, a procedure that allows the use of either historical or instrumental data, or even a combination of the two has been applied in this study. By using this method, we estimated the earthquake hazard parameters, which include the maximum regional magnitude $ \hat{M}_{\max } , $ the activity rate of seismic events and the well-known $ \hat{b} $ value, which is the slope of the frequency-magnitude Gutenberg-Richter relationship. The whole examined area is divided into 15 different seismic regions based on their tectonic and seismotectonic regimes. The probabilities, return periods of earthquakes with a magnitude M?≥?m and the relative earthquake hazard level (defined as the index K) are also evaluated for each seismic region. Each of the computed earthquake hazard parameters is mapped on the different seismic regions to represent regional variation of these parameters. Furthermore, the investigated regions are classified into different seismic hazard level groups considering the K index. According to these maps and the classification of seismic hazard, the most seismically active regions in WA are 1, 8, 10 and 12 related to the Alia?a Fault and the Büyük Menderes Graben, Aegean Arc and Aegean Islands. 相似文献
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Three-dimensional frequency dependent S-wave quality factor (Qβ(f)) value for the central Honshu region of Japan has been determined in this paper using an algorithm based on inversion of strong motion data. The method of inversion for determination of three-dimensional attenuation coefficients is proposed by Hashida and Shimazaki (J Phys Earth. 32, 299–316, 1984) and has been used and modified by Joshi (Curr Sci. 90, 581–585, 2006; Nat Hazards. 43, 129–146, 2007) and Joshi et al. (J. Seismol. 14, 247–272, 2010). Twenty-one earthquakes digitally recorded on strong motion stations of Kik-net network have been used in this work. The magnitude of these earthquake ranges from 3.1 to 4.2 and depth ranging from 5 to 20 km, respectively. The borehole data having high signal to noise ratio and minimum site effect is used in the present work. The attenuation structure is determined by dividing the entire area into twenty-five three-dimensional blocks of uniform thickness having different frequency-dependent shear wave quality factor. Shear wave quality factor values have been determined at frequencies of 2.5, 7.0 and 10 Hz from record in a rectangular grid defined by 35.4°N to 36.4°N and 137.2°E to 138.2°E. The obtained attenuation structure is compared with the available geological features in the region and comparison shows that the obtained structure is capable of resolving important tectonic features present in the area. The proposed attenuation structure is compared with the probabilistic seismic hazard map of the region and shows that it bears some remarkable similarity in the patterns seen in seismic hazard map. 相似文献
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Ground-motion prediction equations (GMPEs) are essential tools in seismic hazard studies to estimate ground motions generated by potential seismic sources. Global GMPEs which are based on well-compiled global strong-motion databanks, have certain advantages over local GMPEs, including more sophisticated parameters in terms of distance, faulting style, and site classification but cannot guarantee the local/region-specific propagation characteristics of shear wave (e.g., geometric spreading behavior, quality factor) for different seismic regions at larger distances (beyond about 80 km). Here, strong-motion records of northern Iran have been used to estimate the propagation characteristics of shear wave and determine the region-specific adjustment parameters for three of the NGA-West2 GMPEs to be applicable in northern Iran. The dataset consists of 260 three-component records from 28 earthquakes, recorded at 139 stations, with moment magnitudes between 4.9 and 7.4, horizontal distance to the surface projection of the rupture (R JB) less than 200 km, and average shear-wave velocity over the top 30 m of the subsurface (V S30) between 155 and 1500 m/s. The paper also presents the ranking results for three of the NGA-West2 GMPEs against strong motions recorded in northern Iran, before and after adjustment for region-dependent attenuation characteristics. The ranking is based on the likelihood and log-likelihood methods (LH and LLH) proposed by Scherbaum et al. (Bull Seismol Soc Am 94: 2164–2185, 2004, Bull Seismol Soc Am 99, 3234–3247, 2009, respectively), the Nash–Sutcliffe model efficiency coefficient (Nash and Sutcliffe, J Hydrol 10:282–290, 1970), and the EDR method of Kale and Akkar (Bull Seismol Soc Am 103:1069–1084, 2012). The best-fitting models over the whole frequency range are the ASK14 and BSSA14 models. Taking into account that the models’ performances were boosted after applying the adjustment factors, at least moderate regional variation of ground motions is highlighted. The regional adjustment based on the Iranian database reveals an upward trend (indicated as high Q factor) for the selected database. Further investigation to determine adjustment factors based on a much richer database of the Iranian strong-motion records is of utmost important for seismic hazard and risk analysis studies in northern Iran, containing major cities including the capital city of Tehran. 相似文献
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Western Yunnan is a region with intensive tectonic activity and serious earthquake risk. It is of significant importance to study three dimensional crustal structure of this region to understand the tectonic setting and disaster mechanism. Densification and digitalization of seismic networks in this region provides an opportunity to study the velocity structure with bulletin data. In this study, we collect P-wave data of 10 403 regional earthquakes recorded by 79 seismic stations from January 2008 to December 2010. In addition to first arrivals data (Pg with epicentral distance less than 200 km and Pn), the Pg (or P) data with epicentral distance more than 200 km are also considered as later direct arrivals in the tomographic inversion. We also compare the quantity and the quality of the seismic data before 2010 and after 2010. The test results show that adding the follow-up Pg phase can effectively improve the inversion ability of crustal imaging, and quantity and the data quality are significantly improved since 2010. The tomographic results show that: (1) The Honghe fault zone, which is the major fault systems in this region, may cut through the entire crust, and the velocity contrasts between two sides at lower crust beneath the Honghe fault are estimated at higher than 10%, while the velocity difference below Nujiang fault zone extends only in the upper crust; (2) Most of the earthquakes in the region occurred at the interface of high-velocity media and low-velocity media, i.e., the areas with high velocity gradient, which has been validated in other areas. 相似文献