Isotropic and Nonisotropic Components of Earthquakes and Nuclear Explosions on the Lop Nor Test Site, China

—?We test the hypothesis that the existence of an observable non-zero isotropic component of seismic moment can be used as a discriminant to distinguish nuclear explosions from shallow earthquakes. We do this by applying the method described herein to a small set of data recorded between 1990 and 1996 following events (seven nuclear explosions, three earthquakes) that occurred on the Lop Nor test site in Western China. We represent each source as a sum of an isotropic component at the surface and a nonisotropic, double-couple component at an estimated depth. The explosions all possess a significant non-zero isotropic component and the estimated depth of the double-couple component of the moment tensor, presumably the result of tectonic release, lies between about 0 and 3?km. For the earthquakes studied, the isotropic component is indistinguishable from zero and the depths of the sources are estimated at 3, 17 and 31?km. The data set we have studied, although still very small, suggests that certain source characteristics (namely, double-couple depth and the ratio of the isotropic to nonisotropic components of seismic moment) may prove useful in discriminating explosions from shallow earthquakes. Further work is needed to determine whether these observations hold for explosions at other test sites, to investigate a much larger set of shallow earthquakes located in regions of interest, and to study the robustness of the estimated source parameters as source magnitude and the number of observing stations decrease.     

Significant release of shear energy of the North Korean nuclear test on February 12, 2013

On February 12, 2013 the Democratic People’s Republic of Korea (DPRK) carried out an announced nuclear test, which was the third after tests conducted in 2006 and 2009. An important task in discriminating a man-made explosion and a natural tectonic earthquake is the analysis of seismic waveforms. To determine the isotropic and non-isotropic characteristics of the detonation source, I invert long-period seismic data for the full seismic moment tensor to match the observed seismic signals by synthetic waveforms based on a 3D Earth model. Here, I show that the inversion of long-period seismic data of the 2013 test reveals a clear explosive (isotropic) component combined with a significant release of shear energy by the double-couple part of the moment tensor. While the isotropic part of the nuclear test in 2009 was similar to that in 2013, the double-couple part was lower by a factor of 0.55 compared to the explosion in 2013. Moreover, the ratio of the isotropic seismic moments of the 2013 and 2009 nuclear tests is 1.4?±?0.1 and lower than published estimations of the yield ratio, which indicates the importance of considering the release of shear energy. The determined orientation of the double-couple fault plane is parallel to the dominating geologic fault structures NNE-SSW to NE-SW, but the calculated normal faulting mechanism does not correspond to the general tectonic strike-slip regime. Thus, explanations for the enhanced release of shear energy might be induced dip-slip motion pre-stressed by the previous test or near source damaging effects due to a changed containment of the nuclear explosion.     

岩石损伤对地下核爆炸震源特性影响研究

本文在考虑动态力源扰动的情况下,对岩石损伤对地震波辐射的影响及其震源表示进行了理论推导,证明了当有动态力源存在时,Ben-Zion和Ampuero于2009年给出的结果只是岩石非弹性响应对震源及相应地震波场的贡献,而非其全部.在此基础上,应用相关结果对岩石损伤破坏对地下核爆炸震源成分的影响进行了分析,给出了地下核爆炸情况下补偿线性偶极子源和构造应力释放与岩石损伤破坏之间的关系.结果表明,地下核爆炸补偿线性偶极子源主要来自于地表反射拉伸波和空腔回弹冲击波等造成的爆心上方锥形区域中的岩石破坏,而构造应力释放则主要来自于整个岩石破坏区内的构造应力松弛.      

2013年前郭MS5.8震群矩张量研究

2013年吉林前郭M_S5.8震群为爆发性震群,目前余震活动仍然在持续.基于吉林、辽宁、黑龙江、内蒙古四省地震台网记录的前郭震群波形资料,利用波形信噪比、震源类型、台站及速度模型组合的指标选择最佳的反演方案,应用矩张量的三种反演模式,对序列中5个M_S≥5.0地震进行矩张量反演研究,获得了全矩张量、偏矩张量和纯双力偶的矩张量.使用F-test对地震的三种模式的矩张量反演结果进行显著性检验来确定最佳反演模式.结果显示,5个地震的最优矩张量解均为全矩张量模式反演获得的结果,其双力偶分量仅有20%~65%,矩心深度位于地下3~4 km处,地震在Hudson震源类型图上的投影远离双力偶震源类型区域.这些结果表明,震源类型并非典型的构造地震,推断前郭地震可能是与人类活动有关的诱发地震.     

Source time-function as discriminant using empirical Green’s function

Since the sign up of CTBT (Comprehensive Test Ban Treaty), the nuclear monitoring and distinguishing has gained great attention by the treaty countries. Seismology is one of the primary technical means available for monitoring compliance to a CTBT. However, there does not exist a single criterion, so far, that can effectively distinguish explorations from earthquakes. It has been known that source time function (abbreviated to STF) of an underground nuclear explosion contains important p…     

不同模型下爆炸源和层裂源的 Lg波特性研究

地下核爆炸区域及远区地震波信号中,有二次源即层裂源的贡献,其对区域震相Lg波具有调制作用.本文利用理论地震图数值模拟方法,分析爆炸源和层裂源在3种典型介质速度模型下的区域震相特征,得到了爆炸源和层裂源所激发的Lg波与介质速度模型的关系,并结合CLVD源所激发的S波随震中距的演化过程,对Lg波的形成机制进行了阐述.结果表明,CLVD源是激发地下核爆炸低频Lg波的主要因素.      

用应变地震观测求解震源矩张量的基本原理

震源机制解,即对地震矩张量的推断,对于地震研究具有至关重要的意义.应变地震观测是张量观测,与摆式地震仪的位移矢量观测不同,可以为地震研究提供新的数据源.本文讨论用应变地震观测求解震源矩张量的基本原理.在距离震源足够远的地方,地震波可以看成平面波,其性质决定于震源矩张量.假设平面地震波的应变张量可以由震源矩张量通过坐标变换计算得到,就可以通过观测应变地震波求解震源机制.这个假设至少对于双力偶震源机制是成立的.由此可以证明,在理想的无限介质中,只要有两个以上不同地点的应变地震波观测,就可以解出震源矩张量.这为解决震源机制问题提供了新的方法.目前的地震矩张量求解方法需要两方面的条件:或者需要很多观测点(例如体波反演),或者需要长周期地震波资料(例如面波反演).这些方法只适用于分析比较大的地震.对于小震,因为通常其震中周围不会有足够多的摆式地震仪观测点观测到其地震波,而地震波周期又短,难以利用传统方法给出可靠的震源机制解,所以只需少数观测点就能求解震源矩张量的新方法特别有意义.用应变地震观测求解震源机制,可以给出更为精确的结果.     

震源性质的时频分析与事件识别

应用时频分析技术研究了近年来发生在朝鲜半岛的核爆炸、化学爆炸与天然地震事件的识别问题,计算了上述三者的瞬时频率、瞬时振幅谱与群延迟等多项参数,提出地震与爆炸的识别指标.初步研究结果表明,对较大事件,上述三者来自震源的激发频率信息有明显差异性,核爆炸源激发的频率明显高于地震,化学爆炸最低.特别是,这些信息指标对于识别小当...     

基于Lg波识别判据的特性分析

Lg波是检测、识别地下核爆炸的重要震相.通常情况下,地下核爆炸的低频段Lg波能量相对较强,基于Lg波的识别判据在高频段表现较好.然而在低频范围内却表现出难以用球对称爆炸源模式解释的现象,如Lg/Pg判据在1 Hz附近失效等现象.本文利用理论地震图方法,分析了伴随层裂过程产生的重要辅助源——CLVD源对Lg波低频成分的调...     

朝鲜2009年和2013年两次核爆的地震学特征对比研究

利用布设在长白山地区临时地震台站接收到的朝鲜核爆的波形资料,对2009年5月25日和2013年2月12日两次朝鲜核试验的地震学特征进行比较.震中距范围从145km到420km.采用P/S型谱比值方法识别朝鲜核爆,通过与2009年3月20日长春地震和2013年1月23日沈阳地震事件的比较,表明在频率大于3 Hz时P/S型谱比值能够有效识别发生在中朝边境地区的地下核试验.选定参考台站,利用区域震相Pg波的振幅谱比值计算朝鲜核爆至各台站路径上的相对衰减.结合介质速度模型,在一定程度上反映了长白山地区衰减情况,为进一步研究长白山地区衰减层析成像提供初始模型.     

Seismic monitoring of explosions: a method to extract information on the isotropic component of the seismic source

The design of a monitoring system for detecting explosions is a very topical problem, both for routine data processing at seismological observatories as well as for the monitoring of a Comprehensive Test Ban Treaty. In this framework it is desirable to have the possibility to quantify the presence of the isotropic component in the seismic source. For this purpose a method is presented, which is based on waveform inversion for the full moment tensor retrieval. The method inverts either full waveforms or separate seismic phases and returns the mechanism and time history of a point source. Moreover, it allows to redefine the hypocentral depth of the event and, in a simplistic way, to optimize the structural model as well. In order to model strong laterally heterogeneous structures, different pairs of structural models can be used for each source-receiver path. The source is decomposed into a volumetric part (V), representing an explosive or implosive component, and into a deviatoric part, containing both the double couple (DC) and the compensated linear vector dipole (CLVD) components. The method is applied to an area in central Switzerland and to the network of the Swiss Seismological Service. The events of interest include both earthquakes and explosions. Despite some modelling inadequacies of the source-time function, the explosions can be well identified with the inverted isotropic component in the source, as long as the number of stations used for the inversion is larger than three. The results of the inversion are better for large epicenter-station distances of the order of 40–90 km.     

三峡库区秭归与巴东交界Ms4.0地震矩张量及应力环境研究

三峡库区湖北秭归与巴东交界地区2013年以来发生5次Ms4.0以上地震.本文基于湖北、重庆等省属13个测震台站宽频带波形数据,采用kiwi软件包和rapidinv12程序反演了这些地震的全矩张量解,结果显示所有地震双力偶解均为走滑兼逆断性质,两个节面走向、倾角、滑动角与P、T轴走向和倾俯角的一致性均较好,主压应力P轴N...     

Induced seismicity: Realia and myths

The problems of initiation of earthquakes by other strong earthquakes and by underground nuclear explosions are considered. For this purpose, special software was designed that made it possible to process all of the world catalog data on earthquakes of 1950–2005. A more effective and reliable method was applied to the analysis of seismic activity, taking into account its background state. As a result, it is unambiguously established that the effect of strong earthquakes or explosions is negligibly small. In any case, their effect cannot be recognized from catalog data that served as a basis for many studies of induced seismicity problems. This conclusion is of great significance for assessment of the possibility of real-time prediction of earthquakes. If this effect were to exist, such prediction would become impossible due to unpredictability of the triggering action.     

首都圈地区爆破、矿塌和天然地震的识别研究

选取首都圈地区2008年8月——2009年9月ML在2.0——2.2范围内的爆破、矿塌和天然地震数据资料,从时间域和频率域进行分析对比,总结出识别爆破、矿塌和天然地震的依据．在时域方面,爆破的初动方向向上,矿塌向下,天然地震的初动方向依赖于台站的分布情况;爆破和矿塌的面波比较发育;天然地震的S波与P波最大振幅比(AS/AP)大于爆破和矿塌,同时,爆破和矿塌的能量衰减比天然地震快．在频域方面,高频成分的能量衰减快于低频;天然地震的拐角频率较高,爆破次之,矿塌的最小;在震中距200 km范围内,爆破的顶峰频率主要分布在5——7 Hz,矿塌分布在2——4 Hz,天然地震的顶峰频率较大,在10——18 Hz范围内.另外,天然地震的频率域较宽,其次为爆破、矿塌．      

Three Decades of Seismic Activity at Mt. Vesuvius: 1972–2000

We analyse the seismic catalogue of the local earthquakes which occurred at Somma-Vesuvius volcano in the past three decades (1972–2000). The seismicity in this period can be described as composed of a background level, characterised by a low and rather uniform rate of energy release and by sporadic periods of increased seismic activity. Such relatively intense seismicity periods are characterised by energy rates and magnitudes progressively increasing in the critical periods. The analysis of the b value in the whole period evidences a well-defined pattern, with values of b progressively decreasing, from about 1.8 at the beginning of the considered period, to about 1.0 at present. This steady variation indicates an increasing dynamics in the volcanic system. Within this general trend it is possible to identify a substructure in the time sequence of the seismic events, formed by the alternating episodes of quiescence and activity. The analysis of the source moment tensor of the largest earthquakes shows that the processes at the seismic source are generally not consistent with simple double-couples, but that they are compatible with isotropic components, mostly indicating volumetric expansion. These components are shown to be statistically significant for most of the analysed events. Such focal mechanisms can be interpreted as the effect of explosion phenomena, possibly related to volatile exsolution from the crystallising magma. The availability of a reduced amount of high quality data necessary for the inversion of the source moment tensor, the still limited period of systematic observation of Vesuvius micro-earthquakes and, above all, the absence of eruptive events during such interval of time, cannot obviously permit the outlining of any formal premonitory signal. Nevertheless, the analysis reported in this paper indicates a progressively evolving dynamics, characterised by a generally increasing trend in the seismic activity in the volcanic system and by a significant volumetric component of recent major events, thus posing serious concern for a future evolution towards eruptive activity.     

Discrimination Between Nuclear Explosions and Earthquakes: An Application of Wigner Distribution

In this paper,the nonstationary theory of Wigner Distribution is used to discriminate between underground nuclear explosions and natural earthquakes.Five underground explosions in Kazakhstan region and seven regional earthquakes in its adjacent areas have been analyzed.The result shows that the transient spectra of underground nuclear explosions are concentrated in the frequency range of 5-10 Hz,while the transient spectra of natural earthquakes are distributed widely from lower frequency to higher frequency.The transient frequency of nuclear explosions shows linearity in the first stage(0相似文献   

Discrimination between nuclear explosions and earthquakes based on consideration of tectonic ambient shear stress values

IntroductionFor the need of a nuclear test ban treaty, international society must make great efforts to find effective methods for discrimination between earthquake and nuclear explosion. Thereupon, many methods of discrimination of nuclear explosion appeared. But, at present, there is some uncertainty to discriminate middle or small nuclear explosion (Peppin, McEvilly, 1974; Richards, Zarales, 1990). When we study tectonic ambient shear stress field of Southern California, we find that str…     

朝鲜核爆的Rayleigh波震级测量

利用1995年至2009年中国东北及邻近地区11个宽频带台站记录到的77个地震事件、3个化学爆炸和2次朝鲜核爆的区域地震资料,标定该区域台网的Rayleigh波震级.通过对8~25 s 周期的垂直分量Rayleigh波形进行分析,获取基于最大振幅的面波震级.计算82个区域事件不同周期的台基响应,经过台基校正后取最大振幅的面波震级为事件震级.2006年和2009年两次朝鲜核爆的面波震级分别为2.93±0.19和3.62±0.21.将地震和核爆事件的面波震级M_s与体波震级m_b(Lg)进行比较,发现根据该区域台网的数据利用M_s-m_b识别方法无法鉴别朝鲜地区的核爆与地震.朝鲜核爆的面波震级相对较大,使M_s-m_b识别方法失效,其原因可能是源区介质的不均匀性、由核爆炸冲击引发的深部的拉伸破坏被抑制,或者是近爆源区存在张性的构造预应力.假定核爆可能的埋藏深度范围是0.01~1.0 km,用Rayleigh波震级估计朝鲜核爆的当量,对2006年和2009年核爆当量的估值范围分别为0.42~3.17 kt和2.06~15.53 kt.     

地震与核爆识别的小波包分量比方法

频谱分析法在核爆与地震识别中具有广泛的应用．但是频谱分析方法是稳态方法,即使采用Gabor变换,也因时-频窗口形状不变而分辨串较低．为提高时-频分辨率,本文将小波变换理论用于乌鲁木齐台记录的地震与核爆事件的分析,并提出了识别核爆和天然地震的小波包分量比判据．通过对加拿大黄刀地震台记录的印度地下核爆的分析,进一步验证了小波包分量比判据对核爆和地震的识别具有较高的识别效率．结果表明：对于地震信号,其小波包分量比U03/U1一般都大于1.0,而对于核爆信号,比值U03／U13一般都小于1.0.     

朝鲜地下核试验的地震学观测

自2006年至2017年,朝鲜民主主义人民共和国在中朝边界地区的试验场进行了6次地下核试验.本文综合报道根据东北亚地区的宽频带数字地震资料利用地震学方法对这六次地下核爆炸的研究.结果表明,朝鲜地下核试验在区域台网产生的地震记录具有典型浅源爆炸的特征.针对上述资料发展了处理核爆数据的方法并据此得出各次朝鲜核爆的地震学参数,包括事件识别、当量测定、以及震中相对定位等.对6次核爆和4次天然地震P/S类型谱振幅比的统计分析表明,2 Hz以上台网平均谱振幅比可以正确地将朝鲜核爆从天然地震中识别出来,从而有效监测在朝鲜半岛进行的当量大于0.5 kt的地下核试验.同时也发现,建立在体波-面波震级比之上的识别方法不适用于朝鲜核试验场.通过建立中朝边界地区基于Lg波的体波震级系统,计算了各次朝鲜核试验的体波震级m_b（Lg）,并由此估计了它们的地震学当量,其值介于0.5 kt至60 kt之间.由于缺少爆炸埋藏深度的数据,上述当量有可能被低估,因而有必要对深度影响做进一步研究.以第一次爆炸的位置为参考震中,利用Pn波相对走时数据和高精度相对定位方法获得了各次核爆在试验场中的精确定位.