云南腾冲火山区地震/次声台阵建设

在中央级公益性科研院所基本科研业务专项《地震重点监视区地震与次声联合台阵探测对比试验》支持下,在云南腾冲火山区建设了一个由4个子台组成的三角形地震/次声台阵,首次将宽频带地震计及次声传感器联合部署在强地震活跃区及火山区。本文详细介绍了腾冲火山区地震/次声台阵的建设及其观测系统组成,特别是与次声观测有关的次声降噪滤波系统,并提出了下一步研究工作。     

四川长宁Ms6.0地震震区上地壳速度结构特征与孕震环境

北京时间2019年6月17日22时55分,四川省宜宾市长宁县发生了Ms6.0地震(28.34°N,104.90°E),四川盆地内部及边缘地带的深部孕震环境和潜在地震危险性再次引起了国内外地震专家和学者们的密切关注.为了揭示长宁Ms6.0震区的深部介质结构特征和孕震环境,综合解译地震活动的构造背景和展布特征,本文充分收集...     

Thermal weathering of granite spheroidal boulders in a dry‐temperate climate,Northern Dobrogea,Romania

Weathering microforms associated with exfoliation were investigated on 40 granitic spheroidal boulders identified on Pricopan Ridge (M?cin Mountains) in order to establish a spatial distribution pattern. Continuous thermal monitoring allowed the frequency and intensity distribution assessment of short‐term temperature changes triggered by summer storms, of intense day–night amplitudes and frost cycles across a uniform rounded boulder. Rock strength estimated by Schmidt hammer tests differentiates a significantly weaker resistance on the southern face of the boulders (rebound values of 27 to 33) in comparison with the northern face (43–50). The lowest resistance of the north–south cross‐boulder profile corresponds to the southern gentle slopes (0°–45°) thus defining the most susceptible area to exfoliation and other weathering processes. It is argued that this low‐resistant sector fits well with the maximum frequency and intensity of thermal processes recorded on the low and mid slopes (0°–45°) of the boulders south side, with small differences from one process to another, whilst the sector of 20° to 30° south corresponds to the peak activity of all. In accordance, the overlay map of exfoliated surfaces places the high frequency area on a spherical cap developed similarly (between 5° north and 45° south). The smallest exfoliated surfaces normally appear around 30° south and are inferred to extend in time both to the boulder top and downslope. The correlations between the frequency/intensity maps of thermal processes and the frequency map of exfoliated surfaces point to a complementary action in the exfoliated surfaces development of the short‐term temperature changes and diurnal cooling and heating due to the directional insolation effect, as similarly inferred in the development of meridional cracks. Copyright © 2016 John Wiley & Sons, Ltd.     

Crustal seismic tomography in the Calabrian Arc region, south Italy

27,646 P- and 15,025 S-wave readings obtained from 2238 earthquakes and 84 artificial sources were used to perform tomographic inversion of P velocity and V_P/V_S ratio in the crust of Calabrian Arc by Thurber’s inversion algorithm. For this investigation a seismic database with more than twelve-thousand events was built, including all local earthquake data recorded between 1978 and 2001 at all stations of the national and local networks in south Italy. Spread Function computations and checkerboard and restore tests proved higher accuracy of velocity estimates in the upper 40 km beneath Calabrian Arc compared to previous investigations in the same area. The obtained three-dimensional velocity model furnished remarkable improvement of hypocenter locations of the global earthquake dataset (RMS reduction of 38% respect to 1D locations) and greater accuracy in the definition of microplates and tectonic units in the study region. Velocity domains evidenced by our tomography correspond to tectonic units locally identified with geological methods by previous investigators and allow us to better detail their shape and geometry at depth. In particular, at a depth of about 20 km beneath Calabria we detected the deep contact between the overthrusting Tyrrhenian crust and the subducting Ionian slab, improving the accuracy of the current subduction model of the Calabrian Arc region.     

珠江三角洲地震活动的若干特点

分析了二十世纪末30年来珠江三角洲地区地震活动的特征，认为珠江三角洲地区与东南沿海地震带在地震序列分布上总体趋势是一致的。在1970～1997年间，珠江三角洲地区b值滑动时间曲线从1984年起至1986年的高值异常可能是东南沿海地震带1986年开始的活跃幕的中期前兆。地震活动指数A(b)值曲线1988年及1994年的两处低值异常，则可能是本区1989年及1997年两个地震能量释放高峰的中期前兆。从本区及东南沿海地震带地震发生的时间进程上来看，本区很可能是东南沿海地震带区域应力场的调整单元。     

Prediction of the strong earthquakes in Vrancea,Romania, using the CN algorithm

The application of the CN algorithm to a new earthquake catalogue, for the period from 1932 to 1993, obtained by merging Romanian and U.S.S.R. data, allows us to monitor, on the intermediate time scale, the preparation of strong, intermediate-depth earthquakes in the Vrancea region. Four of the five strong earthquakes with a magnitude above 6.4 are predicted, the total duration of the Time of Increased Probability of the occurrence of an earthquake (TIP) occupies 21.7% of the time interval under consideration, i.e., about 2.5 years for each strong earthquake.     

Prediction of strong earthquakes in Vrancea,Romania, using the CN algorithm

The application of the CN algorithm to a new earthquake catalogue, for the period from 1932 to 1993, obtained by merging Romanian and U.S.S.R. data, allows us to monitor, on the intermediate time scale. the preparation of strong, intermediate-depth earthquakes in the Vrancea region. Four of the five strong earthquakes with magnitudes above 6.4 are predicted. The total duration of the Time of Increased Probability (TIP) of the occurrence of an earthquake (TIP) occupies 21.7% of the time interval under consideration, i.e., about 2.5 years for each strong earthquake.     

利用模板匹配技术识别大岗山水库库区爆破事件

采用匹配定位方法,利用大岗山水库库区及附近(29.2°—29.9°N,101.9°—102.5°E)5次已知爆破事件对2014年3月1日至2015年12月31日内连续波形进行模板检测与定位,经过人工复核后共获取23次疑爆事件,这些事件与模板事件间有较高的相关性,相关系数达0.7734,匹配后疑爆事件数为模板数的4.6倍...     

Estimate of earthquake hazard in the Vrancea (Romania) region

A maximum likelihood method is used to estimate the earthquake hazard parameters maximum magnitudeM _max, annual activity rate , and theb value of the Gutenberg-Richter equation in the Vrancea (Romania) region. The applied procedure permits the use of mixed catalogs with incomplete historical as well as complete instrumental parts, the consideration of variable detection thresholds, and the incorporation of earthquake magnitude uncertainty.Our imput data, comprises 105 historical earthquakes which occurred between 984 and 1934, and a complete data file containing 1067 earthquakes which occurred during the period 1935–30 August, 1986. The complete part was divided into four subcatalogs according to different thresholds of completeness. Only subcrustal events were considered, and dependent events were removed.The obtained value (=0.65) is at the lower range of the previously reported results, but it appears concurrent with conceptual and observational facts. The same concerns inferred value of _max = 7.8 and activity rate _4.0 = 5.34.     

2014年2月12日新疆于田MW7.0地震源区静态库仑应力变化和地震活动率

2014年2月12日新疆于田M_W7.0地震源区位于巴颜喀拉块体与西昆仑块体的连接部位,东西向拉张构造发育,距离2008年3月21日于田M_W7.1地震震中位置约100 km.根据有限断层地震破裂过程模型,计算了2008年新疆于田地震产生的静态库仑应力变化.此次地震的断层面呈北偏东方向,在断层两端出现3个应力加载区,2014年于田主震位于破裂前端的库仑应力加载区.这一结果表明,2008年于田地震可能对2014年地震事件起到了触发作用.2008和2014年新疆于田地震产生的静态库仑应力变化与余震事件的空间分布具有明显的相关性,大多数余震位于应力加载区,发生在卸载区的余震较少.静态库仑应力变化与余震序列吻合较好.2014年3月21日新疆于田地震之后40天,在北西方向发生M_W5.2强余震,其震中位置的应力增量达到0.63×10⁵Pa.通过比较,发现静态库仑应力变化和地震活动率之间具有较好的相关性.地震活动率较高的区域与静态库仑应力加载区相对应,如康西瓦断裂东段、贡嘎错断裂中段和东北段等区域.     

Intermediate-term,pre-earthquake phenomena in California, 1975–1986, and preliminary forecast of seismicity for the next decade

Intermediate-term observations preceding earthquakes of magnitude 5.7 or greater in California from 1975 through 1986 suggest that: (1) The sudden appearance of earthquakes in a previously inactive area indicates an increased likelihood of a significant earthquake in that area for a period from days to years; (2) these larger earthquakes tend to occur towards the ends of creeping fault segments; (3) one large earthquake in a region increases the likelihood of a subsequent significant event in the adjacent area; and (4) marginal evidence for the occurrence of a regional deformation event suggests that such events increase the probability of earthquake occurrence throughout the entire area. A common element in many of these observed patterns appears to be the transmission and amplification of tectonic stress changes by the mechanism of fault creep, and suggests that surface fault creep is a sensitive indicator of changes in stress. The preceding critieria are used to construct a preliminary forecast of the likely locations of significant earthquakes over the next decade.     

Pattern recognition of seismogenic nodes using Kohonen selforganizing map: example in west and south west of Alborz region

Pattern recognition of seismic and morphostructural nodes plays an important role in seismic hazard assessment. This is a known fact in seismology that tectonic nodes are prone areas to large earthquake and have this potential. They are identified by morphostructural analysis. In this study, the Alborz region has considered as studied case and locations of future events are forecast based on Kohonen Self-Organized Neural Network. It has been shown how it can predict the location of earthquake, and identifies seismogenic nodes which are prone to earthquake of M5.5+ at the West of Alborz in Iran by using International Institute Earthquake Engineering and Seismology earthquake catalogs data. First, the main faults and tectonic lineaments have been identified based on MZ (land zoning method) method. After that, by using pattern recognition, we generalized past recorded events to future in order to show the region of probable future earthquakes. In other word, hazardous nodes have determined among all nodes by new catalog generated Self-organizing feature maps (SOFM). Our input data are extracted from catalog, consists longitude and latitude of past event between 1980-2015 with magnitude larger or equal to 4.5. It has concluded node D1 is candidate for big earthquakes in comparison with other nodes and other nodes are in lower levels of this potential.     

Temporal characteristics of seismicity in the Alborz and Zagros regions of Iran, using a multifractal approach

Multifractal characteristics of the temporal distribution of earthquakes in the Zagros and Alborz regions of Iran were analyzed using the fixed-mass method. The generalized multifractal dimensions, singularity spectrum, mass exponents, and the asymmetry factor were calculated for these regions. The results indicate that the temporal distributions of earthquakes in the Zagros and Alborz regions are likely to be chaotic and have multifractal structures. Although both of the study areas show heterogeneous structures, the D_q and f(α_q) spectra for the Zagros region indicate that densely populated time domains are as heterogeneous as the sparsely populated ones. On the other hand, the multifractal spectra of the Alborz region show that the densely clustered time domains are more heterogeneous than the sparsely populated ones. Such a multifractal spectrum shows that there are many more sparsely populated time domains (i.e. seismic gaps) within the multifractal structure than densely populated ones.     

利用接收函数探讨新疆几次中强地震的孕震位置

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...     

Downstream variation in bed sediment size along the East Carpathian rivers: evidence of the role of sediment sources

Taking as an example six main rivers that drain the western flank of the Eastern Carpathians, a conceptual model has been developed, according to which fluvial bed sediment bimodality can be explained by the overlapping of two grain size distribution curves of different origins. Thus, for Carpathian tributaries of the Siret, coarse gravel joins an unimodal distribution presenting a right skewness with enhanced downstream fining. The source of the coarse material distributions is autohtonous (by abrasion and hydraulic sorting mechanisms). A second distribution with a sandy mode is, in general, skewed to the left. The source of the second distribution is allohtonous (the quantity of sand that reaches the river‐bed through the erosion of the hillslope basin terrains). The intersection of the two distributions occurs in the area of the 0·5–8 mm fractions, where, in fact, the right skewness (for gravel) and left skewness (for sand) histogram tails meet. This also explains the lack of particles in the 0·5–8 mm interval. For rivers where fine sediment sources are low, the 0·5–8 mm fractions have a higher proportion than the fractions under 1 mm. For the Siret River itself, bed sediment bimodality is greatly enhanced due to the fact that the second mode is more than 25% of the full sample. As opposed to its tributaries, the source of the first mode, of gravel, is allohtonous to the Siret river, generated by the massive input of coarse sediment through the Carpathian tributaries, while the second mode, of the sands, is local. In this case we can also observe that the two distributions of particles of different origins overlap in the 0·5–8 mm fraction domain, creating the illusion of ‘particle lack’ in the fluvial bed sediments. Copyright © 2007 John Wiley & Sons, Ltd.     

四川盆地荣县—威远—资中地区发震构造几何结构与构造变形特征:基于震源机制解的认识和启示

四川盆地荣县—威远—资中地区属于历史弱震区,然而2019年相继发生多次破坏性地震事件.本文基于四川区域地震台网宽频带地震仪记录波形资料,利用CAP （Cut and Paste）波形反演方法,获得了2016年以来发生在荣县—威远—资中地区的26个M_S≥3.0地震的震源机制解、震源矩心深度和矩震级,对该区域发震构造几何结构与变形特征及构造应力场特征进行了初步分析.主要获得如下认识：（1）26个M_S≥3.0地震的震源矩心深度在1.5~5 km之间,平均深度3.4 km,表明事件发生在上地壳浅部沉积层内;震源深度分布揭示发震断层面倾向SE、缓倾角.（2）26个地震的震源机制全部为逆冲型,表明发震构造整体为逆断层性质.节面优势方位NNE-NE,结合走向与倾角统计结果,本文推测发震构造可能为威远背斜南翼一系列倾向SE、走向NNE-NE的缓倾角盲冲断层.（3）P、T、B轴优势方位单一,表明研究区域处于相对简单的构造应力环境.区域应力场反演获得的最大主压应力轴σ₁方位NW-SE,近水平,与目前已知的该区域构造应力场水平主压应力方向一致,反映区内构造活动主要受区域构造应力场控制;其明显有别于四川盆地南缘2019年6月17日长宁M_S6.0地震余震区NE-SW向的最大主压应力轴方位也揭示出四川盆地构造应力场具有明显的分区特征.（4）26个地震整体的应变花表现为NW-SE向挤压白瓣形态,表明区内发震构造整体呈NW-SE向纯挤压变形模式,明显有别于2019年长宁M_S6.0地震序列NE-SW向挤压兼具小量NW-SE向拉张分量的构造变形模式,进一步表明四川盆地构造变形模式也具有明显的分区特征.     

Most likely locations of large earthquakes in the Kanto and Tokai areas, Japan, based on the local recurrence times

We examined the hypothesis that minima in local recurrence time, T_L, or equivalently maxima in local probability, P_L, may map asperities in the Kanto and Tokai areas of Japan, where the earthquake catalog of the National Research Institute for Earth Science and Disaster Prevention (NIED) is complete at the M=1.5 (M1.5) level. We mapped T_L (P_L) based on the a- and b-values of the nearest earthquakes within 20 km of every node of a grid spaced 0.01° for M7 target events. Only earthquakes within the top 33 km were used. The b-values increase strongly with depth, in several areas. Therefore, some of the T_L (P_L) anomalies are not revealed if data from the entire crustal seismogenic zone are mixed. Thus, we mapped T_L (P_L) separately for the top 15 km and the rest of the depth range, as well as for the entire seismogenic crust. The resulting T_L- and P_L-maps show that approximately 12% of the total area shows anomalously short recurrence times. Out of six shallow target events with M≥6.5 and which occurred since 1890, five are located within the anomalous areas with T_L <450 years. We interpret this to mean that areas with anomalously short T_L map asperities, which are more likely than other areas to generate future target events. The probability that this result is due to chance is vanishingly small. The great Kanto rupture of 1923 appears to have initiated in the most significant asperity we mapped in the study area. One anomaly is located in the northeastern part of the area of the proposed future rupture of the Tokai earthquake, and another one at its southwestern corner. The absolute values of T_L calculated are uncertain because they depend on the size of the volume used for the calculation.     

四川盆地荣县—威远—资中地区发震构造几何结构与构造变形特征:基于震源机制解的认识和启示

四川盆地荣县—威远—资中地区属于历史弱震区,然而2019年相继发生多次破坏性地震事件.本文基于四川区域地震台网宽频带地震仪记录波形资料,利用CAP（Cut and Paste）波形反演方法,获得了2016年以来发生在荣县—威远—资中地区的26个M_S≥3.0地震的震源机制解、震源矩心深度和矩震级,对该区域发震构造几何结构与变形特征及构造应力场特征进行了初步分析.主要获得如下认识：（1）26个M_S≥3.0地震的震源矩心深度在1.5~5 km之间,平均深度3.4 km,表明事件发生在上地壳浅部沉积层内;震源深度分布揭示发震断层面倾向SE、缓倾角.（2）26个地震的震源机制全部为逆冲型,表明发震构造整体为逆断层性质.节面优势方位NNE-NE,结合走向与倾角统计结果,本文推测发震构造可能为威远背斜南翼一系列倾向SE、走向NNE-NE的缓倾角盲冲断层.（3）P、T、B轴优势方位单一,表明研究区域处于相对简单的构造应力环境.区域应力场反演获得的最大主压应力轴σ₁方位NW-SE,近水平,与目前已知的该区域构造应力场水平主压应力方向一致,反映区内构造活动主要受区域构造应力场控制;其明显有别于四川盆地南缘2019年6月17日长宁M_S6.0地震余震区NE-SW向的最大主压应力轴方位也揭示出四川盆地构造应力场具有明显的分区特征.（4）26个地震整体的应变花表现为NW-SE向挤压白瓣形态,表明区内发震构造整体呈NW-SE向纯挤压变形模式,明显有别于2019年长宁M_S6.0地震序列NE-SW向挤压兼具小量NW-SE向拉张分量的构造变形模式,进一步表明四川盆地构造变形模式也具有明显的分区特征.

     

湖北西部地区小震活动与台湾强震关系研究

简要阐述了湖北西部地区地震活动和台湾地区强震活动特征, 研究了1981年以来湖北西部地区弱震和台湾地区6级以上强震发生的关系。 结果表明, 二个地区地震活动有较好的相关性。 根据这种相关性实现对台湾强震的临震预测, 对应率较高, 预报效能较好。