Estimation of the correlation between magnetotelluric and geothermal data in the Bishkek geodynamic research area

The paper analyzes the correlation between the electrical conductivity and temperature in the upper crust of the Bishkek geodynamic research area (the Northern Tien Shan). Electrical conductivity profiles constructed from magnetotelluric data and thermograms from the boreholes near magnetotelluric sounding (MTS) points are used for estimations. The correlation analysis of conductivity and temperature profiles to depths of 3–4 km showed that, first, the correlation coefficients do not depend on the distance between the borehole and the nearest MTS point; second, the good correlation between the conductivity and temperature observed for the majority of borehole-MTS point pairs is accounted for by the fact that the study parameters vary with depth in a manner normal for laminated sedimentary rocks; and, third, a low correlation is due to specific features of the geological structure between the borehole and MTS point under consideration.     

The local geodynamic test area of CLG-organization and first results of leveling measurement

In 1982, the Central Laboratory for Geodesy (CLG) started a long-term study of the recent crustal movements in a local test area in a mobile region located southwards of Sofia.The recent geodynamic conditions and the deep structure of the Earth's crust in this region are described.Data on the local network of precise leveling are given-the scheme and characteristics of the loops, benchmarks and their monumentation. A first geodynamic analysis of the results of the first and third cycles of measurements is made, a map of the module of horizontal gradient of vertical velocity has been elaborated. The results obtained corroborate the reasons for the selection of this geodynamic test area.     

西宁盆地浅层滑脱面与地震关系探讨

滑脱面空间特征的研究可以反映次级浅断裂与区域深断裂之间的构造关系, 在西宁盆地中, 第三纪地层在NNE向区域挤压应力作用下, 沿近NW向发生弯曲褶皱变形。 利用平衡剖面方法, 通过对垂直构造走向的一条剖面进行反演, 得到西宁盆地的滑脱面深度在4~5 km, 并向南倾, 与物探资料得到的盆地沉积盖层的底界位置和形态基本相同。 因此得出盆地沉积盖层的变形方式以柔皱褶曲为主, 并沿沉积盖层底界进行滑脱。 同时根据区域地震背景分析, 认为在西宁盆地浅滑脱的结构面不具备强震的发震条件。     

日本海沟大震与华东地区地震的相关性

应用模糊相关方法,研究了日本海沟与我国华东地区地震活动的相关性.计算结果表明:日本海沟地区(35～45°N,140～150°E)MS6.8级以上地震和华东地区(29～34°N,119～124°E)MS4.8级以上地震有较好的相关对应关系;用相关分析方法对华东地区尤其是上海附近地区未来发震的可能性进行了分析,并估算了两地区延迟相关的平均概率.     

Methodical questions and accuracy problems of GPS observations by the example of the geodynamic proving ground in Bishkek

The key questions concerning the modern methodical tasks and accuracy of GPS measurements of crustal motion spanning are discussed for a full cycle of the survey from the organization of the field operations to the interpretation of the final results. The presented data rely on the 20-year experience of the geophysicists of the Research Station of the Russian Academy of Sciences in Bishkek (RS RAS) in GPS monitoring at the Geodynamic Proving Ground in Bishkek (GPGB) and in a large part of Central Asia. The comparative characteristics of the constellations of visible GPS and GLONASS satellites are analyzed from the standpoint of their practical application for precise scientific observations of crustal motions. The studies of the contemporary movements of the Earth’s crust by the methods of satellite geodesy generally comprise three stages: (1) organization of the measurement networks and acquisition of the data; (2) data processing; and (3) interpretation of the results. Each stage is associated with its own block of the tasks and problems, and neither is guaranteed against uncertainties and errors which may affect the results, conclusions, and reconstructions.     

Generalized Rydelek-Sacks test for distinguishing between periodic and random patterns in seismicity

For distinguishing the periodicity of strong earthquakes on the time scale of decades, we generalized the Rydelek-Sacks test (Rydelek, Sacks, 1989) to explore whether a time series is modulated by a periodic process or not. The test is conducted by comparing the total phasor of seismicity with that produced by a random Brownian motion. The phase angle is defined by the origin time of earthquakes relative to a reference time scale. Using this method we tested two hypotheses in geodynamics and earthquake prediction study. One is the hypothesis of Romanowicz (1993) who proposed that the great earthquakes alternate in a predictable fashion between strike-slip and thrusting mechanisms on a 20-30 years cycle. The other hypothesis is that the strong earthquakes in and around China have an active period of about ten years. The test obtains a negative conclusion for the former hypothesis and a positive conclusion for the latter at the 95% confidence level.     

福建地壳运动与地震关系初探

利用福建地震台网88个地震台站于2015年记录的10个月的连续波形数据,基于台网约束下的长短窗特征触发式震相检测的模板事件识别方法和匹配滤波自动检测方法,识别出模板事件919个,匹配滤波后重新识别和定位了共计2 243个地震事件,其中M_L1.0以上地震1 991次,主要集中在M_L1.0—1.5之间,这极大扩充了该震级范围内的福建地震台网目录。重新定位的地震震源深度分布在0—20 km之间,多数发生在10 km内的上地壳。沿长乐—诏安断裂带和永安—晋江断裂带,地震分布集中且表现出明显的分段活动性。在长乐—诏安断裂带上检测到较福建台网目录更多的地震,且地震活动性表现为西南段较强、东北段较弱,沿断裂带的震源深度分布由南向北逐渐变浅,与莫霍面深度的变化相一致;在与之共轭的永安—晋江断裂带上则北西段地震活动更为集中,而东南段地震活动稍显分散。重新识别与精定位后的地震与福建地区地壳水平形变南强北弱、东强西弱的特点相一致。     

Modelling of surface ground deformations in the Phlegraean Fields volcanic area,Italy

A preliminary finite elements model of the ground deformations observed at Phlegraean Fields is proposed. The model assumes an oblate-spheroid magma chamber at the depth of 5.4 km with major semiaxis of 1.5 km and minor semiaxis of 0.75 km. The dimensions of the magma chamber have been evaluated by using a thermal model based on the assumptions that a progressively cooling huge magmatic body is responsible for the volcanic activity at Phlegraean Fields in the last 35,000 years. Surface deformations caused by an over-pressure of 30 MPa in the magma chamber have been calculated. Constant, and temperature-dependent elastic parameters of the surrounding medium have been considered. Vertical displacements of the order of those presently observed at Phlegraean Fields can be obtained only with temperature-dependent elastic properties of the medium.     

Tertiary and quaternary volcanism of the Erzurumkars area (Eastern Turkey): Geochronological data and geodynamic evolution

This paper presents new geochemical and geochronological data on the Neogene and Quaternary volcanic products from the area of Erzurum and Kars (Eastern Turkey).The affinity of most of the volcanic rocks concerned is calc-alkaline, with the exception of minor Quaternary alkaline rocks that outcrop in the Kars sector. Ages range from 8 m.y. to 1.3 m.y.The time-space distribution of the calc-alkaline volcanism in Eastern Turkey - NW Iran is characterized by a sudden northward jump, that occurred around 6 m.y. ago, from the Van-Erzurum Southern Belt to the Kars Northern Belt. Available data indicate that this northward migration of volcanism was due to changes in the subduction geometry of the Arabian plate under Eurasia.     

Quantitative studies of global seismicity (2)

In this paper, the seismicity indexes of global earthquakesM ≥ 6 during 1964–1983 were calculated, using data of ISC and USGS. The authors suggested a method suitable to make a set of regression formulas betweenm _bandM _s. Calculation showed that the level of global seismicity of shallow earthquakes during the years 1964–1965, 1968, 1971, 1975–1976 was higher than normal, especially the peak for the years 1975–1976 was more conspicuous. The year 1984 took the place of the year 1954 in the 20th century as the year of lowest global shallow focus seismicity. According to the actual value ofA(b) calculated, the level of deep focus seismicity reached the highest point in 1971 and dropped to the lowest point in 1977. In the time interval of 1977–1983 the global shallow focus seismicity decreased continuously whereas the deep focus seismicity increased with fluctuations.     

Comparison of surface and borehole locations of induced seismicity

Monitoring of induced microseismic events has become an important tool in hydraulic fracture diagnostics and understanding fractured reservoirs in general. We compare microseismic event and their uncertainties using data sets obtained with surface and downhole arrays of receivers. We first model the uncertainties to understand the effect of different acquisition geometries on location accuracy. For a vertical array of receivers in a single monitoring borehole, we find that the largest part of the final location uncertainty is related to estimation of the backazimuth. This is followed by uncertainty in the vertical position and radial distance from the receivers. For surface monitoring, the largest uncertainty lies in the vertical position due to the use of only a single phase (usually P‐wave) in the estimation of the event location. In surface monitoring results, lateral positions are estimated robustly and are not sensitive to the velocity model. In this case study, we compare event location solutions from two catalogues of microseismic events; one from a downhole array and the second from a surface array of 1C geophone. Our results show that origin time can be reliably used to find matching events between the downhole and surface catalogues. The locations of the corresponding events display a systematic shift consistent with a poorly calibrated velocity model for downhole dataset. For this case study, locations derived from surface monitoring have less scatter in both vertical and horizontal directions.     

Relations between surface deformation,fault geometry,seismicity, and rupture characteristics during the El Asnam (Algeria) earthquake of 10 October 1980

The El Asnam earthquake of October 10, 1980 (M_s=7.3) produced surface faulting on a northeast-trending thrust fault of 30 km length with displacements of up to 6.5 m, though average displacements were about 3 m. In addition, widespread tensional features were formed, some in clear association with folding above the thrust, and others, in an area beyond the exposure of the thrust at the surface, which may be related to buried reverse faults.The observed thrust fault is split into southern, central and northern segments. Local and teleseismic data are examined to show that the main shock nucleated at the southwest end of the fault, and propagated 12 km northeast where a second rupture of approximately equal moment occurred, continuing the faulting a further 12 km northeast along the central segment. Both ruptures nucleated at about 8–10 km depth. Displacements were largest on the central segment, where they were probably enlarged by aftershocks, including one of m_b=6.1 three hours after the main shock. The northern segment was much shorter than the other two, and showed smaller displacement.The junctions between fault segments are marked by distinct geomorphological characteristics and a change in strike of the faulting, as well as a sudden drop in the observed displacement. It appears that the rupture development is influenced by the changes in fault geometry between segments, and that such junctions or barriers have persisted through much of the late Quaternary.     

大陆板内地震活动的时空复杂性:地球动力学数值模拟的启示及对地震危险性评估的意义

大陆板内地震活动通常表现为偶发性、丛集和迁移。地震观测数据显示了沿地震带的空间聚集和散布于板内的大部分区域、长期平静后的地震活动时间丛集,以及地震带间的迁移。这里,我们使用三维粘-弹-塑性有限元模型,对板内地震活动时空图像的复杂性进行了探索。模型模拟了动力加载、地震的地壳失稳以及同震和震后的应力演化。对于地壳强度预设随机扰动的横向均匀岩石层,模型预测了不同时间尺度下地震活动不同的时空图像：经过数百年后,空间聚集于窄带和散布于大区域,在数千年后,连成地震带,以及数万年后遍布于模型区域。地震带的方位与动力加载引起的最优失稳方向一致。应力转换和迁移造成地震的时空丛集。当考虑弱化带的影响时,模型预测地震初期在带内活动,之后扩展至远处。如果大震后断层带发生弱化,则在没有强动力加载的条件下,同一断层带也可能再次发生大震。通过简单模型揭示的板内地震活动时空复杂性表明,依赖于有限地震记录的地震危险性评估可能存在偏差,以致于在近代发生过大震的地区高估地震危险性,而在近代少震的地区低估地震危险性。     

Impact of water transfer on interaction between surface water and groundwater in the lowland area of North China Plain

The contradiction between the freshwater shortage and the large demand of freshwater by irrigation was the key point in cultivated lowland area of North China Plain. Water transfer project brings fresh water from water resource‐rich area to water shortage area, which can in turn change the hydrological cycle in this region. Major ions and stable isotopes were used to study the temporal variations of interaction between surface water and groundwater in a hydrological year after a water transfer event in November 2014. Irrigation canal received transferred Yellow River, with 2.9% loss by evaporation during water transfer process. The effect of transferred water on shallow groundwater decreased with increasing distance from the irrigation canal. Pit pond without water transfer receives groundwater discharge. During dry season after water transfer event, shallow groundwater near the irrigation canal was recharged by lateral seepage and deep percolation of irrigation, whereas shallow groundwater far from irrigation canal was recharged by deep percolation of deep groundwater irrigation. Canal water lost by evaporation was 2.7–17.4%. Influence of water transfer gradually disappeared until March as the water usage of agricultural irrigation increased. In the dry season, groundwater discharged to irrigation canal and pond; 2.2–31.6% canal water and 11.3–20.0% pond water were lost by evaporation. In the rainy season (June to September), surface water was fed mainly by precipitation and surface run‐off, whereas groundwater was recharged by infiltration of precipitation. The two‐end member mix model showed that the mixing ratio of precipitation in pond and irrigation canal were 73–83.4% (except one pond with 28.1%) and 77.3–99.9%, respectively. Transferred water and precipitation were the important recharge sources for shallow groundwater, which decreased groundwater salinity in cultivated lowland area of North China Plain. With the temporary and spatial limitation of water transfer effects, increased water transfer amounts and frequency may be an effective way of mitigating regional water shortage. In addition, reducing the evaporation of surface water is also an important way to increase the utilization of transfer water.     

我国近海地震活动特征及其与地球物理场的关系

对我国近海海域有历史记载以来的地震的震级、震中参数进行了整理分析,并分析了各海域地震活动的时、空分布规律,根据历史地震资料,确定海域受历史地震影响的最大影响烈度,然后初步分析了地震活动与现代构造应力场、地球物理场的关系.研究发现:(1)近海海域历史地震资料的精度较低,中强地震存在明显的遗漏.(2)渤海、台湾海峡、南海北部地震活动性较强,黄海次之,东海最弱.(3)近海海域的震害主要来自海域地震和近岸陆地强震的影响,影响强弱依次为:渤海、黄海、东南沿海、东海.(4)现代构造应力场以水平向构造应力场作用下的走滑运动为主,最大主应力方向受印度板决和太平洋板块、菲律宾海板块的俯冲挤压方向影响.(5)海域地球物理场,特别是布格重力异常、地壳厚度分布与强震构造带的空间分布关系的相关性较好.本文的研究结果可为我国海域及滨海重要工程的抗震设防、海域地震危险性区划提供一定的基础.     

On the interaction between ocean surface waves and seamounts

Of the many topographic features, more specifically seamounts, that are ubiquitous in the ocean floor, we focus our attention on those with relatively shallow summits that can interact with wind-generated surface waves. Among these, especially relatively long waves crossing the oceans (swells) and stormy seas are able to affect the water column up to a considerable depth and therefore interact with these deep-sea features. We quantify this interaction through numerical experiments using a numerical wave model (SWAN), in which a simply shaped seamount is exposed to waves of different length. The results show a strong interaction that leads to significant changes in the wave field, creating wake zones and regions of large wave amplification. This is then exemplified in a practical case where we analyze the interaction of more realistic sea conditions with a very shallow rock in the Yellow Sea. Potentially important for navigation and erosion processes, mutatis mutandis, these results are also indicative of possible interactions with emerged islands and sand banks in shelf seas.     

The 1997 Umbria-Marche earthquakes (Italy): relation between the surface tectonic breaks and the area of deformation

We classified the most outstanding rupturesof the 1997 Umbria-Marche seismic sequence assecondary tectonic effects that occur within the zoneof deformation induced by the deep displacement on theseismogenic structure. The trend of the surfacedeformation is homogeneous within the entire area ofinterest and consistent with NE-oriented extensionevidenced by CMT focal solutions of the three mainshocks. We extrapolate the discontinuous sites ofbreak measurements and suggest that the localdeformation concentrates along four narrow bands.Location and direction of these bands are locallycontrolled by pre-existing structures. The comparisonbetween our data with the seismological data – such asmain rupture planes and spatial aftershockdistribution – highlights that three bands mark partof the boundaries of the NW-SE elongated aftershocksarea and the fourth occurs where this area is widest.Moreover, the analysis of the structural setting ofthe area suggests that N-S shear zones have stronglycontrolled the extension of the main rupture segmentsand the aftershock distribution. The surface rupturesare located within the area of coseismic deformationresulting from DInSAR data; we propose that theyrepresent the localized response to the verticalground deformation of the area. Finally, we discussthe contribution of the pattern of the 1997 surfacebreaks to the characterization of the seismogenicsource.     

岳阳及周边地区地震构造与地震活动性研究

陈述了岳阳市及周边地区的主要断裂带及其地震活动，归纳了发震部位。认为利用小震条带预报本区地震具有积极意义，并运用数理统计法预测了本区今后50及100年内的地震活动水平。     

The Bishkek vertical array (BIVA): acquiring strong motion data in Kyrgyzstan and first results

We present results from a vertical array of accelerometers that was recently installed in Bishkek (Kyrgyzstan) with the long-term aim of recording strong motion data. Taking advantage of recordings of a Mb 4.7 earthquake that occurred 40 km from the array site during the installation phase, we provide results of some preliminary data analysis. First, estimates of the S-wave velocity and Qs structure are deduced by the inversion of the deconvolved wavefield between the sensors in the borehole. Furthermore, the application of the nonstationary ray decomposition Kinoshita (Earth Planets Space 61:1297-1312, 2009) allowed at least three reflectors in the shallow velocity structure below the array to be identified. The complex nature of the wavefield (with up-going, down-going waves, and converted phases) due to the coarse, unconsolidated subsoil structure is highlighted by means of numerical simulations of ground motion.