1966～1976年华北地震的时间特性及相关触发因素

阐述了１９６６～１９７６年华北地震的时间特性及其相关触发因素－－地球自转和引潮力。这是３００年来华北地区发生的最强烈的一组地震,强震发生的时间有一个共同的特性;在年尺度上大多数地震发生在季节性地球自转速度极在值或极小值时间点附近,即极点附近（或称极点时段）,在月惊工上多数地震发生在朔望附近（或称朔望时段）,在日尺度上半数地震发生在极大水平引潮力时刻附近。表明这些地震与地球自转和日月引潮力关系密切。     

Typical source areas of May 1998 flow-like mass movements in the Campania region, Southern Italy

Flow-like mass movements in granular materials are among the most serious natural hazards, systematically producing huge amounts of damage and numerous victims, especially when involving volcanic soils. This is the case of the events in Southern Italy in May 1998, when rainfall triggered many destructive landslides along the slopes of a carbonate massif mantled by pyroclastic soils. Due to the complexity of the occurred phenomena, a shared interpretation of their triggering stage is still not available.

As a contribution to the topic, the paper initially discusses the geological and geomorphological features of the massif combining them in three hillslopes models. The models are then associated to the hydrogeological features and anthropogenic factors in order to define six typical landslides source areas that are not casually distributed on the massif. The study subsequently focuses on the most frequent type of source areas, associated to the largest unstable soil volumes and longest run-out distances. For these source areas, the triggering mechanism is discussed, with an example of geotechnical validation being proposed for a well monitored mountain basin. The geotechnical modelling at site scale confirms the geological analyses at massif scale and provides further insights into the events, thus highlighting the potential of a multidisciplinary approach for the interpretation of very complex slope instability phenomena.     

Physical and stochastic models of earthquake clustering

The phenomenon of earthquake clustering, i.e., the increase of occurrence probability for seismic events close in space and time to other previous earthquakes, has been modeled both by statistical and physical processes.From a statistical viewpoint the so-called epidemic model (ETAS) introduced by Ogata in 1988 and its variations have become fairly well known in the seismological community. Tests on real seismicity and comparison with a plain time-independent Poissonian model through likelihood-based methods have reliably proved their validity.On the other hand, in the last decade many papers have been published on the so-called Coulomb stress change principle, based on the theory of elasticity, showing qualitatively that an increase of the Coulomb stress in a given area is usually associated with an increase of seismic activity. More specifically, the rate-and-state theory developed by Dieterich in the ′90s has been able to give a physical justification to the phenomenon known as Omori law. According to this law, a mainshock is followed by a series of aftershocks whose frequency decreases in time as an inverse power law.In this study we give an outline of the above-mentioned stochastic and physical models, and build up an approach by which these models can be merged in a single algorithm and statistically tested. The application to the seismicity of Japan from 1970 to 2003 shows that the new model incorporating the physical concept of the rate-and-state theory performs not worse than the purely stochastic model with two free parameters only. The numerical results obtained in these applications are related to physical characters of the model as the stress change produced by an earthquake close to its edges and to the A and σ parameters of the rate-and-state constitutive law.     

Elastic and inelastic triggering of earthquakes in the North Anatolian Fault zone

Deformation models used to explain the triggering mechanism often assume pure elastic behaviour for the crust and upper mantle. In reality however, the mantle and possibly the lower crust behave viscoelastically, particularly over longer time scales. Consequently, the stress field of an earthquake is in general time-dependent. In addition, if the elastic stress increase were enough to trigger a later earthquake, this triggered event should occur instantaneously and not many years after the triggering event. Hence, it is appropriate to include inelastic behaviour when analysing stress transfer and earthquake interaction.In this work, we analyse a sequence of 10 magnitude M_s > 6.5 events along the North Anatolian Fault between 1939 and 1999 to study the evolution of the regional Coulomb stress field. We investigate the triggering of these events by stress transfer, taking viscoelastic relaxation into account. We evaluate the contribution of elastic stress changes, of post-seismic viscoelastic relaxation in the lower crust and mantle, and of steady tectonic loading to the total Coulomb stress field. We analyse the evolution of stress in the region under study, as well as on the rupture surfaces of the considered events and their epicentres. We study the state of the Coulomb stress field before the 1999 İzmit and Düzce earthquakes, as well as in the Marmara Sea region.In general, the Coulomb stress failure criterion offers a plausible explanation for the location of these events. However, we show that using a purely elastic model disregards an important part of the actual stress increase/decrease. In several cases, post-seismic relaxation effects are important and greater in magnitude than the stress changes due to steady tectonic loading. Consequently, viscoelastic relaxation should be considered in any study dealing with Coulomb stress changes.According to our study, and assuming that an important part of the rupture surface must be stressed for an earthquake to occur, the most likely value for the viscosity of the lower crust or mantle in this region is 5 · 10¹⁷–10¹⁸ Pa · s. Our results cannot rule out the possibility of other time-dependent processes involved in the triggering of the 1999 Düzce event. However, the stress increase due to viscoelastic relaxation brought 22% of the 1999 Düzce rupture area over the threshold value of Δσ_c ≥ 0.01 MPa (0.1 bar), and took the whole surface closer to failure by an average of 0.2 MPa. Finally, we argue that the Marmara Sea region is currently being loaded with positive Coulomb stresses at a much faster rate than would arise exclusively from steady tectonic loading on the North Anatolian Fault.     

Triggering of Seismicity Remote from Active Mining Excavations

Summary. Observations of seismicity and ground control problems in the Sudbury mining camp have shown that late-stage (young) sub-vertical strike-slip faults are sensitive to small mining-induced stress changes. The strength-limited nature of stress measurements made in the region indicates that these structures are in a state of marginal stability. Numerical continuum models are developed to analyze the behavior of such structures. In the models, shear strain localizations (faults) evolve such that there is close interaction between the fault system, stresses, and boundary deformation. Fault slip activity in these systems is naturally sporadic and reproduces the commonly observed Gutenberg-Richter magnitude frequency relation. It is shown that a relatively minor disturbance to such a system can trigger significant seismicity remote from the source of the disturbance, a behavior which cannot be explained by conventional numerical stress analysis methodologies. The initially uniform orientation of the stress field in these systems evolves with increasing disorder, which explains much of the scatter commonly observed in data sets of stress measurements. Based on these results, implications for stress measurement programs and numerical stability analysis of faults in mines are discussed.     

应用化探方法研究断层活动性及发震构造

应用与断层活动有关的断层气资料研究断层的活动性,首先是要确定测区的背景值和异常下限,进而研究断层的活动性和分段特征,查找隐伏断裂及其产状,比较不同强震区断层气的异常值及峰值,判断潜在震源区的未来危险地段。重复测定活动断层的活动段以了解断层的动态变化,为预测断层的活动趋势与孕震关系提供依据。     

1995年7月22日永登5.8级地震发震构造和发震机制分析

在分析地质构造背景和深部地球物理特征的基础上，通过对震区断裂构造、震源机制解、震源深度、极震区展布方向、余震空间分布、地震裂缝和地面运动方向的综合研究，确定了１９９５年７月２２日永登５．８级地震的发震构造，探讨了形成该次地震的构造力学机制问题，认为该次地震是在局部构造应力直接作用下导致窑街—周家台隐伏断裂重新活动的结果     

Static stress changes as a triggering mechanism of a shallow earthquake: case study of the 1999 Chi-Chi (Taiwan) earthquake

The role of static stress changes in triggering an earthquake has long been debated in the fields of geophysics and fault mechanics. Valuable data sets for the study of static triggering were provided within the 1-year period following the devastating 1999 Chi-Chi (Taiwan) earthquake (M_W=7.6), during which more than 20,000 aftershocks occurred. In this study, stress waves generated by the Chi-Chi earthquake were calculated using a source rupture model in conjunction with a layered elastic model. Static (permanent) stress changes were extracted from the long-period offsets in the stressgrams. Correlations between the calculated stress changes and seismicity were analyzed at different depths and over varying time intervals to ascertain the impact effects of stress changes on triggering aftershocks. Correlations between prior seismicity rates and static stress changes imposed by the Chi-Chi event were low, while correlations between late seismicity rates and static stress changes were much higher. This indicates that static stress changes did affect the occurrence of the Chi-Chi aftershock sequence. The percentage of early aftershocks at shallow depths (0-10 km) in static stress-enhanced areas within 2 weeks of the main shock was high but decreased considerably at greater depths (>10 km) and over longer time periods. It is concluded that static stress changes at depths of 0-10 km played a major role in triggering crustal aftershocks, especially those that occurred within 2 weeks of the main shock. In the deeper crust, static stress changes may have been modified by viscous flow, and at later times, perturbed by earlier, larger aftershocks. Although the correlations between seismicity rate changes and static stress changes are imperfect, a region that was anti-triggered is detected when these two results are compared. Static stress changes are presumably not the only aftershock triggering mechanism, but they definitively play a major role in triggering shallow aftershocks.     

GRAPES-MESO模式浅对流参数化的改进与试验

参考Berg 等2005、2013年提出的扰动对流触发函数方法,对GRAPES-Meso模式积云对流参数化方案(KF eta)中的浅对流激发进行改进设计和试验,将单一的温、湿度触发改为对近地层进行一组温度、湿度扰动后的触发,并且用与该组扰动相关的边界层温、湿度分布确定的联合概率密度函数(JPDF)来表征浅对流云的特征参量及计算浅对流的强度。 着重分析了改进方案的浅对流激发、浅对流对环境场的反馈、模式地面降水和2 m气温的相关响应等,并与原方案和相关观测比较,验证了改进方案的合理性。 结果显示,改进方案比原方案能较早地激发出浅对流,且浅对流的激发频次高,浅对流激发的增加致使在模式低层距地数百米至2—3 km的垂直层内对环境温、湿度场和云雨水反馈增大,对GRAPES-Meso浅对流激发偏弱有改进作用,并对格点尺度与次网格尺度降水分配比不协调有改进。 对连续两个月批量试验的检验表明,浅对流激发的改进,可对GRAPES-Meso的24 h降水预报技巧的提高和2 m气温偏差的减小等产生不同程度的正影响。