The first and third asymptotic distributions of extremes as applied to the seismic source regions of India and adjacent areas

The seismic source regions are identified on the basis of spatial and temporal distributions of shocks (1900–1989), recurrence relations and the tectonic architecture of the Indian subcontinent and adjoining areas. The probable occurrence of the maximum magnitude earthquake is estimated using the theory of extreme values of Gumbel. The parameters of the first and third asymptotic distributions of extremes and their uncertainty values are computed for the seven identified seismic source regions of India and adjacent areas. The third-type distribution curve is preferable to the first type in all the regions, as revealed by the χ² test. The results of the third asymptotic distribution indicate the upper bound to earthquake magnitude w is equal to 8.94 ± 0.21 for Assam, 8.56 ± 0.29 for Bihar-Nepal, 8.43 ± 0.10 for Kangra, 8.97 ± 0.27 for Hindukush, 7.61 ± 0.24 for Pakistan-Cutch, 7.34 ± 0.12 for Koyna and 8.98 ± 0.27 for Andaman Sea seismic source regions. The predicted most probable largest earthquake magnitude is computed for return periods of 10, 20, 50, 75 and 100 yr in each source region.     

中国地震发生频率与烈度的空间分布

考虑不同区域地震记录具有时间长度不等的特点,对“震中分布分震级网格点密集值”算法进行改进,结合 GIS 的空间分析方法将地震目录中的点数据空间化为能反映地震发生频率的栅格数据;依据地震震级和烈度的关 系以及地震烈度在空间上的椭圆衰减模型,选择逼近和近似的计算手段,并结合空间插值方法得到中国地震烈度 分布的栅格图。从地震频率分布结果上看,大致以宁夏、甘肃、四川和云南为界,中国西部地区3 级以上的地震发生 频率要高于东部地区;从地震烈度分布结果看,中国甘肃、陕西、宁夏、山西、河北、四川、云南等位于地震带内的区 域在发生地震时产生的烈度较高。     

Non-Poissonian earthquake occurrence in coupled stress release models and its effect on seismic hazard

Most seismic hazard estimations are based on the assumption of a Poisson process for earthquake occurrence, even though both observations and models indicate a departure of real seismic sequences from this simplistic assumption. Instrumental earthquake catalogues show earthquake clustering on regional scales while the elastic rebound theory predicts a periodic recurrence of characteristic earthquakes on longer timescales for individual events. Recent implementations of time-dependent hazard calculations in California and Japan are based on quasi-periodic recurrences of fault ruptures according to renewal models such as the Brownian Passage Time model. However, these renewal models neglect earthquake interactions and the dependence on the stressing history which might destroy any regularity of earthquake recurrences in reality. To explore this, we investigate the (coupled) stress release model, a stochastic version of the elastic rebound hypothesis. In particular, we are interested in the time-variability of the occurrence of large earthquakes and its sensitivity to the occurrence of Gutenberg–Richter type earthquake activity and fault interactions. Our results show that in general large earthquakes occur quasi-periodically in the model: the occurrence probability of large earthquakes is strongly decreased shortly after a strong event and becomes constant on longer timescales. Although possible stress-interaction between adjacent fault zones does not affect the recurrence time distributions in each zone significantly, it leads to a temporal clustering of events on larger regional scales. The non-random characteristics, especially the quasi-periodic behaviour of large earthquakes, are even more pronounced if stress changes due to small earthquakes are less important. The recurrence-time distribution for the largest events is characterized by a coefficient of variation from 0.6 to 0.84 depending on the relative importance of small earthquakes.     

Simulating a seismic series using geostatistical and stochastic methods: application to the seismic series in the Alborán Sea (1997 June 24–?)

Seismic series can be taken as examples of correlated unstationary sets of time-stochastic sequences. We investigate the possibility of estimating what is most probable to occur subsequently, if we know the events that have occurred up to a given moment.
The stochastic methods can be used with data of the seismic series, irrespective of their genesis and origin. Using three stochastic methods, namely (1) simulating the likelihood of occurrence by conditional geostatistical simulation; (2) developing a stochastic analysis of the energy release by means of energy packages; and (3) calculating the occurrence time of the most probable next earthquake, we were able to simulate the occurrence of earthquakes that took place during the Alborán Sea seismic series (1997–1998).
We conclude that it is possible to set limits on the time of occurrence and energy release, understood as the magnitude of the most probable earthquake, during the development of a seismic sequence and prior to the actual occurrence of the earthquake.     

Seismic risk in southern Europe through to India examined using Gumbel's third distribution of extreme values

Summary. A technique is described for the analysis of seismicity using Gumbel's third asymptotic distribution of extreme values. Seismicity of southern Europe through to India, nominally for the period 1900–74, is subdivided in a cellular manner, without recourse to tectonic discrimination between regions, and a covariance analysis on the three parameters of Gumbel's distribution is performed for each cell of seismicity. The results indicate that the upper bound to the magnitude of earthquake occurrence is often uncertain although it is discernible, while curvature of the earthquake occurrence distributions is usually established. Uncertainties in the forecasts of largest earthquakes, with a return period of 75 yr, are distinctly improved by taking into account the large and negative covariance which is measured between the curvature and upper bound to earthquake magnitude for the observed seismicity. These results are then used to map seismic risk for southern Europe through to India.     

Smaller source earthquakes and improved measuring techniques allow the largest earthquakes in Iceland to be stress forecast (with hindsight)

A group of three earthquakes in 2000 June in SW Iceland included the two largest earthquakes in Iceland in the past 30 yr. Previously, temporal changes in shear-wave splitting had not been recognized before these earthquakes as there were too few small earthquakes to provide adequate shear-wave data, and they were not stress forecast, even with hindsight. These large earthquakes were subject to a special investigation by the European Community funded PREPARED Project during which the seismic catalogue was extended to include smaller magnitude earthquakes. This more detailed data set, together with a semi-automatic programme for measuring the parameters of shear-wave splitting greatly increased the number of time-delay measurements.
The new measurements displayed the typical temporal variations before larger earthquakes as seen elsewhere: a long-term increase in time delays, interpreted as stress accumulation before the earthquake; and a decrease, interpreted as crack coalescence, immediately prior to the earthquake. The logarithms of the durations of both the implied accumulation of stress and the crack coalescence have the same self-similar relationships to earthquake magnitude as found elsewhere in Iceland. This means that, in principle, the time and magnitude of the larger earthquakes could have been stress forecast in real time had the smaller source earthquakes of the extended catalogue and the improved measuring procedures been available at the time.     

GIS支持下的黄土高原地震滑坡区划研究

分析了影响黄土滑坡的各项影响因子,利用层次分析法(AHP)确定各影响因子的权重。在GIS支持下,建立包括各因子图的空间数据库,对各因子进行分级赋值,然后进行因子加权叠加分析,完成三种超越概率下(50年超越概率2%、10%和63.5%)黄土高原地震滑坡区划图。黄土地震滑坡灾害最严重地区一个是宁夏南部及与其相邻的甘肃白银地区,另一个是甘肃天水地区。     

Determination of earthquake early warning parameters, τc and Pd, for southern California

We explore a practical approach to earthquake early warning in southern California by determining a ground-motion period parameter  τ _c   and a high-pass filtered displacement amplitude parameter Pd from the initial 3 s of the P waveforms recorded at the Southern California Seismic Network stations for earthquakes with M > 4.0. At a given site, we estimate the magnitude of an event from  τ _c   and the peak ground-motion velocity ( PGV ) from Pd . The incoming three-component signals are recursively converted to ground acceleration, velocity and displacement. The displacements are recursively filtered with a one-way Butterworth high-pass filter with a cut-off frequency of 0.075 Hz, and a P -wave trigger is constantly monitored. When a trigger occurs,  τ _c   and Pd are computed. We found the relationship between  τ _c   and magnitude ( M ) for southern California, and between Pd and PGV for both southern California and Taiwan. These two relationships can be used to detect the occurrence of a major earthquake and provide onsite warning in the area around the station where onset of strong ground motion is expected within seconds after the arrival of the P wave. When the station density is high, the methods can be applied to multistation data to increase the robustness of onsite early warning and to add the regional warning approach. In an ideal situation, such warnings would be available within 10 s of the origin time of a large earthquake whose subsequent ground motion may last for tens of seconds.     

Earthquake deformations in the Lisan deposits and seismotectonic implications

Summary. Earthquake deformations and induced sedimentary structures preserved in Quaternary sediments include faults, folds, fissures, slumps, sand boils and other effects of liquefaction. Such deformations and structures are well preserved in the Lisan deposits of the Dead Sea. Of most importance are the fold-type deformations known as décollement structures which are present all along the eastern side of the Lisan and seem to decrease gradually westwards to disappear in the middle of the Lisan. These may indicate that palaeoearthquakes originating along the Araba fault have triggered such structures due to shaking of elastoplastic unconsolidated sediments over gentle slopes dipping to the west.
Preliminary results from studies on décollement structures preserved in a section representing some 1733 years of continuous deposition in the uppermost? Pleistocene, in the vicinity of Wadi Araba, indicate that: (1) seismic activity has fluctuated with time. Average recurrence period is about 340 ± 20yr for earthquakes with magnitudes greater than or equal to 6.5, Earthquakes with magnitude greater than 7 seem to have occurred along the Araba fault. (2) Deduced earthquake magnitudes conform to the frequency–magnitude relationship: log N = 5.24–0.68 M . (3) The deduced seismic slip rate along the Araba fault seems to be not less than 0.64 ± 0.04 cm yr⁻¹.     

Statistical study of the occurrence of shallow earthquakes

Summary. The time—space-magnitude interaction of shallow earthquakes has been investigated for three catalogues: worldwide ( M ≥ 7.0), Southern and Northern California ( M ≥ 4.0) and Central California ( M ≥ 1.5). The earthquake sequences are considered as a multi-dimensional stochastic point process; the estimates of the parameters for a branching model of the seismic process are obtained by a maximum-likelihood procedure. After applying magnitude—time and magnitude—distance scaling, the pattern of relationship among earthquakes of different magnitude ranges is almost identical. The number of foreshocks diminishes as the magnitude difference between the main shock and the foreshocks increases, while the magnitude distribution of aftershocks has the opposite property. The strongest aftershocks are likely to occur at the beginning of the sequence; later they migrate away with velocities of the order of km/day. The sequences which are composed of smaller aftershocks last longer and there are indications that they remain essentially in the focal region. Foreshocks also appear to migrate, but in this case, toward the main shock. The rate of occurrence of dependent shocks increases as t ^-1 as the origin time of the main shock is approached, effectively making every earthquake a multi-shock event. This interaction of earthquakes was modelled by a Monte-Carlo simulation technique. The statistical inversion of simulated catalogues was undertaken to derive the information we would be able to retrieve from actual data, as well as possible errors of estimates. The possibility of using these results as a tool for seismic risk prediction is discussed and evaluated.     

Likelihood analysis of earthquake catalogues

We apply several classes of stochastic multidimensional models to statistical analysis of earthquake catalogues using likelihood methods. We investigate the importance of including different earthquake parameters in the model: epicentral coordinates, hypocentral depth, time limits for interearthquake interaction, and especially spatial distribution of earthquakes as well as spatial aftershock patterns. Results of this study combined with other investigations, suggest that most distributions controlling earthquake interaction have a fractal or scale-invariant form. Developed models are used for statistical analysis of several earthquake catalogues to evaluate parameters of earthquake occurrence. These parameters are shown to be similar for shallow earthquakes of different magnitude ranges and seismogenic regions, confirming self-similarity of the earthquake process. Whereas intermediate earthquakes seem to emulate the pattern of shallow earthquake occurrence, albeit at a much smaller aftershock rate, deep earthquakes differ significantly in their properties. Predictability of standard shallow earthquake catalogues has been analysed; we present evidence that for the best available catalogues the predictability is close to 10 bits per earthquake. Several synthetic earthquake catalogues have been created and processed through the likelihood inversion scheme. The results from likelihood analysis of these catalogues confirm our approach.     

Simulations of strong ground motion for earthquakes in the Mexicali–Imperial Valley region

Summary. In this paper computer modelling is used to test simple approximations for simulating strong ground motions for moderate and large earthquakes in the Mexicali–Imperial Valley region. Initially, we represent an earthquake rupture process as a series of many independent small earthquakes distributed in a somewhat random manner in both space and time along the rupture surface. By summing real seismograms for small earthquakes (used as empirical Green's functions), strong ground motions at specific sites near a fault are calculated. Alternatively, theoretical Green's functions that include frequencies up to 20 Hz are used in essentially similar simulations. The model uses random numbers to emulate some of the non-deterministic irregularities associated with real earthquakes, due either to complexities in the rupture process itself and/or strong variations in the material properties of the medium. Simulations of the 1980 June 9 Victoria, Baja California earthquake ( M _L= 6.1) approximately agree with the duration of shaking, the maximum ground acceleration, and the frequency content of strong ground motion records obtained at distances of up to 35 km for this moderate earthquake. In the initial stages of modelling we do not introduce any scaling of spectral shape with magnitude, in order to see at what stage the data require it. Surprisingly, such scaling is not critical in going from M = 4–5 events to the M = 6.1 Victoria earthquake. However, it is clearly required by the El Centro accelerogram for the Imperial Valley 1940 earthquake, which had a much higher moment ( Ms ∼ 7). We derive the spectral modification function for this event. The resulting model for this magnitude ∼ 7 earthquake is then used to predict the ground motions at short distances from the fault. Predicted peak horizontal accelerations for the M ∼ 7 event are about 25–50 per cent higher than those observed for the M = 6.1 Victoria event.     

中国地震灾害人口死亡风险定量评估(英文)

基于地震灾害风险形成机理,在建立人口震害脆弱性曲线与确定地震发生参数的基础上,本文利用评估模型对我国Ⅴ-Ⅺ地震烈度下各县域单元的人口死亡风险进行评估并分析其空间分布格局。主要研究内容有:(1)首次采用基于过去—现在—未来的多方面地震孕灾环境资料来处理地震发生的可能性。具体综合历史地震综合烈度、地震活动断裂带分布、地震动峰值加速度三方面来确定全国2355个县域单元的地震发生参数;(2)利用1990-2009年我国历史地震灾情数据,对地震烈度与人员死亡率之间进行线性拟合,建立适合我国地震灾害风险评估的震害人口死亡脆弱性曲线;(3)利用震害风险评估模型对我国各县域单元的人口死亡风险进行定量评估,并分析风险空间分布格局,彻底摸清Ⅴ-Ⅺ地震烈度下我国各县域单元的地震灾害人口死亡风险。研究表明:在不同地震烈度下,我国广大的东、中部地区面临更高的风险,而西部的人口死亡风险相对较低。高风险区域呈零星状分布于山东与江苏大部、安徽北部、黑龙江与吉林东部等人口分布较密集且孕灾环境发育完备的区域。而无风险区域在全国范围内呈斑块状散布,分布格局基本保持不变。     

A structural model for the seismicity of the Arudy (1980) epicentral area (Western Pyrenees, France)

The Western Pyrenees presents a diffuse and moderate ( M ≤ 5.7) instrumental seismicity. It nevertheless historically suffered from strong earthquakes (I = IX MSK). The seismic sources of these events are not yet clearly identified. We focus on the Arudy (1980) epicentral area ( M = 5.1) and propose here the reactivation of early Cretaceous normal faults of the Iberian margin as a potential source. The late Cretaceous inversion of this basin, first in a left-lateral strike-slip mode and then in a more frontal convergence, resulted in a pop-up geometry. This flower structure attests of the presence of a deep crustal discontinuity.
The present-day geodynamic arrangement suggests that this accident is reactivated in a right lateral mode. This reactivation leads to a strain partitioning between the deep discontinuity that accommodates the lateral component of the motion and shallow thrusts, rooted on this discontinuity. These thrusts accommodate the shortening component of the strain. The distribution of the instrumental seismicity fits well the structural model of the Arudy basin. Whatever the compressive regional context, the structural behaviour of the system explains too the extensive stress tensor determined for the Arudy crisis if we interpret it in terms of strain ellipsoid. Indeed numerical modelling has shown that this concomitant activity of strike-slip and thrust faulting results in an extensive component that can rise 50 per cent of the finite strain.
We identify too a 25–30 km long potential seismic source for the Arudy area. The size of the structure and its potential reactivation in a strike-slip mode suggest that a maximum earthquake magnitude of ∼6.5 could be expected. The extrapolation of this model at the scale of the Western Pyrenees allows to propose other potential sources for major regional historical earthquakes.     

Implications of a percolation model for earthquake 'nucleation'

A percolation model is applied to the explanation of some of the qualitative and quantitative aspects associated with the recent observations of earthquake 'nucleation'. An additional assumption is introduced that nucleation starts at the critical point of percolation. The model explains the order of magnitude of the seismic moment release during the nucleation, the dependence of the seismic moment of the main shock on the duration of the nucleation process, and the observation that the fraction of the moment release during the nucleation has no systematic variation with the size of the main shock. The model also suggests that the source time function of the nucleation phase may be complex, and also that not all earthquakes are accompanied by a nucleation process, which is supported by observational results. By assuming that there exists a scale invariance associated with the criticality, a Widom scaling model is proposed to describe the electromagnetic emission during earthquake rupture.     

Effect of a simple mountain range on underground seismic motion

Summary. The influence of a simple mountain range on seismic ground motion is studied. A two-dimensional model of the medium and vertically incident plane SH -waves are considered. Attention is devoted not only to the wavefield along the Earth's surface, but also within the medium. The wavefield is computed in two steps: (1) the computation of the impulse response by the finite-difference method, (2) the computation of the response to a time variation of the incident wave. approximately corresponding to a 'hundred-year' local earthquake at the site. Numerical results (the impulse response, the transfer function, the accelerograms, and their spectra) indicate strong spatial variability of the wavefield due to the topographical anomaly. The differences as large as 100 per cent in the peak amplitudes of the accelerograms, and of the order of 5 Hz in their predominant frequencies, at closely (∼ 200 m) spaced internal points of the medium have been found. Attention is focused also on the effect of causal absorption. Even unrealistically strong absorption seems to be unable to reduce significantly the spatial variability of the ground motion, caused by the topography. A variability like this. implying the occurrence of underground differential strains, might be of engineering importance in the antiseismic design of underground structures (tunnels, for example) in mountainous seismic regions. The ground-motion variability along the surface of the mountain is considerably smaller than within the medium.     

Impacts of seismic activity and climatic change on Chinese history in the recent millennium

General history of disasters in China suggests that China has frequently experienced two major natural disasters in its long history, one is from catastrophic earthquake events, and the other is from extreme climatic events, due to its unique active tectonic environment and climatic complexity. Although these two major natural disasters have caused great damage to human society, it remains unclear whether and how they affect Chinese dynasty alternation on decadal(emperor) timescales. Based on de...     

Low detection capability of global earthquakes after the occurrence of large earthquakes: investigation of the Harvard CMT catalogue

We investigated the detection capability of global earthquakes immediately after the occurrence of a large earthquake. We stacked global earthquake sequences after occurrences of large earthquakes obtained from the Harvard centroid-moment tensor catalogue, and applied a statistical model that represents an observed magnitude–frequency distribution of earthquakes to the stacked sequence. The temporal variation in model parameters, which corresponds to the detection capability of earthquakes, was estimated using a Bayesian approach. We found that the detection capability of global earthquakes is lower than normal for several hours after the occurrence of large earthquakes; for instance, the duration of lowered detection capability of global earthquakes after the occurrence of an earthquake with a magnitude of seven or larger is estimated to be approximately 12 hr.     

Stress drops, wave spectra and recurrence intervals of great earthquakes — implications of the Etorofu earthquake of 1958 November 6

Summary . The great Etorofu earthquake of 1958 November 6 is characterized by a relatively small aftershock area (70 × 150 km²) and an extremely large felt area. The felt area is more extensive than those of any other large earthquakes which have occurred in the southern Kurile to northern Japan arc since the beginning of this century. The mechanism is a pure thrust fault typical of most great earthquakes in island arcs. A body wave magnitude of m _b = 8.2 is obtained at periods around 6 s using more than 40 observations, although an m _b value of only 7.6–7.7 would be expected empirically from the observed surface wave magnitude of M _s= 8.1–8.2. Both an unusually large felt area and a high m _b indicate a dominance of high-frequency components in the seismic waves. A seismic moment of M _o= 4.4 × 10²⁸ dyne cm is determined from long-period surface waves from which a high stress drop of Δσ = 78 bar is obtained using a relatively small aftershock area. Historic data indicate an anomalously long time interval between the 1958 event and any earlier great earthquake from the same source region. The observed high stress drop can be interpreted as a consequence of this long intervening period through which strain built up. The dominance of the high-frequency seismic waves can then be interpreted as a result of this high stress drop. Stress drops, seismic wave spectra and recurrence intervals of great earthquakes are in this way closely related to each other. The 1958 event may represent a high strength extreme of stochastic fluctuation of fracture strength relevant to great earthquakes.