Large European earthquakes of the 20th century

The magnitudes of the largest events in the European area have not exceeded M = 8 (shallow shocks) and m = 7.8 (intermediate depth shocks), respectively during the 20th century. Their geographical and depth distributions are discussed. The magnitude frequency relationships and the Gumbel III model define the statistical expectancy of the extreme events within the whole area. The strain release has a relatively constant trend between 1901–1975.     

Relations estimated at shock discontinuities excited by coronal mass ejections

An analysis of SOHO/LASCO C₃ data shows that there are discontinuities in the radial profiles of the plasma density within limited regions in front of each of ten coronal mass ejections, which represent shocks. The shock velocities in various events reach V ≈ 800–2500 km/s. A comparison of the dependence of the AlfvenicMach numberM _A on the shock strength ρ ₂/ρ ₁ detected at distancesR > 10R⊙ from the center of the Sun with calculations carried out using ideal magnetic hydrodynamics shows that the effective ratio of specific heats γ describing processes inside the shock front varies from 2 to 5/3 (ρ ₁ and ρ ₂ are the densities in front of and behind the shock, and R⊙ is the solar radius). This corresponds to an effective number of degrees of freedom between two and three. A similar dependenceMA(ρ ₂ /ρ ₁) was found for near-Earth bow shocks and interplanetary collisionless shocks. These features support the hypothesis that the studied discontinuities preceding coronal mass ejections are collisionless shocks.     

Annular seismicity structures and the March 11, 2011, earthquake (Mw = 9.0) in Northeast Japan

The characteristics of seismicity prior to the series of eight very strong earthquakes (M _w = 7.0–9.0) in Northeast Japan are discussed. Ring seismicity structures that appeared prior to all eight events in two depth ranges of 0–33 and 34–70 km are identified. The epicenters of the main shocks were located near areas of crossing or touching of shallow and deep rings. It was shown that the sizes of shallow rings and threshold magnitudes corresponding to seismicity rings grow with the energy of the main shocks. It was noted that the prognosis with respect to the place and magnitude of the catastrophic earthquake on March 11, 2011, had been made before it based on the data obtained prior to July 1, 2009. Use of the new data obtained prior to March 10, 2011, enabled us to specify this prognosis significantly. We obtained correlation dependences of threshold magnitudes on the energy of the main shocks (with a high correlation coefficients). It was shown that the duration of the period for seismicity rings to emerge in the considered region nearly did not depend on magnitude. The nature of annular structures and the possibility of application of their parameters for prognosis of strong earthquakes were discussed.     

A model for the υp -pressure function of cracked lunar rocks and some possible seismological consequences

Changes in wave velocity in rocks are mainly caused by pressure and depend on porosity and pore filling. For terrestrial and lunar rocks two formulae can be stated which are comparable with each other and the coefficients of which can be determined from wave velocity and uniaxial stress measurements. The behaviour of rocks may be compared with dynamic phenomena in the earth's crust, and in particular with pre-rupture phenomena (shocks, etc.) in seismic regions. The coefficient K₀ of imperfect bonds in rock increase with the number of shocks and brings about a decrease in wave velocity in seismic regions. The variations in wave velocity are connected with changes in electrical and thermal conductivity and with magnetic variations.     

The possibility of a tsunami on Lake Baikal

Based on the general physical nature of tsunami generation, it is established that it is an attribute of seismically hazardous areas and regions adjacent to large water reservoirs and is threatening to the population and infrastructure of the coastal zones. The main preconditions and possibilities for the occurrence of tsunami on Lake Baikal are considered: the information on earthquakes in the Baikal hollow during the instrumental-historical period (1724–2011) is generalized in the map of epicenters of shocks of magnitude M ⩾ 5 and histograms of the distribution of numbers of shocks with respect to magnitude. It is shown that the tsunami waves start forming on Baikal if the earthquake magnitude M is ≈5, but since a system of tsunami monitoring on Baikal is absent, it can be observed only during the strongest earthquakes of M > 7. The catastrophic Tsagan earthquake (1861, M ≈ 7.5) is given as an example. It happened near the eastern coast of Lake Baikal and caused a tsunami with people’s deaths.     

Verification of our previous definition of preferred earthquake nucleation areas in Kanto-Tokai, Japan

We have proposed that points of future initiation of rupture may be mapped, based on minima in local recurrence times, which are equivalent to local maxima in the probability for main shocks to occur. These minima are often controlled by anomalously low b-values (logN = a − bM). Of the Kanto-Tokai area, approximately 12% showed anomalously short recurrence times and was proposed as asperities, based on seismicity up to 1999. During the period 1999–2003.5, about 75% of the earthquakes with M ≥ 3.5 fell into the asperities, earlier defined (for example 19 out of 23 M ≥ 3.8 events). The probability for this to occur by chance is approximately 2 10^− 14. This supports our idea that the most likely volumes to produce main shocks may be mapped by minima in local recurrence times.     

Effects of thermal discharges on the microstructural growth ofMercenaria mercenaria

The effects of thermal discharges from the Oyster Creek Nuclear Generating Station at Barnegat Bay, New Jersey, are recorded in the microstructural growth ofMercenaria mercenaria, a common coastal marine pelecypod. The analysis of the shell microstructure shows that this bivalve acts as an effective monitor of the environmental conditions existing in the marine waters adjacent to the power station. Many physiological and environmental events such as spawning, winter (freeze) shocks, summer (heat) shocks, thermal shocks, tidal cycles, and major storms are clearly recorded in the shell microstructure. The exact time of occurrence of these events can be determined by counting daily growth increments backwards from the outer shell margins of freshly killed individuals. Microstructural growth patterns reflected in Barnegat Bay specimens indicate that these pelecypods were affected mainly by temperature extremes, temperature variations, tides, type of substratum, and age. Growth patterns in specimens from areas surrounding Oyster Creek (affected by thermal effluent) are significantly different from those from other bay localities (unaffected by thermal effluent).Mercenaria mercenaria within approximately a 1.6km radius of Oyster Creek show a lower summer growth rate (10 percent to 25 percent lower) and a greater number of growth breaks (2 to 6 more per clam) than those away from the creek. The lower summer growth rates occur in bivalves subjected to the effluent because the added heat during the summer months causes water temperatures to exceed a critical threshold for optimum growth in the species. The greater number of growth breaks takes place, in turn, because many of the breaks (thermal shock breaks) are generated by rapidly fluctuating temperatures associated with abrupt shutdowns, massive load reductions and rapid renewal of operations following shutdowns or load reduction periods at the nuclear power station. In addition, the effluent may be upsetting natural spawning events in the clams when abrupt changes in power station operations overlap with spawning periods. In this respect, spawning may be precluded by sharp temperature changes which result in physiological shocks to the animal.     

Process Analysis of In-situ Strain during the Ms8.0 Wenchuan Earthquake—Data from the Stress Monitoring Station at Shandan

Abstract: There were huge life and property losses during the Ms8.0 Wenchuan earthquake on May 12, 2008. Strain fluctuation curves were completely recorded at stress observatory stations in the Qinghai-Tibet plateau and its surroundings in the process of the earthquake. This paper introduces the geological background of the Wenchuan earthquake and the profile of in-situ stress monitoring stations. In particular, data of 174 earthquakes (Ms4.0-Ms8.5) were processed and analyzed with various methods, which were recorded at the Shandan station from August 2007 to December 2008. The results were compared with other seismic data, and further analyses were done for the recoded strain seismic waves, co-seismic strain stepovers, pre-earthquake strain valleys, Earth’s free oscillations before and after the earthquake and their physical implications. During the Wenchuan earthquake, the strainmeter recorded a huge extensional strain of 70 seconds, which shows that the Wenchuan earthquake is a rupture process predominated by thrusting. Significant precursory strain anomalies were detected 48 hours, 30 hours, 8 hours and 37 minutes before the earthquake. The anomalies are very high and their forms are very similar to that of the main shock. Similar anomalies can also be found in strain curves of other shocks greater than Ms7.0, indicating that such anomalies are prevalent before a great earthquake. In this paper, it is shown that medium aftershocks (Ms5.5-6.0) can also cause Earth’s free oscillations. Study of free oscillations is of great significance to understand the internal structure of the Earth and focal mechanisms of earthquakes and to recognize slow shocks, thus providing a scientific basis for the prevention and treatment of geological disasters and the prediction of future earthquakes.     

A forward test of the Decelerating–Accelerating Seismic Strain model to western south and central America

Global observations show that strong mainshocks are preceded by decelerating preshocks which occur in the focal (seismogenic) region of the ensuing mainshock and by accelerating preshocks which occur in a broader (critical) region of the mainshock. Predictive properties of these preshocks have been expressed by empirical relations supported by theory and form the Decelerating–Accelerating Seismic Strain (D–AS) model. A respective algorithm has been developed which is used to identify the critical and seismogenic region and estimate (predict) the corresponding ensuing mainshock. In the present work a forward test of this model is performed by attempting intermediate-term prediction of future big (M ≥ 7.7) mainshocks along the western coast of south and central America. Three regions of decelerating shocks and three corresponding regions of accelerating shocks have been identified. The parameters (origin time, magnitude, epicenter coordinates) as well as their uncertainties have been estimated (predicted) for the corresponding probably ensuing three mainshocks. This forward test allows an objective evaluation of the model's ability for an intermediate-term prediction of strong shallow mainshocks.     

The asymmetric nexus of energy-growth and CO2 emissions: An empirical evidence based on hidden cointegration analysis

Noting the significance of asymmetries in macroeconomic literature, this study aimed to estimate the asymmetric linkages between energy growth and the environment for BRICST countries between 1990 & 2017. For this purpose, this study applied hidden cointegration, panel NARDL, and asymmetric causality tests between the variables. In the first step, the results supported the existence of hidden cointegration between the variables. In the next step, empirical results obtained from panel NARDL results explained that the chosen variables have asymmetric relationships and are highly responsive to macroeconomic shocks. Initially, the positive shocks of energy consumption positively respond to environmental degradation; similarly, the negative shocks also correspond positively to CO₂ emissions. In the economic expansion phase, the positive shocks of growth have insignificant, and adverse shocks negatively respond to CO₂ emissions in BRICST countries. The results of individual countries along BRICST differ at various levels in response to asymmetric shocks. Different asymmetric causalities between the chosen dimension of variables are explored. From the asymmetric associations between the variables, the study proposes to forecast the energy demand and explore alternative ways to energy resources to shift their fossil energy bases to renewable systems. Similarly, adopting ICT products could make energy efficiency in these countries more productive towards improving environmental quality.     

An alternative view of the Bayesian probabilistic prediction of strong shocks in the Hellenic Arc

A Bayesian discrete distribution, as developed by Ferraes (1985), is applied to predict the inter-arrival times for strong shocks in the Hellenic Arc on the basis of nine samples of shocks with seismotectonic locations very different from those used by Ferraes. The results suggest an alternative view of the Bayesian probabilistic prediction of strong earthquakes in the Hellenic Arc, and can be summed up as follows:

• 1.(a) Maximum final Bayesian probabilities of various inter-arrival times in a given seismotectonic segment are very dependent on the data set used and particularly on its time length.
• 2.(b) When using this method to determine the time intervals during which large shocks are to be expected in the Western and Eastern Hellenic arcs, it is very difficult to estimate intervals of less than a decade. The determination of the occurrence time, even in the long-term sense, remains the major problem in the prediction of these shocks.
• 3.(c) Bayesian probabilities in conjunction with seismicity observations indicate that large intermediate depth earthquakes in the Hellenic Arc are long overdue. Shocks of this sort can be expected to occur in the next few years.

It is also pointed out that although Bayesian-type predictions may be useful for engineering purposes, they are not a suitable basis for making specific predictions or taking special precautions.     

Capillary hysteresis and gravity segregation in two phase flow through porous media

We study the gravity driven flow of two fluid phases in a one dimensional homogeneous porous column when history dependence of the pressure difference between the phases (capillary pressure) is taken into account. In the hyperbolic limit, solutions of such systems satisfy the Buckley-Leverett equation with a non-monotone flux function. However, solutions for the hysteretic case do not converge to the classical solutions in the hyperbolic limit in a wide range of situations. In particular, with Riemann data as initial condition, stationary shocks become possible in addition to classical components such as shocks, rarefaction waves and constant states. We derive an admissibility criterion for the stationary shocks and outline all admissible shocks. Depending on the capillary pressure functions, flux function and the Riemann data, two cases are identified a priori for which the solution consists of a stationary shock. In the first case, the shock remains at the point where the initial condition is discontinuous. In the second case, the solution is frozen in time in at least one semi-infinite half. The predictions are verified using numerical results.

     

Concentration of seismic energy within the two active domains beneath individual volcanoes and groups of volcanoes of Java, Indonesia

It is shown that beneath all individual active volcanoes or volcanic groups of Java there are two seismically active domains (Ac₁ and Ac₂), separated by an aseismic space (As₂). The concentration of released seismic energy is calculated for all active domains, in the cases of altogether eighteen individual volcanoes or groups, respectively. The medium value of energy-concentration (E*) in the case of the shallower active domains (Ac₁)is:

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(cerg = 0.01 erg), while the medium value for the deeper active domains (Ac₂) is:

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that is, they are in the same order of magnitude, thus expressing a remarkably uniform process of strain-accumulation and -release inside well-separated domains under active volcanoes if a longer period of time was considered.The variation of the E*-values, especially that of E* (Ac₂) along the arc of the volcanoes of Java, roughly speaking from west to east, shows a general tendency towards decrease. The western part is characterized by high, the eastern one by low values. By and large, a similar graph can be drawn concerning the reciprocal number of tectonic shocks within domains Ac₂. That is, the western part of the belt is characterized by relatively few shocks of higher magnitude while their number is essentially greater in the eastern part. Finally, the variation of the probable minimum depth of the primary magma chambers (sources of andesitic magma), calculated by one of the present authors corresponding to the Toksöz-model and on the basis of the analysis of Benioff-zones underneath Java, also shows a similar tendency, because the primary chambers at the western part of the belt are to be found at a relatively shallower level than at the eastern part.     

Preliminary results of a macroseismic survey of the Colfiorito sequence (Central Italy)

Umbria-Marche region (Central Italy) has been interested by a seismic sequence, which caused a large amount of damage within an extensive area (around 5000 km²). The sequence produced eight shocks with magnitude higher than 5.0, the largest of them occurring on September 26, UTC 09:40, M₁ = 5.8. The incidence of many shocks with a magnitude higher than 4.0 contributed to the creation of a damage pattern that was in evolution for more than one month. Such seismic behavior motivated field operators to perform a real-time macroseismic survey to update the data set. One of the major objectives was to differentiate the effects pertaining to each of the largest shocks. In this paper we present the macroseismic survey performed during the sequence, along with some preliminary results inferred. Intensity points of seven of the main shocks are shown, together with the filtered macroseismic fields produced following the application of specific statistical methods. Finally, consideration is given to the comparison of these study results with corresponding tectonic and geological data.     

Regionalization of seismic hazard in Greece based on seismic sources

A semi-probabilistic approach to the seismic hazard assessment of Greece is presented. For this reason, a recent seismotectonic model for shallow and intermediate depth earthquake sources, based on historical as well as on instrumental data, was used. Different attenuation formulae were proposed for the macroseismic intensity and the strong ground motion parameters for the shallow and the intermediate focal depth shocks. The data were elaborated in terms of McGuire's computer program, which is based on the Cornell's method.A grid of equally spaced points at 20 km distance was made and the seismic hazard recurrence curves for various parameters of the seismic intensity was estimated for each point. Finally, seismic hazard maps for the area of Greece were compiled utilizing the entire range of recurrence curves. These maps depict areas of equal seismic hazard and for every area the analytical relations of the typeSI =f(Tm), whereSI is a seismic intensity parameter andTm is the mean return period, were determined.     

Seismic intensity zoning and earthquake risk mapping in Iraq

The recently published Iraqi earthquake data file over the period 1905–1984 is used to derive a local I _o -M _s formula. This is then combined with a local intensity attenuation relationship to compile the observed I _o (MM) zoning map for Iraq. Earthquake risk is calculated using the log N (M _s )relation for selected design magnitudes and periods and is mapped as the (%) probability of occurrence using a 0.5 deg latitude/longitude grid system. It is observed that the intensity zones and contour distributions are highly influenced by the presence of large magnitude shocks while risk maps reveal the Tauros seismogenic zone as having a greater risk of occurrence than the Zagros zone. The compiled zoning maps are intended for the use of local practising engineers for earthquake-resistant design procedures that are currently being adopted in the country.     

中国地震事件沉积研究的若干问题探讨

地震事件沉积已经成为当今沉积地质学的一个热点领域.文中通过回顾国内震积岩的研究历史,总结了中国震积岩研究的成果及其存在的问题,重点讨论了地震引起的软沉积物变形、地震事件沉积的时序、地震事件沉积的空间分布和地震事件沉积序列等.按照地震对沉积物改造的时间,将软沉积物变形划分为同生、准同生、后生变形3类,并对地震同生断裂、准...     

Structure of the circumbinary envelope around a young binary system

The structure of a circumstellar envelope around a young binary T Tauri star is considered. The supersonic orbital motion of the system components in the envelope gas leads to the formation of bow shocks around the star. Two- and three-dimensional numerical modeling indicates an important role of these shocks in the formation of the structure of the circumbinary envelope. In particular, for systems with circular orbits, the size of the central region of the envelope that is not filled with matter (the “gap”) is essentially determined by the parameters of the bow shocks. These modeling results are supported by comparisons of the obtained estimates for the gap parameters with observations.     

On the seismicity and tectonics associated with the Sinkiang—Tibetan region

A plausible seismo-tectonic boundary of the Sinkiang—Tibetan region is defined on the basis of the trend of higher magnitude earthquakes (M7.0) and energy released by them for the period 1905–1965. In order to study the nature of forces at the northwestern and eastern sides of the region focal mechanisms for eleven shocks have been determined using P-wave first-motion directions reported in the Bulletin of the International Seismological Centre (Edinburgh). Of these, seven mechanisms show thrust faulting, three strike-slip and one normal faulting. The sense of motions of underthrusting blocks in thrust-faulting mechanisms for the two sides are directed towards the Sinkiang—Tibetan region. The slip vectors of strike-slip faulting are also in agreement with the direction of movement of thrust faulting. Thus, the seismicity, energy released, slip vectors and the orientation of T-axes reflect that the northwestern and eastern sides of the Sinkiang—Tibetan region are the plausible seismo-tectonic boundary and the major earthquakes and higher crustal thickness are the results of the movements of surrounding plates towards the region.     

On the possibilities of premonitory swarms for three sequences of earthquakes of the Burma—Szechwan region

Short term spatial and temporal variations in seismicity prior to the three sequences of earthquakes of m_b 5.8 of the Burma—Szechwan region are studied. Six years (1971–1976) of ISC seismicity data, as reported in the Regional Catalogue of Earthquakes, are considered. During the period, six earthquakes of body wave magnitude m_b 5.8 occurred in four sequences. Of these, three sequences are preceded by swarm activity in the epicentral regions. Evison (1977b) suggested that the swarm before the sequences of large shocks is a possible long-term precursor. He derived the conclusion by analyzing earthquakes in New Zealand and California. The analysis of the seismicity data for the region under investigation supports Evison's view and suggests that a relation between swarms and sequences of large events exists. The precursory time period (i.e. the time from beginning of the swarm to the main shock) for the Szechwan earthquakes of m_b = 5.9 (Feb. 6, 1973) and m_b = 5.8 (May 10, 1974) and the Burma earthquake of m_b = 6.2 (Aug. 12, 1976) are 305, 317 and 440 days, respectively.