Review of the Huaytapallana project in Peru

In 1969, two consecutive earthquakes activated a reverse fault at an elevation of 4600 m in the Huaytapallana mountain range near Huancayo in central Peru. In 1975, a small geodetic network was established and measured across the fault covering an area of about 1.5 km². The network has been remeasured in 1976, 1977, 1978, and 1982, using standard geodetic instruments, as a joint effort by two Canadian and one German universities in cooperation with the Peruvian Institute of Geophysics. In 1978, the network was expanded to cover 6 km². High-altitude sickness, logistic problems with old vehicles, civil unrest and riots plagued the survey expeditions. The results show a cyclic rigid body motion of the southwest side versus the northeast side of the fault in a general east-west direction of about ± 3 mm/year. The direction of the motion agrees with the direction of compressive forces expected in this subduction region. The next survey campaign is planned for 1987.     

Crustal structure of the Rhinegraben area

Numerous ge ological and geophysical investigations within the past decades have shown that the Rhinegraben is the most pronounced segment of an extended continental rift system in Europe. The structure of the upper and lower crust is significantly different from the structure of the adjacent “normal” continental crust.

Two crustal cross-sections across the central and southern part of the Rhinegraben have been constructed based on a new evaluation of seismic refraction and reflection measurements. The most striking features of the structure derived are the existence of a well-developed velocity reversal in the upper crust and of a characteristic cushion-like layer with a compressional velocity of 7.6–7.7 km/sec in the lower crust above a normal mantle with 8.2 km/sec. Immediately below the sialic low-velocity zone in the middle part of the crust, an intermediate layer with lamellar structure and of presumably basic composition could be mapped.

It is interesting to note that the asymmetry of the sedimentary fill in the central Rhinegraben seems to extend down deeper into the upper crust as indicated by the focal depths of earthquakes. The top of the rift “cushion” shows a marked relief which has no obvious relation to the crustal structure above it or the visible rift at the surface.     

Recurrence of great earthquakes at subduction zones

Statistics of the recurrence times of great earthquakes at the Pacific subduction margins are made. The mean return period of great earthquakes is different from zone to zone, ranging from 27 to 117 years. The standard deviation of the return period proves to be very small, several years say, in some cases. The probabilities of a great earthquake recurring in each zone are estimated on the basis of Weibull distribution analysis.The mean return periods thus estimated are combined with the relative plate velocities at respective zones as obtained in the plate tectonics in order to estimate the ultimate displacement to rupture at the interface of the continental plate and the downgoing oceanic plate. It is presumed that great earthquakes at subduction zones occur as a result of a rebound of the continental plate at the time of rupture. The ultimate displacement thus estimated ranges from 2 to 8 m, and seems somewhat larger than that estimated on the basis of seismic observations, although the value of ultimate displacement seems to harmonize roughly with estimates based on geodetic observations on land. However, the ultimate displacement at the Aleutian—Alaska zone as estimated here seems much smaller than that estimated from actual observations.The ultimate strains, which are deduced from the displacements obtained on the assumption that the logarithmic extent of the deformed area is proportional to earthquake magnitude, are then calculated, and compared with those estimated for large inland earthquakes as revealed by repetition of geodetic surveys. The mean ultimate strain is estimated as 4.3 · 10⁻⁵ for subduction-zone earthquakes while that for inland earthquakes has been estimated as 4.7 · 10⁻⁵. As the agreement between both the ultimate strains is fairly good, it is tentatively concluded that the strength of the plate interface under the sea bottom is more or less the same as that in the crust on land.     

Space–time distribution of interplate moment release including slow earthquakes and the seismo-geodetic coupling in the Sanriku-oki region along the Japan trench

Along the Japan trench where some Mw8 class interplate earthquakes occurred in the past century such as the 1896 Sanriku tsunami earthquake (M6.8, Mt8.6, 12×10²⁰ N m) and the 1968 Tokachi-oki earthquake (Mw8.2, 28×10²⁰ N m), the Pacific plate is subducting under northeast Japan at a rate of around 8 cm/year. The seismic coupling coefficient in this region has been estimated to be 20–40%. In the past decade, three ultra-slow earthquakes have occurred in the Sanriku-oki region (39°N–42°N): the 1989 Sanriku-oki (Mw7.4), the 1992 Sanriku-oki (Mw6.9), and the 1994 Sanriku-oki (Mw7.7) earthquakes. Integrating their interplate moments released both seismically and aseismically, we have the following conclusions. (1) The sum of the seismic moments of the three ultra-slow earthquakes was (4.8–6.6)×10²⁰ N m, which was 20–35% of the accumulated moment (18.6–23.0)×10²⁰ N m, in the region (39°N–40.6°N, 142°E–144°E) for the 21–26 years since the 1968 Mw8.2 Tokachi-oki earthquake. This is consistent with the previous estimates of the seismic coupling coefficient of 20–40%. On the other hand, the sum of the interplate moments including aseismic faulting is (11–16)×10²⁰ N m, leading to a “seismo-geodetic coupling coefficient” of 50–85%, which is an extension of the seismic coupling coefficient to include slow events. (2) The time constants showed a large range from 1 min (10² s) for the 1968 Tokachi-oki earthquake to 10–20 min (10³ s) for the 1896 Sanriku tsunami earthquake, to one day (10⁵ s) for the 1992 Sanriku-oki ultra-slow earthquake, to on the order of one year (10⁷ s) for the 1994 Sanriku-oki ultra-slow earthquakes. (3) Based on the space–time distribution, three “gaps of moment release,” (40.6°N–42°N, 142°E–144°E) 39°N–40°N, 142°E–143°E) and (39°N–40°N, 142°E–144°E), are identified, instead of the gaps of seismicity.     

Early Ordovician continental break-up in Variscan Europe: Nd---Sr isotope and trace element evidence from bimodal igneous associations of the Southern Massif Central, France

The high-grade Marvejols Group and the low-grade Albigeois-Cévennes sedimentary sequence contain bimodal igneous rocks of Early Ordovician age which are representative of a widespread thermal event in the European Variscides. Comparison of their Nd---Sr isotope and trace-element characteristics provides additional evidence for their origin in an ensialic extensional setting. As an alternative to the back-arc model proposed by previous authors, we propose that these associations record a continental break-up episode unrelated to contemporaneous subduction. In this model, the widespread Early Paleozoic bimodal magmatism marks the birth of a Mid-European oceanic arm. We propose that the break-up was controlled by both transtensional processes and mantle-plume activity.

High grade associations, such as the Marvejols Group, and low-grade bimodal associations, such as the Albigeois-Cévennes, might be regarded as representing opposite rifted passive margins. The “northern”, Marvejols-type margin was involved in a Late Ordovician-Silurian subduction-like process, with HP-HT metamorphism. In contrast, the “southern” Albigeois/Cévennes margin remained largely unaffected, possibly as part of the overriding plate of the subduction zone.

“Pseudo-calc-alkaline” signatures unrelated to subduction processes may occur in magmatic rocks associated with continental break-up episodes. In this case, negative Nb anomalies are produced by the addition of crustal components enriched in Th and LREE relative to Nb. This inferred alternative origin of Nb anomalies has important bearing on the paleogeodynamic settings based on geochemical data.     

Construction of underground caverns for petroleum storage in orogenic areas: Geological stability

Japan is located at the boundary between three continental and oceanic plates, and there is a great variety and complexity of geological features as a result of tectonic activities. The possibility of excavating large underground tunnels in the seemingly “fragile” rocks in orogenic areas was considered as a national project for the underground storage of petroleum. One hundred and seventy sites in 57 areas were selected based on a comprehensive survey over the whole country. After a successful experiment with a test tunnel, 112 m long and 250 m² in cross-section area, excavated in Cretaceous granite, three sites in granites and pyroclastic rocks were selected for construction. The largest of these storage tunnels is 550 m in length and20 × 30 m in cross-section.

Before construction, a detailed survey of the subsurface geology was carried out, taking into consideration the structural geology, the mechanical properties of the rocks and the hydrogeology. It was concluded that even in active orogenic areas, there are many suitable sites for large underground excavations and that these can be detected by detailed, planned surveys.     

Back-arc spreading: Trench migration, continental pull or induced convection?

Mechanisms of the opening of back-arc systems are analyzed. Limited focal mechanisms of intraplate earthquakes are used to determine the stress regime of an overriding plate. Preliminary analyses show that compressive deviatoric stresses exist in the plate except near the spreading center. Based on this observation “trench suction” does not appear to be the primary force that drives back-arc spreading, since it will result in tensional deviatoric stresses within the overriding plate. Even though “continental pull” is able to satisfy the stress requirements, it does not appear to be a likely mechanism either because of the initiation and subsequent symmetric spreading difficulty associated with such a mechanism. The mechanism we favor is the one that involves the induced convective current in the mantle wedge immediately above the slab. Calculations show that the induced flow is able to generate sufficient stress to break up the overriding lithosphere if the tectonic stresses of the region are favorable. Both trench suction and continental pull may help to provide such a favorable tectonic stress regime.     

Geophysical and geodetic observations in the messina straits

The present note is intended as a contribution to the clarification of the collision process, generally assumed to be active between the African and the Eurasian plates in the area of the Messina Straits.For this purpose detailed analyses are made of the surveys carried out in the Straits of Messina in order to investigate the 1908 earthquake. The magnitude and intensity are established; limits are set for the linear dimension of the fault and of the dislocation that gave rise to the earthquake and an estimate is then given of these parameters. The results are then set out of the investigation into the focal mechanism of the earthquake of 1908. The results are also studied of geodetic surveys carried out at the time for the purpose of measuring the variations in height that occurred during the earthquake.A study is also made of the results of geodetic surveys (some of which are still under way) designed to measure the horizontal movements of Sicily with respect to Calabria in order to study locally the continental collision process in the area of the Messina Straits.It is found that the old and recent geodetic measurements as well as the fault-plane solution of the old and recent earthquakes of that area and the slips associated with those earthquakes indicate a motion towards the north of Sicily with respect to Calabria.     

The determination of rates of land uplift in Norway

It is the task and the responsibility of the Geodetic Section within the Geographical Survey of Norway to establish and maintain the national horizontal and vertical geodetic primary control networks of that country.

Provided that relative crustal movements take place within Norway, they will cause deformations to these networks. There is no geodetic proof that any horizontal deformations of the surface layer of the crust take place in continental Norway and there is no established geological evidence of such movements either. In 1984, a small geodetic control network was established and measured for the first time across a possibly active fault. It is not expected that horizontal movements will cause any serious problems in the maintenance of the horizontal network. Vertical movements of the ground, however, are causing us problems both in the establishment and in the maintenance of a national height system.     

Geochemical characteristics of lavas from Broken Ridge, the Naturaliste Plateau and southernmost Kerguelen Plateau: Cretaceous plateau volcanism in the southeast Indian Ocean

Lavas from several major bathymetric highs in the eastern Indian Ocean that are likely to have formed as Early to Middle Cretaceous manifestations of the Kerguelen hotspot are predominantly tholeiitic; so too are glass shards from Eocene to Paleocene volcanic ash layers on Broken Ridge, which are believed to have come from eruptions on the Ninetyeast Ridge. The early dominance of tholeiitic compositions contrasts with the more recent intraplate, alkalic volcanism of the Kerguelen Archipelago. Isotopic and incompatible-element ratios of the plateau lavas are distinct from those of Indian mid-ocean ridge basalts; their Nd, Sr, ²⁰⁷Pb/²⁰⁴Pb and isotopic ratios overlap with but cover a much wider range than measured for more recent oceanic products of the Kerguelen hotspot (including the Ninetyeast Ridge) or, indeed, oceanic lavas from any other hotspot in the world. Samples from the Naturaliste Plateau and ODP Site 738 on the southern tip of the Kerguelen Plateau are particularly noteworthy, with ε_Nd(T) = − 13 to −7, (⁸⁷Sr/⁸⁶Sr)_T=0.7090 to 0.7130 and high ²⁰⁷Pb/²⁰⁴Pb relative to ²⁰⁶Pb/²⁰⁴Pb. In addition, the low-ε_Nd(T) Naturaliste Plateau samples are elevated in SiO₂ (> 54 wt%). In contrast to “DUPAL” oceanic islands such as the Kerguelen Archipelago, Pitcairn and Tristan da Cunha, the plateau lavas with extreme isotopic characteristics also have relative depletions in Nb and Ta (e.g., Th/Ta, La Nb > primitive mantle values); the lowest ε_Nd(T) and highest Th/Ta and La Nb values occur at sites located closest to rifted continental margins. Accepting a Kerguelen plume origin for the plateau lavas, these characteristics probably reflect the shallow-level incorporation of continental lithosphere in either the head of the early Kerguelen plume or in plume-derived magmas, and suggest that the influence of such material diminished after the period of plateau construction. Contamination of asthenosphere with the type of material affecting Naturaliste Plateau and Site 738 magmatism appears unlikely to be the cause of low-²⁰⁶Pb/⁰⁴Pb Indian mid-ocean ridge basalts. Finally, because isotopic data for the plateaus do not cluster or form converging arrays in isotope-ratio plots, they provide no evidence for either a quickly evolving, positive ε_Nd, relatively high-²⁰⁶Pb/²⁰⁴Pb plume composition, or a plume source dominated by mantle with ε_Nd of −3 to 0.     

Tectonic types of marginal and inner seas; their place in the development of the crust

Inner and marginal deep seas are of considerable interest not only for their genesis but also as “micromodels” of oceans. In the latter case it must be noted that some of them essentially differ from oceans in several parameters. They have a shorter period of development, thicker sedimentary cover, less distinct linear magnetic anomalies or an absence of them, high heat-flow values and seismic activity over their whole area. Consequently, the analogy with the oceans has certain limitations as the deep structure of such seas is not homogeneous and they probably vary in genesis.

Only a few marginal seas are cut off from the principal areas of the oceans by island arcs formed, most probably, along transform faults. The origin of this type is more or less reliably demonstrated for the Bering Sea. Other types of marginal seas are more numerous. Some of them (such as the Gulf of Aden and the Gulf of California) are embryonic apophyses connected with the oceans. Others are atrophied (the Tasman and the Labrador seas) small oceans. The group of marginal and inner seas which lie in the inside zone of mature or young island arcs is even more numerous. Only a few basins of this group resulted from linear spreading imprinted in the system of magnetic anomalies (the Shikoku-Parese-Vela basin), the rest are supposed to have been formed in the process of diffusal or polyaxial spreading of recent time as in Afar.

The majority of inner and marginal seas are younger than recent oceans. They are formed by rifting, oriented crosswise to continental margins of the Atlantic type or along the strike of margins of Andean type. More ancient basins of marginal and inner seas have been involved in Phanerozoic orogens or more rarely became parts of platforms (Ciscaspian syneclise).     

Frontiers in large igneous province research

Earth history is punctuated by events during which large volumes of mafic magmas were generated and emplaced by processes distinct from “normal” seafloor spreading and subduction-related magmatism. Large Igneous Provinces (LIPs) of Mesozoic and Cenozoic age are the best preserved, and comprise continental flood basalts, volcanic rifted margins, oceanic plateaus, ocean basin flood basalts, submarine ridges, ocean islands and seamount chains. Paleozoic and Proterozoic LIPs are typically more deeply eroded and are recognized by their exposed plumbing system of giant dyke swarms, sill provinces and layered intrusions. The most promising Archean LIP candidates (apart from the Fortescue and Ventersdorp platformal flood basalts) are those greenstone belts containing tholeiites with minor komatiites. Some LIPs have a substantial component of felsic rocks. Many LIPs can be linked to regional-scale uplift, continental rifting and breakup, climatic shifts that may result in extinction events, and Ni–Cu–PGE (platinum group element) ore deposits.

Some current frontiers in LIP research include:

(1) Testing various mantle plume and alternative hypotheses for the origin for LIPs.

(2) Characterizing individual LIPs in terms of (a) original volume and areal extent of their combined extrusive and intrusive components, (b) melt production rates, (c) plumbing system geometry, (d) nature of the mantle source region, and (e) links with ore deposits.

(3) Determining the distribution of LIPs in time (from Archean to Present) and in space (after continental reconstruction). This will allow assessment of proposed links between LIPs and supercontinent breakup, juvenile crust production, climatic excursions, and mass extinctions. It will also allow an evaluation of periodicity in the LIP record, the identification of clusters of LIPs, and postulated links with the reversal frequency of the Earth's magnetic field.

(4) Comparing the characteristics, origin and distribution of LIPs on Earth with planets lacking plate tectonics, such as Venus and Mars. Interplanetary comparison may also provide a better understanding of convective processes in the mantles of the inner planets.

In order to achieve rapid progress in these frontier areas, a global campaign is proposed, which would focus on high-precision geochronology, integrated with paleomagnetism and geochemistry. Most fundamentally, such a campaign could help hasten the determination of continental configurations in the Precambrian back to 2.5 Ga or greater. Such reconstructions are vital for the proper assessment of the LIP record, as well as providing first-order information related to all geodynamic processes.     

东亚与全球地震分布分析

现代地震学是一门年轻的学科,但人类对地震现象的观察、记录和思索已有数千年历史。特别是在中国,很早就有灾害性地震的详细历史记载。最近40多年,我国、东亚及世界其他大陆地区的多次大地震的发生,推动了地震构造研究的发展,加深了对地震分布规律性及其地球动力环境的认识。从地质背景和发生机制看,全球地震构造可分为三大类:第一是太平洋海底地壳与陆缘地壳浅、中、深俯冲构成的地震带;第二是南半球离散地壳块体对北半球大地块边缘碰撞浅俯冲带;第三是全球三大洋脊张裂转换构造带。地球北半部内陆的中纬度地带有4个多震密布区,它们都处于N25°～55°的纬向大陆带内,与大陆会聚所造成的陆内变形有关。4个多震密布区的东半部则是相对少震区,显示出相对稳定的地壳结构。全球表壳GPS矢量场和北南两个极区各有不同,北半球欧亚大陆是向北呈弓字形运动;南半球是南美、非洲、阿拉伯、印度、澳大利亚等5块离散的大陆块,除南美大陆,其他4块大陆都是向NE和NNE方向运动。这4块大陆都是依次运动加速,澳大利亚陆块运动最快,向NNE方向约10 cm/a;同时从南太平洋南部沿NWW方向左型转换断层的运动也是高速的,这两个方向运动的交叉相碰,现已处在全球最为强烈的地震活动区域。北冰洋内群岛GPS站点向阿留申岛弧推进;南极冰陆的9个GPS站点则呈现旋扭状彼此相差约90°,可能表明北/南半球彼此有明显的1/4左右表壳的扭动。从卫星重力数据推测的地球的形状、全球热流的和地内热散失量的分布、地球磁场的西漂以及大地震引起的地球振荡特征等证据推测,地球的内部结构具有一定程度的非对称性和非均匀性,它们对全球板块运动、板块变形以及大地震的空间分布可能有一定的控制作用。     

Spinel peridotite xenoliths from the Tariat Depression, Mongolia. II: Geochemistry and Nd and Sr isotopic composition and their implications for the evolution of the subcontinental lithosphere

A suite of spinel peridotite xenoliths from the Shavaryn-Tsaram volcano, Tariat Depression (central Mongolia) represents (for major elements) fertile to moderately depleted subcontinental lithosphere. Part of the variation of moderately incompatible trace elements is ascribed to small-scale mineralogical heterogeneities caused by processes like metamorphic differentiation accompanying partial melting or by mechanical segregation. Several bulk lherzolites show a high relative enrichment of the LREE over HREE which can be traced to a grain boundary phase genetically linked to, but not directly representing, the host basanitoid. In Nd and Sr isotopic composition the anhydrous peridotites cover the field of oceanic basalts (¹⁴³Nd/¹⁴⁴Nd = 0.5128-0.5133, ⁸⁷Sr/⁸⁶Sr = 0.7020-0.7039). In contrast, a phlogopite peridotite has a high ⁸⁷Sr/⁸⁶Sr and also a less radiogenic ¹⁴³Nd/¹⁴⁴Nd. The majority of “dry” lherzolites have Nd and Sr “bulk earth” model ages around 2 Ga. They may be interpreted as dating a small-degree (< ˜5%) melting event which would not have severely affected the major element chemistry of the xenoliths. The ˜2 Ga model ages may indicate a genetic relation between the lithospheric mantle and the stabilization of the continental crust in Mongolia at that time. Alternatively, if the peridotites are unrelated to the overlying crust, they may be pieces of a young asthenospheric diapir. Coexisting ortho-and clinopyroxenes are in Nd isotopic equilibrium for Iherzolites having equilibrated at temperatures around 950°C at mantle pressures. Disequilibrium melting models of mantle rocks are not supported by our data because for medium to coarse-grained mantle spinel peridotite the Rb-Sr and Sm-Nd isotopic systems close with respect to diffusional exchange at temperatures around 900°C, as indicated by recently published diffusion experiment results and supported by our data.     

岩浆泡破裂引发地震的模式——以吉林松原2013年地震群为例

2013年10月31日,吉林省松原前郭尔罗斯蒙古族自治县（44.60°N,124.18°E）发生震级为5.5级地震,此后的40 d内发生了700多次地震,其中5级以上地震5次。松原地区近年来地震活动频繁,2014年1月以来又发生4级以上地震9次、5级以上地震1次,震中处于松辽盆地油气田开采区,地震活动序列十分特殊。为了揭示松原地震的发震机制与发震模式,研究深部地质过程与地震的关系,根据此次实测的通过震中25 km长的大地电磁测深剖面,结合地热梯度、He同位素比值（³He/⁴He）、CO₂碳同位素、地震序列等资料的综合分析,发现震中地区存在两个位于不同深度的低阻体,地震发生与地幔深部岩浆活动有关;据此提出了一种新的地震发生模式——岩浆泡破裂发震模式,描述了来自地幔的基性岩浆通过向上侵入、在脆-韧性转换带附近聚集形成岩浆泡、岩浆泡破裂及岩浆泡上覆岩层中聚集能量引发岩层破裂产生地震的过程,并使来自地幔的无机成因的CO₂气在储层中形成CO₂气藏。该模式可以解释许多发生在大陆内部地震和深源地震的发生机制。     

Seismicity and velocity structures along the south-Alpine thrust front of the Venetian Alps (NE-Italy)

In this paper we show the seismicity and velocity structure of a segment of the Alpine retro-belt front along the continental collision margin of the Venetian Alps (NE Italy). Our goal is to gain insight on the buried structures and deep fault geometry in a “silent” area, i.e., an area with poor instrumental seismicity but high potential for future earthquakes, as indicated by historical earthquakes (1695 Me = 6.7 Asolo and 1936 Ms = 5.8 Bosco del Cansiglio). Local earthquakes recorded by a dense temporary seismic network are used to compute 3-D Vp and Vp/Vs tomographic images, yielding well resolved images of the upper crust underneath the south-Alpine front. We show the presence of two main distinct high Vp S-verging thrust units, the innermost coincides with the piedmont hill and the outermost is buried under a thick pile of sediments in the Po plain.Background seismicity and Vp/Vs anomalies, interpreted as cracked fluid-filled volumes, suggest that the NE portion of the outermost blind thrust and its oblique/lateral ramps may be a zone of high fluid pressure prone to future earthquakes.Three-dimensional focal mechanisms show compressive and transpressive solutions, in agreement with the tectonic setting, stress field maps and geodetic observations. The bulk of the microseismicity is clustered in two different areas, both in correspondence of inherited lateral ramps of the thrust system. Tomographic images highlight the influence of the paleogeographic setting in the tectonic style and seismic activity of the region.     

Microstrain stability of Peninsular India 1864–1994

We report the results of the South Indian Strain Measuring Experiment (SISME) designed to determine whether strain related to microseismicity in the past century may have deformed the networks of the 19th century Great Trigonometrical Survey of India (GTS). More than a dozen GTS points were measured between Mangalore, Madras, and Kanyakumari in southernmost India using GPS geodesy to determine regional deformation. Detailed measurements were made near two of the original baselines of the survey to determine the reliability of dilatational strain data for the network. The regional measurements revealed negligible regional dilatational (+ 11.2 + 10 microstrain) and shear strain changes (0.66± 1.2μradians) in the southernmost 530 km of India. In addition to these measurements, we determined the rate of northward and eastward motion of a point in Bangalore (1991–1994) in the ITRF92 reference frame to be 39 ± 3.5 mm/year, and 51 ± 11 mm/year respectively. This is consistent with NUVEL-1A plate motion estimate for India. Simultaneous measurements to a point near Kathmandu reveal that the Indian plate and the Southern Himalaya are moving approximately in unison, placing an upper limit on the rate of creep processes beneath the lesser Himalaya of ≈6 mm/year, and suggesting relatively rigid behavior of the Indian plate north of Bangalore. The stability of the Indian plate is confirmed by the absence of significant changes in the lengths of the two baselines at Bangalore and Cape Comorin, which, within the limits of experimental error have not changed since 1869. The measurements place an upper limit for recent deformation in the southern peninsula, and hence a lower limit for the renewal time for intraplate earthquakes in the region of approximately 10,000 years, assuming shear failure strain of approximately 100 μradians. This, in turn, implies that recurrence intervals for Peninsular Earthquakes far exceed the length of the written historic record, suggesting that the characterisation of seismic recurrence intervals from historical studies is likely to be fruitless. In contrast, the SISME experiment demonstrates that the noise level of geodetic studies based on 19th century GTS data is less than 0.02 μstrain/year, providing considerable scope for delineating regions of anomalously high seismogenic strain, by GPS measurements at all available trig points of the 19th century GTS survey.     

Plate tectonics in Russia

After a short period of propagation of Wegener's continental drift ideas in Russia in the twenties and first half of the thirties of this century, there came a much longer period (1935–1960) of fixist reaction', when vertical tectonic movements were regarded as primary and most important and horizontal ones as secondary and subsidiary. In the sixties, interest in the manifestation of horizontal movements on strike-slip faults, overthrusts and nappe formation began to grow, and at the verge of sixties and seventies ideas of plate tectonics began to penetrate into Russia. But at the begining they met strong resistance mainly from the older generation of scientists. In spite of this, these ideas finally gained the support of the majority of Earth scientists in this country. Russian geologists and geophysicists made a significant contribution to the development of the plate tectonics theory as well as in its regional, global and theoretical aspects.