Late Quaternary deformation on the island on Pantelleria: New constraints for the recent tectonic evolution of the Sicily Channel Rift (southern Italy)

Structural observations carried out on the volcanic Island of Pantelleria show that the tectonic setting is dominated by NNE trending normal faults and by NW-striking right-lateral strike-slip faults with normal component of motion controlled by a ≈N 100°E oriented extension. This mode of deformation also controls the development of the eruptive fissures, dykes and eruptive centres along NNE–SSW belts that may thus represent the surface response to crustal cracking with associated magma intrusions. Magmatic intrusions are also responsible for the impressive vertical deformations that affect during the Late Quaternary the south-eastern segment of the island and producing a large dome within the Pantelleria caldera complex. The results of the structural analysis carried out on the Island of Pantelleria also improves the general knowledge on the Late Quaternary tectonics of the entire Sicily Channel. ESE–WNW directed extension, responsible for both the tectonic and volcano-tectonic features of the Pantelleria Island, also characterizes, at a greater scale, the entire channel as shown by available geodetic and seismological data. This mode of extension reactivates the older NW–SE trending fault segments bounding the tectonic troughs of the Channel as right-lateral strike-slip faults and produces new NNE trending pure extensional features (normal faulting and cracking) that preferentially develop at the tip of the major strike-slip fault zones. We thus relate the Late Quaternary volcanism of the Pelagian Block magmatism to dilatational strain on the NNE-striking extensional features that develop on the pre-existing stretched area and propagate throughout the entire continental crust linking the already up-welled mantle with the surface.     

Aseismio fault slip and block deformation in North China

In North China, the tectonic fault-block system enables us to use the Discontinuous Deformation Analysis (DDA) method to simulate the long-term cross-fault survey and other geodetic data related to aseismic tectonic deformation. By the simulation we have found that: (1) Slips on faults with different orientation are generally in agreement with the ENE-WSW tectonic stress field, but the slip pattern of faulting can vary from nearly orthogonal, to pure shear along the strike of the faults, this pattern cannot be explained by simple geometric relation between the strike of the fault and the direction of the tectonic shortening. This phenomenon has been observed at many sites of cross-fault geodetic surveys, and might be caused by the interactions between different blocks and faults. (2) According to the DDA model, if the average aseismic slip rate along major active faults is at the order of several tenths of millimeter per year as observed by the cross-fault geodetic surveys, the typical strain rate inside a block is at the order of 10^–8 year^–1 or less, so that the rate of 10^–6 year^–1, as reported by observations in smaller areas, cannot be the representative deformation rate in this region. (3) Between the slips caused by regional compression and block rotation, there is a possibility that the sense of slip caused by rigid body rotation in two adjacent blocks is opposite to the slip caused by the tectonic compression. But the magnitude of slip resulting from the tectonic compression is much larger than that due to the block rotation. Thus, in general, the slip pattern on faults as a whole agrees with the sense of tectonic compression in this region. That is to say, the slip caused by regional compression dominates the entire slip budget. (4) Based on (3), some observed slips in contradiction to ENE tectonic stress field may be caused by more localized sources, and have no tectonic significance.     

Geodetic Measurements of Crustal Deformation in the Western Mediterranean and Europe

—Geodetic measurements of crustal deformation over large areas deforming at slow rates (<5 mm/yr over more than 1000 km), such as the Western Mediterranean and Western Europe, are still a challenge because (1) these rates are close to the current resolution of the geodetic techniques, (2) inaccuracies in the reference frame implementation may be on the same order as the tectonic velocities. We present a new velocity field for Western Europe and the Western Mediterranean derived from a rigorous combination of (1) a selection of sites from the ITRF2000 solution, (2) a subset of sites from the European Permanent GPS Network solution, (3) a solution of the French national geodetic permanent GPS network (RGP), and (4) a solution of a permanent GPS network in the western Alps (REGAL). The resulting velocity field describes horizontal crustal motion at 64 sites in Western Europe with an accuracy on the order of 1 mm/yr or better. Its analysis shows that Central Europe behaves rigidly at a 0.4 mm/yr level and can therefore be used to define a stable Europe reference frame. In that reference frame, we find that most of Europe, including areas west of the Rhine graben, the Iberian peninsula, the Ligurian basin and the Corsica-Sardinian block behaves rigidly at a 0.5 mm/yr level. In a second step, we map recently published geodetic results in the reference frame previously defined. Geodetic data confirm a counterclockwise rotation of the Adriatic microplate with respect to stable Europe, that appears to control the strain pattern along its boundaries. Active deformation in the Alps, Apennines, and Dinarides is probably driven by the independent motion of the Adriatic plate rather than by the Africa-Eurasia convergence. The analysis of a global GPS solution and recently published new estimates for the African plate kinematics indicate that the Africa-Eurasia plate motion may be significantly different from the NUVEL1A values. In particular, geodetic solutions show that the convergence rate between Africa and stable Europe may be 30–60% slower than the NUVEL1A prediction and rotated 10–30° counterclockwise in the Mediterranean.     

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.     

Seismotectonic characteristics of the northern flank and axial part of the Tajik Depression (the Garm Geodynamic Research Area)

Detailed estimates of seismotectonic strain (STS) characteristics are obtained for the upper crust from focal mechanisms of numerous earthquakes (M ≥ 1) in the northern and axial parts of the Tajik Depression (the Garm area, Tajikistan). It is shown that, in the majority of cases, a close interrelation exists between tectonic structures and the STS type. Changes in the STS characteristics in various areas of the depression admit a reasonable geological interpretation. Based on geological, seismological, and geodetic data, a unified scheme of deformation of layered rocks of the Tajik Depression is presented. The main factor controlling the deformation process is the extrusion of the rocks in the axial part of the depression in the NNW and SSE directions (with the formation of imbricate thrusts) and in the WSW direction. The latter case is characterized by left-lateral motions in fault zones in the south of the depression (including the Darvaz fault) and by right-lateral motions in northern zones (the Peter the First Range) located from seismological data. In our opinion, such expulsion is caused mainly by an increase of the volume of layered rocks in the Tajik Depression, apparently due to deep fluids penetrating into these rocks and supplying additional mineral material. However, it is also possible that the region is influenced, to an extent, by the general subhorizontal N-S compression associated with the convergence of the Indian and Eurasian lithospheric plates in accordance with the concept of plate tectonics.     

龙门山断裂带深部构造变形的黏弹性模拟及其与强震活动的关联性探讨

根据龙门山断裂带地区的主要构造特征,建立该地区的有限元模型,同时考虑地下深处的黏弹性蠕动和不同部位间的接触关系,模拟计算了研究区在强震轮回活动中的时间演化历程.模拟结果表明:龙门山断裂带深处的滑动速率比浅表的滑动速率大,龙门山断裂带周围是相对容易发生应变积累的地区,其5~19km深度也是高应力聚集成核区,随时间推移的应力集中程度加剧而引发强震.本模拟分析证实了重复地震观测所揭示的龙门山断裂带存在深浅活动速率差异的现象,这在一定程度上可以解释出乎预料的汶川MW7.9地震的孕育机理.综合分析研究提出:应充分利用重复地震这一天然的"地下蠕变计(subsurface creepmeter)"来探测深部构造变形的活动,为强震危险性分析提供必要的"原位(in situ)观测"约束信息.     

唐山及大同－阳高地震大地形变与重力前兆综合研究

本大概还了近年来利用大地形变及重力复测资料研究唐山及大同－阳高地震的丰富成果，对这２次地震震前大地形变及重力前兆综合研究认为：震中区震前呈现闭锁状态；断层蠕滑及深部物质的运移，是震前的显著标志；地震成因的组合模式可以较好地解释唐山及大同一阳高地震的机制；跟踪监测形变场、重力场及断层活动时空演化特性，是利用大地形变及重力测量手段进行地震预测的基本出发点。     

Quaternary faults and seismicity in the Umbro-Marchean Apennines (Central Italy): evidence from the 1997 Colfiorito earthquake

Analyses of structural and geomorphological data combined with remote sensing interpretation confirm previous knowledge on the existence of an extensional Quaternary tectonic regime in the Colfiorito area (Umbro-Marchean Central Apennines). This is characterized by a maximum principal axis of finite strain oriented approx. NE–SW, which is the result of a progressive deformation process due to pure and radial extension. Surface geological data, the crustal tectonic setting (reconstructed using a CROP 03 seismic reflection profile), and seismological data relative to the autumn 1997 Colfiorito earthquake sequence constrain the following seismotectonic model. We interpret the seismogenic SW-dipping low-angle normal fault pictured by seismic data as an inverted thrust ramp located in the basement at depth between 5 and 10 km. The surface projection of this seismogenic structure defines a crustal box within which high-angle normal faults are responsible for the deformation of the uppermost crust. The regional patterns of pre-existing basement thrusts therefore control the seismotectonic zoning of the area that cannot be directly related to the high-angle normal fault systems which cut through different crustal boxes; the latter system records, in fact, re-shear along pre-existing normal faults. Moreover, Quaternary slip-rates relative to high-angle normal faults in the Central Apennines are closely related to seismic hazard within each crustal box.     

Eruptive mechanism on Piton de la Fournaise volcano associated with the December 4, 1983, and January 18, 1984 eruptions from ground deformation monitoring and photogrammetric surveys

Two photogrammetric aerial surveys were carried out over the summit area of the basaltic shield volcano Piton de la Fournaise (Indian Ocean), one survey in 1981 and the second one in 1984. During this time, only two eruptions occurred; both the December 4, 1983, and the January 18, 1984, eruptions opened fissures on the southwestern part of the summit. Because of the slight and erratic ground deformation measured on the dry-tilt network, by continuous tilt stations, and within the geodetic network between 1981 and November 1983, and between February 1984 and June 1984, ground deformations revealed by the two photogrammetric surveys can be essentially associated with the two eruptions. Large displacement vectors were obtained, up to 40 cm. Horizontal displacement vectors indicate a northeastward ground deformation of the southwestern part of the cone where the effusive vents opened. A more diffuse uplift along the main fracture zones that cut the volcanic edifice was observed, while east of these fractures only slight—less than 10 cm—and opposite displacements were observed. This displacement field can be associated with the main geological structures of the dome of Piton de la Fournaise volcano. Some consequences of the observed displacement field may be outlined for the volcanic observational ground deformation networks. To estimate the displacement field revealed by the photogrammetric surveys, a simple model of dyke intrusion has been computed. This model is based on dislocations and takes into account the main fracture zones. Good agreement is observed between computed and observed data in the area of the effusive vents. Some disagreement remains in the northwestern part of the survey area, where horizontal deformations are small and erratic, and also in the northern part, where an uplift was observed that can be associated with the northern active fracture zones.     

Analysis of central western Europe deformation using GPS and seismic data

The kinematic field of central western Europe is characterized by relatively small movements (around 1–2 mm/year) and diffuse seismicity with earthquakes occurring mostly in the shallow crust (within 15 km), prevalently concentrated along the Alps and the European Cenozoic Rift System (ECRIS). In order to study and constrain the current crustal kinematic field we reconstructed the velocity and the strain field using permanent GPS stations, belonging to different networks (AGNES, EUREF, REGAL, RGP). The 2D strain rate tensor has been calculated using the method of least-squares collocation. Our results show that the area of maximum compression is located along the Alpine chain, where maximum values of 7 ± 2 nstrain/year are found, while maximum extension is measured between the Armorican Massif and the Massif Central, where values of 4 ± 2 nstrain/year are reached.The earthquakes with M > 3.0, have been used to estimate the seismic strain rates, while the style of the seismic deformation was reconstructed from the fault plane solutions (FPS) available from the literature. Relatively high values of seismic strain rates (around 10 nstrain/year) are measured along the Alpine Chain and the ECRIS. Results obtained by geodetic and seismic data are quite in agreement and reflect the different tectonic evolution of the geological features characterizing the area of study. The orientation of the compressional geodetic and seismic strain axes are NW-SE in most of the area of study, on account of the action of plate boundary forces. A rotation of the same axes to N-S direction along the eastern Alps, possibly related to the Adria convergence, is found.     

Amount of clockwise rotation of Southwest Japan — fan shape opening of the southwestern part of the Japan Sea

Paleomagnetic measurements have been carried out on welded tuffs ranging in age between 58 Ma and 112 Ma from Yamaguchi and Go¯river areas in the central part of Southwest Japan. The new data, together with those of younger igneous rocks published previously, define the change of paleomagnetic field direction during the late Mesozoic/ Cenozoic period for Southwest Japan. The paleomagnetic direction from this area has pointed 56 ± 3° clockwise from the expected field direction estimated from APWP (apparent polar wandering path) of the whole of Eurasia during the period between 100 and 20 Ma. In comparison with the expected one from the eastern margin of Eurasia (Korea, China, Siberia), the Cretaceous field direction of Southwest Japan shows the clockwise deflection by 44–49°. These results establish that while the eastern margin of Eurasia, including Southwest Japan, was rotated more or less with respect to the main part of Eurasia during last 100 Ma, Southwest Japan was rotated clockwise through more than 40° with respect to the eastern margin of Eurasia since 20 Ma. The large amount of rotation for Southwest Japan implies that it is rotated by an opening of the southwestern part of the Japan Sea, which widens northeastward (fan shape opening). The tectonic feature of Southwest Japan and the Japan Sea is analogous to that of Corso-Sardinia and the Ligurian Sea in the Mediterranean, indicating that the fan shape opening is a specific feature of the rifting of the continental sliver at the continental rim.     

Present-day geodynamics of the circum-Adriatic region: An overview

This volume builds on presentations made at two thematic sessions on “The Active Tectonics of the Circum-Adriatic Region” at the EGU 2007 and 2008 General Assemblies in Vienna. In both sessions, contributions were invited from workers incorporating structural, geophysical, seismological, remote sensing, geodetic and thermochronological methods to better understand the crustal evolution and ongoing development of one of Europe's most interesting tectonic regions. The Adriatic region occupies a central position within the geodynamic framework of the Central Mediterranean. It is surrounded by actively deforming belts of diverse character including transpressional, contractional, strike-slip and extensional domains, collectively defining the structurally complex and kinematically varied boundaries of the Adria plate. Because many countries occupy the circum-Adriatic region, international collaborative research into the tectonic activity and associated natural hazards of the region is relevant and important to European society. In this context, the papers presented in this volume provide important new data that bear on various aspects of the active tectonics of the circum-Adriatic region. These contributions typically draw on multidisciplinary structural, geophysical and geochronological datasets to draw new conclusions concerning the spatial and temporal evolution of Adria's bounding deformation zones, especially the southeastern and southern Italian regions and NE Adriatic region. In this overview, we provide a state-of-the-art summary of different aspects of present-day Adria geodynamics to provide a common background for the individual contributions that follow.     

The two-stage opening of the western–central Mediterranean basins: a forward modeling test to a new evolutionary model

The Algero–Provençal and the Tyrrhenian extensional basins developed in two stages in a geodynamic setting characterized by the nearly N–S convergence between Africa and Eurasia. The spreading of the Provençal basin occurred in the early Miocene following a long period of rifting in the western Mediterranean area. A dramatic eastward shift of the active extensional deformation resulted in the Tortonian to Quaternary opening of the Tyrrhenian basin. In a companion paper, Carminati et al. propose that: a trench retreat process in a geodynamic setting locked by the continental collisions in the Alps and in the Betic chain is a viable mechanism for the late Oligocene–early Langhian opening of the western Mediterranean; a Langhian slab detachment episode along the north African margin is likely to have caused the end of the trench retreat along this part of the boundary determining the end of active expansion in the western Mediterranean and the beginning of active extension in the Tyrrhenian basin. The objective of the present paper is to quantitatively test this proposed scenario. We calculate, by means of a thin shell model, the effects of these plate boundary reorganizations on the European stress and strain field. We show that the two-stage opening of the western and central Mediterranean can be explained by the evolution proposed by Carminati et al. and that, in particular, the eastward shift of the active extension which produced the termination of the first opening stage and the beginning of the second is likely to have been triggered by the slab detachment episode along the north African margin.     

Current tectonic deformation and seismogenic characteristics along the northeast margin of Qinghai -Xizang block

Introduction The northeast margin of Qinghai-Xizang block has become the place with close attentions from geo-specialists at home and abroad for its significant tectonic movement and intensive seismicity. Quite a number of achievements have been obtained from the studies on geological structures and strong earthquake activities (DING, LU, 1989, 1991; GUO, et al, 1992, 2000; GUO, XIANG, 1993; HOU, et al, 1999; Tapponnier, et al, 1990; Gaudemer, et al, 1995). In the Development Program…     

Recent Geodetic Results in the Azores Triple Junction Region

—GPS (Global Positioning System) observations started to be carried out in the Azores region under the scope of the TANGO (TransAtlantic Network for Geodesy and Oceanography) project in 1988. The measurements carried out between 1993 and 2000 (five campaigns) on nine GPS sites (one per island) were reprocessed using two state–of–the-art software packages. Different methodologies were applied to compute each campaign solution and the derived velocity field. The velocity fields, including the motions of two permanent stations, recently installed in the Azores, were computed within the most recent geodetic reference frame, ITRF2000 (International Terrestrial Reference Frame, solution 2000). They are compared with the motions of the stable rigid tectonic plates using as reference DEOS2k, a global tectonic model developed using geodetic data. The relative motions between the Western and Central groups of islands yield to evaluate the opening rate of the Mid-Atlantic Ridge (boundary between the North American plate and the Eurasian and African plates). Concerning the boundary between the Eurasian and African plates, the motion of the TANGO sites in the Central and Eastern groups clearly identifies the transition pattern between those two plates. Two of the sites are considered to be located in the stable part of these plates, whereas the remaining five are within the deformation region of the Eurasia-Africa boundary. The conclusions are analyzed in view of the different deformation models, derived from geodynamic or geophysical data that have been proposed for the region.     

南北地震带和青藏块体东部近期大地形变与地震特征

通过研究南北地震带及青藏块体东部地区２０多年来大地形变场演化特征及其与地震活动的呼应关系，发现大地形变既具有时空分布的不均匀性，各分区形变场又具有同时段的宏观相似性；继承性运动是现代地壳运动的总趋势，而运动方式为波浪式，涌动式推进。地壳运动过程中存在着区域为能积累阶段和释放调整阶段，这可能是地震活动的相对平静与活跃的动力机制。     

Shear localisation in upper mantle peridotites

Upper mantle peridotite bodies at the earth's surface contain relict structures and microstructures which provide direct information on the role and the mechanisms of shear localisation in the upper mantle. Deformation which occurred at high temperatures (T>950±50°C) is relatively homogeneous within domains ranging in scale from a few kilometres to a few tens of kilometres. Below 950±50°C strain is localised into centimetre to several hundred metre wide shear zones which commonly contain hydrated mylonitic peridotites. The microstructures developed in the peridotites suggest there is a correlation between the occurrence of shear localisation and the occurrence of strain softening and brittle deformation processes. The most important strain softening processes are inferred to be structural and reaction induced softening. Structural softening processes include dynamic recrystallisation and strain-induced transitions from dislocation creep to some form of grain-size-sensitive (GSS) creep. Reaction induced softening is related to the formation of fine grained polyphase reaction products which deform by GSS creep and the formation of weak sheet silicates such as phlogopite, chlorite, talc and antigorite. From experimental studies these softening processes and brittle deformation processes are inferred to occur mainly at temperatures less than about 910±160°C. This temperature range is inferred to be a significant rheological transition in the upper mantle. Below 910±160°C deformation during orogenesis may be accommodated by an anastomosing network of hydrated mylonitic shear zones with a distinct, perhaps weak, rheology. At higher temperatures strain is accommodated in much wider deformation zones.On the scale of the lithosphere the degree of localisation may be different to that determined at the scale of the periodotite massif. An anastomosing network of hundred metre wide mylonitic shear zones forming 0.05–0.3 by volume fraction of the mantle lithosphere atT<950°C could accommodate inhomogeneous or homogeneous bulk deformation depending on the spatial distribution and ordering of the mylonite zones. The higher temperature deformation at deeper levels in the mantle could be markedly inhomogeneous being concentrated in shear zones with widths in the range of 2–20 km, alternatively these zones may widen significantly during deformation, resulting in a decrease in the degree of localisation with increasing bulk strain.     

Evolution of the deformation and stress patterns of the East Asia continent under multi-driving force

Introduction Seismological observation and all kinds of ways of geodesy measurement imply that there is significant correlation between crustal movement and seismic activity (MEI, 1993). Therefore, it is very important to get the materials of the continental crust deformation and the patterns of stress field for the studying of the mechanism and prediction of the continental strong earthquake. Data of the continental deformation and patterns of stress field can be mainly obtained by the follo…     

Assessment of strong earthquake risk in the Chinese mainland from 2021 to 2030

The long-term earthquake prediction from 2021 to 2030 is carried out by researching the active tectonic block boundary zones in the Chinese mainland. Based on the strong earthquake recurrence model, the cumulative probability of each target fault in the next 10 years is given by the recurrence period and elapsed time of each fault, which are adopted from relevant studies such as seismological geology, geodesy, and historical earthquake records. Based on the long-term predictions of large earthquakes throughout the world, this paper proposes a comprehensive judgment scheme based on the fault segments with the seismic gap, motion strongly locked, sparse small-moderate earthquakes, and apparent Coulomb stress increase. This paper presents a comprehensive analysis of the relative risk for strong earthquakes that may occur in the coming 10 years on the major faults in the active tectonic block boundary zones in the Chinese mainland. The present loading rate of each fault is first constrained by geodetic observations; the cumulative displacement of each fault is then estimated by the elapsed time since the most recent strong earthquake.     

利用强震震源机制解资料反演中国大陆及其邻区的形变场模型

搜集了1900-2013年间发生在中国大陆及其邻区的震源机制解资料,详细整理了其中的70个7级及以上大震的震源参数、地表破裂带和地表位移资料。根据资料的完整程度将地震分成三类: A类存在地表破裂和地表位移观测资料; B类存在地表破裂资料,但缺少地表位移观测数据;C类缺少地表破裂带和地表位移观测资料。对B类和C类缺少地表位移观测数据的地震,利用三角形模型模拟其位移分布。再根据地表位移分布及地震破裂带与本文使用网格模型之间的位置关系将地震分段。最后,利用分段前、后的地震数据和改进的双三次样条方法反演研究区域的形变场模型。结果表明:①大震资料的分段处理改进了地震数据的反演结果,提高了反演模型的合理性和空间一致性;在喜马拉雅断裂带,形变场具有更好的连续性,其变形特征与地质等数据的反演结果基本吻合;塔里木盆地和阿尔金断裂的形变量减小,与该区域较低的地震活动性一致;戈壁一阿尔泰的变形从SE的挤压和NE的拉张调整到NE的挤压和NW的拉张;鄂尔多斯西缘的拉张分量明显减小。②113年的地震资料解释了印度板块向欧亚板块运动总速率的30~50%,存在20 mm/a左右的速度亏损,该亏损量可能包括断层蠕动、褶皱等非震形变,未监测到或者缺失的地震,及以弹性应变能形式存在通过潜在地震释放的应变