Timing of the cataclastic deformation along the Akaishi Tectonic Line,central Japan

This paper describes K-Ar ages of cataclasites and fault gouges from the Akaishi Tectonic Line (ATL), central Japan. Petrological and mineralogical features of these rocks are also examined. Based on the results, we test the hypothesis that the K-Ar ages of these rocks represent the age of hydrothermal alteration associated with the fault movement. Intensity of deformation and alteration increase passing from host rock into cataclasite and finally into fault gouge. This increase corresponds to an increase of the value of crystallinity index (Kübler index) of the micaceous minerals contained in these rocks. Furthermore, the degree of rejuvention of K-Ar ages of the micaceous minerals increases in the same sense. A correlation of K-Ar ages (plotted on the y axis) versus Kübler index (plotted on the x axis) yields a concave curve asymptotically parallel with the x axis at approximately 15 Ma. This curve is interpreted to represent the mode of decrease of the relative amounts of inherited argon in the K-Ar system of the micaceous minerals, corresponding to an increase in the intensity of deformation and alteration. Inclination of the curve becomes zero if all the inherited argon is lost from the K-Ar system of the micaceous minerals. Thus, it is concluded that the hydrothermal alteration occurred at approximately 15 Ma. The strike-slip basin along the ATL formed the middle Miocene. The K-Ar dating of ATL gouges indicates that the ATL was active simultaneously with formation of the strike-slip basin along its trace during the middle Miocene.     

Frictional properties of simulated anhydrite-dolomite fault gouge and implications for seismogenic potential

The frictional properties of anhydrite-dolomite fault gouges, and the effects of CO₂ upon them, are of key importance in assessing the risks associated with CO₂ storage in reservoir formations capped by anhydrite-dolomite sequences, and in understanding seismicity occurring in such formations (such as the Italian Apennines). Therefore, we performed velocity-stepping direct-shear experiments on simulated dolomite, anhydrite and 50:50 anhydrite/dolomite gouges, at representative in-situ conditions (120 °C and σ_n^e = 25 MPa). They were conducted under vacuum, or else using water or CO₂-saturated water as pore fluid (P_f = 15 MPa). Friction coefficients varied between 0.55 and 0.7. All dry samples exhibited velocity-weakening behavior, whereas all wet samples exhibited velocity-strengthening behavior, without or with CO₂. This is consistent with trends previously reported for such gouges. A compilation of literature data shows that the transition from velocity-strengthening to velocity-weakening occurs in these materials between 80 and 120 °C when dry, and between 100 and 150 °C when wet. This implies little seismogenic potential for wet dolomite, anhydrite and mixed gouges under CO₂ storage conditions at 2–4 km depth. Seismic slip in the Italian Apennines at depths of ∼6 km and beyond may be explained by the velocity-weakening behavior expected in anhydrite and especially dolomite at temperatures above 150 °C.     

Crustal structure, fault segmentation, and activity of the Median Tectonic Line in Shikoku, Japan

We conducted a seismic tomographic analysis to estimate the crustal structure beneath the Shikoku and Chugoku regions in Japan. The Philippine Sea slab (PHS slab) subducts continuously in a SE–NW direction beneath this region, and the crustal structure is complex. Furthermore, the Median Tectonic Line (MTL), one of the longest and most active arc-parallel fault systems in Japan (hereafter, the MTL active fault system), is located in this area, and the right-lateral strike–slip movement of this fault system is related to the oblique subduction of the PHS slab. The MTL active fault system has ruptured repeatedly during the last 10 000 years, and has high seismic potential. Our tomographic analysis clarified the heterogeneous crustal structure along the MTL active fault system. This fault system in Shikoku can be divided into two segments, an east segment and a west segment, on the basis of the velocity structure. This segmentation model is consistent with other such models that have been determined from geological and geomorphological data such as fault geometry, slip rate, and faulting history. This consistency suggests that the surface characteristics of the MTL active fault system are related to structural properties of the crust. In particular, a prominent low-velocity (low-V) zone is present in the lower crust beneath the east segment. Our tomographic images show that the lower crust structure beneath the east segment is obviously different from that of the other segment. Furthermore, this low-V zone may indicate the presence of fluid, possibly related to dehydration of the PHS slab. As the presence of fluid in the lower crust affects the activity of the fault, stress accumulation and the fault failure mechanism may differ between the two segments of the MTL active fault system.     

Active right-lateral strike-slip fault zone along the southern margin of the Japan Sea

We describe an active right-lateral strike-slip fault zone along the southern margin of the Japan Sea, named the Southern Japan Sea Fault Zone (SJSFZ). Onshore segments of the fault zone are delineated on the basis of aerial photograph interpretations and field observations of tectonic geomorphic features, whereas the offshore parts are interpreted from single-/multichannel seismic data combined with borehole information. In an effort to evaluate late Quaternary activity along the fault zone, four active segments separated by uplifting structures are identified in this study. The east–northeast-trending SJSFZ constitutes paired arc-parallel strike-slip faults together with the Median Tectonic Line (MTL), both of which have been activated by oblique subduction of the Philippine Sea plate during the Quaternary. They act as the boundaries of three neotectonic stress domains around the eastern margin of the Eurasian plate: the near-trench Outer zone and NW–SE compressive Inner zone of southwest Japan arc, and the southern Japan Sea deformed under E–W compression from south to north.     

Implications of mylonitic microstructures for the geotectonic evolution of the Median Tectonic Line,central Japan

The Median Tectonic Line (MTL), the most prominent onshore fault in Japan, demarcates the Cretaceous Hiji quartz dioritic gneiss of the Ryoke belt on the west from the high P/T type Sambagawa metamorphic rocks on the east in the Takato area. Toward the MTL, the Hiji gneiss grades into strongly mylonitized rocks characterized by grain-size reduction of quartz. In the mylonitic rocks, the development of fluxion banding (Sm) is remarkably influenced by the existence of K-feldspar, forming a myrmekitic intergrowth. Brittle microstructures indicative of truly cataclastic deformation are observed only in mylonitic rocks close to the MTL. Early deep-level ductile deformation apparently gave way to shallower, brittle deformation at a later stage. The attitude of stretching lineations (Lm) and asymmetric microstructures observed in the mylonites suggest that sinistral strike-slip shearing with a subordinate component of vertical-slip took place during mylonitization in mid-Cretaceous time. The mylonitic rocks and their protolith, supposed to have constituted the eastern limb of the shear zone, were probably eroded out and lost by upheaval of the Sambagawa belt relative to the Ryoke belt.     

Discontinuity of the Mozumi–Sukenobu fault low-velocity zone, central Japan, inferred from 3-D finite-difference simulation of fault zone waves excited by explosive sources

We delineate shallow structures of the Mozumi–Sukenobu fault, central Japan, using fault zone waves generated by near-surface explosions and detected by a seismometer array. Two explosive sources, S1 and S2, were placed at a distance of about 2 km from the array, and the other two, S3 and S4, were at a distance of about 4 km. Fault zone head waves and fault zone trapped waves following direct P wave arrivals were clearly identified in the seismograms recorded by a linear seismometer array deployed across the fault in a research tunnel at a depth of 300 m. Synthetic waveforms generated by a 3-D finite-difference (3-D FD) method were compared with observed fault zone waves up to 25 Hz. The best fitting model indicates a 200-m-wide low-velocity zone extending at least to shot site S1 located 2 km east of the seismic array with a 20% decrease in the P wave velocity relative to the wall rock. The width of the low-velocity zone is consistent with the fault zone defined by direct geological observation in the research tunnel. However, the low-velocity zone should disappear just to the east of the site S1 to explain the observed fault zone waves for shot S3 and S4 located 4 km east of the seismometer array. Yet the observation and the simulation show notable trapped wave excitation even though shots S3 and S4 are outside the fault zone. These results indicate that (1) the effective waveguide for seismic waves along the fault does not exist east of source site S1 although the surface traces of the fault are observed in this region, and (2) considerable trapped waves can be excited by sources well outside the fault zone. These results highlight the along-strike variability in fault zone structure.     

Intra-plate seismicity gap along the Median Tectonic Line and oblique plate convergence in southwest Japan

The intra-plate seismicity map for southwest Japan, based on fairly complete historical data for the past four hundred years, reveals an inverse correlation between the seismic activity along the island arc and the slip-rate along the Median Tectonic Line during the Late Quaternary. In the eastern part, the tectonic line is geologically inactive but regional historic seismicity has been high. The intra-plate seismic activity is probably related with the well developed mosaic-like conjugate system of strike-slip faults there. Conversely, the historic seismicity has been low in the western part, especially low in an area along the most geologically active segment of the Median Tectonic Line. Since no creep movement has been found there, energy greater than that of the Mino-Owari earthquake of 1891 (M = 8.0) seems to be stored in this seismicity gap. The difference in seismic released energy between the two regions for the last four hundred years would be balanced by the strain energy accumulated in the seismic gap. The fairly uniform strain release is conformable to the idea, proposed on the basis of the trend of maximum compression axes, that the Philippine Sea plate is dragging southwest Japan southwestward along the Nankai trough.     

On the mechanical properties of synthetic kaolinite/quartz fault gouge

The mechanical properties and microstructures of mixed kaolinite/ quartz fault gouge have been studied by means of triaxial tests, wherein a 1 mm thickness of fault gouge was sheared between rigid, sintered alumina sliders. Test conditions ranged up to 200 MPa confining pressure, 175 MPa pore water pressure and temperatures to 600°C. Constant displacement rate tests were carried out at 5×10^-4 mm s^-1, and the stress relaxation technique was used to access a wide range of lower displacement rates down to 10^-10 mm s^-1. The effects of different ratios of clay: quartz were studied, and some experiments were cafried out using crushed Tennessee sandstone gouge and pre-faulted cylinders of Tennessee sandstone. Deformation-induced microstructures were studied by optical, scanning and transmission electron microscopy, and mineral chemistry changes were identified using EDS analysis in the STEM. The most important factor determining the strength of these gouges is effective confining pressure, and the effective stress law was obeyed at all test conditions. Increasing the proportion of quartz in the gouge slightly increases the strength, as does increase of temperature. Under all test conditions the gouges deformed by strain-hardening stable sliding. At 2 mm displacement the friction coefficient is similar to that for rock and rock sliding (μ= 0.85). Over wide ranges of strain-rate and temperature the strength of these gouges is little affected if the effective pressure is high, but strength drops rapidly with decreasing strain-rate if effective pressure is low (or if pore water pressure is high). Reloading of the gouge after stress relaxation at high temperatures demonstrated hardening arising from hydrothermal cementation during stress relaxation, which led to sudden rupture of the cemented gouge. This phenomenon may be responsible for cyclic rupture of natural faults. New mineral phases were produced in these experiments only at 600°C. At 400°C, anticipated production of pyrophyllite from kaolinite plus quartz was not found, but recrystallization of kaolinite is believed to have occurred and evidence of healing of cracks in quartz was seen. Microstructural studies revealed the ubiquitous development of P and R₁ foliations and other features, which are identical to those found in natural clay-bearing fault zones. Microstructural evolution is associated with the strain-hardening, and apparent hardening is strongly associated with the stress path during loading.     

Spatial variations in 3He/4He ratios along a high strain rate zone,central Japan

A linear zone with high strain rates along the Japan Sea coast, the Niigata-Kobe Tectonic Zone (NKTZ), is considered to be associated with rheological heterogeneities in the lower crust and/or upper mantle. Helium isotope variations along the NKTZ reveal a close association with the geophysical evidence for rheological heterogeneities in the crust and mantle. In the southern NKTZ, the ³He/⁴He ratios lower than 3.4 Ra (Ra denotes the atmospheric ³He/⁴He ratio of 1.4 × 10⁻⁶) could be interpreted as a two-component mixture of helium stored in aqueous fluids driven off the subducting oceanic crust and radiogenic crustal helium. Higher ³He/⁴He ratios are observed in the central NKTZ where Quaternary volcanoes and high-temperature hot springs are concentrated, suggesting that the ³He emanation manifest in the central NKTZ results from the effective transfer of mantle helium by intrusion and degassing of mantle-derived magma in the crust. In the northern NKTZ where two large inland earthquakes occurred recently, there appears to be many samples with ³He/⁴He ratios significantly higher than those observed in the fore-arc side of northeast Japan. A plausible source of mantle helium could be attributed to upward mobilization of aqueous fluids generated by dehydration of the subducting Pacific Plate slab.     

冷俯冲带深部的板块断裂过程——以日本中部侏罗纪燧石-碎屑岩杂岩体中的断裂带为例

近年来,深海大洋钻探已证实在洋陆俯冲带的浅部,板块边界断裂高度集中在特征性岩层中,然而对于这种断裂高度集中化现象是否发生在俯冲带深部仍然缺乏充分的认识,因此对日本中部侏罗纪燧石-碎屑岩杂岩体中一个露头宽度约50 m的断裂带进行了调查。该断裂带沿古俯冲带深部的板块边界延伸而出的逆冲断层发育,断裂带中的剪切变形集中在数层黑色有机质黏土岩中,表现为沿交织鳞片状叶理的分散剪切,剪切方向分为左行走滑和逆冲走滑,可能形成于俯冲带中的滑动分异或左行斜俯冲过程。体现滑动集中化的拆离面切割了黑色有机质黏土岩层,拆离面表现为左行滑动。利用碳物质拉曼光谱测量了拆离面上及黑色有机质黏土岩层中的碳物质。结果表明,相对于黑色有机质黏土岩,拆离面中的碳物质具有更高的成熟度,表明在左行滑动过程中产生了快速的摩擦升温。野外观测和实验结果表明,这一古断裂带记录的俯冲带深部板块边界断裂高度集中在黑色有机质黏土岩层中,发育于其中的拆离面的左行剪切可能产生于深部地震性滑动。     

太行山东缘断裂南支断层性质及断层泥K-Ar同位素定年

太行山东缘断裂是华北盆地西边界的控制性断裂,对研究华北盆地中-新生代油气藏、地震分布及成矿作用具有重要意义。通过对太行山东缘断裂南支断层几何学、运动学的详细研究以及对断层泥的X射线衍射分析、K-Ar同位素年代学研究,确定了太行山东缘断裂为枢纽性质正断层,由一系列北北东走向正断层组成,呈左阶阶梯状展布,断层活动时间为113.42±2.31 Ma。断裂在新生代再次活动,形成多幕式的断陷盆地。     

Principal fault zone width and permeability of the active Neodani fault, Nobi fault system, Southwest Japan

The internal structure and permeability of the Neodani fault, which was last activated at the time of the 1891 Nobi earthquake (M8.0), were examined through field survey and experiments. A new exposure of the fault at a road construction site reveals a highly localized feature of the past fault deformation within a narrow fault core zone. The fault of the area consists of three zone units towards the fault core: (a) protolith rocks; (b) 15 to 30 m of fault breccia, and (c) 200 mm green to black fault gouge. Within the fault breccia zone, cataclastic foliation oblique to the fault has developed in a fine-grained 2-m-wide zone adjacent to the fault. Foliation is defined by subparallel alignment of intact lozenge shaped clasts, or by elongated aggregates of fine-grained chert fragments. The mean angle of 20°, between the foliation and the fault plane suggests that the foliated breccia accommodated a shear strain of γ<5 assuming simple shear for the rotation of the cataclastic foliation. Previous trench surveys have revealed that the fault has undergone at least 70 m of fault displacement within the last 20,000 years in this locality. The observed fault geometry suggests that past fault displacements have been localized into the 200-mm-wide gouge zone. Gas permeability analysis of the gouges gives low values of the order of 10⁻²⁰ m². Water permeability as low as 10⁻²⁰ m² is therefore expected for the fault gouge zone, which is two orders of magnitude lower than the critical permeability suggested for a fault to cause thermal pressurization during a fault slip.     

Tectonic stages along a traverse cross cutting the Rhodopian zone (Greece)

In a cross section along the Rhodopian zone from the Greece/Bulgarian border through the postalpine basins in the Xanthi area to Thasos island detailed structural mapping and collection of field data enable us to determine a sequence of tectonic stages that affected this area. This allows us to propose a model of continental collision.During the early Eocene, NE-SW directed movements produced a southwest facing pile of crystalline nappes with internal deformation comprising NW and NE trending isoclinal folds and a NE-SW trending stretching lineation. After a short time interval, nappe movements started again under brittle deformation conditions and produced composite thrust sheets, WNW- and NNE trending chevron folds and thick cataclasite. Late erogenic uplift and extension caused the formation of NW- and NE trending normal faults. These faults bounded the Oligocene flysch- and molasse basins and provided pathways for voluminous magmatic suites. This tectonic process was interrupted at the Oligocene/Miocene boundary by a late orogenic compression reflected in NW open folds and dissolution cleavages. Subsequently, differential uplift and subsidence associated with NW- and NE trending normal faults has continued up to the present time. From the early Pliocene new fragmentation and thinning of the crust reflected in WNW listric faults and NNE transfer faults has affected the southern parts of the Rhodopian zone.Nappe forming movements are the result of a progressive collisional process involving a Kimmerian microcontinent lying between the Eurasia and Apulia continents. In the final stages of this collision, uderplating processes led to regional uplift and extension. Additional extensional movements were related to the formation of the Aegean back arc basin caused by the Late Cenozoic Hellenic subduction zone.

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Zusammenfassung Durch Gefügedatensammlung und strukturelle Kartierung in einer Geotraverse durch die Rhodopische-Zone von der griechisch-bulgarischen Grenze, die sich über das postalpine Becken der Xanthi-Gegend bis zur Insel Thassos hinzieht, wurde sowohl die Zeitabfolge der tektonischen Ereignisse definiert als auch ein Kontinental-Kollisionsmodel aufgestellt.Während dem unteren Eozän haben NE-SW streichende Bewegungen einen südwestlich vergenten kristallinen Deckenstappel gebildet, der von NW- und NE streichenden Isoklinalfalten und einer SW streichenden Strekkungslineation innendeformiert wurde. Nach einer kurzen Zeitspanne haben Deckenbewegungen unter Bruchbedingungen wiederbegonnen. Dadurch wurden zusammengesetztes Deckenstappel, WNW and NNE streichende Knickfalten und mächtige Kataklasite gebildet. Postorogenetisches Aufsteigen des Gebirges wird von NW- und NE streichenden Abschiebungen gekennzeichnet. Diese Verwerfungen begrenzen Oligozäne Flysch- und Molassebecken und stellen Aufstiegswege von magmatischen Produkten dar, die stellenweise die Erdoberfläche erreichten. An der Grenze Oligozän-Miozän zeigt eine postorogene Kompression NW gerichtete geöffneteFalten und eine begleitende Lösungsschieferung. Nach dieser kurzen Unterbrechung setzt sich das Aufsteigen des Gebirges bis heute fort bei gleichzeitigen NW- und NE gerichteten Abschiebungen. Seit dem unteren Pliozän wird eine Zerspaltung und Ausdünnung der Kruste sowohl durch WNW gerichtete-listrische-Abschiebungen als auch durch NNE gerichtete »Transfer«-Verwerfungen hervorgerufen.Deckenbewegungen sind das Ergebnis eines kontinuierlichen Kollisionsprozesses, der einen Kimmerischen Mikrokontinent miteinbezieht, welcher zwischen dem Eurasischen- und dem Apulischen Kontinent lag. In den letzten Stadien der Kollision führte Plattenverdickung zu einem Aufsteigen des Gebirges, das von regionaler Ausdehnung begleitet wird. Eine weitere Ausdehnung bezieht sich auf die Bildung des Ägäischen »black arc basin« das durch die rezente Hellenische Subduktionszone hervorgerufen wurde.

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Résumé Dans une géotraverse de la zone du Rhodope, depuis la frontière gréco-bulgare, à travers les bassins post-alpins de la région de Xanthi et jusqu'à l'île de Thasos, on a effectué une cartographie structurale de détail et diverses observations de terrain. Cette investigation a permis de définir la succession des événements tectoniques et de proposer un modèle de collision continentale.Pendant l'Eocène inférieur, des mouvements de direction NE-SW ont engendré un empilement de nappes cristallines à vergence SW dont les structures de déformation interne comprennent des plis isoclinaux de directions NW et NE ainsi qu'une linéation d'étirement NE-SW. Après une courte pause, le mouvement des nappes a repris dans des conditions de déformation cassante, avec production de lames charriées composites, de plis en chevrons orientés WNW et NNE et de zones cataclasitiques épaisses. Un soulèvement orogénique tardif accompagné d'une extension crustale a ensuite engendré des failles normales de directions NW et NE. Ces failles ont délimité les bassins oligocènes de flysch et de molasse et ont ouvert la voie à de volumineuses venues magmatiques qui, par endroits, ont atteint la surface. Ces processus tectoniques ont été interrompus à la limite Oligocène-Miocène parune compression tardi-orogénique responsable de plis ouverts orientés NW et d'une schistosité de dissolution. Par la suite, des mouvements de soulèvement et de subsidence différentiels se sont poursuivis jusqu'aujourd'hui. A partir du début du Pliocène, les parties méridionales de la zone du Rhodope ont été le siège de nouveaux processus de fragmentation et d'amincissement de la croûte, qui se sont traduits par des failles listriques WNW et par des décrochements.La genèse des nappes résulte d'un processus progressif de collision impliquant un microcontinent kimmérien compris entre les continents eurasien et apulien. Lors des stades finals de cette collision, des phénomènes d' «underplating» ont provoqué un soulèvement de l'ensemble accompagné d'une extension à l'échelle régionale. Des mouvements d'extension ultérieurs sont en relation avec la formation du bassin d'arrière-arc égéen engendré par la zone de subduction hellénique au Cénozoïque supérieur.

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, - - Xanthi Thassos, . , NE SW , , , , - -, , -. , . , WNW NNE . , NW NE . , - . - - NW . , , NW NE. , - , - . , , . , . («back arc basin»), .

     

Electron spin resonance dating of fault gouge from Desamangalam, Kerala: Evidence for Quaternary movement in Palghat gap shear zone

The field investigations in the epicentral area of the 1994 Wadakkancheri (Desamangalam), Kerala, earthquake (M 4.3) indicate subtle, but clearly recognizable expressions of geologically recent fault zone, consisting of fracture sets showing brittle displacement and a gouge zone. The fracture zone confines to the crystalline basement, and is spatially coincident with the elongation of the isoseismals of the 1994 mainshock and a 10-km-long WNW-ESE trending topographic lineament. The preliminary results from the electron spin resonance (ESR) dating on the quartz grains from the fault gouge indicate that the last major faulting in this site occurred 430 ± 43 ka ago. The experiments on different grain sizes of quartz from the gouge showed consistent decrease in age to a plateau of low values, indicating that ESR signals in finer grains were completely zeroed at the time of faulting due to frictional heat. The results show a relatively young age for displacement on the fault that occurs within a Precambrian shear zone. Discrete reactivated faults in such areas may be characterized by low degree of activity, but considering the ESR age of the last significant faulting event, the structure at Desamangalam may be categorized as a potentially active fault capable of generating moderate earthquakes, separated by very long periods of quiescence.     

Tectonic interpretations of enigmatic structures in the North Anatolian fault zone

Two geometrically distinct groups of syn-sedimentary and post-depositional mesofaults and joints cut Neogene-Quaternary sediments in basins situated along the convex-northwards arc of the North Anatolian fault zone between Çerkes and Erbaa. One group comprises second-order fractures interpreted as having developed during episodes of right-lateral shear along the fault zone, while the morphologically identical fractures in the other group have been interpreted as secondary products of left-lateral shear; thus apparently implying one or more former episodes of eastwards motion of the Anatolian scholle. Because such a reversal of motion would be counter to the well-established westward escape of Anatolia the structures have been called anomalous or incompatible.Alternative hypotheses which have been advanced to explain the development of the anomalous mesofractures include: localized reversals related to displacements of rigid blocks acting as buttresses within basins; selective operation of intra-pull-apart strike-slip faults; stress release; the coincidence of the present western sector of the fault with an older left-lateral fault zone; and the influence of a North Turkish neotectonic stress regime.     

四川省鲜水河断裂带温泉的CO2释放量的定量化研究

通过对四川西部鲜水河深大活动断裂带温泉的观测和分析,得出了温泉的幔源CO2年释放量,由此推断深大活动断裂的CO2释放作用对碳循环具有重大影响.     

东至断裂带构造变形特征及其构造演化

东至断裂带是皖西南一条重要的北北东向断裂带。详细的构造解析表明,该断裂带主要经过3期构造变形,分别是发生在晚侏罗世末—早白垩世初的左行平移断层、早白垩世期间的伸展构造和晚白垩世—新生代的右行平移断层。通过断层擦痕矢量反演和断层叠加改造关系分析,认为东至断裂带及其两侧多期构造变形对应的区域应力场分别为近南北向挤压、北北西—南南东向挤压、北西—南东向伸展和近东西向挤压应力场。东至断裂带的形成和演化与郯庐断裂带相似,主要与华南与华北板块俯冲碰撞、伊泽奈崎板块和古太平洋板块向欧亚板块俯冲碰撞与弧后扩张、及印度板块向北碰撞后产生向东的构造挤出等多构造体制共同作用有关。     

红河断裂北段断层泥中自生伊利石K-Ar年龄及地质意义

印度板块与欧亚板块之间约50Ma以来的持续碰撞作用,导致了地壳块体沿红河断裂带的侧向挤出[1]。研究表明,红河断裂带第三纪为左旋走滑运动,并有过从左旋运动到右旋运动的转化[1,2]。     

郯庐断裂带昌邑北段隐伏活动断层探测

正活动断层是大陆地震的主要载体。活动断层有的出露地表,有的则隐伏于地下。隐伏于地下的断层称为隐伏断层或盲断层。大地震和强震不只是发生在突破地表的活动断层上,还可以发生在隐伏活动断层上。如华北地区1668年郯城Ms 8.5、1679年三河—平谷Ms 8.0和1976年唐山Ms 7.8等大地震都是未知隐伏活动断层产生的,造成了惨重的人员伤亡和巨大的经济损失。