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1.
The latest hydraulic fracturing and stress relief measurement data in the Chinese mainland were collected. The total of 3856 data entries are measured at 1474 locations. The measured area covers 75–130°E and 18–47°N, and the depth range varies from surface to 4000 meters depth, which generally includes each active tectonic block of China and each segment of North–South seismic belt. We investigated the tectonic stress field by removing the effect of gravity. For this, we assume lateral constraints and Heim’s rule. The gravity contribution is removed by using the assumption of lateral constraint and Heim’s rule. Our results show: (1) the maximum and the minimum horizontal principal stress σH, σh and the vertical stress σV in the shallow crust of China all increase linearly with depth: σH = 0.0229D + 4.738, σh = 0.0171D + 1.829, σV = 0.0272D. Maximum and minimum horizontal tectonic stress varies as a function of depth D linearly 4.738 < σT < 0.0139D + 4.738 and 1.829 < σt < 0.0162D + 1.829. The horizontal tectonic differential stress is σT − σt = 0.0058D + 2.912. (2) The intermediate value of σT1 (regression value of tectonic stress inferred from the assumption of lateral constraint at 2000 m depth) changes in different areas, the maximum value of which is 45.6 MPa, while the minimum value of which is 26.8 MPa. Horizontal tectonic differential stress σT − σt increases linearly with depth and the maximum and minimum of σT − σt is 25.3 MPa and 13.0 MPa, respectively. In general, the stress magnitude is much higher in western than in eastern China. This indicates that the strong Indo-Eurasian collision dominates the present tectonic stress field in Chinese mainland. (3) Compared with other study regions, the northward crustal compression to the Qinghai-Tibet block is relatively lower in magnitude in the shallow subsurface and higher at deeper depth. (4) The orientations of σT in China mainland generally form a radial scattering pattern centered in Tibetan Plateau. From western to eastern China, they rotate gradually clockwise from NS to NNE, NE, NEE, and SE, which is consistent with the result of focal mechanism solutions.  相似文献   

2.
The seismological study of recent seismic crises near Oleron Island confirms the coexistence of an extensional deformation and a transtensive regime in the Atlantic margin of France, which is different from the general western European stress field corresponding to a strike-slip regime. We argue that the switch of the principal stress axes σ1/σ2 in a NW–SE vertical plane is linked with the existence of crustal heterogeneities. Events of magnitude larger than 5 sometimes occur along the Atlantic margin of France, such as the 7 September 1972 (ML = 5.2) earthquake near Oleron island and the 30 September 2002 (ML = 5.7) Hennebont event in Brittany. To test the mechanism of local strain localization, we model the deformation of the hypocentral area of the Hennebont earthquake using a 3D thermo-mechanical finite element code. We conclude that the occurrence of moderate earthquakes located in limited parts of the Hercynian shear zones (as the often reactivated swarms near Oleron) could be due to local reactivation of pre-existing faults. These sporadic seismic ruptures are favoured by stress concentration due to rheological heterogeneities.  相似文献   

3.
NE Iran, including the Kopeh Dagh and Allah Dagh-Binalud deformation domains, comprises the northeastern boundary of the Arabia–Eurasia collision zone. This study focuses on the evolution of the Plio-Quaternary tectonic regimes of northeast Iran. We present evidence for drastic temporal changes in the stress state by inversion of both geologically and seismically determined fault slip vectors. The inversions of fault kinematics data reveal distinct temporal changes in states of stress during the Plio-Quaternary (since ～ 5 Ma). The paleostress state is characterized by a regional transpressional tectonic regime with a mean N140 ± 10°E trending horizontal maximum stress axis (σ1). The youngest (modern) state of stress shows two distinct strike-slip and compressional tectonic regimes with a regional mean of N030 ± 15°E trending horizontal σ1. The change from the paleostress to modern stress states has occurred through an intermediate stress field characterized by a mean regional N trending σ1. The inversion analysis of earthquake focal mechanisms reveals a homogeneous, transpressional tectonic regime with a regional N023 ± 5°E trending σ1. The modern stress state, deduced from the youngest fault kinematics data, is in close agreement with the present-day stress state given by the inversions of earthquake focal mechanisms. According to our data and the deduced results, in northeast Iran, the Arabia–Eurasia convergence is taken up by strike-slip faulting along NE trending left-lateral and NNW trending right-lateral faults, as well as reverse to oblique-slip reverse faulting along NW trending faults. Such a structural assemblage is involved in a mechanically compatible and homogeneous modern stress field. This implies that no strain and/or stress partitioning or systematic block rotations have occurred in the Kopeh Dagh and Allah Dagh-Binalud deformation domains. The Plio-Quaternary stress changes documented in this paper call into question the extrapolation of the present-day seismic and GPS-derived deformation rates over geological time intervals encompassing tens of millions of years.  相似文献   

4.
In 2001, a special issue of the Bulletin of the Seismological Society of America (BSSA) featured seismological research for the 1999 Chi–Chi Taiwan earthquake. This study uses source parameters suggested by the first author in this special issue to estimate static stress drop associated with the Chi–Chi earthquake. The waveform simulation method was used to carefully examine these source parameters. The simulation results indicate that source parameters, inferred from near-fault observations, are well determined. According to the rupture area and slip, the static stress drops (Δσs) obtained were distributed between a small value of 47 bars near the epicentral region and a much larger value (>200 bars) to the north. Similar trends in dynamic stress drop (Δσd) were also recognized by the first author in his paper published in 2001 BSSA special issue. Comparing the Δσs with Δσd, satisfies the relation Δσs/Δσd ≈ 1. This relation suggests that fault motion is mostly spent releasing seismic wave energy during the rupture process of the Chi–Chi earthquake. The consistency between static and dynamic stress drops thus provides a measure of energy-moment (Es/M0) ratios, which range from 9.0 × 10−5 to 6.5 × 10−4. The average Es/M0 ratio estimated for the northern portions of the fault is 3.4 × 10−4, which is about 3 times that of the south. Such a high Es/M0 ratio can be interpreted as having low strength in the rupture for the northern portions of the fault, where the fault would release less energy per unit rupture surface to create the new rupture.  相似文献   

5.
The natural stress state in the lithosphere consists of the vertical load and Poisson ratio, and then additional horizontal compression and extension (denoted by ΔσH and ΔσT, respectively) are assumed to be superimposed upon this gravitational stress field. The resulting stress state is composed of the maximum, medium and minimum stresses denoted by σ1, σ2, and σ3, respectively. The stress ratio is given as Φ = (σ2 − σ3)/(σ1 − σ3). A linear relation is found between Φ or 1/Φ and the vertical load in wrench-faulting and extensional stress regimes, respectively. The slope and intercept of the linear relation result in the additional horizontal stresses and level of (average) paleo-surface, respectively. Stress ratio is also determinable by the stress tensor inversion of fault-slip data. The earliest tectonic event (T_1 Event) in the Cretaceous Gyeongsang Basin consists of coexisting E–W compression and N–S extensional faulting episodes. Plots of Φ or 1/Φ against the burial depth (or vertical load) display several linear trends: two clusters in extensional episodes, and two or three clusters in wrench-faulting episodes. Because ΔσH is assumed to be null or negligible in the extensional regime, ΔσT is determinable from the slopes of two linear clusters as being −2.5 to −4.0 MPa. In wrench-faulting episodes, the values of ΔσH are given to be 61.6–101.4 MPa by applying determined additional horizontal extensions. Determined levels of average paleo-surfaces and those of syndepostional structures illustrate that more than five wrench-faulting or extensional episodes have occurred during the T_1 Event, whose active age, consequently, ranges from the Barremian to the Coniacian. This supports that the coexisting coaxial faulting episodes with the same extension may correspond to the alternation of wrench-faulting and extensional episodes.  相似文献   

6.
Torsion experiments were performed on synthetic aggregates of calcite with a 50% volume of muscovite. The tests were performed at 627–727 °C with a confining pressure of 300 MPa at constant shear strain rates of 3 × 10?5–3 × 10?4 s?1 on cylindrical samples with the starting foliation parallel and perpendicular to the cylinder axis. Both the foliation parallel and the foliation perpendicular experiments show similar stress–strain patterns, with an initial hardening stage followed by significant strain weakening (>60%) before a catastrophic rupture. Microstructural analysis shows that in low-strain experiments calcite grains are intensely twinned while muscovite grains appear slightly bent and kinked. Higher strains promote a segregation of the two phases with calcite forming thin layers of fine, dynamically recrystallized grains, which act as localized shear bands, while muscovite grains keep their original size and rotate assuming a strong shape preferred orientation. This strain localization of the calcite from an initially homogeneous rock produced catastrophic failure at moderate bulk shear strains (γ ～ 3). Localization of the strain first involved ductile deformation to produce a new calcite layering with fine dynamically recrystallized grains along which cavities nucleated. The orientation and kinematics of the cavities are comparable to R1 Riedel structures. All experiments on calcite–muscovite mixtures resulted in heterogeneous strain. In these torsion experiments chemical changes and crystallization of new phases (anorthite and kalsilite) are observed at 627 °C. Whereas, samples hot pressed or deformed in compression at 670 °C did not show such reactions or any localization. The effect of stress-field geometry and pore pressure upon mineral reactions is discussed. It is concluded that deformation-induced heterogeneous phase distributions caused local strength differences initiating strain localization in the calcite–muscovite mixtures, eventually leading to plastic failure.  相似文献   

7.
The footwall of the Main Central Thrust (MCT) Zone along the Bhagirathi valley comprises a wide zone of mylonitic quartzite and deep-level tectonites. The systematic variation of finite strain parameters (Es, k and v) in the mylonites indicates heterogeneous deformation, which is determined to vary between, simple shear and non-coaxial flattening type. In such a strain regime the outer boundary of the quartz clasts are no longer preserved thus leading to an error in finite strain measurement.In order to supplement the finite strain studies, Anisotropy of Magnetic Susceptibility (AMS) analyses were carried out on the mylonitic quartzites. A systematic variation in degree of anisotropy (P′) with distance from the MCT is documented and is interpreted to be tectonic in origin. Based on these results it is concluded that P′ can be used as a strain-intensity gauge at least on an outcrop scale, where a systematic variation in P′ values from one part of the outcrop to the other can be established. However, the quantitative relation between principal axes of finite strain ellipsoid and AMS axes, magnitude of principal susceptibility difference (ΔK1 and ΔK3) and finite strain magnitude (ε1=ln 1 + e1 and ε3=ln 1 + e3) were related by a logarithmic relationship with a correlation coefficient of 0.844.  相似文献   

8.
This paper presents an experimental investigation revisiting the anisotropic stress–strain–strength behaviour of geomaterials in drained monotonic shear using hollow cylinder apparatus. The test programme has been designed to cover the effect of material anisotropy, preshearing, material density and intermediate principal stress on the behaviour of Leighton Buzzard sand. Experiments have also been performed on glass beads to understand the effect of particle shape. This paper explains phenomenological observations based on recently acquired understanding in micromechanics, with attention focused on strength anisotropy and deformation non-coaxiality, i.e. non-coincidence between the principal stress direction and the principal strain rate direction. The test results demonstrate that the effects of initial anisotropy produced during sample preparation are significant. The stress–strain–strength behaviour of the specimen shows strong dependence on the principal stress direction. Preloading history, material density and particle shape are also found to be influential. In particular, it was found that non-coaxiality is more significant in presheared specimens. The observations on the strength anisotropy and deformation non-coaxiality were explained based on the stress–force–fabric relationship. It was observed that intermediate principal stress parameter b(b = (σ 2 ? σ 3)/(σ 1 ? σ 3)) has a significant effect on the non-coaxiality of sand. The lower the b-value, the higher the degree of non-coaxiality is induced. Visual inspection of shear band formed at the end of HCA testing has also been presented. The inclinations of the shear bands at different loading directions can be predicted well by taking account of the relative direction of the mobilized planes to the bedding plane.  相似文献   

9.
We conduct shear wave splitting measurements on waveform data from the Hi-net and the broadband F-net seismic stations in Kanto and SW Japan generated by shallow and intermediate-depth earthquakes occurring in the subducting Philippine Sea and Pacific slabs. We obtain 1115 shear wave splitting parameter pairs. The results are divided into those from the shallow (depth < 50 km) and the deep (depth > 50 km) events. The deep events beneath Kanto are further divided into PHS1 and PHS2 (upper and lower planes of the double seismic zone in the Philippine Sea slab, respectively), PAC1 and PAC2 (western and eastern Pacific slab, respectively) events. The results from the shallow events represent the crustal anisotropy, and their fast directions are more or less aligned in the σHmax directions, implying that the anisotropy is produced by the alignment of the vertical cracks in the crust induced by the compressive stresses. In Kanto, Kii Peninsula and Kyushu regions, the results from the deep events suggest a contribution from the mantle wedge anisotropy. Events from all groups beneath Kanto show NW, NE and EW fast directions. This complex pattern seems to be produced by the corner flows induced by both the WNW PAC plate subduction and the oblique NNW PHS slab subduction with the associated olivine lattice-preferred orientations (LPOs), and the anisotropy frozen in the PHS slab. The deep events beneath Kii Peninsula show NE and NW fast directions and may be produced by the corner flow produced by the NNW PHS slab subduction with the associated olivine LPOs. The NE directions might also be produced by the segregated melts in the thin layers parallel to the PHS slab subduction. The deep events beneath N Kyushu show NNW fast directions, which may result from the southeastward flow in the upper mantle inferred from the stresses in the upper plate. Results from the deep events beneath middle-south Kyushu show dominantly E–W fast directions, in both the fore- and back-arcs. They may be produced by the corner flow of the westward PHS slab subduction with the olivine LPOs. Because the source regions with multiple fast directions are not resolved in this study, further detailed analyses of shear wave splitting are necessary for a better understanding of the stress state, the induced mantle flow, and the melt-segregation processes.  相似文献   

10.
This paper examines the neotectonic stress field and faulting in the fold-and-thrust belt of the Nepal Himalaya using the 2D finite element technique, incorporating elastic material behavior under plane strain conditions. Three structural cross-sections (eastern, central and western Nepal), where the Main Himalayan Thrust (MHT) has different geometries, are used for the simulation, because each profile is characterized by different seismicity and neotectonic deformation. A series of numerical models are presented in order to understand the influence of a mid-crustal ramp on the stress field and on neotectonic faulting. Results show that compressive and tensional stress fields are induced to the north and south of the mid-crustal ramp, and consequently normal faults are developed in the thrust sheets moving on the mid-crustal ramp. Since the shear stress accumulation along the northern flat of the MHT is entirely caused by the mid-crustal ramp, this suggests that, as in the past, the MHT will be reactivated in a future large (Mw > 8) earthquake. The simulated fault pattern explains the occurrence of several active faults in the Nepal Himalaya. In all models, the distribution of the horizontal σ1 (maximum principal stress) is consistent with the sequence of thrusting observed in the fold-and-thrust belt of the Himalaya. Failure elements around the flat–ramp–flat coincide with the microseismic events in the area, which are believed to release elastic stress partly during interseismic periods.  相似文献   

11.
孙奇  董全杨  蔡袁强  王军  胡秀青 《岩土力学》2015,36(8):2261-2269
利用空心圆柱扭剪仪对饱和砂土进行了应力主轴固定和偏应力比增大（即定向剪切）、偏应力比不变和应力主轴单调旋转（即纯应力主轴单调旋转）、偏应力比和应力主轴偏转角同时增加、偏应力比和应力主轴偏转角分段增加4个系列的排水剪切试验,着重分析不同应力路径下饱和砂土的变形特性及主应力和主应变增量方向变化规律。试验结果表明,纯应力主轴单调旋转下,主应力增量方向在45°～135°范围内变化,主应变增量方向逐渐偏向主应力方向;偏应力比和应力主轴偏转角同时增加下,砂土变形不断增大,当主应力增量方向 45°时,主应变增量方向与主应力增量方向基本一致,但当 45°时,主应变增量方向逐渐偏离主应力增量方向。当应力状态在偏应力比 0.75、应力主轴偏转角 45°范围内时,体应变、最大剪应变与应力路径无关,且后期纯应力主轴旋转下砂土变形不受前期加载历史的影响。  相似文献   

12.
True triaxial shear tests have been performed to determine the peak shear strengths of tension-induced fractures in three Thai sandstones. A polyaxial load frame is used to apply mutually perpendicular lateral stresses (σp and σo) to the 76 × 76 × 126 mm rectangular block specimens. The normal to the fracture plane makes an angle of 59.1° with the axial (major principal) stress. Results indicate that the lateral stress that is parallel to the fracture plane (σp) can significantly reduce the peak shear strength of the fractures. Under the same normal stress (σn) the fractures under high σp dilate more than those under low σp. According to the Coulomb criterion, the friction angle decreases exponentially with increasing σp/σo ratio and the cohesion decreases with increasing σp. The lateral stress σp has insignificant effect on the basic friction angle of the smooth saw-cut surfaces. The fracture shear strengths under σp = 0 correlate well with those obtained from the direct shear tests. It is postulated that when the fractures are confined laterally by σp, their asperities are strained into the aperture, and are sheared off more easily compared to those under unconfined condition.  相似文献   

13.
A consistent methodology based on the critical state framework to characterize the different regimes of fine-grained soil behavior under earthquake loads is put forward. Shear strength and deformation behavior of soils depend in a major way on the combination of volume and confining stress. Depending on their combination, a soil aggregate may fracture into clastic debris, fail with fault planes, or yield plastically. This characterization of the class of limiting soil behavior is used to analyze the potential for large deformation and liquefaction in fine grained soils. The central piece of the proposed characterization is the (η, LI5) stability diagram where η = q/p′ and LI5 = LI + 0.5 log (p′/5). This diagram captures the effects of soil plasticity through liquidity index LI, confinement through mean normal effective stress p′, and shear stress q through the stress ratio η. The three regions of behavior; fracture, fault, and fold/yield are identified. Soils become susceptible to liquefaction when they shift into the fracture zone (LI5 ≤ 0.4), or if they plot outside of the stable yielding region.Under earthquake loading, the initial soil states will migrate into different regions in the stability diagram depending on their initial location, shear stress increment, and, pore pressure response. The final position of the soil state would dictate the type of limiting behavior expected in the field; fracture, rupture or yield. The final states which fall into the fracture region have the potential for catastrophic failures including “liquefaction”; the ones which fall onto the rupture region would experience the attainment of a peak stress ratio followed by softening along failure planes; the ones in the yield region would continue to yield in a stable manner. The latter two types of deformations while resulting in large deformation may not be of a catastrophic nature. The proposed characterization is used to examine the liquefaction susceptibility of fine grained soils from China, Taiwan, and Turkey. Use of simplified empirical criteria based on parameters such as plasticity index and fines contents may not capture the true nature of the type of undrained limiting behavior of fine grains soils in the field including liquefaction.  相似文献   

14.
The Linzizong Group (64–44 Ma) of the Lhasa Terrane in Tibet is critically positioned for establishing the paleoposition of the southern leading edge of the Asian continent during Paleogene times and constraining onset of the India–Asia collision. Here we report paleomagnetic results from a collection comprising 384 drill-core samples from 34 sites embracing all three formations of this group. Comprehensive demagnetization and field tests isolate characteristic remanent magnetizations (ChRM) summarized by overall tilt-corrected formation-mean directions of D = 183.6°, I = −12.4° (α95 = 8.1°) for the Dianzhong (64–60 Ma), D = 1.0°, I = 18.1° (α95 = 8.1°) for the Nianbo (60–50 Ma), and D = 12.4°, I = 23.2° (α95 = 7.3°) for the Pana (50–44 Ma). Fold tests are positive in each formation suggesting a pre-folding origin and we interpret the magnetizations as quasi-primary and acquired at, or slightly later than, formation of the Linzizong Group. Revised Paleogene paleopoles with Ar–Ar age constraints for the Lhasa Terrane indicate that onset of the India–Asia collision occurred no later than ∼60.5 ± 1.5 Ma at a low paleolatitude of ∼10°N. Analysis of 60 site-mean observations from a range of studies of the Pana Formation in the higher part of the succession highlight a large dispersion of ChRM directions; a number of possible causes are suggested but further study of this formation over a wider area is required to resolve this issue.  相似文献   

15.
《Comptes Rendus Geoscience》2019,351(2-3):113-120
A polycrystalline specimen of liebermannite [KAlSi3O8 hollandite] was synthesized at 14.5 GPa and 1473 K using glass starting material in a uniaxial split-sphere apparatus. The recovered specimen is pure tetragonal hollandite [SG: I4/m] with bulk density of within 98% of the measured X-ray value. The specimen was also characterized by Raman spectroscopy and nuclear magnetic resonance spectroscopy. Sound velocities in this specimen were measured by ultrasonic interferometry to 13 GPa at room T in a uniaxial split-cylinder apparatus using Al2O3 as a pressure marker. Finite strain analysis of the ultrasonic data yielded KS0 = 145(1) GPa, K0′ = 4.9(2), G0 = 92.3(3) GPa, G0′ = 1.6(1) for the bulk and shear moduli and their pressure derivatives, corresponding to VP0 = 8.4(1) km/s, VS0 = 4.9(1) km/s for the sound wave velocities at room temperature. These elasticity data are compared to literature values obtained from static compression experiments and theoretical density functional calculations.  相似文献   

16.
《Gondwana Research》2009,15(4):644-662
The integration of new and published geochronologic data with structural, magmatic/anatectic and pressure–temperature (P–T) process information allow the recognition of high-grade polymetamorphic granulites and associated high-grade shear zones in the Central Zone (CZ) of the Limpopo high-grade terrain in South Africa. Together, these two important features reflect a major high-grade D3/M3 event at ~ 2.02 Ga that overprinted the > 2.63 Ga high-grade Neoarchaean D2/M2 event, characterized by SW-plunging sheath folds. These major D2/M2 folds developed before ~ 2.63 Ga based on U–Pb zircon age data for precursors to leucocratic anatectic gneisses that cut the high-grade gneissic fabric. The D3/M3 shear event is accurately dated by U–Pb monazite (2017.1 ± 2.8 Ma) and PbSL garnet (2023 ± 11 Ma) age data obtained from syntectonic anatectic material, and from sheared metapelitic gneisses that were completely reworked during the high-grade shear event. The shear event was preceded by isobaric heating (P = ~ 6 kbar and T = ~ 670–780 °C), which resulted in the widespread formation of polymetamorphic granulites. Many efforts to date high-grade gneisses from the CZ using PbSL garnet dating resulted in a large spread of ages (~ 2.0–2.6 Ga) that reflect the polymetamorphic nature of these complexly deformed high-grade rocks.  相似文献   

17.
The Longquan–Shan fault and the Huya fault are two major neighboring faults of the Longmen–Shan fault zone where the 12 May 2008 Wenchuan earthquake (Mw 7.9) occurred. To study the influence of the Wenchuan event on these two active faults, we calculate changes of Coulomb stress on the Longquan–Shan fault and the Huya fault caused by the Wenchuan mainshock. Our results indicate that the Coulomb stress in the northern section (Zone A) of the Longquan–Shan fault is increased by 0.07–0.10 bars, that in the middle section (Zone B) by 0.04–0.11 bars, and that in the southern section (Zone C) shows almost no change. For the Huya fault, the Coulomb stress is decreased by 0.01–0.03 bars in the northern section (Zone A), 0.10–0.35 bars in the middle section (Zone B), and nearly 0.5 bars in the southern section (Zone C). The epicenter distribution of small earthquakes (ML ⩾ 1.5) on the Longquan–Shan fault and the Huya fault after the Wenchuan earthquake is consistent with the distribution of the Coulomb stress change. This implies that the Wenchuan earthquake may have triggered small events on the Longquan–Shan fault, but inhibited those on the Huya fault. We then use the rate/state friction law to calculate the occurrence probability of future earthquakes in the study region for the next decade. They include the distribution of b-values, magnitude of completeness (Mc), the background seismicity rate, a value of Aσn and the duration for the transient effect (ta) in the study region. We also estimate the earthquake occurrence probabilities on the neighboring faults after the Wenchuan earthquake. Our results show that, the occurrence probability of future earthquakes in the Longquan–Shan has a slight increase, being 7% for M ⩾ 5.0 shocks during the next decade, but the earthquake probability in the Huya region is reduced obviously, being 5–20%, 7–26% and 3–9% for M ⩾ 5.0 shocks during the next decade in sections A, B and C of the Huya fault, respectively.  相似文献   

18.
The study area lies between latitude 18–26°N and longitude 73–83°E, and mainly covers the Central India Tectonic Zone (CITZ). The frequency-dependent shear wave quality factor (Qs) has been estimated over the CITZ and its surroundings using Double Spectral Ratio (DSR) method. We have considered 25 local earthquakes with magnitude (ML) varies from 3.0 to 4.7 recorded at 11 stations running under national seismic network. The Fast Fourier Transformed (FFT) spectra were computed from the recorded waveform having time-window from onset of S-phase to 1.0 s and for a frequency-band of 0.1–10 Hz. Three different shear wave velocities (i.e., 3.87, 3.39 and 3.96 km/s) were obtained over the study area based on a pair of earthquakes recorded at a pair of stations. The low Qs values of 51–96 at 1 Hz (i.e., Qs = 51f0.49; Qs = 90f0.488 and Qs = 96f0.53) were found in the area covering the Son–Narmada–Tapti (SONATA) lineament, CITZ, eastern part of the Satpura fold belt, Vindhyan and Gondwana basins, Godavari and Mahanadi grabens, and southern part of Gangetic plain. Intermediate Qs values of the order of 204–277 (i.e., Qs = 204f0.56 and Qs = 277f0.55) were noted in the cartonic areas, namely, Bundelkhand, Dharwar-Bhandara and Bastar. While the higher Qs values of 391–628 at 1 Hz (i.e., Qs = 391f0.49, Qs = 409f0.48, Qs = 417f0.48, Qs = 500f0.66, Qs = 585f0.65 and Qs = 628f0.69) were found in the eastern part of the SONATA, CITZ, and the northeastern part of the Satpura fold belt. The low Qs values might be attributing to the more heterogeneous SONATA rift system. Low Qs values further may presumably be associated with lower-level of seismicity and apparently account for higher tectonic stress accumulation over long duration. The long-term accumulated stress is generally released through occasional triggering of moderate magnitude earthquakes in the SONATA zone. Surrounding the SONATA region, the higher Qs values possibly accounts for a more homogeneous subsurface structure along the SONATA zone.  相似文献   

19.
《Earth》2007,80(1-2):75-109
The soil's resistance to concentrated flow erosion is an important factor for predicting rill and (ephemeral) gully erosion rates. While it is often treated as a calibration parameter in process-based soil erosion models, global change studies require the estimation of erosion resistance from measurable soil properties. Several laboratory and field experiments have been conducted to determine the erosion resistance of various types of soils, but no attempts have been made hitherto to summarize all these data and to explore them for general trends. In this study, all available data on the resistance of topsoils to concentrated flow erosion in terms of channel erodibility (Kc) and critical shear stress (τcr) has been collected together with all soil and environmental properties reported in literature to affect the soil erosion resistance. Reported Kc values for cropland topsoils range between 0.002 10− 3 s m− 1 and 250 10− 3 s m− 1 (n = 470), whereas τcr values range between 0 and 15 Pa (n = 522). It is demonstrated that so far, the heterogeneity of measurement methods, the lack of standardized definitions and the shortcomings of the flow shear stress model hamper the comparability of soil erosion resistance values from different datasets. Nevertheless, combining Kc and τcr data from different datasets, a general soil erosion resistance ranking for different soil textures can be proposed. The compiled dataset also reveals that tillage practices clearly affect Kc (Kc for conventional tillage > Kc for reduced tillage > Kc for no tillage) but not τcr.It was concluded that Kc and τcr are not related to each other and that soil and macro-environmental properties affecting the foremost do not necessarily affect the latter as well and vise versa. Often Kc seems to be a more appropriate parameter than τcr to represent the differences in soil erosion resistance under various soil and environmental conditions (e.g. bulk density, moisture content, consolidation, tillage). The two parameters represent different quantities and are therefore both needed to characterize the soil's resistance to concentrated flow erosion.  相似文献   

20.
The 10 June 2012 Mw 6.0 aftershock sequence in southwestern Anatolia is examined. Centroid moment tensors for 23 earthquakes with moment magnitudes (Mw) between 3.7 and 6.0 are determined by applying a waveform inversion method. The mainshock is a shallow focus strike-slip with reverse component event at a depth of 30 km. The seismic moment (Mo) of the mainshock is estimated as 1.28 × 1018 Nm and rupture duration of the Fethiye mainshock is 38 s. The focal mechanisms of the aftershocks are mainly strike-slip faulting with a reverse component. The geometry of the focal mechanisms reveals a strike-slip faulting regime with NE–SW trending direction of T-axis in the entire activated region. A stress tensor inversion of focal mechanism data is performed to obtain a more accurate picture of the Fethiye earthquake stress field. The stress tensor inversion results indicate a predominant strike-slip stress regime with a NW–SE oriented maximum horizontal compressive stress (SH). According to variance of the stress tensor inversion, to first order, the Fethiye earthquake area is characterized by a homogeneous interplate stress field. The Coulomb stress change associated with the mainshock and the largest aftershock are also investigated to evaluate any significant enhancement of stresses along the Gulf of Fethiye and surrounding region. Positive lobes with stress more than 0.4 bars are obtained, indicating that these values are large enough to increase the Coulomb stress failure towards NNW–SSE and E–W directions.  相似文献   

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