End effects on stress dependent permeability measurements     

R.I. Korsnes  R. Risnes  I. Faldaas  T. Norland 《Tectonophysics》2006,426(1-2):239

Permeability changes have been studied under deviatoric stresses for chalk cores and under both hydrostatic- and deviatoric stresses for sandstone cores at room temperature. To avoid end effects in the triaxial cell, caused by friction between the axial steel pistons and the sample, the cell was modified to have pressure outlets from the mid-section of the sample with pressure tubes connected to the outside of the cell for pressure recording. Both permeabilities over the mid-section and over the total core were determined during the action of stresses. The chalk cores with permeability in the range of 1–3 × 10^− 15 m² and porosity of about 40–45% were flooded with methanol, while the sandstone cores with permeability values varying from 8 to 100 × 10^− 15 m² and porosity of about 30% were flooded with a mineral oil. Major observations were:

(1) For the chalk cores, 4 out of 8 samples showed a mid-section permeability with a factor of 1.2 to 1.4 higher than the overall permeability, the remaining 4 samples did not show differences in permeability values taking into account the error on measurements.

(2) For the sandstone samples, the mid-section permeability was a factor of 1.2 to 2.4 higher than the overall permeability.

(3) In all cases during the deviatoric phase, the change in permeability was rather small, even if the tests were run beyond the yield point.

(4) The permeability generally decreased with increasing hydrostatic stresses.

Density-dependent hydromechanical behaviour of a compacted expansive soil     

Hossein Nowamooz  Farimah Masrouri 《Engineering Geology》2009,106(3-4):105-115

To further our knowledge of the coupling between the hydraulic and mechanical behaviours of the swelling soils, this paper presents an experimental study on a bentonite/silt mixture using an osmotic odometer. A loading/unloading cycle was applied to samples with different initial dry densities (1.27, 1.48, and 1.55 Mg m^− 3) at different constant suctions (0, 2, and 8 MPa). We noted that the initial state of the soils after compaction significantly influenced the values of the apparent preconsolidation stress p₀(s), the virgin compression index λ(s), and the elastic compression index κ.These experimental results provided a sufficient database to interpret the mechanical behaviour of the swelling soil and define three yielding surfaces:

– the suction limit between micro- and macrostructure (s_m/M) and the suction limit between nano- and microstructure (s_n/m), which depend completely on the soil fabrics and the diameter separating the nano-, micro-, and macrostructure,

– the Loading Collapse (LC) curve, representing the preconsolidation stress variation as a function of suction,

– the Saturation Curve (SC), representing the variation of the saturation stress (P_sat) as a function of suction.

In general, we can state that the increase of compaction pressure unified the LC and SC surfaces and decreased the (s_m/M) value without modifying the (s_n/m) value.  相似文献   

Analysis of crustal deformation in Luzon, Philippines using geodetic observations and earthquake focal mechanisms   总被引：1，自引：0，他引：1  

Gerald Galgana  Michael Hamburger  Robert McCaffrey  Ernesto Corpuz  Qizhi Chen 《Tectonophysics》2007,432(1-4):63-87

We utilize regional GPS velocities from Luzon, Philippines, with focal mechanism data from the Harvard Centroid Moment Tensor (CMT) Catalog, to constrain tectonic deformation in the complex plate boundary zone between the Philippine Sea Plate and Eurasia (the Sundaland block). Processed satellite imagery and digital elevation models are used with existing gravity anomaly, seismicity, and geologic maps to define a suite of six elastic blocks. Geodetic and focal mechanism data are inverted simultaneously to estimate plate rotations and fault-locking parameters for each of the tectonic blocks and faults comprising Luzon. Major tectonic structures that were found to absorb the plate convergence include the Manila Trench (20–100 mm yr^− 1) and East Luzon Trough ( 9–15 mm yr^− 1)/Philippine Trench ( 29–34 mm yr^− 1), which accommodate eastward and westward subduction beneath Luzon, respectively; the left-lateral strike-slip Philippine Fault ( 20–40 mm yr^− 1), and its northward extensions, the Northern Cordillera Fault ( 17–37 mm yr^− 1 transtension), and the Digdig Fault ( 17–27 mm yr^− 1 transpression). The Macolod Corridor, a zone of active volcanism, crustal thinning, extension, and extensive normal and strike-slip faulting in southwestern Luzon, is associated with left-lateral, transtensional slip of  5–10 mm yr^− 1. The Marikina Fault, which separates the Central Luzon block from the Southwestern Luzon block, reveals  10–12 mm yr^− 1 of left-lateral transpression. Our analysis suggests that much of the Philippine Fault and associated splays are locked to partly coupled, while the Manila and Philippine trenches appear to be poorly coupled. Luzon is best characterized as a tectonically active plate boundary zone, comprising six mobile elastic tectonic blocks between two active subduction zones. The Philippine Fault and associated intra-arc faults accommodate much of the trench-parallel component of relative plate motion.  相似文献   

Tectonic plate motion and deformation inferred from very long baseline interferometry   总被引：1，自引：0，他引：1  

Kachishige Sato   《Tectonophysics》1993,220(1-4):69-87

We inverted 76 rates of change of baseline lengths measured with very long baseline interferometry (VLBI) during the period 1979–1989 to estimate the parameters of motions of the North American (noam) and Eurasian (eura) plates relative to the Pacific (pcfc) plate. We considered two types of plate motion models, namely, rigid and non-rigid models. In the non-rigid models, we simultaneously determined the non-rigid motions of several stations near plate boundaries due to intraplate deformation. Intraplate deformation in the regions far away from plate boundaries is assumed to be negligible.Among several models considered, a non-rigid model called M2 is found to fit most closely to the observed data. In this model, six stations are assumed to be capable of the non-rigid motion; those are goldvenu, hatcreek, mojave12, ovro 130 and vndnberg, in the southwestern United States and kashima, in Japan. M2 gives parameter sets of 0.827 ± 0.035°/m.y., about 50.5 ± 1.2°N, 78.5 ± 5.3°W and 0.889 ± 0.049°/m.y., about 59.7 ± 1.9°N, 85.1 ± 7.4 °W, representing the noam-pcfc and eura-pcfc relative motions. The plate motion parameters of M2 are nearly identical to those of the newest global-scale plate motion model nuvel-1. The noam-pcfc and eura-pcfc rotation rates of M2 respectively deviate only 0.044°/m.y. and 0.010°/m.y. from those of nuvel-1 (these deviations are only about 6% and 1%, respectively, of the rotation rates themselves). The noam-pcfc and eura-pcfc poles of M2 both lie only 2° from those of nuvel-1 (within a 2σ error ellipse of each pole). nuvel-1 is determined from spreading rates at mid-ocean ridges, azimuths of transform faults and earthquake slip vectors. Since the spreading rates are estimated from marine magnetic anomalies integrated over a geological timescale, nuvel-1 gives the plate motions averaged over this timescale. Thus, we may conclude that there is no appreciable difference between the plate motions averaged over a geological timescale (millions of years) and those in a recent short period ( ~ 10 yr).M2 also gives the horizontal non-rigid motions of VLBI stations in the southwestern United States at rates of 6–9 mm/yr and roughly in opposite direction to the rigid motion of each station associated with plate motion. hatcreek, located near the northern part of the Basin and Range Province (B&R), also shows additional westward motion of about 9 mm/yr, suggesting crustal stretching in the northern B&R. The US VLBI stations show subsidence at rates of about 5–7 mm/yr, except for goldvenu and ovro 130, whose subsidence is negligible. The Japanese VLBI station, kashima, has a horizontal non-rigid motion of about 20 mm/yr in the west-northwest direction, roughly opposite to the direction of the rigid motion. kashima also shows subsidence at a rate of about 12 mm/yr, which is larger than that deduced from geodetic data but consistent with the result from GPS.  相似文献   

Lithospheric flexure, uplift and expected horizontal strain rate in the Pannonian Carpathian region     

Alessandro Caporali   《Tectonophysics》2009,474(1-2):337

The Apuseni Mountains are located between the Pannonian Basin and the Transylvanian Basin along a direction of SE convergence with the Carpathian belt. A flexural model based on the cylindrical bending of a semi-infinite, isostatically supported, thin elastic plate is here examined with the Apuseni playing the role of flexural bulge, and under the assumption that the plate is deforming under the action of a vertical shear force and a bending moment applied at the end of the plate, beneath the Carpathians. The model yields estimates of the plate thickness ranging between 13 and 14.5 km, depending on the assumed density contrast between crust/sediments and mantle providing buoyancy. The vertical shear force which is necessary to bend the plate is in the range between 60 and 300 × 10¹¹ N m^− 1, depending on the assumed density contrast. This force is shown to be modelled by a gravitational ‘slab pull’ force, using model parameters derived from seismic tomography. If the height of the flexural bulge, after correction for erosion, is allowed to increase, the model yields an estimate of the horizontal strain rate at the top of the bulge. For example, 5 mm/yr vertical change of the flexural bulge of a 14 km thick plate results in a horizontal deformation rate of approximately 7 nanostrain/yr at the top of the bulge, a value which is at the threshold of sensitivity of continuous GPS measurements. Different vertical rates will change the horizontal strain rate almost proportionally.  相似文献   

Insights into Wasatch fault vertical slip rates using the age of sediments in Timpanogos Cave, Utah     

Alan L. Mayo  Jiri Bruthans  David Tingey  Jaroslav Kadlec  Steve Nelson 《Quaternary Research》2009,72(2):275-283

Timpanogos Cave, located near the Wasatch fault, is about 357 m above the American Fork River. Fluvial cave sediments and an interbedded carbonate flowstone yield a paleomagnetic and U–Th depositional age of 350 to 780 ka. Fault vertical slip rates, inferred from calculated river downcutting rates, range between 1.02 and 0.46 mm yr^− 1. These slip rates are in the range of the 0–12 Ma Wasatch Range exhumation rate ( 0.5–0.7 mm yr^− 1), suggesting that the long-term vertical slip rate remained stable through mid-Pleistocene time. However, the late Pleistocene (0–250 ka) decelerated slip rate ( 0.2–0.3 mm yr^− 1) and the accelerated Holocene slip rate ( 1.2 mm yr^− 1) are consistent with episodic fault activity. Assuming that the late Pleistocene vertical slip rate represents an episodic slowing of fault movement and the long-term (0–12 Ma) average vertical slip rate, including the late Pleistocene and Holocene, should be  0.6 mm yr^− 1, there is a net late Pleistocene vertical slip deficit of  50–75 m. The Holocene and late Pleistocene slip rates may be typical for episodes of accelerated and slowed fault movement, respectively. The calculated late Pleistocene slip deficit may mean that the current accelerated Wasatch fault slip rate will extend well into the future.  相似文献   

Age estimates of coastal terraces in the Andaman and Nicobar Islands and their tectonic implications     

Kusala Rajendran  C.P. Rajendran  Anil Earnest  G.V. Ravi Prasad  K. Dutta  D.K. Ray  R. Anu 《Tectonophysics》2008,455(1-4):53-60

The great Indian Ocean earthquake of December 26, 2004 caused significant vertical changes in its rupture zone. About 800 km of the rupture is along the Andaman and Nicobar Islands, which forms the outer arc ridge of the subduction zone. Coseismic deformation along the exposed land could be observed as uplift/subsidence. Here we analyze the morphological features along the coast of the Andaman and Nicobar Islands, in an effort to reconstruct the past tectonics, taking cues from the coseismic effects. We obtained radiocarbon dates from coastal terraces of the island belt and used them to compute uplift rates, which vary from 1.33 mm yr^− 1 in the Little Andaman to 2.80 mm yr^− 1 in South Andaman and 2.45 mm yr^− 1 in the North Andaman. Our radiocarbon dates converge on  600 yr and  1000 yr old coastal uplifts, which we attribute to the level changes due to two major previous subduction earthquakes in the region.  相似文献   

Kinematics of the Iberia–Maghreb plate contact from seismic moment tensors and GPS observations   总被引：2，自引：0，他引：2  

Daniel Stich  Enrico Serpelloni  Flor de Lis Mancilla  Jose Morales 《Tectonophysics》2006,426(3-4):295-317

The Iberian Peninsula and the Maghreb experience moderate earthquake activity and oblique,  NW–SE convergence between Africa and Eurasia at a rate of  5 mm/yr. Coeval extension in the Alboran Basin and a N35°E trending band of active, left-lateral shear deformation in the Alboran–Betic region are not straightforward to understand in the context of regional shortening, and evidence complexity of deformation at the plate contact. We estimate 86 seismic moment tensors (M_W 3.3 to 6.9) from time domain inversion of near-regional waveforms in an intermediate period band. Those and previous moment tensors are used to describe regional faulting style and calculate average stress tensors. The solutions associated to the Trans-Alboran shear zone show predominantly strike-slip faulting, and indicate a clockwise rotation of the largest principal stress orientation compared to the regional convergence direction (σ₁ at N350°E). At the N-Algerian and SW-Iberian margins, reverse faulting solutions dominate, corresponding to N350°E and N310°E compression, respectively. Over most of the Betic range and intraplate Iberia, we observe predominately normal faulting, and WSW–ENE extension (σ₃ at N240°E). From GPS observations we estimate that more than 3 mm/yr of African (Nubian)–Eurasian plate convergence are currently accommodated at the N-Algerian margin,  2 mm/yr in the Moroccan Atlas, and  2 mm/yr at the SW-Iberian margin. 2 mm/yr is a reasonable estimate for convergence within the Alboran region, while Alboran extension can be quantified as  2.5 mm/yr along the stretching direction (N240°E). Superposition of both motions explains the observed left-lateral transtensional regime in the Trans-Alboran shear zone. Two potential driving mechanisms of differential motion of the Alboran–Betic–Gibraltar domain may coexist in the region: a secondary stress source other than plate convergence, related to regional-scale dynamic processes in the upper mantle of the Alboran region, as well as drag from the continental-scale motion of the Nubian plate along the southern limit of the region. In the Atlantic Ocean, the  3.5 mm/yr, westward motion of the Gibraltar Arc relative to intraplate Iberia can be accommodated at the transpressive SW-Iberian margin, while available GPS observations do not support an active subduction process in this area.  相似文献   

Role of strike-slip faults in the Betic-Rifian orogeny   总被引：1，自引：0，他引：1  

D. Leblanc  Ph. Olivier 《Tectonophysics》1984,101(3-4)

A new model for the Betic-Rifian orogeny of the Western Mediterranean (Spain and North Africa) is proposed in which four strike-slip faults play an important role; the faults are not of the same age. Two faults, the left-lateral Jebha fault to the south (in Morocco and principally in the Mediterranean Sea) and the right-lateral North Betic fault (southern Spain) to the north, define the boundaries of the Alboran block (Betic and Rifian internal zones). Final movement along these faults was during the Burdigalian time. Two other faults, the left-lateral Nekor fault (North Africa) to the south of the Jebha fault and the right-lateral Crevillente fault, somewhat to the north of the North Betic fault, define a larger Alboran block (including part of the Betic and Rifian external zones) that was present during the Tortonian.The following sequence of events is proposed:

1. (a) During the Eocene and Oligocene, the African and European plates converged in a N-S sense causing the breakup and overthrusting of the Betic, Rifian and Kabyle internal zones and then the movement towards the WSW of the Alboran block by slip along the Jebha and North Betic faults.

2. (b) By the end of Burdigalian time, movement along the Jebha and North Betic faults ceased.

3. (c) With continued N-S convergence, the Nekor and Crevillente faults, which bound a larger Alboran block, were formed during the mid- and late Miocene. The Arc of Gibraltar (the zone lying between the four major faults) seems to be a result of WSW motion of a crustal block being thrust over external zones.

The model proposed adds to the earlier idea that tectogenesis proceeds from the interior to the exterior of an erogenic belt. In the Betic-Rifian orogeny major strike-slip fracture zones shifted to the exterior of the orogenic belt as the orogeny progressed in order to relieve the stress caused by locking of the more internal faults.  相似文献   

Seismicity, gravity anomalies and lithospheric structure of the Andaman arc, NE Indian Ocean     

M. Radhakrishna  S. Lasitha  Manoj Mukhopadhyay 《Tectonophysics》2008,460(1-4):248-262

The Andaman arc in the northeastern Indian Ocean defines nearly 1100 km long active plate margin between the India and Burma plates where an oblique Benioff zone develops down to 200 km depth. Several east-trending seismologic sections taken across the Andaman Benioff Zone (ABZ) are presented here to detail the subduction zone geometry in a 3-D perspective. The slab gravity anomaly, computed from the 3-D ABZ configuration, is a smooth, long-wavelength and symmetric gravity high of 85 mGal amplitude centering to the immediate east of the Nicobar Island, where, a prominent gravity “high” follows the Nicobar Deep. The Slab-Residual Gravity Anomaly (SRGA) and Mantle Bouguer Anomaly (MBA) maps prepared for the Andaman plate margin bring out a double-peaked SRGA “low” in the range of − 150 to − 240 mGal and a wider-cum-larger MBA “low” having the amplitude of − 280 to − 315 mGal demarcating the Andaman arc–trench system. The gravity models provide evidences for structural control in propagating the rupture within the lithosphere. The plate margin configuration below the Andaman arc is sliced by the West Andaman Fault (WAF) as well as by a set of sympathetic faults of various proportions, often cutting across the fore-arc sediment package. Some of these fore-arc thrust faults clearly give rise to considerably high post-seismic activity, but the seismic incidence along the WAF further east is comparatively much less particularly in the north, although, the lack of depth resolution for many of the events prohibits tracing the downward continuity of these faults. Tectonic correlation of the gravity-derived models presented here tends to favour the presence of oceanic crust below the Andaman–Nicobar Outer Arc Ridge.  相似文献   

Outline of the tectonic evolution of southwestern China     

Fan Pow-Foong 《Tectonophysics》1978,45(4):261-267

  相似文献   

Kinetics of leaching of oxidized and reduced ilmenite in dilute hydrochloric acid solutions     

M.K. Sarker  A.K.M.B. Rashid  A.S.W. Kurny 《International Journal of Mineral Processing》2006,80(2-4):223-228

Ilmenite separated from beach sands of Bangladesh was oxidized for 1 h at 950 °C and then reduced in charcoal for 4 h at 1050 °C. This was followed by leaching in 5% to 15% hydrochloric acid solution in temperature range of 30 to 75 °C for periods of up to 2 h. The results were compared with those obtained by leaching of ilmenite reduced without oxidizing. Oxidation prior to reduction of the ilmenite was found to increase both the extent and the rate of leaching. The residual iron contents after leaching were also found to be lower than that obtained for non-oxidized samples. The kinetic data of leaching of ilmenite reduced after oxidation was found to follow first order reaction model, i.e., G(α) = − ln(1 − α) up to an α value of 0.5 (i.e. up to 50% reduction) and then changed to spherical model, i.e., G(α) = [1 − (1 − α)]³. On the other hand, leaching of ilmenite reduced without oxidizing was found to follow the Ginstling-Brounshtein reaction, i.e., G(α) = 1 − (2/3)α − (1 − α)^2/3 throughout the leaching process. Oxidation of ilmenite prior to reduction was also found to have decreased the activation energy of leaching from 43 kJ/mol, found for samples leached after reduction without oxidizing, to 30 kJ/mol.  相似文献   

Possible effects of collisions on plate motions     

Makoto Yamano  Seiya Uyeda 《Tectonophysics》1985,119(1-4)

A large-scale collision at a plate boundary is expected to play an important role not only in the deformation at the boundary but also in the motion of the plate carrying the buoyant material to be accreted. Possible changes in rates and directions of such motions may be calculated provided that certain assumptions are made about the nature of the driving forces. In this model we shall assume basically that:

1. (1) an oceanic plate is driven by slab pull and ridge push, being resisted by basal asthenospheric drag and slab resistance; and

2. (2) because of detachment, slab pull is lost upon collision.

If, however, the calculated motion following collision has a convergent component at the boundary, a new subduction zone, with an increasing slab pull force, forms seaward of the accreting buoyant material.Calculations were first made on an idealized planar octagonal plate. Results indicated that, so long as the scale of collision is limited, changes in motion take place but the motion returns to the initial state. However, for large-scale collisions, the plate motion suffers a large directional change, which also changes the nature of some boundaries, and hence the motion approaches a new steady-state motion irreversibly. Calculations were then conducted on an idealized Philippine Sea plate on a spherical earth. For a sizable collision along the Taiwan-Philippine-Mindanao boundary, this boundary and perhaps the Bonin-Mariana boundary, may become a transform fault provided that slab pull-ridge push is the driving force. These results provide some support to Uyeda-McCabe model (1983) of episodic spreading of the Philippine Sea basins, as well as the predominance of strike-slip motion along collision boundaries. Finally, in agreement with prior studies, subduction of a ridge system, assumed to have been located along the southwestern rim of the Paleo-Pacific plate, was shown to be consistent with the change in direction of motion of that plate at 43 m.y.B.P.Calculations conducted in this study show that predicted changes are model dependent so that comparisons with observed or inferred motions may be useful as a means of estimating the relative importance of the various potential driving forces.  相似文献   

Models for convergence, subduction and back-arc development: Plate motions, boundary forces, and horizontal temperature gradients: Implications for the driving mechanism     

R.L. Carlson 《Tectonophysics》1983,99(2-4)

Largely because of the wide variety of observational constraints which must be satisfied, the search for a viable driving mechanism is perhaps the most perplexing problem related to plate tectonics. The mechanism must be compatible with the rigid behavior of lithospheric plates, and with a wide range of plate sizes, shapes and motions. It must be consistent with complex configurations of plate boundaries and equally complex boundary interactions, such as the destruction of ridges at subduction zones. The mechanism must produce steady-state relative and absolute plate motions which persist for tens of millions of years, but must also account for sudden dramatic changes. Finally, the plate driving mechanism must be consistent with the non-Newtonian properties of olivine and with the fabrics of upper mantle peridotites.Mounting evidence suggests that plate motions result from forces associated with plate boundaries and that the principal resisting force is drag at the base of the lithosphere, particularly beneath continents Several investigators have suggested that gravitational forces acting on thermally-induced, lateral density variations in the upper mantle are the principal driving forces for plate tectonics. If so, plate motions are ultimately controlled by the temperature distribution in the upper mantle, and plate tectonics represents a state of dynamic equilibrium in which plate motions are both the cause and the consequence of temperature and density variations in the mantle. This concept requires that average absolute plate velocities be predictable from the characteristics of individual plates, and that plates tend to move down horizontal temperature gradients.A simple linear relation which includes contributions from ridge push (RP), slab pull (SP), trench suction (TS) and continental drag (CD): (cm/y) = (2.6 ± 0.4) + (4.8 ± 1.8) RP + (14.3 ± 1.7) SP +(3.5 ± 2.5) TS−(5.1 ±0.7) CD predicts plate velocities with an rms error of 0.44 cm/y, and a correlation coefficient of 0.98. That plate velocities can be accurately predicted from their own boundary configurations and proportions of continental lithosphere is strong evidence that plate motions result from negative buoyancy forces associated with plate boundaries.  相似文献   

East Asia plate tectonics since 15 Ma: constraints from the Taiwan region   总被引：4，自引：0，他引：4  

Jean-Claude Sibuet  Shu-Kun Hsu  Xavier Le Pichon  Jean-Pierre Le Formal  Donald Reed  Greg Moore  Char-Shine Liu   《Tectonophysics》2002,344(1-2)

15 Ma ago, a major plate reorganization occurred in East Asia. Seafloor spreading ceased in the South China Sea, Japan Sea, Taiwan Sea, Sulu Sea, and Shikoku and Parece Vela basins. Simultaneously, shear motions also ceased along the Taiwan–Sinzi zone, the Gagua ridge and the Luzon–Ryukyu transform plate boundary. The complex system of thirteen plates suddenly evolved in a simple three-plate system (EU, PH and PA). Beneath the Manila accretionary prism and in the Huatung basin, we have determined magnetic lineation patterns as well as spreading rates deduced from the identification of magnetic lineations. These two patterns are rotated by 15°. They were formed by seafloor spreading before 15 Ma and belonged to the same ocean named the Taiwan Sea. Half-spreading rate in the Taiwan Sea was 2 cm/year from chron 23 to 20 (51 to 43 Ma) and 1 cm/year from chron 20 (43 Ma) to 5b (15 Ma). Five-plate kinematic reconstructions spanning from 15 Ma to Present show implications concerning the geodynamic evolution of East Asia. Amongst them, the 1000-km-long linear Gagua ridge was a major plate boundary which accommodated the northwestward shear motion of the PH Sea plate; the formation of Taiwan was driven by two simple lithospheric motions: (i) the subduction of the PH Sea plate beneath Eurasia with a relative westward motion of the western end (A) of the Ryukyu subduction zone; (ii) the subduction of Eurasia beneath the Philippine Sea plate with a relative southwestward motion of the northern end (B) of the Manila subduction zone. The Luzon arc only formed south of B. The collision of the Luzon arc with Eurasia occurred between A and B. East of A, the Luzon arc probably accreted against the Ryukyu forearc.  相似文献   

Strength and stability of frictional sliding of gabbro gouge at elevated temperatures   总被引：7，自引：1，他引：7  

Changrong He  Wenming Yao  Zeli Wang  Yongsheng Zhou   《Tectonophysics》2006,427(1-4):217

To investigate the strength of frictional sliding and stability of mafic lower crust, we conducted experiments on oven-dried gabbro gouge of 1 mm thick sandwiched between country rock pieces (with gouge inclined 35° to the sample axis) at slip rates of 1.22 × 10^− 3 mm/s and 1.22 × 10^− 4 mm/s and elevated temperatures up to 615 °C. Special attention has been paid to whether transition from velocity weakening to velocity strengthening occurs due to the elevation of temperature.Two series of experiments were conducted with normal stresses of 200 MPa and 300 MPa, respectively. For both normal stresses, the friction strengths are comparable at least up to 510 °C, with no significant weakening effect of increasing temperature. Comparison of our results with Byerlee's rule on a strike slip fault with a specific temperature profile in the Zhangbei region of North China shows that the strength given by experiments are around that given by Byerlee's rule and a little greater in the high temperature range.At 200 MPa normal stress, the steady-state rate dependence a − b shows only positive values, probably still in the “run-in” process where velocity strengthening is a common feature. With a normal stress of 300 MPa, the values of steady-state rate dependence decreases systematically with increasing temperature, and stick-slip occurred at 615 °C. Considering the limited displacement, limited normal stress applied and the effect of normal stress for the temperatures above 420 °C, it is inferred here that velocity weakening may be the typical behaviour at higher normal stress for temperature above 420 °C and at least up to 615 °C, which covers most of the temperature range in the lower crust of geologically stable continental interior. For a dry mafic lower crust in cool continental interiors where frictional sliding prevails over plastic flow, unstable slip nucleation may occur to generate earthquakes.  相似文献   

Some parameters of rockbursts derived from underground seismological measurements   总被引：2，自引：0，他引：2  

Karel Holub  Vladimír Petro&#x; 《Tectonophysics》2008,456(1-2):67

A total of 240 three-component recordings from 80 rockbursts, which occurred in various coal mines in the Ostrava-Karviná Coal Basin (Czech Republic) between 1993 and 2005, was used to examine the decrease in maximum particle velocities u_i (m/s) with a scaled distance of d = d/√E (m/√J) or d/³√E (m/³√J) and the rate of predominant frequencies of body waves. The energetic span of rockbursts was within the interval of E = 6.2 × 10³ − 5.0 × 10⁸ J, while calculated hypocentral distances d of four underground seismic stations varied from 0.6 to 7 km. The slopes b of regression straight lines for the maximum particle velocities u_i (m/s) of P- and S-waves in the bilogarithmic scale correspond to the values of − 1.004, − 1.297, − 1.183 and − 1.527. The results of the linear regression are as follows:

P_max-waves u_i = 1.184 × 10^− 4 × d^− 1.004 (m/s) (square root scaling)

P_max-waves u_i = 3.055 × 10^− 3 × d^− 1.297 (m/s) (cube root scaling)

S_max-waves u_i = 5.280 × 10^− 4 × d^− 1.183 (m/s) (square root scaling)

S_max-waves u_i = 2.397 × 10^− 2 × d^− 1.527 (m/s) (cube root scaling).

The evaluation of the abovementioned dynamic parameters was based on seismic events data gathered in the database of the regional seismic array, and calculations were carried out either by using special programs applied as part of the automated data processing in the computation center, or by usual linear regression approaches. The aim of the detailed analysis of the maximum particle velocity and predominant frequencies was a) to set up input data from underground seismological observations for laboratory experiments dealing with the comparison of rock mass behaviour under modeled laboratory conditions simulating manifestation of rockbursts, and b) to incorporate particle velocity into the design of support in order to control damage and evident devastation of workings by rockbursts. The investigation of peak particle velocities was based on the recognition that they are the best criterion to assess vibration damage to surface structures and in mines.  相似文献   

Internal structure of the Dead Sea leaky transform (rift) in relation to plate kinematics   总被引：13，自引：0，他引：13  

Zvi Garfunkel 《Tectonophysics》1981,80(1-4):81-108

The structures along the Dead Sea transform (rift) are related to the motions of the Sinai and Arabia plates which border it, and to the irregularities of their boundaries. The total slip was 105 km left-lateral, but the present structures were formed mainly during the last 40 km of slip, which probably occurred in the Plio-Pleistocene. Along the southern half of the transform the strike-slip motion takes place on en-echelon faults. This produces rhomb-shaped grabens or pull-aparts, which are sometimes composite, and in which there is local crustal separation. Thus, much of the transform is “leaky”. These structures occur in a morpho-tectonic “rift-valley” delimited by normal faults, which express a small component of transverse extension. Along a few segments the shape of the transform is such that lateral motion produces local transverse compression. The geometric relations of the structures along the transform define an Eulerian pole of relative plate motions at 32.8° N 22.6° E ± 0.5°. The older motion was somewhat different and is described by a pole located about 5° west of the above. Then the component of transverse extension and crustal separation was much smaller than now, while local transverse compression was more important. The northern half of the Dead Sea transform has an irregular shape, and the bordering plates did not remain rigid as lateral motion continued. Here transverse compression is often important.  相似文献   

Gondwana breakup via double-saloon-door rifting and seafloor spreading in a backarc basin during subduction rollback   总被引：1，自引：0，他引：1  

A.K. Martin   《Tectonophysics》2007,445(3-4):245-272

A model has been developed where two arc-parallel rifts propagate in opposite directions from an initial central location during backarc seafloor spreading and subduction rollback. The resultant geometry causes pairs of terranes to simultaneously rotate clockwise and counterclockwise like the motion of double-saloon-doors about their hinges. As movement proceeds and the two terranes rotate, a gap begins to extend between them, where a third rift initiates and propagates in the opposite direction to subduction rollback. Observations from the Oligocene to Recent Western Mediterranean, the Miocene to Recent Carpathians, the Miocene to Recent Aegean and the Oligocene to Recent Caribbean point to a two-stage process. Initially, pairs of terranes comprising a pre-existing retro-arc fold thrust belt and magmatic arc rotate about poles and accrete to adjacent continents. Terrane docking reduces the width of the subduction zone, leading to a second phase during which subduction to strike-slip transitions initiate. The clockwise rotated terrane is caught up in a dextral strike-slip zone, whereas the counterclockwise rotated terrane is entrained in a sinistral strike-slip fault system. The likely driving force is a pair of rotational torques caused by slab sinking and rollback of a curved subduction hingeline.By analogy with the above model, a revised five-stage Early Jurassic to Early Cretaceous Gondwana dispersal model is proposed in which three plates always separate about a single triple rift or triple junction in the Weddell Sea area. Seven features are considered diagnostic of double-saloon-door rifting and seafloor spreading:

i) earliest movement involves clockwise and counterclockwise rotations of the Falkland Islands Block and the Ellsworth Whitmore Terrane respectively;

ii) terranes comprise areas of a pre-existing retro-arc fold thrust belt (the Permo-Triassic Gondwanide Orogeny) attached to an accretionary wedge/magmatic arc; the Falklands Islands Block is initially attached to Southern Patagonia/West Antarctic Peninsula, while the Ellsworth Whitmore Terrane is combined with the Thurston Island Block;

iii) paleogeographies demonstrate rifting and extension in a backarc environment relative to a Pacific margin subduction zone/accretionary wedge where simultaneous crustal shortening occurs;

iv) a ridge jump towards the subduction zone from east of the Falkland Islands to the Rocas Verdes Basin evinces subduction rollback;

v) this ridge jump combined with backarc extension isolated an area of thicker continental crust — The Falkland Islands Block;

vi) well-documented EW oriented seafloor spreading anomalies in the Weddell Sea are perpendicular to the subduction zone and propagate in the opposite direction to rollback;

vii) the dextral strike-slip Gastre and sub-parallel faults form one boundary of the Gondwana subduction rollback, whereas the other boundary may be formed by inferred sinistral strike-slip motion between a combined Thurston Island/Ellsworth Whitmore Terrane and Marie Byrd Land/East Antarctica.

Finite-fault slip models for the 15 April 1979 (M_w 7.1) Montenegro earthquake and its strongest aftershock of 24 May 1979 (M_w 6.2)     

Christoforos Benetatos  Anastasia Kiratzi   《Tectonophysics》2006,421(1-2):129-143

We revisit the April 1979 Montenegro earthquake sequence to invert for finite-fault slip models for the mainshock of 15 April 1979 (M_w 7.1) and of the strongest aftershock of 24 May 1979 (M_w 6.2) using P, SH and SV waveforms, retrieved from IRIS data center. We also used body waveform modelling inversion to confirm the focal mechanism of the mainshock as a pure thrust mechanism and rule out the existence of considerable strike slip component in the motion. The mainshock occurred along a shallow (depth 7 km), low angle (14°) thrust fault, parallel to the coastline and dipping to the NE. Our preferred slip distribution model for the mainshock indicates that rupture initiated from SE and propagated towards NW, with a speed of 2.0 km/s. Moment was released in a main slip patch, confined in an area of L  50 km × W  23 km. The maximum slip ( 2.7 m) occurred  30 km to the NW of the hypocenter (location of rupture initiation). The average slip is 49 cm and the total moment release over the fault is 4.38e19 Nm. The slip model adequately fits the distribution of the M_w ≥ 4.3 aftershocks, as most of them are located in the regions of the fault plane that did not slip during the mainshock. The 24 May 1979 (M_w 6.2) strongest aftershock occurred  40 km NW of the mainshock. Our preferred slip model for this event showed a characteristic two-lobe pattern, where each lobe is  7.5 × 7.5 km². Rupture initiated in the NW lobe, where the slip obtained its maximum value of 45 cm, very close to the hypocenter, and propagated towards the south-eastern lobe where it reached another maximum value — for this lobe — of 30 cm, approximately 10 km away from the hypocenter. To indirectly validate our slip models we produced synthetic PGV maps (Shake maps) and we compared our predictions with observations of ground shaking from strong motion records. All comparisons were made for rock soil conditions and in general our slip models adequately fit the observations especially at the closest stations where the shaking was considerably stronger. Through the search of the parameter space for our inversions we obtained an optimum location for the mainshock at 42.04°N and 19.21° E and we also observed that better fit to the observations was obtained when the fault was modeled as a blind thrust fault.  相似文献