The permeability of faults within siliciclastic petroleum reservoirs of the North Sea and Norwegian Continental Shelf

Faulting in Middle Jurassic reservoirs occurred at shallow depth during regional extension. Clean sandstones (<15% clay) deformed without significant grain fracturing and permeability reduction. Faults in impure sandstones (15–40% clay) experienced significant syn-deformation compaction and permeability reduction. Enhanced compaction during deeper burial reduced their permeabilities further from an average of 0.05 mD at <2.5 km to 0.001 mD at >4 km. Clay-rich sediments (>40% clay) deformed to produce clay smears with very low permeabilities (<0.001 mD). Faulting in the Rotliegendes occurred at greater depth during both basin extension and inversion. Extensional faulting produced cataclasites with permeability reductions of <10–>10⁶; their permeabilities range from 0.2 to 0.0001 mD and are inversely related to their maximum burial depth. Faults formed or reactivated during inversion experienced permeability increase. These results can be extrapolated to other hydrocarbon reservoirs if differences in stress and temperature history are taken into account.The permeability of most (>80%) faults is not sufficiently low, compared to their wallrock, to retard single-phase fluid flow on a km-scale. Nevertheless, most faults could retard the flow of a non-wetting phase if present at low saturations. It may be necessary to incorporate the two-phase fluid flow properties of fault rocks into reservoir simulators using upscaling or pseudoisation techniques. Fault property data should be calibrated against production data before it can be used confidently.     

Displacement-length scaling relations for faults on the terrestrial planets

Displacement-length (D/L)scaling relations for normal and thrust faults from Mars, and thrust faults from Mercury, for which sufficiently accurate measurements are available, are consistently smaller than terrestrial D/L ratios by a factor of about 5, regardless of fault type (i.e. normal or thrust). We demonstrate that D/L ratios for faults scale, to first order, with planetary gravity. In particular, confining pressure modulates: (1) the magnitude of shear driving stress on the fault; (2) the shear yield strength of near-tip rock; and (3) the Young's (or shear) modulus of crustal rock. In general, all three factors decrease with gravity for the same rock type and pore-pressure state (e.g. wet conditions). Faults on planets with lower surface gravities, such as Mars and Mercury, demonstrate systematically smaller D/L ratios than faults on larger planets, such as Earth. Smaller D/L ratios of faults on Venus and the Moon are predicted by this approach, and we infer still smaller values of D/L ratio for faults on icy satellites in the outer solar system. Collection of additional displacement-length and down-dip height data from terrestrial normal, strike-slip, and thrust faults, located within fold-and-thrust belts, plate margins, and continental interiors, is required to evaluate the influence of fault shape and progressive deformation on the scaling relations for faults from Earth and elsewhere.     

Discrete element modelling of the influence of cover strength on basement-involved fault-propagation folding

A discrete element model is used to investigate the influence of sedimentary cover strength on the development of basement-involved fault-propagation folds. We find that uniformly weak cover best promotes the development of classical, trishear-like fault-related folds showing marked anticlinal thinning and synclinal thickening, with cover dips increasing downwards towards the fault tip. Uniformly strong cover results in more rounded fold forms with only minor hinge thickening/thinning and significant basement fault-propagation into the sedimentary cover. Heterogeneous, layered, cover sequences with marked differences in strength promote the development of more complex and variable fold forms, with a close juxtaposition of brittle and macroscopically ductile features, which diverge from the predictions of simple kinematic models. In these structures the upper layers are often poor indicators of deeper structure. In addition, we find that in layered cover sequences fault-propagation into the cover is a complex process and is strongly buffered by the weaker cover units.     

小江断裂带中段盆地的发育阶段及其与区域构造运动的关系

小江断裂带中段新生代发育的系列盆地，根据其发育阶段可分为始新世—渐新世、上新世—早更新世、中更新世—晚更新世和晚更新世—全新世４个阶段，并根据发育持续性可分为继承性、阶段性、复活性、新生性４种类型。由大比例尺填图所获资料及前人成果，介绍了各阶段盆地的分布特征和成因机制，讨论了盆地发育与区域构造运动、断裂活动的关系     

Processing and interpretation of the gravity field of the East African Rift: implication for crustal extension

Compilation of new and existing gravity data were undertaken to assess the nature of the crust beneath the East African Rift System. Using 3D gravity modeling code crustal model of gravity profiles across two sectors of the rift were computed. The results are discussed in light of the structure of the rift system.The results of the 3D modeling of gravity profiles across the two rift zones revealed northward thinning of the crust. The maximum crustal attenuation occurs beneath the Afar depression, indicating the Afar rift undergoes an intense fragmentation of the crust resulting from faulting and magmatic activity. However, our computed crustal thickness below the Afar depression falls within an upper bound compared to elsewhere below tectonically active rift zones. This can be explained in terms of crustal accretion resulting from an impact of the Afar mantle plume since 30 Ma ago.The residual gravity obtained using high-cut filtering techniques reveals significant density contrast between the northern and southern sectors of the rift. The northern part of the rift is characterized by regular patterns of positive gravity anomalies, which can be interpreted in terms of a zone of crustal thinning through which relatively dense materials have intruded the overlying crust. In contrast, south of the Main Ethiopian Rift, the anomalies are characterized by random patterns and low amplitudes. The along-rift-axis variation in gravity anomalies implies that the style of crustal deformation changed progressively, beginning with regionally distributed crustal deformation, such as the one we observe within the more juvenile and wider southern segment of the rift, to localized deformation within the active and narrow rift zones of the northern sector of the Ethiopian Rift. We suggest that the key parameters controlling along-rift-axis variation in gravity anomalies are the rate of crustal extension, faulting and magmatic activities.     

Sequence of faulting and deformation during the 2000 eruptions of the Usu Volcano, Hokkaido, Japan—interpretation and image analyses of aerial photographs

Significant faulting and deformation of the ground surface has been rarely known during volcanic eruptions. Usu Volcano, Hokkaido, Japan, is a unique example of deformation due to felsic magma intrusion. Usu Volcano has a history of such types of eruptions as phreatic, pumice eruption (Plinian type), pyroclastic flowing and lava doming since 1663. On March 31, 2000, phreatomagmatic to phreatic eruptions took place after 23 years of dormancy in the western piedmont, followed by explosions on the western flank of Usu Volcano. They were associated with significant deformation including faulting and uplift. The eruptions and deformation were continuing up to the end of May 2000.We identified the faulting using total nine sets of aerial photographs taken from before the eruption (March 31, 2000) to more than 1 year (April 27, 2001) after the end of the activity, and traced deformation processes through image processing using aerial photographs. We found that some of the new faults and the associated phreatic eruptions were related to old faults formed during the 1977–1981 eruptive episode.The image processing has revealed that the surface deformation is coincident with the area of faulting forming small grabens and the phreatic explosion vents. However, the faulting and main explosive eruptions did not take place in the highest uplift area, but along the margin. This suggests that the faulting and explosive activities were affected by small feeder channels diverging from the main magma body which caused the highest uplift.     

Late Pleistocene and Holocene paleoseismology of an intraplate seismic zone in a large alluvial valley, the New Madrid seismic zone, Central USA

The New Madrid seismic zone (NMSZ) is an intraplate right-lateral strike-slip and thrust fault system contained mostly within the Mississippi Alluvial Valley. The most recent earthquake sequence in the zone occurred in 1811–1812 and had estimated moment magnitudes of 7–8 (e.g., [Johnston, A.C., 1996. Seismic moment assessment of stable continental earthquakes, Part 3: 1811–1812 New Madrid, 1886 Charleston, and 1755 Lisbon. Geophysical Journal International 126, 314–344; Johnston, A.C., Schweig III, E.S, 1996. The enigma of the New Madrid earthquakes of 1811–1812. Annual Reviews of Earth and Planetary Sciences 24, 339–384; Hough, S.E., Armbruster, J.G., Seeber, L., Hough, J.F., 2000. On the modified Mercalli intensities and magnitudes of the New Madrid earthquakes. Journal of Geophysical Research 105 (B10), 23,839–23,864; Tuttle, M.P., 2001. The use of liquefaction features in paleoseismology: Lessons learned in the New Madrid seismic zone, central United States. Journal of Seismology 5, 361–380]). Four earlier prehistoric earthquakes or earthquake sequences have been dated A.D. 1450 ± 150, 900 ± 100, 300 ± 200, and 2350 B.C. ± 200 years using paleoliquefaction features, particularly those associated with native American artifacts, and in some cases surface deformation ([Craven, J. A. 1995. Paleoseismology study in the New Madrid seismic zone using geological and archeological features to constrain ages of liquefaction deposits. M.S thesis, University of Memphis, Memphis, TN, U.S.A.; Tuttle, M.P., Lafferty III, R.H., Guccione, M.J., Schweig III, E.S., Lopinot, N., Cande, R., Dyer-Williams, K., Haynes, M., 1996. Use of archaeology to date liquefaction features and seismic events in the New Madrid seismic zone, central United States. Geoarchaeology 11, 451–480; Guccione, M.J., Mueller, K., Champion, J., Shepherd, S., Odhiambo, B., 2002b. Stream response to repeated co-seismic folding, Tiptonville dome, western Tennessee. Geomorphology 43(2002), 313–349; Tuttle, M.P., Schweig, E.S., Sims, J.D., Lafferty, R.H., Wolf, L.W., Haynes, M.L., 2002. The earthquake potential of the New Madrid seismic zone, Bulletin of the Seismological Society of America, v 92, n. 6, p. 2080–2089; Tuttle, M.P., Schweig III, E.S., Campbell, J., Thomas, P.M., Sims, J.D., Lafferty III, R.H., 2005. Evidence for New Madrid earthquakes in A.D. 300 and 2350 B.C. Seismological Research Letters 76, 489–501]). The two most recent prehistoric and the 2350 B.C. events were probably also earthquake sequences with approximately the same magnitude as the historic sequence.Surface deformation (faulting and folding) in an alluvial setting provides many examples of stream response to gradient changes that can also be used to date past earthquake events. Stream responses include changes in channel morphology, deviations in the channel path from the regional gradient, changes in the direction of flow, anomalous longitudinal profiles, and aggradation or incision of the channel ([Merritts, D., Hesterberg, T, 1994. Stream networks and long-term surface uplift in the New Madrid seismic zone. Science 265, 1081–1084.; Guccione, M.J., Mueller, K., Champion, J., Shepherd, S., Odhiambo, B., 2002b. Stream response to repeated co-seismic folding, Tiptonville dome, western Tennessee. Geomorphology 43 (2002), 313–349]). Uplift or depression of the floodplain affects the frequency of flooding and thus the thickness and style of vertical accretion or drowning of a meander scar to form a lake. Vegetation may experience trauma, mortality, and in some cases growth enhancement due to ground failure during the earthquake and hydrologic changes after the earthquake ([VanArdale, R.B., Stahle, D.W., Cleaveland, M.K., Guccione, M.J., 1998. Earthquake signals in tree-ring data from the New Madrid seismic zone and implications for paleoseismicity. Geology 26, 515–518]). Identification and dating these physical and biologic responses allows source areas to be identified and seismic events to be dated.Seven fault segments are recognized by microseismicity and geomorphology. Surface faulting has been recognized at three of these segments, Reelfoot fault, New Madrid North fault, and Bootheel fault. The Reelfoot fault is a compressive stepover along the strike-slip fault and has up to 11 m of surface relief ([Carlson, S.D., 2000. Formation and geomorphic history of Reelfoot Lake: insight into the New Madrid seismic zone. M.S. Thesis, University of Arkansas, Fayetteville, Arkansas, U.S.A]) deforming abandoned and active Mississippi River channels ([Guccione, M.J., Mueller, K., Champion, J., Shepherd, S., Odhiambo, B., 2002b. Stream response to repeated co-seismic folding, Tiptonville dome, western Tennessee. Geomorphology 43 (2002), 313–349]). The New Madrid North fault apparently has only strike-slip motion and is recognized by modern microseismicity, geomorphic anomalies, and sand cataclasis ([Baldwin, J.N., Barron A.D., Kelson, K.I., Harris, J.B., Cashman, S., 2002. Preliminary paleoseismic and geophysical investigation of the North Farrenburg lineament: primary tectonic deformation associated with the New Madrid North Fault?. Seismological Research Letters 73, 393–413]). The Bootheel fault, which is not identified by the modern microseismicity, is associated with extensive liquefaction and offset channels ([Guccione, M.J., Marple, R., Autin, W.J., 2005, Evidence for Holocene displacements on the Bootheel fault (lineament) in southeastern Missouri: Seismotectonic implications for the New Madrid region. Geological Society of America Bulletin 117, 319–333]). The fault has dominantly strike-slip motion but also has a vertical component of slip. Other recognized surface deformation includes relatively low-relief folding at Big Lake/Manila high ([Guccione, M.J., VanArdale, R.B., Hehr, L.H., 2000. Origin and age of the Manila high and associated Big Lake “Sunklands”, New Madrid seismic zone, northeastern Arkansas. Geological Society of America Bulletin 112, 579–590]) and Lake St. Francis/Marked Tree high ([Guccione, M.J., VanArsdale, R.B., 1995. Origin and age of the St. Francis Sunklands using drainage patterns and sedimentology. Final report submitted to the U. S. Geological Survey, Award Number 1434-93-G-2354, Washington D.C.]), both along the subsurface Blytheville arch. Deformation at each of the fault segments does not occur during each earthquake event, indicating that earthquake sources have varied throughout the Holocene.     

鲜水河断裂带在虾拉沱附近的现今活动特征

本文利用虾拉沱跨断层测量资料,通过必要的数学处理,分析了鲜水河断裂带在该处的总体活动趋势和年周期变化,研究了断层活动在主破裂带及其两侧的分布情况,提出了一个该处断层活动模型     

Plate tectonics,palaeoenvironments and limestone geomorphology in West-Central Britain

The variety of active, exhumed, and buried limestone landforms of northern England, North Wales, and the Isle of Man arises in part from the way in which Dinantian (Lower Carboniferous) sedimentation was affected by a tilt-block basement structure evolved during the closure of the Iapetus Ocean suture to the north, and partly to subsequent plate tectonic movements associated with the closure of the proto-Tethys ocean, the opening of the Atlantic Ocean and the Alpine orogeny. Landforms created during the Dinantian now form important exhumed and buried landscape features. The Permian half-graben structures of the eastern Irish Sea-Cheshire-Worcester Basins account for many of the contrasts between the upland karsts of the Pennines and the lowland karsts of coastal areas.     

Rapid deglaciation as an initiator of volcanic activity: An hypothesis

Volcanic activity on sub-Antarctic Marion Island is found to have occurred only during the interglacials. The present volcano distribution is associated with a radial and peripheral fault system, the location of which appears to be related to the former glacier distribution. An hypothesis is presented suggesting that the faulting is a result of deglaciation and that the specific location of the faults is due to the differential stresses occurring between ice-covered and ice-free areas during isostatic uplift. The faulting initiates volcanism due to the location of the island within a volcanic region.