1,721,107 research outputs found
Laboratory friction measurements of Nankai Trough basalts
No full textWe obtained altered basaltic upper basement from the modern Nankai Trough seaward of the trench, recovered by drilling on IODP Expedition 333. We performed laboratory friction experiments on bare surfaces and gouge powders of this material, in addition to and in combination with other materials for comparison. Based our friction data, we suggest that in addition to creep the altered Nankai basalts may also allow the possibility of slow slip events
Evolution of permeability across the transition from brittle failure to cataclastic flow in porous siltstone
No full textPorous sedimentary rocks fail in a variety of modes ranging from localized, brittle deformationto pervasive, cataclastic flow. To improve our understanding of this transition and its affect on fluid flowand permeability, we investigated the mechanical behavior of a siltstone unit within the Marcellus Forma-tion, PA USA, characterized by an initial porosity ranging from 41 to 45%. We explored both hydrostaticloading paths (r15r25r3) and triaxial loading paths (r1>r25r3) while maintaining constant effectivepressure (Pe5Pc–Pp). Samples were deformed with an axial displacement rate of 0.1lm/s (strain rate of 231026s21). Changes in pore water volume were monitored (drained conditions) to measure the evolutionof porosity. Permeability was measured at several stages of each experiment. Under hydrostatic loading, wefind the onset of macroscropic grain crushing (P*) at 39 MPa. Triaxial loading experiments show a transitionfrom brittle behavior with shear localization and compaction to cataclastic-flow as confining pressureincreases. When samples fail by shear localization, permeability decreases abruptly without significantchanges in porosity. Conversely, for cataclastic deformation, permeability reduction is associated with signif-icant porosity reduction. Postexperiment observation of brittle samples show localized shear zones charac-terized by grain comminution. Our data show how zones of shear localization can act as barriers to fluidflow and thus modify the hydrological and mechanical properties of the surrounding rocks. Our results haveimportant implications for deformation behavior and permeability evolution in sedimentary systems, and inparticular where the stress field is influenced by injection or pumping
(Table 2) Experimental testing and best-fit curve measurements on unsheared sediments from different IODP Holes of Leg 316 and from IODP Hole 315-C0001E and ODP Hole 190-1174B
No full text(Table 2) Experimental testing and best-fit curve measurements on unsheared sediments from different IODP Holes of Leg 316 and from IODP Hole 315-C0001E and ODP Hole 190-1174
(Table T2) Consolidation properties and in situ porosity and permeability estimates of sediments from ODP Leg 205 sites
No full text(Table T2) Consolidation properties and in situ porosity and permeability estimates of sediments from ODP Leg 205 site
(Table T5) Permeabilities of sediments from ODP Leg 205 sites
No full text(Table T5) Permeabilities of sediments from ODP Leg 205 site
(Table T4) Flow-through permeability properties of sediments from ODP Leg 205 sites
No full text(Table T4) Flow-through permeability properties of sediments from ODP Leg 205 site
Measurements of velocity-dependent and slip-dependent frictional strength in laboratory friction experiments on natural samples from IODP Expedition 316 and ODP Hole 190-1174B
No full textSlowslip forms part of the spectrum of fault behaviour between stable creep and destructive earthquakes. Slow slip occurs near the boundaries of large earthquake rupture zones and may sometimes trigger fast earthquakes. It is thought to occur in faults comprised of rocks that strengthen under fast slip rates, preventing rupture as a normal earthquake, or on faults that have elevated pore-fluid pressures. However, the processes that control slow rupture and the relationship between slow and normal earthquakes are enigmatic. Here we use laboratory experiments to simulate faulting in natural rock samples taken from shallow parts of the Nankai subduction zone, Japan, where very low-frequency earthquakes - a form of slow slip - have been observed.We find that the fault rocks exhibit decreasing strength over millimetre-scale slip distances rather than weakening due to increasing velocity. However, the sizes of the slip nucleation patches in our laboratory simulations are similar to those expected for the very lowfrequency earthquakes observed in Nankai. We therefore suggest that this type of fault-weakening behaviour may generate slow earthquakes. Owing to the similarity between the expected behaviour of slow earthquakes based on our data, and that of normal earthquakes during nucleation, we suggest that some types of slow slip may represent prematurely arrested earthquakes
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