Wenlu Zhu

University of Maryland, College Park | UMD, UMCP, University of Maryland College Park · Department of Geology

A global study of subduction zone dynamics indicates that the thermal structure of the overriding plate may control arc location. A fast convergence rate and a steep slab dip bring a hotter mantle further into the wedge corner, forming arc volcanoes closer to the trench. Separately, laboratory and numerical experiments showed that the development o...

We report the strength and deformation behavior of Solnhofen limestone across its brittle (localized) to ductile (distributed) transition. We conducted conventional triaxial compression tests on water‐saturated and nominally dry cores of Solnhofen at temperatures up to 200°C and effective confining pressures up to 350 MPa to evaluate the roles of p...

Significant reduction in mechanical properties, i.e., elastic moduli and seismic wave velocities, as well as enhanced inelastic attenuation is often associated with areas of partially molten rocks. In this paper we suggest a new mechanism responsible for significant reduction of wave velocity and enhanced attenuation. The suggested mechanism consid...

Significant reduction in mechanical properties, i.e., elastic moduli and seismic wave velocities, as well as enhanced inelastic attenuation is often associated with areas of partially molten rocks. In this paper we suggest a new mechanism responsible for significant reduction of wave velocity and enhanced attenuation. The suggested mechanism consid...

The continuum of behavior that emerges during fracture network development in crystalline rock may be categorized into three end-member modes: fracture nucleation, isolated fracture propagation, and fracture coalescence. These different modes of fracture growth produce fracture networks with distinctive geometric attributes, such as clustering and...

Fluids released from dehydration reactions occurring in subducting slabs trigger partial melting in the mantle wedge. The resulting magma rises through the overlying mantle wedge and lithosphere and forms arc volcanoes at subduction zones. In general, the location of the volcanic arc is narrowly defined even though the melting region in the mantle...

Plain Language Summary Aqueous fluids that circulated beneath the seafloor play an important role in heat transfer, chemical exchange, and microbial activity in the oceanic lithosphere. The Oman Drilling Project was successful in obtaining continuous drill cores through the crust‐mantle sequences in the Samail ophiolite, where the paleo‐oceanic bas...

Different modes of fracture growth produce fracture networks with distinctive geometric attributes that exert important controls on the extent of fluid-rock interactions. We perform in situ X-ray tomography triaxial compression experiments on monzonite to investigate the influence of fracture nucleation, preexisting fracture propagation, and coales...

We conducted experiments to investigate the influence of pore fluid pressure on the frictional strength and slip behavior of gouge bearing faults. Saw cut porous sandstone samples with a layer of gouge powders placed between the precut surfaces were deformed in the conventional triaxial loading configuration. A series of velocity-step tests were pe...

Hydration reactions influence rock density and rheology. For example, volume increases produced in hydration reactions may generate sufficient tensile and shear stress to fracture both the rock undergoing the reaction and the surrounding host rock. We performed in situ dynamic X-ray synchrotron microtomography experiments to investigate reaction-in...

Advances in triaxial compression deformation apparatus design, dynamic X-ray microtomography imaging, data analysis techniques, and digital volume correlation analysis provide unparalleled access to the in situ four-dimensional distribution of developing strain within rocks. To demonstrate the power of these new techniques and acquire detailed info...

The formation of deformation bands can significantly modify the strength and transport properties of porous sedimentary rocks. Among the different types of deformation bands, compaction bands exhibit porosity reduction with little to no shear displacement. Natural compaction bands have previously been reported and studied in only a few areas. They...

Hydration of a nominally dry rock can cause expansion of the solid volume, resulting in reaction-induced fracturing and an associated increase in the porosity and permeability of the rock. We study the effect of confinement on the coupling between stress generation, reaction-induced fracturing and porosity evolution during the hydration of periclas...

The olivine carbonation reaction, in which carbon dioxide is chemically incorporated to form carbonate, is central to the emerging carbon sequestration method using ultramafic rocks. The rate of this retrograde metamorphic reaction is controlled, in part, by the available reactive surface area: as the solid volume increases during carbonation, the...

The olivine carbonation reaction, in which carbon dioxide is chemically incorporated to form carbonate, is central to the emerging carbon sequestration method using ultramafic rocks. The rate of this retrograde metamorphic reaction is controlled, in part, by the available reactive surface area: as the solid volume increases during carbonation, the...

The rupture, localization, and slip of faults in serpentinite were studied under varying pore fluid pressure conditions to understand deformation mechanisms potentially responsible for slow slip in fault zones. Experiments were conducted at a constant effective confining pressure of 10 MPa and under pore fluid pressures from 0 to 120 MPa and at tem...

Olivine and pyroxene-bearing rocks in the oceanic crust react with hydrothermal fluids producing changes in the physical characteristics and behaviors of the altered rocks. Notably, these reactions tend to increase solid volume, reducing pore volume, permeability, and available reactive surface area, yet entirely hydrated and/or carbonated rocks ar...

Storing carbon dioxide in the subsurface as carbonate minerals has the benefit of long-term stability and immobility. Ultramafic rock formations have been suggested as a potential reservoir for this type of storage due to the availability of cations to react with dissolved carbon dioxide and the fast reaction rates associated with minerals common i...

The microstructural relationship between melt and solid grains in partially molten rocks influences many physical properties, including permeability, rheology, electrical conductivity and seismic wave speeds. In this study, the connectivity of melt networks in the olivine–basalt system is explored using a systematic survey of 3-D X-ray microtomogra...

The planets and larger rocky bodies of the inner solar system are differentiated, and consist of metallic, iron-rich cores surrounded by thick shells of silicate. Core formation in these bodies, i.e. the segregation of metal from silicate, was a key process in the early solar system, and one which left a lasting geochemical signature. It is commonl...

The planets and larger rocky bodies of the inner solar system are differentiated, and consist of metallic, iron-rich cores surrounded by thick shells of silicate. Core formation in these bodies, i.e. the segregation of metal from silicate, was a key process in the early solar system, and one which left a lasting geochemical signature. It is commonl...

Mineral carbonation, a process that binds CO2 in the form of carbonates by silicate weathering, is widespread on the Earth's surface. Because of the abundance of silicate rocks and the permanence of the carbonated solids, sequestering CO2 via mineral carbonation has generated lots of interests. However, it is unclear how the fluid-rock reaction pro...

Porous carbonate rocks are natural reservoirs for freshwater and hydrocarbons. More recently, due to their potentials for geothermal energy generation as well as carbon sequestration, there are renewed interests in better understanding of the deformation behavior of carbonate rocks. We conducted a series of deformation experiments to investigate th...

Observations of dunite channels in ophiolites and uranium-series disequilibria in mid-ocean ridge basalt suggest that melt transport in the upper mantle beneath mid-ocean ridges is strongly channelized. We present experimental evidence that spatial variations in mineralogy can also focus melt on the grain-scale. This lithologic melt partitioning, w...

The practice of injecting fluids into the crust is linked to regional increases in seismicity. Increasing fluid pressure along preexisting faults is believed to enhance seismicity rates by reducing the shear stress required for slip, but the processes that cause faults to slip under conditions of fluid pressurization are poorly constrained. We use...

Estimates of melt content beneath fast-spreading mid-ocean ridges inferred from magnetotelluric tomography (MT) vary between 0.01 and 0.10. Much of this variation may stem from a lack of understanding of how the grain-scale melt geometry influences the bulk electrical conductivity of a partially molten rock, especially at low melt fraction. We comp...

Pore fluid pressure is known to play an important role in brittle fracture initiation and propagation yet the underlying mechanisms remain unclear. We conducted triaxial experiments on saturated porous sandstones to investigate effects of pore pressure build-up on the slowness of shear rupture propagation at different confining pressures. At low to...

Shale is now commonly exploited as a hydrocarbon resource. Due to the high degree of geochemical and petrophysical heterogeneity both between shale reservoirs and within a single reservoir, there is a growing need to find more efficient methods of extracting petroleum compounds (crude oil, natural gas, bitumen) from potential source rocks. In this...

The presence of pore fluid in rocks generally reduces brittle strength. The role of water-weakening in porous carbonate rocks and the effect of enhanced deformation on concomitant transport property evolution are poorly understood. The interaction between pore fluid and deformation mechanisms in carbonate rocks is complicated by crystal plasticity...

The coupling between damage accumulation, dilation, and compaction during loading of sandstones is responsible for different structural features such as localized deformation bands and homogeneous inelastic deformation. We distinguish and quantify the role of each deformation mechanism using new mathematical model and its numerical implementation....

Sandstones display non-linear and inelastic behaviour such as hysteresis when subjected to cyclic loading. We present three hydrostatic compaction experiments with multiple loading-unloading cycles on Berea and Darley Dale sandstones and explain their hysteretic behaviour using non-linear inelastic compaction and dilation. Each experiment included...

Melt percolation in mantle rocks is currently poorly constrained, especially at low melt fractions. At mid-ocean ridges, for example, geochemical and geophysical observations produce divergent estimates of how much melt is present in the mantle and how quickly it moves. Accurate estimates of permeability and grain-scale melt distribution in mantle...

A new modular X-ray-transparent experimental cell enables tomographic investigations of fluid rock interaction under natural reservoir conditions (confining pressure up to 20 MPa, pore fluid pressure up to 15 MPa, temperature ranging from 296 to 473 K). The portable cell can be used at synchrotron radiation sources that deliver a minimum X-ray flux...

Pore fluid pressure and shear rupture are long known to be interwoven: an increase in pore fluid pressure can unclamp the fault by reducing the effective normal stress and thus cause the fault to slip at lower shear stress. This mechanism is well illustrated by induced seismicity near fluid injection. More recently, several lines of evidence sugges...

Slow slip behaviors are suggested to have a close correlation with the presence of excess pore fluid pressure. In this study, we conducted deformation experiments with and without excess pore pressure on intact porous sandstone samples to investigate effect of pore fluid pressure on rupture growth and slip instability. Experimental conditions are s...

Slow slip events, including non-volcanic tremors, low-and very low-frequency earthquakes, are observed at both the updip and downdip limits of several subduction regions. Recent studies indicate that similar to regular earthquake, these low frequency events rise from shear slip. It is generally accepted that elevated pore fluid pressure plays a sig...

It is known that microstuctural damage precedes macroscopic fracture in rocks during brittle failure. The quantitative relationship between the grain-scale damage and fault growth is not yet clearly understood, partly due to the unstable nature of the faulting process. A lateral relaxation path was devised so that a rock sample can be deformed to f...

Faults were first thought to relieve stress either through continuous aseismic sliding, or as earthquakes resulting from sudden rupture of locked faults. Recent data from geodetic and global seismic networks revealed a remarkable array of new slip instabilities. This discovery creates new challenges to our understanding of the mechanics of earthqua...

Seafloor hydrothermal vents accommodate the convective transfer of fluids from subsurface environments to the oceans. In addition to black smoker chimneys, a variety of other deposit-types form. Flanges protrude from the sides of edifices as horizontal ledges, below which vent fluids pool. Slabs are hydrothermally silicified layered volcaniclastic...

Knowledge of temporal and spatial variations in fluid flow, which is of critical importance to resource recovery, requires better understanding of the changes and the rates of changes of permeability and porosity at reservoir conditions. Permeability and porosity are dynamic physical properties that are sensitive to mechanical and thermal loads. Wi...

Understanding the mechanics of earthquakes requires quantitative knowledge of fault instability. While the rate-and-state theory provides a general framework for understanding earthquake nucleation processes, recent discoveries of slow slip events, from low frequency earthquakes to episodic tremor and slip events, create new challenges to our under...

Recent discoveries of slow slip phenomena, from low frequency earthquakes to episodic tremor and slip events, create new challenges to our understanding of source processes. High pore pressure is often cited as the likely cause for these slow slip events. The working hypothesis is that pore pressure excess reduces effective normal stress on the fau...

Evolution of Permeability and Pore Structure of Porous Limestone at Elevated Temperature Harrison Lisabeth, Katherine Watter and Wenlu Zhu Dept. of Geology, University of Maryland, College Park 20742 Permeability of porous rocks depends strongly on porosity and pore geometry. Natural situations are often complex, with concurrent inelastic deformati...

A succession of short-lived, E-W trending cracks at the Galapagos Triple Junction north and south of the Cocos-Nazca (C-N) Rift, has been explained by a simple crack interaction model. The locations of where the cracks initiate are controlled by tensile stresses generated at the East Pacific Rise (EPR) by two interacting cracks: One representing th...

The Galapagos triple junction is not a simple ridge-ridge-ridge (RRR) triple junction. The Cocos-Nazca Rift (C-N Rift) tip does not meet the East Pacific Rise (EPR). Instead, two secondary rifts form the link: Incipient Rift at 2°40‧N and Dietz Deep volcanic ridge, the southern boundary of the Galapagos microplate (GMP), at 1°10‧N. Recently collect...

Seafloor bathymetry north of the Galápagos microplate in the Eastern Pacific Ocean contains evidence for a sequence of short-lived rifts cross-cutting abyssal hills adjacent to the East Pacific Rise. These secondary rifts are sub-parallel to the Incipient Rift that marks the current triple junction at 2°40′N and are nearly perpendicular to the dire...

The permeability of the upper mantle controls melt segregation beneath spreading centers. Reconciling contradictory geochemical and geophysical observations at ocean ridges requires a better understanding of transport properties in partially molten rocks. Using x-ray synchrotron microtomography, we obtained three-dimensional data on melt distributi...

Slow slip events such as very low frequency earthquakes (VLFEs) are detected in the Nankai accretionary prism [Ito and Obara, 2006]. It is proposed that high pore fluid pressure weakens the out-of-sequence-thrusts and mega-splay faults by reducing effective normal stress on the fault plane and consequently generates slip instability producing low s...

Seafloor hydrothermal vents accommodate the convective transfer of material from Earth's interior to the oceans. A variety of seafloor deposits form at vent fields, including flanges, slabs, and crust. Flanges recovered from Guaymas Basin and the Main Endeavour Field (MEF) are horizontal ledges that protrude from the sides of larger structures. Flu...

Quantitative knowledge of the distribution of small amounts of silicate melt in peridotite and of its influence on permeability are critical to our understanding of melt migration and segregation processes in the upper mantle, as well as interpretations of the geochemical and geophysical observations at ocean ridges. For a system containing a singl...

Although kinematically stable, Ridge-Ridge-Ridge (RRR) triple junctions often display a complex sequence of short-lived rifts and no direct connection between the ridges. We propose that the mechanics of crack interaction, combined with ridge azimuth, can explain the apparent instability of several RRR triple junctions. The Galápagos Triple Junctio...

Quantitative knowledge of the distribution of small amounts of silicate melt in peridotite and of its influence on permeability are critical to our understanding of melt migration and segregation processes in the upper mantle. Estimates for the permeability of partially molten rock require 3D melt distribution at the grain-scale. Existing studies o...

We report a new bathymetry survey of the Galapagos microplate (GMP), which separates the Pacific, Nazca, and Cocos plates at the Galapagos Triple Junction. Prior to the formation of the microplate, 1.5-1.0 Ma, there was a succession of transient minor rifts forming triple junctions north and south of the propagating Cocos-Nazca rift (see Schouten e...

The precursory phenomena associated with dilatancy have been extensively studied as a potential means of earthquake prediction. It is known that microstuctural damage induced dilatancy precedes macroscopic failure of a rock. However, the quantitative relationship between microcrack damage and fault development is not clearly understood. To better u...

The Galapagos triple junction is a ridge-ridge-ridge triple junction where the Cocos, Nazca, and Pacific plates meet around the Galapagos microplate (GMP). On the Cocos plate, north of the large gore that marks the propagating Cocos-Nazca (C-N) Rift, a 250-km-long and 50-km-wide band of NW-SE-trending cracks crosscuts the N-S-trending abyssal hills...

In Taiwan an international project to drill into the Chelungpu fault (TCDP) was initiated after the M w 7.6 Chi-Chi earthquake in 1999. At Takeng, two vertical holes (A and B) to depths of about 2 km have been drilled through the northern portion of the Chelungpu fault system. In this study, we conducted systematic hydromechanical tests on TCDP dri...

The Galápagos triple junction features the Cocos-Nazca Ridge (CNR) propagating towards the East Pacific Rise (EPR) without connecting to it. Instead, secondary rifts like the Incipient Rift initiate from the EPR and delimitate a distributed deformation zone encompassing the Galápagos microplate. To the north of the triple junction, a succession of...

Evolution of permeability-porosity relationships (EPPRs) of different seafloor vent deposit sample types provide crucial information about how fluid flows within the deposits. In this study, we conducted permeability and porosity measurements on a wide range of vent sample types recovered from many different active seafloor vent fields. The sample...

Interpreting the geochemical and geophysical observations at ocean ridges requires knowledge of permeability and melt distribution of partially molten rocks. Recent developments in 3-D modeling of complex flows in porous media lead to estimates of the permeability of partially molten rock to complement values obtained through laboratory measurement...

The Galapagos triple junction is a ridge-ridge-ridge triple junction where the Cocos, Nazca, and Pacific plates meet around the Galapagos microplate. Directly north of the large scarps of the Cocos-Nazea Rift, a 250-km-long and 50-km-wide band of northwest-southeast-trending cracks with volcanics at their western ends crosscuts and blankets the nor...

A cumulative damage model was formulated to quantify the stress-induced permeability reduction during the shear-enhanced compaction. Using this model, we are able to link the transient permeability anisotropy during cataclastic flow to the influence of stress state and loading path on the yield stress and microscopic stress heterogeneities. A gener...

A fundamental understanding of the effect of stress on permeability evolution is important for many fault mechanics and reservoir engineering problems. Recent laboratory measurements demonstrate that in the cataclastic flow regime, the stress-induced anisotropic reduction of permeability in porous rocks can be separated into 3 different stages. In...

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): B05208, doi:10.1029/2006JB004716. Systematic laboratory measurements of permeability and porosity we...

We have developed an experimental methodology to investigate the compactive yield behavior of porous sandstones under undrained condition and to distinguish it from the conventional method we refer to it as “modified undrained”. In a conventional undrained test a sample is deformed while the confining pressure and pore volume are fixed. Our novel m...

Rock is porous, with a connected network of cracks and pores. The static and dynamic behaviors of a rock sample under load depend on both the solid mineral matrix and the porous phase. In general, the configuration of the pore phase is complex; thus, most studies on the effect of the porous phase on rock deformation are conducted numerically and th...

Pore pressure excess has been frequently invoked in understanding seismogenic processes. Many working hypotheses for generating high pore pressure are proposed. However, one important ingredient still missing in these models is quantitative knowledge of the rate of change of permeability and porosity of rocks under various conditions of stress, tem...

Hydromechanical behavior TCDP core samples are being investigated in the laboratory. Initial tests focused on country rock cores at depths of ~588 m and 837 m. Cylindrical samples were cored in three orthogonal directions, one parallel and two perpendicular to the core axis. Triaxial compression tests were performed at room temperature to determine...

The poromechanical behavior of rocks under undrained condition is of fundamental importance in many geologic and geotechnical problems. In a conventional undrained experiment the saturated sample is deformed under constant confining pressure while fluid movement in or out of the pore volume is inhibited. Maintaining a constant pore volume requires...

Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): B05208, doi:10.1029/2004JB003027. Sliding of a rough surface having a range of asperity heights is a...

The "Incipient Rift" (IR), first identified by P. Lonsdale and co-workers, is located immediately east of and orthogonal to the East Pacific Rise (EPR) at 2o40'N. The IR is a slowly diverging (approx. 15 mm/yr full-rate) spreading center separating the Cocos and Galapagos plates. Interest in the IR stems, first, from the fact that because it is adj...

The east-west-trending Incipient Rift (IR) is located adjacent to the East Pacific Rise (EPR) at 2o40'N in the equatorial Pacific. This slow-spreading ( ˜0-30 mm/yr), magmatic rift forms the boundary between the Cocos plate and Galapagos microplate (Lonsdale, 1988) and connects to the East Pacific Rise (EPR) through a magmatically active linking ri...

Estimation of permeability in partially molten rocks requires knowledge of the melt phase distribution at the grain-scale. The melt distribution in an isotropic two-phase (solid+melt) system under equilibrium conditions is well defined. In such a system, all of the melt channels are identical and they are either interconnected or isolated depending...

The initiation and growth of shear localization is of fundamental importance in understanding the mechanics of earthquake and faulting. Because dilatancy is generally observed as a precursor to brittle faulting, early laboratory and theoretical studies tended to focus on dilatant materials. However, recent laboratory studies demonstrated that inves...