P-wave Velocity Variations Research Articles

Downward continued ocean bottom seismometer data show continued hydrothermal evolution of mature oceanic upper crust

Abstract Heat flow measurements indicate hydrothermal activity in oceanic crust continues at least for 65 m.y. after formation. Hydrothermal activity progressively fills cracks and pores with alteration products, which is expected to lead to a trend of increasing seismic velocities with age. Compilations of seismic-P-wave velocity models inverted from ocean bottom seismometer (OBS) data have failed to detect such an aging trend beyond crustal ages of ca. 10 Ma. However, in these models, the velocities of the uppermost crust, where fluid flow would be most concentrated, are poorly resolved. This is because as the oceanic crust matures, the first crustal arrivals on OBS records (which best resolve upper crustal velocities using tomographic inversion), become hidden in the coda of the water wave. This may lead to the masking of any aging trend in the seismic velocities. For the first time, we show how including downward continuation (DC) in the analysis of OBS data collected across 65 Ma seafloor significantly improves measurements of the P-wave velocities of the upper crust. Our new analysis reveals a highly heterogeneous upper crust, with ridge-parallel P-wave velocity variations of 25%, implying local porosity values that are up to double that of global averages. Our new results, combined with other most recent advanced seismic analyses, reveal that seismic velocities indeed evolve with age up to at least 70 Ma, confirming that hydrothermal activity continues in mature oceanic crust.

Effect Mechanism of Material Ratio on Ultrasonic P-wave Velocity in Coal Based Paste Fill Materials

This research is designed to investigate the variations in ultrasonic p-wave velocity in various coal based paste fill materials used for recovering standing pillars in closed/closing coal mines, with consideration given to the effects of numerous material-related factors. For this purpose, orthogonal tests were designed. The evaluation was performed on the effects of four variables on the ultrasonic p-wave velocities in samples, using coal grains as the primary material. These variables consisted of the coal grains’ particle size (PA), high-water material content (PB), cement content (PC), and water content (PD). The experimental results show the following: (1) Ultrasonic p-wave velocity of coal based paste fill materials are measured within the range of 1.596 to 2.357 km/s, and these are classified (in descending order) as PD, PB, PC, and then PA, based on their effects on ultrasonic p-wave velocity. (2) Ultrasonic p-wave velocity is positively correlated with compressive strength and shear strength; the correlation coefficients are 0.82 and 0.69, respectively. (3) Changes in the ultrasonic p-wave velocity of coal based paste fill materials, when exposed to various factors, have been characterized by fitted formulae. It was observed that the velocity maintained a quadratic polynomial correlation with factor PB and exponential correlations with factors PA, PC, and PD. The comprehensive predictive model, reflecting the characteristics of the ultrasonic p-wave velocity in response to the combined influence of these four factors, was developed through the utilization of fitted equations pertaining to individual factor variations. Subsequently, this model underwent verification.

Deformation microstructures of blueschists in Alpine Corsica, France, and implications for seismic anisotropy and the low-velocity layer in subducting oceanic crust

Understanding the deformation microstructures and seismic properties of blueschists is important for interpreting the seismic anisotropy at the top of subducting oceanic crust. The deformation microstructures and seismic properties of epidote blueschist, epidote-lawsonite blueschist, and lawsonite blueschist from Alpine Corsica, France, were studied using electron backscatter diffraction mapping and transmission electron microscopy. The crystal-preferred orientations (CPOs) of glaucophane show a strong maximum of the [001] axes aligned sub-parallel to the lineation. The maximum of the (010) poles of epidote is aligned sub-parallel to the lineation. The [001] axes of lawsonite are strongly aligned sub-normal to the foliation. Intracrystalline misorientation, dislocation, and occasional fragmentation of glaucophane indicate that glaucophane CPO was developed mainly by dislocation creep. The intracrystalline deformation features of epidote, such as subgrain boundaries and dislocations, indicate that the CPO of the epidote was formed by dislocation creep. In contrast, our data indicate that lawsonite CPO was developed by a combination of rigid-body rotation and dislocation creep with a minor effect of twinning. The P-wave anisotropy (AVp) and maximum S-wave anisotropy (max.AVs) of epidote blueschists (AVp = 12.3–16.9% and max.AVs = 6.53–11.75%) are higher than those of lawsonite blueschists. The seismic velocities of the blueschists are lower than those of mantle peridotites. The coexistence of epidote and lawsonite in the blueschist results in variations in seismic anisotropy and P-wave velocity in the whole rock, depending on the modal content of epidote and lawsonite. A high content ratio of epidote to lawsonite in blueschist produces strong P- and S-wave anisotropies of blueschist when the glaucophane content is more than ∼50%. The P-wave velocity of blueschist decreases proportionally with increasing epidote content. Our results indicate that the seismic properties of deformed blueschists contribute to the seismic anisotropy and the low-velocity layer in subducting oceanic crusts in subduction zones.

Application of Borehole Geophysical Prospecting Method in Pile Foundation Detection of Existing Buildings

It is particularly important to find out the pile foundation of existing buildings for building safety protection and engineering construction safety during the development and utilization of urban underground space. As a non-destructive, efficient and economic method, the borehole geophysical techniques such as magnetic gradient method, ground penetrating radar method and parallel seismic test method are used to detect the pile foundation of existing buildings, which have obvious advantages. According to the combined abnormal characteristics such as "strong magnetic anomaly, electromagnetic wave in-phase axis change and diffraction wave anomaly at the pile end, P-wave velocity variation", the pile foundation length can be judged.

Abnormal variation of P-wave velocity of red sandstone after cyclical thermal shock in water

Hot dry rock (HDR) has great development potential because of its advantages of clean, environmental protection and renewable. The study of physical and mechanical properties of HDR is one of the important links in the process of geothermal energy development. Previous studies have mainly focused on the granite thermal reservoir but research on the sandstone thermal reservoir, especially the physical properties of sandstone after multiple thermal shocks, is scarce. Therefore, in this study, cyclic thermal shock experiments of sandstone at different temperatures are carried out, and the variation law of P-wave velocity of sandstone after heat treatment is revealed. It is found that the P-wave velocity of red sandstone decreases with the increase of temperature and cycle times, especially when the temperature is higher than 400 °C, the maximum change rate of wave velocity reaches 52.6%. It is particularly noteworthy that the P- wave velocity of sandstone increases abnormally at about 600 °C. And this article puts forward three hypotheses to explain the wave velocity anomaly. In addition, the nonlinear relationship model among P-wave velocity, temperature and number of cycles is established for the first time, and the correlation coefficient R2 is more than 0.9. This study serves as a reference for the development and utilization of the sandstone geothermal reservoir.

Experimental Research into the Ultrasonic P-Wave Velocity of Coal Slime Based Backfill Material

To study the influences of different mix proportions of materials on the ultrasonic p-wave velocity of coal slime based backfill materials, influences of four factors on the p-wave velocity of specimens were investigated by designing orthogonal tests and taking coal slime as the principal raw material. The four factors included the following: (A) the mass concentration of coal slime, (B) the content of high-water-content material, (C) cement content, (D) and content of fly ash. Test results revealed the following: (1) the ultrasonic p-wave velocity is in the range of 3.916 to 8.319 km/s and various factors are listed in a descending order as A, D, B, and C according to their influences on the ultrasonic p-wave velocity; (2) the ultrasonic p-wave velocity is positively correlated with the compressive strength and shear strength, with correlation coefficients separately of 0.87 and 0.65; (3) the equations for variations in the ultrasonic p-wave velocity under influences of different factors are fitted. The ultrasonic p-wave velocity has a quadratic polynomial relationship with factor A, while following exponential relationships with factors B, C, and D. A predictive model for characteristic parameters of the ultrasonic p-wave velocity of coal slime based backfill materials jointly influenced by the four factors was established based on the fitting equation for variations of single factors and ultrasonic p-wave velocity. The predictive model was then verified.

Experimental study on deterioration of bedrock strength and P-wave velocity by pressurized seawater

Bedrock has to be excavated before the construction of rock-socketed pile foundations for offshore wind power turbines, leading to the exposure of fresh and dry rocks to seawater. The pile-rock interface is partially separated under the long-term action of various cyclic loads during the operation stage of offshore wind turbines, and the infusion of seawater will further weaken the bedrock. To comprehensively investigate the deterioration of bedrocks by pressurized seawater, tests on point load strength and slake durability were carried out to study the long-term deterioration of mechanical properties of granite, sandstone, and tuff collected from an offshore wind power farm. The elastic P-wave velocity was measured to analyze the variation trend of P-wave velocity, the mechanism of which was revealed by means of Gassmann’s equation. The results of mechanical experiments indicate that granite is almost impervious to pressurized seawater, while the mechanical properties of sandstone and tuff are deteriorated by water, especially by the pressurized seawater. After 60 days of immersion in seawater at 0.5 MPa pressure, decreasing amplitude of point load strength and slake durability index for the sandstone specimens in seawater reaches 53.2% and 18.5%, respectively, and that for the tuff specimens is 14.6% and 1.52%, respectively. The elastic P-wave velocity of granite shows an upward trend with increasing immersion time in different environments, but there exists a different tendency between the P-wave velocity of sandstone and tuff specimens in water or seawater with normal pressure and that in seawater with 0.5 MPa pressure. The variation of P-wave velocity of different types of rocks is studied based on Gassmann’s equation that takes into account the change of saturation degree, porosity, and compressibility of the matrix material.

Lateral Variations of P-Wave Velocity from Deep Borehole Data in the Southern Apennines, Italy

We have selected 28 deep wells in the Southern Apennine area, most of which are located along and around the Val d’Agri Basin. The Southern Apennines, one of the most seismically active regions of the Italian peninsula, is a NE-verging fold-and-thrust belt characterised by the Meso–Cenozoic Apulia carbonate duplex system overlain by a thick column of Apennine carbonate platform and Lagonegro basin units. These units are unconformably covered by Neogene siliciclastic successions. Among the many Quaternary tectonic basins in the area, the Val d’Agri Basin is the most important intramontane depression, and is bordered by a ~ NW–SE-trending active fault system that represents one of the main seismogenic structures of the region. Moreover, the Val d’Agri Basin is the largest onshore oil field basin in Europe. In this context, we have analysed sonic log records from 28 deep wells and compared them with the corresponding stratigraphy and the other geophysical logs. We have obtained detailed measurements of the P-wave velocity (Vp) for each well from 0 to ~ 6 km depth, and found important lateral variations of Vp over very small distances. From these values, we have retrieved the densities of the main units crossed by the wells and the range of the overburden gradient in this area.

Identification of the relatively low permeability area in coal and gas outburst seams by seismic wave tomography technique: Field application and validation

Identifying relatively low permeability areas (RLPA) is significant for site selection and parameter design for implementing enhanced gas mining measures (e.g. hydraulic fracturing, hydraulic perforation, etc.) in coal and gas outburst seams. The P-wave velocity of coal is sensitive to the variation of porosity. This paper researched the P-wave velocity change of coal with respect to confining pressure and gas pressure, the mathematical relationship model between P-wave velocity with porosity and permeability, and the relative permeability identification index. The research found that the P-wave velocity response to gas pressure varies non-monotonically. When the gas pressure is <2 MPa, the confining pressure is the main control factor leading to P-wave velocity variation. The mathematical model of P-wave velocity versus porosity and permeability was derived based on the linear relationship between wave velocity and porosity in dense rocks and the Seidle permeability model for porous media. Then the wave velocity anomaly coefficient (An) is used as the identification index for the relative permeability of the coal seam. That is, when the anomaly coefficient of coal seam wave velocity An < -8%, the coal seam is a relatively high permeability area (RHPA); when −8% <An < 8%, the coal seam is relatively normal permeability area (RNPA); when An > 8%, the coal seam is (RLPA). Based on the identification indexes studied, two RHPA (H1 and H2) and two RLPA (L1 and L2) were identified in the field engineering application. Comparing the drainage parameters in different relative permeability areas, the gas drainage volume fraction and flow in the RLPA are 56% and 90% lower than RHPA, respectively, validating the accuracy of identifying RLPA in the coal seam.

Stability of hydrate-bearing sediment during methane hydrate production by depressurization or intermittent CO2/N2 injection

Ensuring reservoir stability during natural gas hydrates production is the key to balance the geology-engineering-environment nexus. Under the overlying stress of 10 MPa, a series of experiments were conducted to investigate the variations of P-wave velocity, subsidence, and stratum stiffness during hydrate depressurization mining. The influence of hydrate saturations, gas production pressure, and sediment type were examined. The stratum stiffness of hydrate-bearing sediment gradually decreased with the decomposition of hydrate, despite the continuous compaction of overlying stress. Higher hydrate saturation led to larger subsidence and slower sedimentation rate. Lower gas production pressure resulted in greater subsidence and faster sedimentation rate. In sandy sediments, a larger particle size generated a larger sedimentation rate due to the strong heterogeneity of hydrate. However, the subsidence of silty clay is smaller with slower sedimentation rate. Hence, a novel method of intermittent CO2/N2 injection below the freezing point was proposed, which kept the stratum stiffness, reduced the sedimentation rate and subsidence of the reservoir, but also realized the sequestration of CO2 simultaneously. The method greatly enhanced the recovery ratio of methane hydrate below the freezing point. These findings provide guidance for the safe and efficient exploitation of natural gas hydrate in future.

Shear wave velocity structure and crustal lithology beneath the ultraslow spreading Southwest Indian Ridge at 50° E

SUMMARY Shear wave velocities provide an important constraint on crustal lithology. Limited crustal shear wave data are available from the ultraslow spreading mid-ocean ridges. We combine observations of both compressional (P) and shear (S) waves in ocean–bottom seismometer data from the Southwest Indian Ridge to determine crustal P-wave velocity (Vp), S-wave velocity (Vs), Vp/Vs and Poisson's ratio variations along the ridge at 49°17′E–50°49′E. Similar layered crustal structures were revealed beneath both the magmatically robust segment centres (Vp/Vs of 1.76–1.94, Poisson's ratio of 0.26–0.32) and the non-transform discontinuity (NTD) between them (Vp/Vs of 1.76–2.03 and Poisson's ratio of 0.26–0.34). Because laboratory measurements show an overlap in Poisson's ratio between mafic igneous and ultramafic rocks, particularly at Vp values typical of oceanic Layer 3, it can be difficult to distinguish crustal composition using this parameter only. However, our observed Vp gradients of 0.1 ± 0.1 s−1 suggest that in this area, oceanic Layer 3 consists primarily of mafic igneous rocks both at segment centres and at the NTD. Oceanic crustal Layers 2A and 2B above are likely also to consist of mafic igneous rocks, with some evidence for increased fracturing at the NTD.

P-wave velocity structure in the crust and the uppermost mantle of Chao Lake region of the Tan-Lu Fault inferred from teleseismic arrival time tomography

Chao Lake is a Geoheritage site on the active Tan-Lu Fault between the Yangtze craton, the North China craton, and the Dabie orogenic belt in the southeast. This segment of the fault is not well constrained at depth partly due to the overprinting of the fault zone by intrusive materials and its relatively low seismic activity and sparse seismic station coverage. This study took advantage of a dense seismic array deployed around Chao Lake to delineate the P-wave velocity variations in the crust and uppermost mantle using teleseismic earthquake arrival time tomography. The station-pair double-difference with waveform cross-correlation technique was employed. We used a multiscale resolution 3-D initial model derived from the combination of high-resolution 3-D vS models within the region of interest to account for the lateral heterogeneity in the upper crust. The results revealed that the velocity of the upper crust is segmented with structures trending in the direction of the strike of the fault. Sedimentary basins are delineated on both sides of the fault with slow velocities, while the fault zone is characterized by high velocity in the crust and uppermost mantle. The high-velocity structure in the fault zone shows characteristics of magma intrusion that may be connected to the Mesozoic magmatism in and around the Middle and Lower Yangtze River Metallogenic Belt (MLYMB), implying that the Tan-Lu fault might have formed a channel for magma intrusion. Magmatic material in Chao Lake is likely connected to the partial melting, assimilation, storage, and homogenization of the uppermost mantle and the lower crustal rocks. The intrusions, however, seem to have suffered severe regional extension along the Tan-Lu fault driven by the eastward Paleo-Pacific plate subduction, thereby losing its deep trail due to extensional erosion.

Crustal structure and tectonic implications of the southernmost Merida Andes, Venezuela, from wide-angle seismic data analysis

The crustal structure of the Merida Andes in southwestern Venezuela is crucial to our understanding of both, the complex regional geodynamics of the northern part of South America, as well as the development of the hydrocarbon basins located along its flanks. Symmetric and asymmetric models of the Merida Andes have been proposed based on geological and geophysical (principally gravimetric) surveys, without counting detailed structures from wide-angle seismic. This work examines the crustal structure of the southwestern part of the Merida Andes in Venezuela using controlled seismic sources along a 500 km wide-angle seismic profile (named ANDES SUR). Forward modeling is carried out to obtain a layer-based, P-wave, crustal velocity model. An alternative velocity model is obtained by applying a first arrival tomography for the upper 20 km depth, and a joint PmP and Pn inversion for the deeper crust. Important lateral P-wave velocity variations and low-velocity zones (LVZ) are observed within the upper crust. To the northwest, these lateral velocity variations are probably related to the deformation zones of Icotea and Tarra Faults, and the southeast to the Mantecal and Apure grabens. The integration of seismological data to the profile provides some clues about a possible slow-shear movement between the upper and the lower crust (brittle-ductile transition zone) at the NW end of the profile, as well as the possible northwestward incipient subduction of the South American Plate beneath the Maracaibo Triangle Block. We interpret the Boconó Fault's main trace as a take-off surface detaching from the interface between the upper and lower crust and dipping to the SE. A slight NW displaced crustal root of the Merida Andes is observed in all models, being the root ∼150 km wide with an approximately 9 km downward deflection (from ∼46 to 55 km depth) of the Moho. The crustal structure along the profile ANDES SUR, together with the observations along two profiles located further north, provide information about the tectonic implication along the strike of the Merida Andes, favoring an asymmetric model with possible NW directed South American lower crust and upper mantle underthrusting or incipient subduction beneath the Maracaibo Triangle Block beneath the center of the Merida Andes.

Wide-angle seismic transect reveals the crustal structure of(f) southern Sri Lanka

We present results derived from a seismic refraction experiment and gravity measurements about the crustal structure of southern Sri Lanka and the adjacent Indian Ocean. A P-wave velocity model was derived using forward modelling of the observed travel times along a 509 km long, N-S trending profile at 81°E longitude. Our results show that the continental crust below southern Sri Lanka is up to 38 km thick. A ~ 65 km wide transition zone, which thins seawards to ~7 km thickness, divides stretched continental from oceanic crust. The adjacent, 4.7 to 7 km thick normal oceanic crust is covered by up to 4 km thick sediments. The oceanic crust is characterized by intra-crustal reflections and displays P-wave velocity variations, especially in oceanic layer 2, along our profile. In the central part of the profile, the uppermost mantle layer is characterized by normal P-wave mantle velocities of 8.0–8.1 km/s. At the southern end of the profile, unusual low upper mantle seismic velocities, ranging from 7.5 to 7.6 km/s only, characterize the uppermost mantle layer. These low upper mantle velocities are probably caused by partially serpentinized upper mantle. At even greater depths the upper mantle layer is characterized by velocities of 8.3 km/s on average. The type of margin along our profile is difficult to identify, since it is characterized by features typical for different types of margins.

Wave Velocity in Sandstone and Mudstone under High Temperature and Overpressure in Yinggehai Basin

Wave velocity under different pressure and temperature (PT) conditions plays an important role in the exploration of oil and gas reservoirs. We obtained the mineral composition and porosity of 20 underground sandstone and mudstone samples in Yinggehai Basin via X-ray diffraction and porosity measurements. Using high-frequency ultrasound, the P- and S-wave velocities of four samples under high temperature and overpressure conditions were found to vary significantly, owing to the material composition and porosity. According to the comparison between the experimental conclusion and the well-logging data, the genesis of false bright spot and dark spot gas reservoirs in the study area was analyzed. The variation in P-wave velocity under different temperature and pressure conditions was explained with the PT coefficient. The traditional pressure–velocity and temperature–velocity prediction methods were improved and applied to well-logging data. Herein, the velocity of P- or S-waves of sand and mudstone under high temperature and overpressure via rock physics experiments and the genesis of false bright spot and dark spot gas reservoirs in the Yinggehai Basin was observed. Overall, the results serve as a theoretical basis for seismic exploration in the study area.

P-Wave Velocity of Limestone Influenced by Saturation: Experimental Study

This study aims to investigate the variation of P-wave velocity as a function of water saturation. In addition, by using a regression analysis, a predictability of saturated P-wave velocity from dry P-wave velocity and rock's hardness has been examined. In order to perform this study, one hundred cylindrical rock core samples, fifty samples each obtained from Ruweished in northeastern Jordan and from Ajloun in northwestern Jordan, have been extracted and prepared with a height of 20 cm and a diameter of 10 cm. P-wave velocity has been measured five times in each sample in dry and saturated states and the average value has been taken. The results indicate that the water saturation leads to an increase of the P-wave velocity, where the increase in more porous samples is less than what has been found in slightly porous samples. Moreover, the saturated P-wave velocity can be predicted through strong statistical models, which link the saturated P-wave velocity with dry P-wave velocity and hardness.

Feasibility study of fracture interpretation using multicomponent seismic data: SEAM Phase II Barrett model

Several P-wave azimuthal anisotropy studies have been conducted for the SEG Advanced Modeling Program Phase II Barrett model data. However, these analyses provide fracture property estimation that is inconsistent with the actual model properties. Therefore, we perform a feasibility study to understand the influence of the overburden and reservoir properties, and processing and inversion steps, which together determine the success of the fracture interpretation from seismic data. The 1D model properties (orthorhombic for overburden and reservoir) are first extracted from the actual Barrett model properties at two locations. Anisotropic prestack reflectivity modeling exposes the true orthorhombic response of the 1D medium in the form of common-offset and common-azimuth gathers. The true anisotropic response is obscured in the Barrett data (generated by finite-element modeling) due to the mild lateral velocity variations and orthorhombic anisotropy in the overburden. We then expose the reservoir anisotropic response using an isotropic overburden in the reflectivity modeling. This indicates that the P-wave velocity variation with azimuth (VVAZ) responses generated by the reservoir itself are weak, which leads to an unstable VVAZ inversion to estimate the interval normal moveout (NMO) velocity anisotropy. The reservoir thickness (125 m or 65 ms of two-way traveltime) or NMO velocity anisotropy (6%–7%) needs to be at least doubled to obtain a stable VVAZ inversion. Anisotropic geometric-spreading correction improves the amplitude variation with azimuth inversion results when reflectivity modeling models the orthorhombic overburden. The converted wave (C-wave) has a stronger VVAZ response compared to that of the P-wave. We suggest that the C-wave data could be useful to constrain fracture interpretation in the Barrett model. We conclude that the results of previous studies are due to the combination of the residual influence of overburden after processing and imaging and the weak anisotropy responses from the reservoir.

Upper mantle structure under the Zagros collision zone; insights from 3D teleseismic P-wave tomography

We map the lateral variations of P-wave velocity beneath the Zagros collision zone in Iran down to 800 km depth by regional travel time tomography. We invert 32,293 relative travel time residuals from five temporary seismic networks across the collision zone in NW and central Zagros and northern Iran, and a large number of permanent stations distributed over the Iranian Plateau. A salient feature of our model is a ~225 km thick lithosphere beneath the Zagros, almost twice as thick as in the rest of Iran. Slab detachment at a depth range of 250–300 km from the base of the subducted continental Arabia is clearly distinguishable in central Zagros. In NW Zagros detachment appears to be at an earlier stage. Beneath the central Iran Plateau, we observe shallow low-velocity regions down to 200 km depth, and smaller patches with significantly higher velocity in the 200–400 km depth range. This pattern might suggest a post-collisional foundering of the mantle lithosphere in the upper plate. The subducted slab seems to penetrate into the lower mantle in a segmented fashion, with no evidence for a stagnant slab above the 660 km interface.

Investigations of variations in physical and mechanical properties of granite, sandstone, and marble after temperature and acid solution treatments

Natural rock is a very common building material, and its stability plays an important role in the safety and durability of tunnels, rock slopes, and other projects. However, tunnels and other underground projects often face the threat of disasters such as fires, and during their service, the surrounding rocks are also subject to erosion by acidic groundwater. Therefore, it is of great engineering significance to study the damage of the surrounding rocks under the threat of fire and acid groundwater. In this study, the variations in chromatic aberration, mass, P-wave velocity, porosity, thermal conductivity, and tensile strength of granite, sandstone, and marble induced by high temperature and chemical erosion are investigated from room temperature to 1000 °C. The results show that the rock materials exhibit different degrees of variation in physical and mechanical properties under the effect of high temperatures and acidic solution corrosion. Then, according to the variation of physical and mechanical properties, the formation mechanism of damage is discussed and the damage process verified by the deterioration of mechanical properties. For rocks heated to different temperatures and eroded by acid solution, the main reason for damage is the increase of cracks which destroy the structure and weaken the bonding between particles.

A new generation Griggs apparatus with active acoustic monitoring

High pressure and temperature experiments are necessary to understand geological processes at deep earth conditions. Here, we present a new generation Griggs-type apparatus, designed to perform deformation experiments at P-T conditions of the lower crust and upper mantle, i.e. up to 5 GPa and 1000 °C. We first detail the experimental design, set-up and procedure, as well as the calibration protocol of the apparatus. The main innovation of this new set-up is the development of an active acoustic monitoring pulse-transmission technique, which enables us to monitor the evolution of P-wave elastic velocities, at 5 MHz, contemporaneously with deformation. This may provide information on the evolution of the microstructure, in particular when mineralogical (metamorphic) reactions are taking place. For instance, P-wave velocity variations across the α → β quartz transition are recorded for the first time within a Griggs apparatus, at 0.5 and 0.8 GPa. This new set-up opens up important perspectives for the study of the complex couplings that may take place between mineral reactions and deformation under in lithospheric stress and temperature conditions.