Zooming in on crystal mush: recent advances in volcano tomography

2021 ◽  
Author(s):  
Michele Paulatto ◽  
Joanna Morgan ◽  
Kajetan Chrapkiewicz ◽  
Emilie Hooft ◽  
Doug Toomey ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Elastic Properties ◽  
Melt Inclusions ◽  
Pore Space ◽  
Waveform Inversion ◽  
Elastic Response ◽  
Crystal Mush ◽  
Low Velocity ◽  
Volcanic System ◽  
Trade Offs

<p>The lack of direct seismological evidence for large molten magma chambers is considered to be one of the most important arguments in support of the mush paradigm. However, most published melt fraction estimates based on interpretation of seismological data are associated with large uncertainties because of two limitations: i) inherent limits to resolution of seismic tomography and, ii) trade-offs in the constitutive relationships that tie seismic properties to melt fraction. Low-velocity volumes associated with magma storage are particularly difficult to image with conventional travel-time tomography due to limited resolution and wavefront healing, resulting in blurred images and a high velocity bias. We tackle these limitation by applying full waveform inversion to active source seismic data collected over the Kolumbo submarine volcano (Greece). We recover a previously undetected Vp anomaly of –50% beneath the volcano and interpret this as a shallow magmatic intrusion. Extension of this approach to the wider Santorini volcanic system is ongoing. Concurrently, we are tackling the second limitation, which is the result of the dependence of elastic properties on the microgeometry of the melt. Seismological melt estimates rely on the assumption that the melt pore space can be represented by simple geometrical shapes, usually ellipsoids, with a given aspect ratio. Since the aspect ratio is poorly constrained, this results in a trade-off between melt fraction and melt geometry. We have adapted a method for the homogenisation of the elastic properties of multi-phase composites and applied it to calculating the elastic properties of partially molten rocks starting from the melt microstructure determined by X-ray CT scanning. The microgeometry of the mush can be inferred from the study of glomerocrysts: crystal mush inclusions with quenched interstitial melt that are carried to the surface by erupted lava. After the sample is digitized and segmented into its constitutive phases (crystals, melt, vesicles), the average elastic properties are determined by numerical homogenisation which consists of numerically simulating the deformation of the sample under load and predicting its elastic response. The results are compared to a semi analytical solution for ellipsoidal inclusions. We apply this approach to a plutonic nodule from St Kitts and show that the melt microstructure leads to an elastic response equivalent to that of ellipsoidal melt inclusions with an aspect ratio of 0.1 (oblate spheroids). This equivalent aspect ratio is used to refine melt estimates for Montserrat, Santorini and Kolumbo volcano.</p>

Modeling squirt dispersion and attenuation in fluid-saturated rocks using pressure dependency of dry ultrasonic velocities

Geophysics ◽  
2012 ◽  
Vol 77 (3) ◽  
pp. WA157-WA168 ◽  
Author(s):  
Osni Bastos de Paula ◽  
Marina Pervukhina ◽  
Dina Makarynska ◽  
Boris Gurevich
Keyword(s):  
Aspect Ratio ◽  
Elastic Properties ◽  
Elastic Moduli ◽  
Pore Space ◽  
Geometrical Parameters ◽  
Laboratory Measurements ◽  
Significant Linear Trend ◽  
Aspect Ratios ◽  
Pressure Dependency ◽  
Dispersion And Attenuation

Modeling dispersion and attenuation of elastic waves in fluid-saturated rocks due to squirt flow requires the knowledge of a number of geometrical parameters of the pore space, in particular, the characteristic aspect ratio of the pores. These parameters are usually inferred by fitting measurements on saturated rocks to model predictions. To eliminate such fitting and thus make the model more predictive, we propose to recover the geometrical parameters of the pore space from the pressure dependency of elastic moduli on dry samples. Our analysis showed that the pressure dependency of elastic properties of rocks (and their deviation from Gassmann’s prediction) at ultrasonic frequencies is controlled by the squirt flow between equant, stiff, and so-called intermediate pores (with aspect ratios between [Formula: see text]). Such intermediate porosity is expected to close at confining pressures of between 200 and 2000 MPa, and thus cannot be directly obtained from ultrasonic experiments performed at pressures below 50 MPa. However, the presence of this intermediate porosity is inferred from the significant linear trend in the pressure dependency of elastic properties of the dry rock and the difference between the bulk modulus of the dry rock computed for spherical pores and the measured modulus at 50 MPa. Moreover, we can infer the magnitude of the intermediate porosity and its characteristic aspect ratio. Substituting these parameters into the squirt model, we have computed elastic moduli and velocities of the water-saturated rock and compared these predictions against laboratory measurements of these velocities. The agreement is good for a number of clean sandstones, but not unexpectedly worse for a broad range of shaley sandstones. Our predictions showed that dispersion and attenuation caused by the squirt flow between compliant and stiff pores may occur in the seismic frequency band. Confirmation of this prediction requires laboratory measurements of elastic properties at these frequencies.

scholarly journals Modeling compaction effects on the elastic properties of clay-water composites

Geophysics ◽  
2012 ◽  
Vol 77 (5) ◽  
pp. D171-D183 ◽  
Author(s):  
Bernardo Moyano ◽  
Kyle T. Spikes ◽  
Tor Arne Johansen ◽  
Nazmul Haque Mondol
Keyword(s):  
Aspect Ratio ◽  
Elastic Properties ◽  
Large Scale ◽  
Effective Medium Theory ◽  
Pore Space ◽  
Shear Velocity ◽  
Sem Images ◽  
Critical Porosity ◽  
Shear Moduli ◽  
Percolation Behavior

Modeling the elastic properties of clay-bearing rocks (shales) requires thorough knowledge of the mineral constituents, their elastic properties, pore space microstructure, and orientations of clay platelets. Information about these variables and their complex interrelationships is rarely available for real rocks. We theoretically modeled the elastic properties of synthetic clay-water composites compacted in the laboratory, including estimates of pore space topology and percolation behavior. The mineralogy of the samples was known exactly, and the focus was on two monomineralic samples comprised of kaolinite and smectite. We used differential effective medium theory (DEM) and analysis of scanning electron microscope (SEM) images of the compacted kaolinite and smectite samples. Percolation behavior was included through calculations of critical porosities from measurements of the liquid limits of the individual clay powders. Quantitative analysis of the SEM images showed that the large scale ([Formula: see text]) pore space of the smectite composite had more rounded pores (mean aspect ratio [Formula: see text]) than the kaolinite composite (mean pore’s aspect ratio [Formula: see text]). However, models that used only these large-scale pore shapes could not explain the compressional and shear velocity measurements. DEM simulations with a single pore aspect ratio showed that bulk and shear moduli are controlled by different pore shapes. Conversely, modeling results that combined critical porosity and dual porosity models into DEM theory compared well with the measured bulk and shear moduli of compacting kaolinite and smectite composites. The methods and results we used could be used to model unconsolidated clay-bearing rocks of more complex mineralogy.

Nature of the low velocity zone in Cascadia from receiver function waveform inversion

2012 ◽  
Vol 337-338 ◽  
pp. 25-38 ◽  
Author(s):  
Ralf T.J. Hansen ◽  
Michael G. Bostock ◽  
Nikolas I. Christensen
Keyword(s):  
Receiver Function ◽  
Waveform Inversion ◽  
Low Velocity ◽  
Low Velocity Zone ◽  
Velocity Zone

Two types of reservoir-induced seismicity

1988 ◽  
Vol 78 (6) ◽  
pp. 2025-2040
Author(s):  
D.W. Simpson ◽  
W.S. Leith ◽  
C.H. Scholz
Keyword(s):  
Normal Stress ◽  
Pore Pressure ◽  
Induced Seismicity ◽  
Elastic Stress ◽  
Pore Space ◽  
Temporal Distribution ◽  
The Other ◽  
Elastic Response ◽  
Reservoir Induced Seismicity ◽  
Effective Normal Stress

Abstract The temporal distribution of induced seismicity following the filling of large reservoirs shows two types of response. At some reservoirs, seismicity begins almost immediately following the first filling of the reservoir. At others, pronounced increases in seismicity are not observed until a number of seasonal filling cycles have passed. These differences in response may correspond to two fundamental mechanisms by which a reservoir can modify the strength of the crust—one related to rapid increases in elastic stress due to the load of the reservoir and the other to the more gradual diffusion of water from the reservoir to hypocentral depths. Decreased strength can arise from changes in either elastic stress (decreased normal stress or increased shear stress) or from decreased effective normal stress due to increased pore pressure. Pore pressure at hypocentral depths can rise rapidly, from a coupled elastic response due to compaction of pore space, or more slowly, with the diffusion of water from the surface.

On-the-Fly Full Hessian Kernel Calculations Based upon Seismic-Wave Simulations

2021 ◽  
Author(s):  
Yujiang Xie ◽  
Catherine A. Rychert ◽  
Nicholas Harmon ◽  
Qinya Liu ◽  
Dirk Gajewski
Keyword(s):  
Wave Equations ◽  
Convergence Rates ◽  
Waveform Inversion ◽  
Computational Cost ◽  
Random Access ◽  
Spectral Element ◽  
Source Codes ◽  
Full Waveform ◽  
Trade Offs ◽  
Adjoint Tomography

Abstract Full waveform inversion or adjoint tomography has routinely been performed to image the internal structure of the Earth at high resolution. This is typically done using the Fréchet kernels and the approximate Hessian or the approximate inverse Hessian because of the high-computational cost of computing and storing the full Hessian. Alternatively, the full Hessian kernels can be used to improve inversion resolutions and convergence rates, as well as possibly to mitigate interparameter trade-offs. The storage requirements of the full Hessian kernel calculations can be reduced by compression methods, but often at a price of accuracy depending on the compression factor. Here, we present open-source codes to compute both Fréchet and full Hessian kernels on the fly in the computer random access memory (RAM) through simultaneously solving four wave equations, which we call Quad Spectral-Element Method (QuadSEM). By recomputing two forward fields at the same time that two adjoint fields are calculated during the adjoint simulation, QuadSEM constructs the full Hessian kernels using the exact forward and adjoint fields. In addition, we also implement an alternative approach based on the classical wavefield storage method (WSM), which stores forward wavefields every kth (k≥1) timestep during the forward simulation and reads required fields back into memory during the adjoint simulation for kernel construction. Both Fréchet and full Hessian kernels can be computed simultaneously through the QuadSEM or the WSM code, only doubling the computational cost compared with the computation of Fréchet kernels alone. Compared with WSM, QuadSEM can reduce the disk space and input/output cost by three orders of magnitude in the presented examples that use 15,000 timesteps. Numerical examples are presented to demonstrate the functionality of the methods, and the computer codes are provided with this contribution.

scholarly journals A Portable & Disposable Ultra-Low Velocity Flow Sensor from Bioinspired Hair-Like Microstructures

Proceedings ◽  
2018 ◽  
Vol 2 (13) ◽  
pp. 731 ◽  
Author(s):  
Harish Devaraj ◽  
Rajnish Sharma ◽  
Enrico Haemmerle ◽  
Kean Aw
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Modular Design ◽  
Measurement Range ◽  
Flow Sensor ◽  
Design Development ◽  
Low Velocity ◽  
Velocity Flow ◽  
Loop Feedback ◽  
Air Flow Velocity

We present, for the first time, the design, development and testing of a portable ultra-lowvelocity flow sensor with a disposable architecture for use in medical applications. 3Dmicroprintingtechnique was used to fabricate high aspect ratio microscopic hair-like structuresfrom conducting polymers, in particular, poly(3,4-ethylenedioxythiophene):polystyrene-sulfonate(PEDOT:PSS). These high aspect ratio micro-hairs are flexible and conductive that can respond toair flowing over them. A disposable and portable flow sensor with a modular design that allowstuning of measurement range was developed, for integration with an automated neonatalresuscitator to provide closed-loop feedback. The developed portable sensor architecture is capableof real-time indication of the air flow velocity range down to few millimeters/second.

Full-waveform inversion with borehole constraints for elastic VTI media

Geophysics ◽  
2020 ◽  
Vol 85 (6) ◽  
pp. R553-R563
Author(s):  
Sagar Singh ◽  
Ilya Tsvankin ◽  
Ehsan Zabihi Naeini
Keyword(s):  
Objective Function ◽  
Reservoir Characterization ◽  
Waveform Inversion ◽  
Low Frequency ◽  
Rock Physics ◽  
Anisotropic Media ◽  
Full Waveform Inversion ◽  
Full Waveform ◽  
Trade Offs ◽  
Vti Media

The nonlinearity of full-waveform inversion (FWI) and parameter trade-offs can prevent convergence toward the actual model, especially for elastic anisotropic media. The problems with parameter updating become particularly severe if ultra-low-frequency seismic data are unavailable, and the initial model is not sufficiently accurate. We introduce a robust way to constrain the inversion workflow using borehole information obtained from well logs. These constraints are included in the form of rock-physics relationships for different geologic facies (e.g., shale, sand, salt, and limestone). We develop a multiscale FWI algorithm for transversely isotropic media with a vertical symmetry axis (VTI media) that incorporates facies information through a regularization term in the objective function. That term is updated during the inversion by using the models obtained at the previous inversion stage. To account for lateral heterogeneity between sparse borehole locations, we use an image-guided smoothing algorithm. Numerical testing for structurally complex anisotropic media demonstrates that the facies-based constraints may ensure the convergence of the objective function towards the global minimum in the absence of ultra-low-frequency data and for simple (even 1D) initial models. We test the algorithm on clean data and on surface records contaminated by Gaussian noise. The algorithm also produces a high-resolution facies model, which should be instrumental in reservoir characterization.

Micromechanics-based analyses of short fiber-reinforced composites with functionally graded interphases

2019 ◽  
Vol 54 (8) ◽  
pp. 1031-1048 ◽  
Author(s):  
Yang Yang ◽  
Qi He ◽  
Hong-Liang Dai ◽  
Jian Pang ◽  
Liang Yang ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Elastic Properties ◽  
Effective Properties ◽  
Micromechanical Model ◽  
Short Fiber ◽  
Functionally Graded ◽  
Fiber Reinforced Composites ◽  
Reinforced Composites ◽  
Fiber Reinforced ◽  
The Matrix

A micromechanical model for short fiber-reinforced composites (SFRCs) with functionally graded interphases and a systematic prediction scheme to determine the effective properties are presented. The matrix and the fibers are regarded to be linear elastic, isotropic, and homogeneous. Fibers are assumed to be ellipsoids coated perfectly by functionally graded interphases, which is supposed to be formed chemically or physically by the constituents near the interface. First, to analyze the grading interphase effect, layer-wise concept is followed to divide the functionally graded interphases into multi-homogeneous sub-layers. Next, to take the effect of functionally graded interphases into account, a combination of multi-inclusion method and Mori–Tanaka method is applied to predict effective elastic properties of this unidirectional SFRCs with respect to the content and aspect ratio of the inclusions. By employing coordinate transformation, spatially elastic moduli are obtained. Finally, Voigt homogenization scheme is used to obtain the overall, averaged, symmetrical elastic properties of the SFRCs. Numerical examples and analyses demonstrate the applicability of the proposed method and indicate the influences of graded interphase, orientation, and aspect ratio of inclusions as well as properties and contents of the constituents on the overall properties of SFRCs.

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