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USGS2017

Magnetotelluric imaging of lower crustal melt and lithospheric hydration in the Rocky Mountain Front transition zone, Colorado, USA

We present an electrical resistivity model of the crust and upper mantle from two‐dimensional (2‐D) anisotropic inversion of magnetotelluric data collected along a 450 km transect of the Rio Grande rift, southern Rocky Mountains, and High Plains in Colorado, USA. Our model provides a window into the modern‐day lithosphere beneath the Rocky Mountain Front to depths in excess of 150 km. Two key features of the 2‐D resistivity model are (1) a broad zone (~200 km wide) of enhanced electrical conductivity (<20 Ωm) in the midcrust to lower crust that is centered beneath the highest elevations of the southern Rocky Mountains and (2) hydrated lithospheric mantle beneath the Great Plains with water content in excess of 100 ppm. We interpret the high conductivity region of the lower crust as a zone of partially molten basalt and associated deep‐crustal fluids that is the result of recent (less than 10 Ma) tectonic activity in the region. The recent supply of volatiles and/or heat to the base of the crust in the late Cenozoic implies that modern‐day tectonic activity in the western United States extends to at least the western margin of the Great Plains. The transition from conductive to resistive upper mantle is caused by a gradient in lithospheric modification, likely including hydration of nominally anhydrous minerals, with maximum hydration occurring beneath the Rocky Mountain Front. This lithospheric “hydration front” has implications for the tectonic evolution of the continental interior and the mechanisms by which water infiltrates the lithosphere.

Colorado↗

USGS2005

Magmatic unrest beneath Mammoth Mountain, California

Mammoth Mountain, which stands on the southwest rim of Long Valley caldera in eastern California, last erupted ∼57,000 years BP. Episodic volcanic unrest detected beneath the mountain since late 1979, however, emphasizes that the underlying volcanic system is still active and capable of producing future volcanic eruptions. The unrest symptoms include swarms of small ( M ≤ 3) earthquakes, spasmodic bursts (rapid-fire sequences of brittle-failure earthquakes with overlapping coda), long-period (LP) and very-long-period (VLP) volcanic earthquakes, ground deformation, diffuse emission of magmatic CO 2 , and fumarole gases with elevated 3 He/ 4 He ratios. Spatial-temporal relations defined by the multi-parameter monitoring data together with earthquake source mechanisms suggest that this Mammoth Mountain unrest is driven by the episodic release of a volume of CO 2 -rich hydrous magmatic fluid derived from the upper reaches of a plexus of basaltic dikes and sills at mid-crustal depths (10–20 km). As the mobilized fluid ascends through the brittle–plastic transition zone and into overlying brittle crust, it triggers earthquake swarm activity and, in the case of the prolonged, 11-month-long earthquake swarm of 1989, crustal deformation and the onset of diffuse CO 2 emissions. Future volcanic activity from this system would most likely involve steam explosions or small-volume, basaltic, strombolian or Hawaiian style eruptions. The impact of such an event would depend critically on vent location and season.

California↗

USGS2014

A review of environmental impacts of salts from produced waters on aquatic resources

Salts are frequently a major constituent of waste waters produced during oil and gas production. These produced waters or brines must be treated and/or disposed and provide a daily challenge for operators and resource managers. Some elements of salts are regulated with water quality criteria established for the protection of aquatic wildlife, e.g. chloride (Cl − ), which has an acute standard of 860 mg/L and a chronic standard of 230 mg/L. However, data for establishing such standards has only recently been studied for other components of produced water, such as bicarbonate (HCO 3 − ), which has acute median lethal concentrations (LC50s) ranging from 699 to > 8000 mg/L and effects on chronic toxicity from 430 to 657 mg/L. While Cl− is an ion of considerable importance in multiple geographical regions, knowledge about the effects of hardness (calcium and magnesium) on its toxicity and about mechanisms of toxicity is not well understood. A multiple-approach design that combines studies of both individuals and populations, conducted both in the laboratory and the field, was used to study toxic effects of bicarbonate (as NaHCO 3 ). This approach allowed interpretations about mechanisms related to growth effects at the individual level that could affect populations in the wild. However, additional mechanistic data for HCO 3 − , related to the interactions of calcium (Ca 2 + ) precipitation at the microenvironment of the gill would dramatically increase the scientific knowledge base about how NaHCO 3 might affect aquatic life. Studies of the effects of mixtures of multiple salts present in produced waters and more chronic effect studies would give a better picture of the overall potential toxicity of these ions. Organic constituents in hydraulic fracturing fluids, flowback waters, etc. are a concern because of their carcinogenic properties and this paper is not meant to minimize the importance of maintaining vigilance with respect to potential organic contamination.

International Journal of Coal Geology↗

USGS2013

Chemical controls on fault behavior: weakening of serpentinite sheared against quartz-bearing rocks and its significance for fault creep in the San Andreas system

The serpentinized ultramafic rocks found in many plate-tectonic settings commonly are juxtaposed against crustal rocks along faults, and the chemical contrast between the rock types potentially could influence the mechanical behavior of such faults. To investigate this possibility, we conducted triaxial experiments under hydrothermal conditions (200-350°C), shearing serpentinite gouge between forcing blocks of granite or quartzite. In an ultramafic chemical environment, the coefficient of friction, µ, of lizardite and antigorite serpentinite is 0.5-0.6, and µ increases with increasing temperature over the tested range. However, when either lizardite or antigorite serpentinite is sheared against granite or quartzite, strength is reduced to µ ~ 0.3, with the greatest strength reductions at the highest temperatures (temperature weakening) and slowest shearing rates (velocity strengthening). The weakening is attributed to a solution-transfer process that is promoted by the enhanced solubility of serpentine in pore fluids whose chemistry has been modified by interaction with the quartzose wall rocks. The operation of this process will promote aseismic slip (creep) along serpentinite-bearing crustal faults at otherwise seismogenic depths. During short-term experiments serpentine minerals reprecipitate in low-stress areas, whereas in longer experiments new Mg-rich phyllosilicates crystallize in response to metasomatic exchanges across the serpentinite-crustal rock contact. Long-term shear of serpentinite against crustal rocks will cause the metasomatic mineral assemblages, which may include extremely weak minerals such as saponite or talc, to play an increasingly important role in the mechanical behavior of the fault. Our results may explain the distribution of creep on faults in the San Andreas system.

California↗

USGS2006

An effective medium inversion algorithm for gas hydrate quantification and its application to laboratory and borehole measurements of gas hydrate-bearing sediments

The presence of gas hydrate in marine sediments alters their physical properties. In some circumstances, gas hydrate may cement sediment grains together and dramatically increase the seismic P- and S-wave velocities of the composite medium. Hydrate may also form a load-bearing structure within the sediment microstructure, but with different seismic wave attenuation characteristics, changing the attenuation behaviour of the composite. Here we introduce an inversion algorithm based on effective medium modelling to infer hydrate saturations from velocity and attenuation measurements on hydrate-bearing sediments. The velocity increase is modelled as extra binding developed by gas hydrate that strengthens the sediment microstructure. The attenuation increase is modelled through a difference in fluid flow properties caused by different permeabilities in the sediment and hydrate microstructures. We relate velocity and attenuation increases in hydrate-bearing sediments to their hydrate content, using an effective medium inversion algorithm based on the self-consistent approximation (SCA), differential effective medium (DEM) theory, and Biot and squirt flow mechanisms of fluid flow. The inversion algorithm is able to convert observations in compressional and shear wave velocities and attenuations to hydrate saturation in the sediment pore space. We applied our algorithm to a data set from the Mallik 2L–38 well, Mackenzie delta, Canada, and to data from laboratory measurements on gas-rich and water-saturated sand samples. Predictions using our algorithm match the borehole data and water-saturated laboratory data if the proportion of hydrate contributing to the load-bearing structure increases with hydrate saturation. The predictions match the gas-rich laboratory data if that proportion decreases with hydrate saturation. We attribute this difference to differences in hydrate formation mechanisms between the two environments.

Geophysical Journal International↗

USGS2009

The source of infrasound associated with long-period events at mount St. Helens

During the early stages of the 2004-2008 Mount St. Helens eruption, the source process that produced a sustained sequence of repetitive long-period (LP) seismic events also produced impulsive broadband infrasonic signals in the atmosphere. To assess whether the signals could be generated simply by seismic-acoustic coupling from the shallow LP events, we perform finite difference simulation of the seismo-acoustic wavefield using a single numerical scheme for the elastic ground and atmosphere. The effects of topography, velocity structure, wind, and source configuration are considered. The simulations show that a shallow source buried in a homogeneous elastic solid produces a complex wave train in the atmosphere consisting of P/SV and Rayleigh wave energy converted locally along the propagation path, and acoustic energy originating from , the source epicenter. Although the horizontal acoustic velocity of the latter is consistent with our data, the modeled amplitude ratios of pressure to vertical seismic velocity are too low in comparison with observations, and the characteristic differences in seismic and acoustic waveforms and spectra cannot be reproduced from a common point source. The observations therefore require a more complex source process in which the infrasonic signals are a record of only the broadband pressure excitation mechanism of the seismic LP events. The observations and numerical results can be explained by a model involving the repeated rapid pressure loss from a hydrothermal crack by venting into a shallow layer of loosely consolidated, highly permeable material. Heating by magmatic activity causes pressure to rise, periodically reaching the pressure threshold for rupture of the "valve" sealing the crack. Sudden opening of the valve generates the broadband infrasonic signal and simultaneously triggers the collapse of the crack, initiating resonance of the remaining fluid. Subtle waveform and amplitude variability of the infrasonic signals as recorded at an array 13.4 km to the NW of the volcano are attributed primarily to atmospheric boundary layer propagation effects, superimposed upon amplitude changes at the source.

Washington↗

USGS2025

Impact of gas/liquid phase change of CO2 during injection for sequestration

CO 2 sequestration in deep saline formations is an effective and important process to control the rapid rise in CO 2 emissions. The process of injecting CO 2 requires reliable predictions of the stress in the formation and the fluid pressure distributions – particularly since monitoring of the CO 2 migration is difficult – to mitigate leakage, prevent induced seismicity, and analyze wellbore stability. A key aspect of CO 2 is the gas–liquid phase transition at the temperatures and pressures of relevance to leakage and sequestration, which has been recognized as being critical for accurate predictions but has been challenging to model without ad hoc empiricisms. This paper presents a robust multiphase thermodynamics-based poromechanics model to capture the complex phase transition behavior of CO 2 and predict the stress and pressure distribution under super- and sub- critical conditions during the injection process. A finite element implementation of the model is applied to analyze the behavior of a multiphase porous system with CO 2 as it displaces the fluid brine phase. We find that if CO 2 undergoes a phase transition in the geologic reservoir, the spatial variation of the density is significantly affected, and the migration mobility of CO 2 decreases in the reservoir. A key feature of our approach is that we do not a priori assume the location of the CO 2 gas/liquid interface – or even if it occurs at all – but rather, this is a prediction of the model, along with the spatial variation of the phase of CO 2 and the change of the saturation profile due to the phase change.

Journal of the Mechanics and Physics of Solids↗

USGS2001

An analytical solution for transient flow of Bingham viscoplastic materials in rock fractures

We present below an analytical solution to model the one-dimensional transient flow of a Bingham viscoplastic material in a fracture with parallel walls (smooth or rough) that is subjected to an applied pressure gradient. The solution models the acceleration and the deceleration of the material as the pressure gradient changes with time. Two cases are considered: A pressure gradient applied over a finite time interval and an applied pressure gradient that is constant over time. The solution is expressed in dimensionless form and can therefore be used for a wide range of Bingham viscoplastic materials. The solution is also capable of capturing the transition that takes place in a fracture between viscoplastic flow and rigid plug flow. Also, it shows the development of a rigid central layer in fractures, the extent of which depends on the fluid properties (viscosity and yield stress), the magnitude of the pressure gradient, and the fracture aperture and surface roughness. Finally, it is shown that when a pressure gradient is applied and kept constant, the solution for the fracture flow rate converges over time to a steady-state solution that can be defined as a modified cubic law. In this case, the fracture transmissivity is found to be a non-linear function of the head gradient. This solution provides a tool for a better understanding of the flow of Bingham materials in rock fractures, interfaces, and cracks. ?? 2001 Elsevier Science Ltd. All rights reserved.

International Journal of Rock Mechanics and Mining↗

USGS2024

Brittle regime slip partitioned damage and deformation mechanisms along the eastern Denali fault zone in southwestern, Yukon

Rare bedrock exposures of the eastern Denali fault zone in southwestern Yukon allow for the measurement, sampling, and analyses of brittle regime fault slip data and deformation mechanisms to explore relations to far field, oblique plate motions. Host rock lithologies and associated slip surfaces show episodic damage zone‐related deformation and calcite ± hematite ± chlorite related hydrothermal fluid flow. This regional scale network of asymmetric fault damage is spatially and kinematically linked to a discrete and narrow fault core. Fault network observations, orientations, slip data, and strain inversions document a slip partitioned strike‐slip fault system with locally and mutually overprinting strike‐, oblique‐, and dip‐slip components. Microstructural analyses reveal crystal plastic and co‐seismic brittle deformation mechanisms active in a narrow range of upper crustal temperature, pressure, fluid, and chemical conditions. The net damage related slip is not exclusively formed by a single kinematic system, but rather a fully partitioned, time integrated system likely operative for much of the fault's brittle regime evolution temporally constrained by previously published thermochronometric data. Although the fault slip data was collected from outcrop‐scale exposures at sites tens of kilometers apart, results show remarkable correlation between fault kinematics and plate motions along the ∼580 km long eastern Denali fault segment. End member, subhorizontal, northeast directed reverse and north directed dextral strike slip fault strain axes closely reflect relative plate motion interactions over at least the last 30 m.y. and act as a proxy for far‐field stresses compatible with the kinematics of the damage zone network.

Alaska↗

USGS2010

Seismic source mechanism of degassing bursts at Kilauea volcano, Hawaii: Results from waveform inversion in the 10–50 s band

The current (March 2008 to February 2009) summit eruptive activity at Kilauea Volcano is characterized by explosive degassing bursts accompanied by very long period (VLP) seismic signals. We model the source mechanisms of VLP signals in the 10–50 s band using data recorded for 15 bursts with a 10‐station broadband network deployed in the summit caldera. To determine the source centroid location and source mechanism, we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous medium that takes topography into account. The VLP signals associated with the bursts originate in a source region ∼1 km below the eastern perimeter of Halemaumau pit crater. The observed waveforms are well explained by the combination of a volumetric component and a vertical single force component. For the volumetric component, several source geometries are obtained which equally explain the observed waveforms. These geometries include (1) a pipe dipping 64° to the northeast; (2) two intersecting cracks including an east striking crack (dike) dipping 80° to the north, intersecting a north striking crack (another dike) dipping 65° to the east; (3) a pipe dipping 58° to the northeast, intersecting a crack dipping 48° to the west–southwest; and (4) a pipe dipping 57° to the northeast, intersecting a pipe dipping 58° to the west–southwest. Using the dual‐crack model as reference, the largest volume change obtained among the 15 bursts is ∼24,400 m 3 , and the maximum amplitude (peak to peak) of the force is ∼20 GN. Each burst is marked by a similar sequence of deflation and inflation, trailed by decaying oscillations of the volumetric source. The vertical force is initially upward, synchronous with source deflation, then downward, synchronous with source reinflation, followed by oscillations with polarity opposite to the volumetric oscillations. This combination of force and volume change is attributed to pressure and momentum changes induced during a fluid dynamic source mechanism involving the ascent, expansion, and burst of a large slug of gas within the upper ∼150 m of the magma conduit. As the slug expands upon approach to the surface and more liquid becomes wall supported by viscous shear forces, the pressure below the slug decreases, inducing conduit deflation and an upward force on the Earth. The final rapid slug expansion and burst stimulate VLP and LP oscillations of the conduit system, which slowly decay due to viscous dissipation and elastic radiation. Consideration of the fluid dynamic arguments leads us to prefer the dual‐crack VLP source model as it is the only candidate model capable of producing plausible values of length scales and pressure changes. The magnitudes of the vertical forces observed in the 15 bursts appear consistent with slug masses of 10 4 to 10 6 kg.

Hawaii↗

USGS2022

Detection of aseismic slip and poroelastic reservoir deformation at the North Brawley Geothermal Field from 2009 to 2019

The North Brawley Geothermal Field, located within the Brawley Seismic Zone of Southern California, presents a case study for understanding seismic hazards linked to fluid injection and geothermal energy extraction. An earthquake swarm near the geothermal field in 2012 included two earthquakes with magnitudes greater than 5 and was potentially preceded by a years-long aseismic slip transient. To better understand ground deformation around the geothermal field, including its evolution with time and its physical mechanisms, we analyze deformation before, during, and after the swarm using ground- and satellite-based geodetic techniques between 2009 and 2019. We integrate observations from GNSS, Sentinel-1, TerraSAR-X, UAVSAR, and leveling surveys into a single deformation history. Modeling of this new collection of observations at the North Brawley Geothermal Field provides evidence for 80% more pre-swarm aseismic slip than previously recognized from 2009 to 2012. During the 2012 Brawley swarm, our geodetic slip inversions closely match the results of seismic waveform inversions from the swarm events. After the 2012 swarm, surface deformation is dominated by poroelastic deformation of a shallow fluid reservoir at <1 km depth rather than fault slip. The deformation history and seismicity catalogs at North Brawley suggest a cessation of fault-related slip during the ∼7 years after the 2012 earthquake swarm.

California↗

USGS1998

Waveform inversion of very long period impulsive signals associated with magmatic injection beneath Kilauea Volcano, Hawaii

We use data from broadband seismometers deployed around the summit of Kilauea Volcano to quantify the mechanism associated with a transient in the flow of magma feeding the east rift eruption of the volcano. The transient is marked by rapid inflation of the Kilauea summit peaking at 22 μrad 4.5 hours after the event onset, followed by slow deflation over a period of 3 days. Superimposed on the summit inflation is a series of sawtooth displacement pulses, each characterized by a sudden drop in amplitude lasting 5–10 s followed by an exponential recovery lasting 1–3 min. The sawtooth waveforms display almost identical shapes, suggesting a process involving the repeated activation of a fixed source. The particle motion associated with each sawtooth is almost linear, and its major swing shows compressional motion at all stations. Analyses of semblance and particle motion are consistent with a point source located 1 km beneath the northeast edge of the Halemaumau pit crater. To estimate the source mechanism, we apply a moment tensor inversion to the waveform data, assuming a point source embedded in a homogeneous half-space with compressional and shear wave velocities representative of the average medium properties at shallow depth under Kilauea. Synthetic waveforms are constructed by a superposition of impulse responses for six moment tensor components and three single force components. The origin times of individual impulses are distributed along the time axis at appropriately small, equal intervals, and their amplitudes are determined by least squares. In this inversion, the source time functions of the six tensor and three force components are determined simultaneously. We confirm the accuracy of the inversion method through a series of numerical tests. The results from the inversion show that the waveform data are well explained by a pulsating transport mechanism operating on a subhorizontal crack linking the summit reservoir to the east rift of Kilauea. The crack acts like a buffer in which a batch of fluid (magma and/or gas) accumulates over a period of 1–3 min before being rapidly injected into a larger reservoir (possibly the east rift) over a timescale of 5–10 s. The seismic moment and volume change associated with a typical batch of fluid are approximately 10 14 N m and 3000 m 3 , respectively. Our results also point to the existence of a single force component with amplitude of 10 9 N, which may be explained as the drag force generated by the flow of viscous magma through a narrow constriction in the flow path. The total volume of magma associated with the 4.5-hour-long activation of the pulsating source is roughly 500,000 m 3 in good agreement with the integrated volume flow rate of magma estimated near the eruptive site.

Journal of Geophysical Research B: Solid Earth↗

USGS2002

The potential for free and mixed convection in sedimentary basins

Free thermal convection and mixed convection are considered as potential mechanisms for mass and heat transport in sedimentary basins. Mixed convection occurs when horizontal flows (forced convection) are superimposed on thermally driven flows. In cross section, mixed convection is characterized by convection cells that migrate laterally in the direction of forced convective flow. Two-dimensional finite-element simulations of variable-density groundwater flow and heat transport in a horizontal porous layer were performed to determine critical mean Rayleigh numbers for the onset of free convection, using both isothermal and semi-conductive boundaries. Additional simulations imposed a varying lateral fluid flux on the free-convection pattern. Results from these experiments indicate that forced convection becomes dominant, completely eliminating buoyancy-driven circulation, when the total forced-convection fluid flux exceeds the total flux possible due to free convection. Calculations of the thermal rock alteration index (RAI=q·∇T) delineate the patterns of potential diagenesis produced by fluid movement through temperature gradients. Free convection produces a distinct pattern of alternating positive and negative RAIs, whereas mixed convection produces a simpler layering of positive and negative values and in general less diagenetic alteration.

Hydrogeology Journal↗

USGS2012

Correlation of clayey gouge in a surface exposure of the San Andreas fault with gouge at depth from SAFOD: Implications for the role of serpentinite in fault mechanics

Magnesium-rich clayey gouge similar to that comprising the two actively creeping strands of the San Andreas Fault in drill core from the San Andreas Fault Observatory at Depth (SAFOD) has been identified in a nearby outcrop of serpentinite within the fault zone at Nelson Creek. Each occurrence of the gouge consists of porphyroclasts of serpentinite and sedimentary rocks dispersed in a fine-grained, foliated matrix of Mg-rich smectitic clays. The clay minerals in all three gouges are interpreted to be the product of fluid-assisted, shear-enhanced reactions between quartzofeldspathic wall rocks and serpentinite that was tectonically entrained in the fault from a source in the Coast Range Ophiolite. We infer that the gouge at Nelson Creek connects to one or both of the gouge zones in the SAFOD core, and that similar gouge may occur at depths in between. The special significance of the outcrop is that it preserves the early stages of mineral reactions that are greatly advanced at depth, and it confirms the involvement of serpentinite and the Mg-rich phyllosilicate minerals that replace it in promoting creep along the central San Andreas Fault.

California↗

USGS2018

Ground ruptures attributed to groundwater overexploitation damaging Jocotepec city in Jalisco, Mexico: 2016 field excursion of IGCP-641

IGCP Project 641 (Mechanisms, Monitoring and Modeling Earth Fissure generation and Fault activation due to subsurface Fluid exploitation – M3EF3) held its second international workshop from November 2 to 6, 2016, in Puerto Vallarta and included a two-day field trip to Guadalajara and Jocotepec in the Mexican state of Jalisco (Fig. 1a). M3EF3 is aimed at i) understanding the mechanisms that cause the formation of “ground ruptures”, as a response to changes in the stress state in the subsoil, ii) monitoring their occurrence, and iii) developing appropriate approaches to model their formation and growth. Notice that many times it is difficult to discern whether a particular instance of a “ruptured” land surface is due to an earth fissure with a surface manifestation or a surface failure associated with the activation of a pre-existing fault, especially where a fault has not been mapped and where there is no obvious scarp. Therefore, in M3EF3 we preferred to use the term “ground rupture”, to refer to both such occurrences.

Jalisco↗

USGS2014

Interrelations among the soil-water retention, hydraulic conductivity, and suction-stress characteristic curves

The three fundamental constitutive relations that describe fluid flow, strength, and deformation behavior of variably saturated soils are the soil-water retention curve (SWRC), hydraulic conductivity function (HCF), and suction-stress characteristic curve (SSCC). Until recently, the interrelations among the SWRC, HCF, and SSCC have not been well established. This work sought experimental confirmation of interrelations among these three constitutive functions. Results taken from the literature for six soils and those obtained for 11 different soils were used. Using newly established analytical relations among the SWRC, HCF, and SSCC and these test results, the authors showed that these three constitutive relations can be defined by a common set of hydromechanical parameters. The coefficient of determination for air-entry pressures determined independently using hydraulic and mechanical methods is >0.99, >0.98 for the pore size parameter, and 0.94 for the residual degree of saturation. One practical implication is that one of any of the four experiments (axis-translation, hydraulic, shear-strength, or deformation) is sufficient to quantify all three constitutive relations.

Journal of Geotechnical and Geoenvironmental Engin↗

USGS1981

A transient laboratory method for determining the hydraulic properties of 'tight' rocks-I. Theory

Transient pulse testing has been employed increasingly in the laboratory to measure the hydraulic properties of rock samples with low permeability. Several investigators have proposed a mathematical model in terms of an initial-boundary value problem to describe fluid flow in a transient pulse test. However, the solution of this problem has not been available. In analyzing data from the transient pulse test, previous investigators have either employed analytical solutions that are derived with the use of additional, restrictive assumptions, or have resorted to numerical methods. In Part I of this paper, a general, analytical solution for the transient pulse test is presented. This solution is graphically illustrated by plots of dimensionless variables for several cases of interest. The solution is shown to contain, as limiting cases, the more restrictive analytical solutions that the previous investigators have derived. A method of computing both the permeability and specific storage of the test sample from experimental data will be presented in Part II.

International Journal of Rock Mechanics and Mining↗

USGS2024

Earthquake cycle mechanics during caldera collapse: Simulating the 2018 Kīlauea eruption

In multiple observed caldera-forming eruptions, the rock overlying a draining magma reservoir dropped downward along ring faults in sequences of discrete collapse earthquakes. These sequences are analogous to tectonic earthquake cycles and provide opportunities to examine fault mechanics and collapse eruption dynamics over multiple events. Collapse earthquake cycles have been studied with zero-dimensional slider-block models, but these do not account for the complicated interplay between fluid and elastic dynamics or for factors such as the heterogeneous fault properties and non-vertical ring fault geometries often inferred at volcanoes. We present two-dimensional axisymmetric mafic piston-like collapse earthquake cycle models that include rate-and-state friction, fully-dynamic elasticity, and compressible viscous fluid magma flow. We demonstrate that collapse earthquake intervals and magnitudes are highly sensitive to inertial effects, evolving stress fields, fault geometry, and depth-varying fault friction. Given the consistent earthquake cycles observed in most eruptions, this suggests that ring faults can quickly stabilize and often become nearly vertical at depth. We use the well-monitored 2018 collapse sequence at Kı̄lauea as a case study. Our model can produce many features of Kı̄lauea seismic and geodetic observations, except for a significant amount of interseismic slip, which cannot be readily explained with simple rate-and-state friction parameterizations.

Hawaii↗