Tidal Strain Research Articles

Processes of stratification and vertical turbulent mixing in a choked lagoon system

This work concentrates on the processes of stratification and turbulent mixing in a choked shallow lagoon, Xiaohai Lagoon, by using a three-dimensional hydrodynamic model. The model results were processed to derive buoyancy frequency, shear production, gradient Richardson number, and buoyancy flux during the tidal cycles. The parameters regarding stratification and turbulent mixing exhibited significant heterogeneity within the lagoon. Shear production primarily occurred in the downstream region with complex shoreline and bed morphology, whereas stratification was predominantly developed in the flat upstream region by tidal strain and baroclinic strain, especially during the ebb tide. The salinity mixing indicated by buoyancy flux was thus mainly confined during the ebbs in the downstream region and the middle-lower layer of the upstream region. In addition, the distribution of the gradient Richardson number indicated dominances of shear instability and buoyancy effects in the downstream and upstream regions, respectively. By simulating various combinations of river discharges and offshore tidal ranges, we examined the variations of stratification and turbulent mixing within the lagoon's parameter space. The results revealed the influence of the interaction between tidal and runoff forces through a modulation of the salinity interface's moving range. Further investigation of the buoyancy balance underlying the variation in stratification revealed the dominance of straining and mixing, while advection played a secondary role. Straining dominance appeared at locations with sufficient streamwise density gradients in the upstream region during the ebb. The contribution of advection was essential, as straining and mixing largely counteracted each other's effects through their persistent competition. A conceptual model for the stratification and mixing patterns in choked lagoons during the tidal cycle was then proposed. This conceptual model clarifies the process of the interaction between stratification and turbulent mixing in the distinctive hydrological and geomorphic environments of choked lagoons and could serve as a conference for investigating other lagoon systems in the world.

The response of borehole water levels in an ophiolitic, peridotite aquifer to atmospheric, solid Earth, and ocean tides

Peridotite aquifers are ubiquitous on Earth, but most are in the deep-sea, and thus difficult to access. Ophiolites provide a unique opportunity to study peridotite aquifers, and the Oman Drilling Project established a Multi-Borehole Observatory in a peridotite terrain of the Samail ophiolite. We use the water level response of two 400-m deep boreholes (BA1B, BA1D) to solid Earth, ocean, and atmospheric tides to investigate the hydromechanical structure of the aquifer. The two boreholes are offset by ∼ 100 m but exhibit markedly different tidal responses, indicating a high degree of short-length-scale heterogeneity. Hole BA1B does not respond to tidal strain or barometric loading, consistent with the behavior of an unconfined aquifer. Hole BA1D responds to both tidal strain and barometric loading, indicating some degree of confinement. The response to applied strain, which includes a non-negligible ocean tidal loading component, is consistent with a partially confined, low conductivity aquifer. The response to barometric loading appears to be affected by the complex hydrological structure of the surficial zone and we were not able to fit the observations to within error. Aquifer conductivity estimates for Hole BA1D based on the response to tidal strain are within a factor of ∼ 3 of pumping test estimates.

Anisotropic seismic velocity variations in response to different orientations of tidal deformations

SUMMARY Microcracks or micropores in rocks cause the elastic moduli to change with the applied strain owing to the nonlinear elasticity of the geomaterial, which causes temporal changes in the seismic wave velocity. Thus, variations in seismic wave velocity can be used as a proxy for understanding the strain or stress variations in the crust, which are crucial for figuring out the dynamics of the fault zones and volcanic domains. According to the theory of nonlinear elasticity, the second- and third-order elastic constants and strain tensors contribute to the strain derivative of seismic wave velocity changes. Although laboratory experiments have estimated third-order elastic constants for rock samples, the in situ values of those constants for the crust are difficult to obtain. In this study, seismic velocity changes were investigated in different directions of tidal deformations to provide constraints on the third-order elastic constants in the shallow crust by applying a seismic interferometry method to ambient noise records. We observed that negative velocity changes were of larger magnitude in the station-pair direction parallel to the tidal strain’s direction. Nonlinear elasticity in shallow crust may cause anisotropic velocity variations in response to tidal deformations. Our results highlight the use of velocity change measurements in different directions of tidal strain to constrain nonlinear elastic parameters on a field scale.

S Hmax orientation in the Alpine region from observations of stress-induced anisotropy of nonlinear elasticity

SUMMARY The orientation of SHmax is commonly estimated from in situ borehole breakouts and earthquake focal mechanisms. Borehole measurements are expensive, and therefore sparse, and earthquake measurements can only be made in regions with many well-characterized earthquakes. Here, we derive the stress-field orientation using stress-induced anisotropy in nonlinear elasticity. In this method, we measure the strain derivative of velocity as a function of azimuth. We use a natural pump-probe (NPP) approach which consists of measuring elastic wave speed using empirical Green’s functions (probe) at different points of the earth tidal strain cycle (pump). The approach is validated using a larger data set in the Northern Alpine Foreland region where the orientation of maximum horizontal compressive stress is known from borehole breakouts and drilling-induced fractures. The technique resolves NNW-SSW to N-S directed SHmax which is in good agreement with conventional methods and the recent crustal stress model. We confirm that the NPP method can be applied to dense large-scale seismic arrays. The technique is then applied to the Southern Alps to understand the contemporary stress pattern associated with the ongoing deformation due to counterclockwise rotation of the Adriatic plate with respect to the European plate. Our results explain why the two major faults in Northeastern Italy, the Giudicarie Fault and the Periadriatic Line (Pustertal–Gailtal Fault) are currently inactive, while the currently acting stress field allows faults in Slovenia to deform actively. We have demonstrated that the pump-probe method has the potential to fill in the measurement gap left by conventional approaches, both in terms of regional coverage and in depth.

Detailed View of the Seismogenic Structures and Processes of the 2022 Bayan Har Intraplate Earthquake Swarm on the East Margin of the Qinghai–Tibet Plateau

Abstract At 16:03 on 9 June 2022 (UTC), an Mw 5.5 earthquake followed by several Mw>4 events, including the largest event of Mw 5.8 within a few hours, occurred in the Maerkang area near the Caodeng Hot Spring Town, located in the south-central part of the Bayan Har plate on the eastern margin of the Qinghai–Tibet plateau. The earthquake swarm allows understanding the tectonic stress environment of the Bayan Har plate and is an example of a typical moderate-to-strong intraplate earthquake swarm. This article comprehensively analyzes the detailed seismogenic fault structure of the swarm by means of precise hypocenter relocation, focal mechanism inversion for Mw>4 earthquakes, inversion of the tectonic stress field in different regions of the Bayan Har plate, tidal strain calculation, and seismicity statistics. The results show that the swarm was not directly related to the nearby mapped Songgang fault, but rather resulted from the successive activation of a series of unknown faults. The precise hypocenter distribution, together with focal mechanism solutions of major earthquakes, illuminates five major seismogenic faults with conjugate relationships and stepover. Spatial and temporal migration of hypocenters, stress transfer, and tidal correlations demonstrate that cascade triggering, afterslip, and overpressured fluid might have jointly played a role in causing the earthquake swarm. As an output of this research, a set of verifiable datasets are provided as a basis for further in-depth research.

Step-over of strike-slip faults and overpressure fluid favor occurrence of foreshocks: Insights from the 1975 Haicheng fore-main-aftershock sequence, China

This study analyzed and summarized in detail the spatial and temporal distributions of earthquakes, tidal responses, focal mechanisms, and stress field characteristics for the M 7.3 Haicheng earthquake sequence in February 1975. The foreshocks are related to the main fault and the conjugate faults surrounding the extension step-over in the middle. The initiation timing of the foreshock clusters and the original time of the mainshock were clearly modulated by the Earth's tidal force and coincided with the peak of dilational volumetric tidal strain. As a plausible and testable hypothesis, we proposed a fluid-driven foreshock model, by which all observed seismicity features can be more reasonably interpreted with respect to the results of existing models. Together with some other known examples, the widely existing step-over along strike-slip faults and associated conjugate faults, especially for extensional ones in the presence of deep fluids, favor the occurrence of short-term foreshocks. Although clustered seismicity with characteristics similar to those of the studied case is not a sufficient and necessary condition for large earthquakes to occur under similar tectonic conditions, it undoubtedly has a warning significance for the criticality of the main fault. Subsequent testing would require quantification of true/false positives/negatives.

Earthquakes and Heavy Rainfall Influence on Aquifer Properties: A New Coupled Earth and Barometric Tidal Response Model in a Confined Bi‐Layer Aquifer

AbstractAmong the impacts of earthquakes on aquifers, permeability change is one of the most challenging to quantify, since techniques to measure permeability evolution are scarce. The study of tidal response of boreholes is one of the most promising, yet complex to use in practice. We used 14 years of piezometric level measurements and two concurrent source signals, earth tidal strain and barometric pressure, for which we separated the respective contribution in a state‐of‐the‐art tidal analysis. We developed a new general analytical hydrogeological model, based on geological observations of a confined bi‐layer aquifer. It is able to match combined observations of earth and barometric tide phase lags which could not be explained by existing models. We demonstrate that its relative complexity can be overcome thanks to the results of tidal analysis, yielding a simpler model adapted to the Fond Lahaye site of the Martinique Island. The resulting evolution of diffusivity and loading efficiency, was validated independently with several pumping tests occurring all along the studied period. The transient diffusivity increases and decreases indicate which earthquakes impacted the aquifer, enabling to establish an empirical magnitude‐distance relationship criterion. This criterion confirms the suspected dependence on dynamic stresses, which decrease as the square of the hypocentral distance. Additionally, we investigate two other factors of diffusivity changes: heavy rainfall events and aquifer withdrawals, which demonstrates the sensitivity of volcanic aquifers properties to environmental and anthropogenic influence.

Respiratory Rate as a Factor in Lung Injury-Not Just What You Set, but How You Set.

Respiratory Rate as a Factor in Lung Injury-Not Just What You Set, but How You Set.

Prone position decreases acute lung inflammation measured by [11C](R)-PK11195 positron emission tomography in experimental acute respiratory distress syndrome.

Whether prone positioning (PP) modulates acute lung inflammation by the modulation of biomechanical forces of ventilator-induced lung injuries (VILIs) remains unclear. We aimed to demonstrate that PP decreases acute lung inflammation in animals with experimental acute respiratory distress syndrome (ARDS). Animals were under general anesthesia and protective ventilation (tidal volume 6 mL·kg-1, PEEP 5 cmH2O). ARDS was induced by intratracheal instillation of chlorohydric acid. Animals were then randomized to PP, or to supine position (SP). After 4 h, a positron emission tomography (PET) acquisition with [11C](R)-PK11195 was performed coupled with computerized tomography (CT) acquisitions, allowing the CT quantification of VILI-associated parameters. [11C](R)-PK11195 lung uptake was quantified using pharmacokinetic multicompartment models. Analyses were performed on eight lung sections distributed along the antero-posterior dimension. Six animals were randomized to PP, five to SP (median [Formula: see text]/[Formula: see text] [interquartile range]: 164 [102-269] mmHg). The normally aerated compartment was significantly redistributed to the posterior lung regions of animals in PP, compared with SP. Dynamic strain was significantly increased in posterior regions of SP animals, compared with PP. After 4 h, animals in PP had a significantly lower uptake of [11C](R)-PK11195, compared with SP. [11C](R)-PK11195 regional uptake was independently associated with the study group, dynamic strain, tidal hyperinflation, and regional respiratory system compliance in multivariate analysis. In an experimental model of ARDS, 4 h of PP significantly decreased acute lung inflammation assessed with PET. The beneficial impact of PP on acute lung inflammation was consecutive to the combination of decreased biomechanical forces and changes in the respiratory system mechanics.NEW & NOTEWORTHY Prone position decreases acute lung macrophage inflammation quantified in vivo with [11C](R)-PK11195 positron emission tomography in an experimental acute respiratory distress syndrome. Regional macrophage inflammation is maximal in the most anterior and posterior lung section of supine animals, in relation with increased regional tidal strain and hyperinflation, and reduced regional lung compliance.

Numerical Simulations of Drainage Grooves in Response to Extensional Fracturing: Testing the Phobos Groove Formation Model

The long, shallow, parallel grooves that cut across the surface of the Martian moon Phobos remain enigmatic, with distinct implications for understanding the evolution of loose airless soils and the origin of Mars and its satellites. Phobos orbits deep inside the fluid Roche limit and is gradually spiraling in, creating global tidal strain, which leads to a model in which orbital decay is driving the formation of surface grooves on Phobos. Here we test this model by simulating the extension of a mildly cohesive regolith shell, driven by Phobos’s tidal strain imposed by orbital migration. Modeling Phobos as a rubble-pile interior overlaid by a cohesive layer, we find that the tidal strain could create parallel fissures with regular spacing, depending on the latitude and longitude. Fracture opening triggers drainage of upper loose material into these deep-seated valleys, which we show could lead naturally to the formation of groove-like structures. We map the prominent linear depressions on Phobos and find that some at midlatitudes correlate with the model-predicted groove orientations. Our analysis supports a layered heterogeneous structure for Phobos with possible underlying failure-induced fractures, as the precursor of the eventual demise of the de-orbiting satellite. However, we do observe significant areas showing absences and anomalies that are not consistent with the tidal fracturing model. The in situ observations on Phobos by the Mars Moons eXploration mission will conclusively determine the origin of its enigmatic striations.

Results From a Decade of Optical Fiber Strainmeters at Piñon Flat Observatory

AbstractOptical fibers, stretched between anchors attached to the Earth and buried in boreholes and shallow trenches, offer an inexpensive and robust means to observe Earth strain. We have deployed several optical fiber strainmeters (OFSs) in boreholes, where thermal stability helps mitigate the noise from temperature changes. We have also constructed horizontal OFSs in 1‐m‐deep trenches of lengths 221 and 174 m. In these, a second optical fiber having a contrasting temperature coefficient provides a means to separate true strain from thermal noise. Signals in the seismic band from the horizontal strainmeters agree well with records from collocated seismometers, and the predominant ambient noise recorded by both techniques are consistent. Solid Earth strain tides with amplitude of 30 nε (nanostrain) are observed in these horizontal OFSs that agree well with those observed by collocated vacuum laser strainmeters. Noise at periods of a few days amounts to 50 nε. The two horizontal strainmeters show drift rates of up to 1 µε per month, and occasional false signals (evident from comparisons with the vacuum laser strainmeters) can accumulate occasionally to the order of 50 nε over times from hours to weeks. Results to date indicate that this technology on land could detect slow‐slip events of amplitude 100 nε and higher.

Test of ocean tide loading models on the basis of strain data measured at the Vyhne Tidal Station, Slovakia

Tidal strain time series recorded at the Vyhne Tidal Station are used to test thirteen different ocean tide loading models. Ten models have been calculated using SPOTL: EOT11a, HAMTIDE11a, OSU.TPXO72atlas, OSU.TPXO72, TPX070, DTU10, CSR4.0, FES2004, FES95.2.1, SCHW1 and three other models were chosen from the Free Ocean Tide Loading Provider (FOTLP) created by Scherneck and Bos: FES2012, FES2014b, GOT00.2. Hourly sampled strain data, corrected for temperature, were subjected to correction for ocean tide loading. The test of models was focused on the diurnal and semi-diurnal tidal harmonic constituents O1, P1, K1 and M2. A negligible difference between the individual global ocean tide loading models was only found mainly due to using different Earth models and Green functions. The amplitude factors for O1, P1, K1 and M2 derived from the measurements are 1.019, 1.226, 0.842 and 1.131, respectively. The average amplitude factors for these tidal components were obtained after ocean load correction using SPOTL routines: 1.121, 1.332, 0.916, 1.283, and in the case of the three models using FOTLP: 1.046, 1.486, 1.067, 1.317. The corrected amplitude factor became closer to the theoretical value only for K1.

Comparison of Ocean Tide Loading Models Using Strain Data Measured in the Sopronbánfalva Geodynamic Observatory, Hungary

Tidal strain observations carried out in the Sopronbánfalva Geodynamic Observatory (SGO) in Hungary are used to test thirteen different ocean tide loading models for diurnal and semi-diurnal tidal harmonic constituents O1, K1 and M2. Strain data with one minute sampling rate were corrected for temperature and barometric pressure and decimated to one hour sampling rate.

ВАРИАЦИИ ОБЪЕМНОЙ ДЕФОРМАЦИИ И УРОВНЯ ВОДЫ В СКВАЖИНАХ, ИХ ВЛИЯНИЯ НА РЕЗУЛЬТАТЫ ГРАВИМЕТРИЧЕСКИХ ИЗМЕРЕНИЙ

Precise gravity measurements at g0·10 -9 level requires taking into account density change, caused by the Earth’s crust deformation and the movement and position of the fluid in the layer. The paper presents analysis of water level observation in three boreholes situated at Primorie, at Kamchatka and at Baikal region. Water-level fluctuations were influenced by earth tides, barometric pressure, co-seismic effects and season precipitations. Water tidal signal was analyzed for calculations of level-strain coefficients, its values changed from 0.1 mm/10-9 to 1.6 mm/10-9. Gravity corrections were developed by volume variation. For borehole drilled at monolithic rock we used the phaselag effect for tidal strain and crack-system orientation was studied in Pribaikalie mountain valley. Longterm gravity results were tested with water level data at Talaya station (Pribaikalie). Talaya gravity point situated at monolithic rock had no influence from water level variation. Level-correction was less than absolute gravity measurement error. Quick coseismic effects of earthquakes are well registered by level measuring, deformation graphical and absolute gravimetric methods.

Parameters of the Earth\u2019s Free Core Nutation from Diurnal Strain Tides

Earth deformation at the diurnal tidal frequencies includes the resonant tidal-forcing response caused by the Free Core Nutation (FCN), a retrograde mode related to the slight misalignment of the rotation axes of the outer core and mantle. We analyse data from four underground high-sensitivity laser extensometers, whose signal-to-noise ratio in the diurnal tidal band is particularly high, and provide an alternative independent estimate of the FCN complex frequency with respect to more usual techniques (nutation and gravity). Firstly, we differentiate displacements due to diurnal solid tides to obtain extension along any azimuthal direction in terms of three complex parameters (A, S, C) which depend on latitude and frequency. Then, we demonstrate that we can invert the FCN complex frequency and the sensitivity of Im(A) and Re(S) to the resonance from our data. Lastly we obtain the probability distributions of those four parameters. Our results are in full agreement with those from nutation and gravity, as well as with reference IERS (International Earth Rotation and Reference Systems Service) values. Sensitivities of Im(A) and Re(S) to the resonance are estimated here for the first time and are in agreement with values computed using reference Love and Shida numbers from IERS.

Airway smooth muscle adapting in dynamic conditions is refractory to the bronchodilator effect of a deep inspiration.

Airway smooth muscle (ASM) is continuously strained during breathing at tidal volume. Whether this tidal strain influences the magnitude of the bronchodilator response to a deep inspiration (DI) is not clearly defined. The present in vitro study examines the effect of tidal strain on the bronchodilator effect of DIs. ASM strips from sheep tracheas were mounted in organ baths and then subjected to stretches (30% strain), simulating DIs at varying time intervals. In between simulated DIs, the strips were either held at a fixed length (isometric) or oscillated continuously by 6% (length oscillations) to simulate tidal strain. The contractile state of the strips was also controlled by adding either methacholine or isoproterenol to activate or relax ASM, respectively. Although the time-dependent gain in force caused by methacholine was attenuated by length oscillations, part of the acquired force in the oscillating condition was preserved postsimulated DIs, which was not the case in the isometric condition. Consequently, the bronchodilator effect of simulated DIs (i.e., the decline in force postsimulated versus presimulated DIs) was attenuated in oscillating versus isometric conditions. These findings suggest that an ASM operating in a dynamic environment acquired adaptations that make it refractory to the decline in contractility inflicted by a larger strain simulating a DI.

A numerical study on salinity stratification at the Oujiang River Estuary, China

The Oujiang River Estuary (ORE) is a macrotidal estuary with drastic variation of river discharge and large tidal range. Numerical simulations based on the unstructured grid, Finite-Volume, primitive equation Community Ocean Model (FVCOM) are conducted to investigate the intratidal and intertidal variations of salinity with an extremely upstream river boundary and large computational domain. The dynamic equation of potential energy anomaly is adopted to evaluate the stratification and mixing processes from model results. Meanwhile, the stability of estuarine stratification on different timescales and its spatial variation are studied using estuarine Richardson number and stratification parameter. The critical values of tidal range and river discharge that determine the stratification state are obtained. The critical values exhibit distinct spatial difference. The north branch of the ORE exhibits well-mixed conditions when the tidal range exceeds 3.8, 4.0 and 4.6 m at upper inlet, middle segment and the river mouth, respectively. When river discharge is below 280 m3/s or exceeds 510 m3/s, the upper part of the north branch is well-mixed sustainably. Near the river mouth, river discharge of 280 m3/s is a rough critical value that separates well-mixed and stratified states. It is also concluded that periodic stratification exists in the North Channel. The lower estuary appears to be partially stratified at early ebb or early flood tide, and well-mixed in other tidal stages. The stratification only develops during early ebb in the upper segment. The enhancement of stratification is mainly caused by longitudinal advection and lateral velocity shear, while turbulent mixing and longitudinal tidal strain are the main factors of stratification attenuation.

Tidal Coulomb Failure Stresses in the northern Andean intermediate depth seismic clusters: Implications for a possible correlation between tides and seismicity

A recent statistical analysis of the relationship between tides and seismic activity in Colombia has suggested the existence of correlation anomalies for the case of intermediate depth events in the Bucaramanga nest and the Cauca cluster (Moncayo et al., 2019). In this work, we explore in detail the hypothesis that tides may be triggering seismic activity in these regions and extend the analysis to two other seismic clusters in northern-central South America, specifically in the areas of El Puyo (Ecuador) and Pucallpa (Peru). For this purpose, we use the available focal mechanism information for seismic events at these locations, and calculate for each event the Tidal Coulomb Failure Stress (TCFS) as obtained from estimations of the tidal strain tensor. Tidal strains are computed considering the Earth body tides and the effect of the ocean tidal loading. Since our purpose is to elucidate the role of tides in earthquake nucleation, calculations of the TCFS are conducted not only for the time of earthquake, but also for the time of the closest maximum strain within a window of a few hours before the events. Our results tend to support the hypothesis that tidal stresses are contributing to earthquake generation in all the studied areas; this trend is especially stronger when TCFS are calculated at pre-earthquake times. The physical explanation for the positive contribution of tides to earthquake triggering in intermediate depth clusters may lie in the fact that a wide diversity of fault plane orientations is possible within a relatively small volume of subducted lithosphere, so making the tides more likely to help loosening up the blocks at the fault plane to promote slip.

Sensitivity of Seismic Velocity Changes to the Tidal Strain at Different Lapse Times: Data Analyses of a Small Seismic Array at Izu‐Oshima Volcano

AbstractWe investigate seismic velocity changes in response to the tidal strain at Izu‐Oshima volcano, Japan, by analyzing the data of permanent seismic stations and a small seismic array to evaluate the characteristics of strain sensitivity of velocity changes. We estimate the seismic velocity changes by phase differences between cross‐correlations functions of ambient noises at the frequency of 2–4 Hz stacked for time periods with different tidal strain amplitudes. The seismic velocity changes decrease and increase during dilatation and contraction periods, respectively, when analyzing the cross‐correlations functions at early lapse times ranging from 2 to 7 s. The strain sensitivity of seismic velocity changes is estimated to be at the early lapse times. However, we find that strain sensitivity of the seismic velocity changes decreases when analyzing the cross‐correlation functions at later lapse times from 7 s to 35 s. Applying an array analysis to the cross‐correlation functions, we observe apparent velocities of about 1 km/s at the early lapse times and those of higher than 1 km/s at the late lapse times. Since the group velocity of Rayleigh waves is 1.1 km/s at Izu‐Oshima volcano, the apparent velocities at the late lapse times may indicate the scattered or reflected body waves incident from a deeper region. Decrease of strain sensitivity with the lapse times therefore results from the emergence of body waves on the late lapse times. These results highlight the need to pay attention to wave types of cross‐correlation functions and their paths to interpret seismic velocity changes.

Leakage and Increasing Fluid Pressure Detected in Oklahoma's Wastewater Disposal Reservoir

AbstractThe Arbuckle Group is the principal reservoir used for wastewater disposal in Oklahoma. In Osage County—a seismically quiet part of the state—continuous measurements of fluid pressure reveal that pressure in the reservoir is increasing by at least 5 kPa annually and sometimes at a much higher rate. Tidal analysis reveals that fluid level changes lead the local strain tides, with no apparent influence from transient permeability changes; this indicates a response that is inconsistent with flow in a radially extensive, confined reservoir. We investigate whether this is due to vertical flow to the water table, vertical flow within the Arbuckle, or local distortions from fractures. While none of these alternative models can fully explain both the observed tidal phases and amplitude ratios, the observed response to teleseismic waves supports a mechanism related to leakage rather than fracture effects. At this location fluid influx associated with wastewater disposal is offset by migration into surrounding layers, which include the Precambrian basement below. Thus, our findings suggest the need to monitor for changes in the induced seismicity hazard, while pore pressures increase in a leaky disposal reservoir.