Faunistic study on hover flies (Diptera:Syrphidae) in the eastern part of Zanjan province, Iran

Abstract In order to study on Syrphidae faunistic in the eastern part of Zanjan province in the years of 2008 and 2009, some adult specimens were collected and identified. In total, 31 species belong to 16 genus from 2 subfamilies were collected. Among the specimens, 28 species as follow are new records for Zanjan province and the species marked with an asterisk is the first record from Iran

Active and passive seismic monitoring of laboratory-based injection-driven fault reactivation

Robust and reliable prediction of (induced) earthquakes remains a challenging task. Seismicity predictions are made using probabilistic models, precursors such as average earthquake size distribution. Pore pressure variations cause stress perturbations along pre-existing fault planes in the subsurface, resulting in shear slip and seismicity. Monitoring these stress changes before fault reactivation and its resulting seismicity could greatly improve forecasting seismicity. Stress changes can be determined by changes in acoustic or seismic velocities. Therefore, experiments are performed to detect the preparatory phase of an earthquake using acoustic monitoring. Faulted sandstone samples are reactivated in the laboratory by imposing pore pressure changes by fluid injection under reservoir pressures, while continuously performing passive and active (transmission) acoustics measurements. Using coda wave interferometry (CWI) and decorrelation (K), changes in velocity and scattering are obtained before and during fault reactivation. We show that fault reactivation can be identified by a large velocity drop and an increase in K or by micro-seismic foreshocks. We show that CWI velocity change is most sensitive to both the preparatory phase and the fault reactivation. These results show acoustic monitoring of fault reactivation in the laboratory is feasible, which could improve the prediction of induced seismicity.Applied Geophysics and Petrophysic

Acoustic Precursors to Laboratory Induced Fault Slip and Failure

With human activities in the subsurface increasing, so does the risk of induced seismicity. For mitigation of the seismic hazard and limiting the risk, monitoring and forecasting are essential. A laboratory study was performed to find precursors to fault failure. In this study, Red Pfaelzer sandstones samples were used, which are analog to the Groningen gas reservoir sandstones. A saw-cut fault was cut at 35 degrees, and the samples were saturated. Fault slip was induced by loading the sample at a constant strain rate, and simultaneously active acoustic transmission measurements were performed. Every 3 seconds 512 S-waves were sent, recorded, stacked to reduce the signal-to-noise ratio, and analyzed. The direct seismic wave velocity, coda wave velocity, and transmissivity were monitored before and during the reactivation of the faulted samples. Different loading patterns and confining pressures were investigated in combination with active acoustic monitoring. Velocity and amplitude variations were observed before the induced fault slip and can be used as precursory signals. Two methods to determine changing velocities were used. Direct S-wave velocities are compared to velocity change obtained by coda wave interferometry. Both analyses gave similar precursory signals, showing a clear change in slope, from increase to decreasing velocities and amplitudes prior to fault reactivation. Fault reactivation is preceded by fault creep and the destroying of some of the asperities on the fault plane, causing the seismic wave amplitude and velocity to decrease. Combining all precursors, the onset of fault slip can be determined and therefore upcoming slip can be forecasted in a laboratory setting. Our results show precursory changes in seismic properties under different loading situations and show a clear variation to the onset of fault reactivation. These results show the potential of continuous acoustic monitoring for detection and forecasting seismicity and help the mitigation of earthquakes.Applied Geophysics and Petrophysic

Precursors to rock failure in the laboratory using ultrasonic monitoring methods

Forecasting the occurrence of natural hazards, such as earthquakes or landslides, remain very challenging. These hazards are often caused by stress changes in the subsurface, therefore detecting and monitoring these changes can help the prediction and mitigation. Active ultrasonic transmission experiments were performed on Red Pfaelzer sandstones to investigate the monitoring and forecasting potential of these measurements. The sandstone samples were loaded until failure at different initial confining stress conditions. The forecasting potential to failure of different analysis methods, such as coda wave interferometry or wave attenuation, is investigated and compared. Our results show we can detect the forecast the upcoming failure of the samples from 40 to 70% of its failure point. Small differences between each analysis method are visible, but the trend of the signal is leading and therefore a robust prediction of failure can be made by combining analysis methods. In this paper, we propose a traffic light forecasting system using the precursory signals from ultrasonic monitoring. This system is applicable for monitoring failure at various depths and or stress conditions, for a better prediction of small stress-induced changes in the subsurface and thus mitigation of failure (natural hazards) in the subsurface.Applied Geophysics and Petrophysic

Active and passive monitoring of fault reactivation under stress cycling

Increased seismicity due to subsurface activities has led to increased interest in monitoring and seismic risk mitigation. In this study we combined passive and active acoustic monitoring methods to monitor fault sliding and reactivation in the laboratory. Acoustic emission (AE) and ultrasonic transmission measurements were performed during stress-cycling to monitor stress-driven fault reactivation. We show the use of the transmissivity and coda wave interferometry of the active acoustic measurements and the number of generated AE events for fault reactivation monitoring. Combining these two methods, we are able to detect the different phases of fault reactivation process under stress cycling including, early aseismic creep (pre-slip), fault slip, and continuous sliding. Combining both active and passive monitoring increases accuracy of monitoring and can lead to better seismic risk mitigationGreen Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Applied Geophysics and Petrophysic

Experimental and numerical investigation of sandstone deformation under cycling loading relevant for underground energy storage

Considering the storage capacity and already existing infrastructures, underground porous reservoirs are highly suitable to store green energy, for example, in the form of green gases such as hydrogen and compressed air. Depending on the energy demand and supply, the energy-rich fluids are injected and produced, which induces cyclic change of state-of-the-stress in the reservoir and its surrounding. Detailed analyses of the geo-mechanical deformations under variable storage conditions i.e., storage frequency and fluid fluctuating pressures, are crucially important for safe and efficient operations. The present work presents an integrated analysis, based on experimental and constitutive modeling aspects, to investigate sandstones’ geomechanical response to cyclic loading relevant to underground energy storage (UES). To this end, sandstone rock samples were subjected to cyclic loading above and below the onset of dilatant cracking under different frequencies and loading amplitudes. Axial strains and Acoustic Emissions (AE) were measured in both regimes to quantify the total deformation (strain) of the rock and its AE characteristics. It is found that the inelastic strain and number of AE events is the highest in the first cycle and reduce subsequently cycle after cycle. Moreover, cyclic inelastic deformations are affected by the mean stress, amplitude, and frequency of the stress waveform. On the one hand, the higher the mean stress and the amplitude, the higher the total inelastic strains. On the other hand, the lower the frequency, the higher the total inelastic strain. From the modeling perspectives, five types of deformation mechanisms were identified based on the governing physics: elastic, viscoelastic, compaction-based cyclic inelastic, inelastic brittle creep, and dilatation-based inelastic deformation. To model elastic, viscoelastic, and brittle creep, the Nishihara model was used. A cyclic modified cam clay model (MCC) and hardening–softening model were applied to capture plastic deformation. The results show a very good fit of the constitutive model with the experimental results, which could help in studying the response of reservoirs to injection and production.</p

Early detection of stress changes and failure using acoustic measurements

Accepted Author ManuscriptApplied Geophysics and Petrophysic

Laboratory study on the effect of stress cycling pattern and rate on seismicity evolution

Recent laboratory and field studies suggest that temporal variations in injection patterns (e.g., cyclic injection) might trigger less seismicity than constant monotonic injection. This study presents results from uniaxial compressive experiments performed on Red Felser sandstone samples providing new information on the effect of stress pattern and rate on seismicity evolution. Red Felser sandstone samples were subjected to three stress patterns: cyclic recursive, cyclic progressive (CP), and monotonic stress. Three different stress rates (displacement controlled) were also applied: low, medium, and high rates of 10−4 mm/s, 5 × 10−4 mm/s, and 5 × 10−3 mm/s, respectively. Acoustic emission (AE) waveforms were recorded throughout the experiments using 11 AE transducers placed around the sample. Microseismicity analysis shows that (i) Cyclic stress patterns and especially cyclic progressive ones are characterized by a high number of AE events and lower maximum AE amplitude, (ii) among the three different stress patterns, the largest b-value (slope of the log frequency-magnitude distribution) resulted from the cyclic progressive (CP) stress pattern, (iii) by reducing the stress rate, the maximum AE energy and final mechanical strength both decrease significantly. In addition, stress rate remarkably affects the detailed AE signature of the events classified by the distribution of events in the average frequency (AF)—rise angle (RA) space. High stress rates increase the number of events with low AF and high RA signatures. Considering all elements of the AE analysis, it can be concluded that applying cyclic stress patterns in combination with low-stress rates may potentially lead to a more favourable induced seismicity effect in subsurface-related injection operations.Applied Geophysics and PetrophysicsCivil Engineering & Geoscience