We present a novel experimental approach devised to test the hydro-mechanical behaviour of different structural elements of carbonate fault rocks during experimental re-activation. Experimentally ...faulted core plugs were subject to triaxial tests under water saturated conditions simulating depletion processes in reservoirs. Different fault zone structural elements were created by shearing initially intact travertine blocks (nominal size: 240×110×150mm) to a maximum displacement of 20 and 120mm under different normal stresses. Meso-and microstructural features of these sample and the thickness to displacement ratio characteristics of their deformation zones allowed to classify them as experimentally created damage zones (displacement of 20mm) and fault cores (displacement of 120mm). Following direct shear testing, cylindrical plugs with diameter of 38mm were drilled across the slip surface to be re-activated in a conventional triaxial configuration monitoring the permeability and frictional behaviour of the samples as a function of applied stress.
All re-activation experiments on faulted plugs showed consistent frictional response consisting of an initial fast hardening followed by apparent yield up to a friction coefficient of approximately 0.6 attained at around 2mm of displacement. Permeability in the re-activation experiments shows exponential decay with increasing mean effective stress. The rate of permeability decline with mean effective stress is higher in the fault core plugs than in the simulated damage zone ones.
It can be concluded that the presence of gouge in un-cemented carbonate faults results in their sealing character and that leakage cannot be achieved by renewed movement on the fault plane alone, at least not within the range of slip measureable with our apparatus (i.e. approximately 7mm of cumulative displacement). Additionally, it is shown that under sub seismic slip rates re-activated carbonate faults remain strong and no frictional weakening was observed during re-activation.
•Re-activation experiments conducted on faulted carbonate samples;•Experimentally created damage zones and fault cores;•Permeability and its stress sensitivity assessed for damage zone and fault core analogues;•Microstructure of experimental faults consistent with natural fault zones;•Friction coefficient of the samples is the same during faulting and re activation;
We calculated surface displacements produced by a synthetic megathrust earthquake using two spherical, layered, elastic dislocation models which differ only in that one model accounts for the ...coupling between elasticity and gravity and the other does not. We show that including gravity perturbs the displacement field differently in the near‐, medium‐, and far‐fields. As a result, slip inversions based on an Earth model without gravity cannot simultaneously fit the near‐, medium‐ and far‐field displacements generated using a forward model including gravity. This suggests that the spatially systematic misfits between observations and dislocation predictions seen in the literature arise, at least in part, because these studies are based on models that neglect gravity. Although the magnitude of the far‐field displacements is small compared to those of the near‐field, our slip inversions show the most improvement when we both up‐weight the far‐field observations and use a physically consistent model in the inversion.
Key Points
Including gravity into elastic dislocation models significantly modifies the predicted displacement field
The way in which gravity influences elastic displacement differs in the near‐, medium‐, and far‐fields of the dislocation
Far‐field observations help to constrain slip inversions, especially when they are up‐weighted relative to near‐field observations
The Baikal Rift is the largest Cenozoic continental rift in Asia and has developed at the boundary between the Siberian craton and a collage of microplates composing the Amurian lithospheric plate. ...GPS data show that the Amurian plate moves southeastward at a rate of 3–4 mm/yr with respect to stable Eurasia but the slip rates along the main faults that control the opening of basins within the Baikal Rift System, are still poorly quantified. The recent graben system of the Olkhon region of the central Baikal Rift is a key example for studying of synrift faulting. We discovered a previously unknown paleoseismic structure in the course of our morphometric study of the Primorsky fault scarp, one of the youngest grabens within the Baikal Rift. Detailed topographic mapping of the deformation area and trenching across the fault scarp revealed two paleoseismic events responsible for scarp formation. Dating of organic remnants found in the trench walls allowed us to estimate a late Holocene age for the paleoearthquakes and bracket the vertical slip rates along the Primorsky Fault to between 0.5 ± 0.1 mm/yr (min) and 0.9 ± 0.2 mm/yr (max) over the last ~2.5 kyr. The geomorphological and paleoseismological data, in combination with the analysis of recent seismicity and horizontal geodetic rates, suggest that the Primorsky Fault has accumulated elastic stress with the potential for a ~M 6.6 earthquake. Large earthquakes of this magnitude have occurred at least twice on the investigated fault segment during the last ~1.4 kyr.
•Vertical slip rates along the Primorsky fault are ~0.5–0.9 mm/yr over the last 2.5 Ky.•Primorsky fault accumulates the stress, which may cause a ~M 6.6 earthquake.•Geologic slip rates correspond to geodetic ones at a gentle dip of the fault at depth.
•Three-dimensional displacements were estimated from the multi-orbital InSAR observations.•Active thickness was inverted by combining InSAR displacements with mass conservation method.•The estimated ...thickness was integrated to simulate the dynamic movement of the landslide.•The Xiongba landslide moved from top to bottom and converges to the riverbank.
The active thickness of the translational landslides plays a pivotal role in evaluating its hazards and simulating its instability. Existing techniques have difficulties in estimating the accurate active thickness due to the limitations of observation conditions and imaging geometry, leading to deviations in failure simulations. To overcome these challenges, this study proposes an enhanced method that utilizes multi-orbit Interferometric Synthetic Aperture Radar (InSAR) observations to estimate the active thickness of the translational landslides and subsequently conduct more accurate instability simulations. The method involves integrating multi-orbit InSAR imaging parameters with the spatial geometry of the landslide to establish a slope coordinate system. This system enables the projection of one-dimensional InSAR Line Of Sight (LOS) displacements onto the three-dimensional displacements of the landslide. Subsequently, the active thickness is estimated by combining InSAR three-dimensional displacements with the mass conservation method. Finally, the estimated thickness is incorporated into the geological model construction to simulate the dynamic movement of the landslide. The method was applied to the Xiongba translational landslide in Gongga County, Tibet Autonomous Region, China. The results show that the deformation is mainly concentrated at its forefront, with maximum three-dimensional deformation rates of 4.7 m/a, 2.3 m/a, and 1.24 m/a. The landslide encompasses an estimated area of around 5.33 square kilometers, and its active thickness varies from 0 to 106.59 m. The maximum displacement distance reaches 1469.76 m, with a peak velocity of 60.37 m/s. The proposed method provides scientific support for assessing, analyzing, and preventing landslide disasters.
We estimated the spatial and temporal evolution of the preceding aseismic slip from January 2003 to January 2011, the coseismic slip of the Tohoku earthquake, and the postseismic slip after the ...earthquake based on global positioning system (GPS) data. Time‐dependent analysis indicates aseismic slip offshore of Miyagi and Fukushima prefectures from 2004 associated with a series of subduction earthquakes that overlap the aseismic slip area. These preceding aseismic and coseismic slip areas are centered between the centers of the coseismic and afterslip areas of the Tohoku earthquake offshore of Miyagi prefecture, while they overlap the coseismic and afterslip areas of the Tohoku earthquake off Fukushima prefecture. The timing of moment magnitude nine (Mw9) ‐class earthquakes appears to be controlled by multiple preceding slip events, smaller earthquakes and their afterslip. The preceding aseismic and coseismic slip decreased the coupling rate off the Tohoku coast, suggesting the possibility that the preceding slip represented a precursive stage of the Tohoku earthquake. The afterslip of the Tohoku earthquake occurred in an area where the coseismic slip was not large, complementing the large coseismic slip zone. The afterslip along Iwate‐Miyagi extends up to 80 km in depth and is currently the sole mechanism of strain release in this depth range. The source region of the anticipated Miyagi‐Oki earthquake shows small postseismic slip after the Tohoku earthquake, reflecting the energy release at the time of the earthquake. Aftershock activity is roughly governed by an afterslip process.
Key Points
Preceding slip occurred in a down‐dip area of the Tohoku earthquake
Huge energy was accumulated near the Japan trench
Afterslip is occurring in an area complementing the cosesimic rupture zone
We conduct finite element analysis to investigate the effect of sharp topography on surface ground deformation caused by pressure changes in a magma reservoir. Tilt data express the horizontal ...gradient of vertical displacement and therefore can emphasize small variations in deformation that go unnoticed using other methods. We find that the vertical displacement profile at a surface with a cliff can be thought of as the superposition of the deformation from shallow and deeper sources. This combination can create a small peak in vertical displacement that acts as a pseudo‐source, creating a reversal of the deformation gradient and therefore anomalous tilt magnitude and a rotation of up to 180°. We apply these models to Kīlauea Caldera and find that surface geometry creates a tilt rotation of ∼10°, partially explaining anomalous tilt that has been observed. Our analysis highlights the importance of considering topography when assessing tilt measurements at active volcanoes.
Key Points
Finite element analysis is used to investigate the effect of sharp topography on deformation
Tilt magnitude and azimuth are drastically affected by the presence of a cliff
Anomalous tilt at Kīlauea can be partially explained by the caldera topography
On April 25th, 2015, the magnitude Mw 7.8 Gorkha earthquake ruptured the Main Himalaya Thrust (MHT) in central Nepal as a result of a thrust type event. Comprehensive evaluations of this event and ...its aftershocks have been undertaken to understand the locations and mechanisms of the aftershocks. Here we model co-seismic displacement and strain caused by the Gorkha earthquake using different slip models, and then compare those results with the focal information. We have the following conclusions: 1) previous work suggests that there are two aftershock belts after the Gorkha earthquake, and we further suggest that the negative ΔCFS lobe(s) beneath the maximum slip led to the seismic gap between the two seismic belts; 2) aftershocks associated with the Gorkha earthquake occurred not only along the MHT fault plane, but also 10–20 km deeper than the depth of the maximum slip zone, triggered by the ΔCFS increase, this stress change pattern and distribution of aftershocks coincide with the recently proposed ‘top-down’ effect, that the stress pulses produced by earthquake in upper crust can drive aftershocks in the lower crust; 3) we suggest that the normal-fault aftershock 40 km north of the maximum slip zone was triggered by the Gorkha earthquake, the ΔCFS on the nodal plane (strike 178, dip 52, rake −78) driven from different slip models all increase more than 1 bar; 4) The aftershocks' mechanisms are strongly related to the deformation field caused by the mainshock, the displacement directions always nearly parallel to the maximum principal stress directions or the shear directions of the aftershocks' focal mechanism solutions. Our studies give suitable explanations to the distribution of the aftershocks accompanied with the Gorkha earthquake, which is also of great significance for the analysis of aftershocks under the similar seismogenic environments.
•Deep aftershocks triggered by the Gorkha earthquake•Stress change pattern associated with a buried low-angle thrust fault•Normal fault type events induced by a thrust type main shock•Relationship between deformation and focal mechanism solutions
Peak ground displacement (PGD) and peak ground velocity (PGV) are critical parameters during earthquake early warning, as they can provide rapid magnitude estimation before rupture end. In this ...study, we used the high-rate Global Navigation Satellite System (GNSS) data from 55 continuous stations to estimate the magnitude of the 2021 Maduo earthquake in western China. We used the relative positioning method and variometric approach to acquire real-time GNSS displacement and velocity waveforms, respectively. The results showed the amplitude of displacement and velocity waveforms gradually decreased with increasing hypocentral distance. Our results showed that the fluctuation of PGD magnitudes over time is smaller than that of PGV magnitudes. Nonetheless, the earthquake magnitudes estimated from both methods were consistent with their counterparts (Mw 7.3) reported by the United States Geological Survey (USGS). The final magnitude estimated from the PGD and PGV methods were Mw 7.25 and Mw 7.31, respectively. In addition, our results highlighted how the number of high-rate GNSS stations could influence the stability and convergence time of magnitude estimation.
Buried pipelines crossing reverse faults is a common case in practice, while their mechanical responses are not very clear. To analyze buried pipelines subjected to reverse faults, a beam-shell ...coupling scheme is proposed based on the Vector Form Intrinsic Finite Element (VFIFE or V-5) method. Particular emphasis is given to identifying pipeline failure with three performance based limit states: the local buckling, the tensile strain limit and the flattening parameter limit. The critical fault displacements, at which the specified performance criteria are reached, are presented in diagram form. Effects of fault displacement, crossing angle, as well as fault dip angle on critical fault displacements are examined. This study shows that when the fault dip angle is 40°, the critical fault displacements of local buckling and pipe-wall rupture are the largest when a pipeline is oriented approximately parallel to a reverse fault plane. And for a perpendicularly crossing pipeline, the smaller the dip angle is, the more severe the cross-section distortion will be. Moreover, the critical strain of local buckling are obtained and compared with the recommendation of CSA Z662.
•Developing a highly-paralleled beam-shell coupling procedure based on the VFIFE method.•Presenting the critical fault displacements of different performance criteria.•Obtaining the optimal values of the crossing angle and the fault dip angle.
A major landslide in Zhouqu, China occurred on August 8, 2010 and caused widespread damage and over 1700 casualties. We study the deformation of the slopes over a time period of about three years ...prior to the landslide by an enhanced StaMPS-SB technique with 16 ascending ALOS/PALSAR images. In particular, the orbit error and stratified troposphere that were not well dealt with in the original StaMPS-SB method have been satisfactorily corrected by a novel phase ramp correction method. The deformation in four regions of the study area has been retrieved with a maximum of up to 70mm/yr. In the Luojiayu–Sanyanyu valley, the slopes where the 2010 giant landslide occurred have been found to be quite unstable before the event. Deformation exceeding 30mm/yr has been detected in the Suoertou slope, which is a well-known place for an ancient fault zone landslide. Fast movement larger than 40mm/yr is observed in the Xieliupo slope, which poses threats of landslide dam and dammed lake to the Pai-lung River together with another slope deformation detected in the opposite slope. In the Nanshanqiaotou slope, the detected ~30mm/yr deformation can be viewed as the prelude of the large landslide occurred in October 2010. More important, it is found that the slope deformation time series has strong correlation with the precipitation in the area as well as with the devastating Wenchuan earthquake that occurred in May 2008 whose epicenter is about 300km away from Zhouqu.
•Landslides in Zhouqu, China are investigated by InSAR for the first time.•We propose a phase ramp correction for the single-look SAR interferogram.•Strong correlation is found between landslides, precipitations and earthquake.
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