Ground Fractures Research Articles

The effect of recent resurfacing in volcanic areas on the distribution of co-seismic ground deformation due to strike-slip earthquakes: New insights from the 12/26/2018 seismic event at Mt. Etna

We analyzed the dispersion of the co-seismic fracturing due to the December 26, 2018 event at Mt. Etna (Italy) along the deformation belt matching the seismogenic source at depth. Our study, based on measurement of 390 ground fractures, reconstructed the variability of the geometry and the changes in the rank (length and displacement) of the ground breaks, through different compound lava fields. The study evidenced that the narrow capable dextral fault zone emerges where ancient lavas crop out or are draped by a thin layer of younger lava flows. Conversely, within recent compound lava fields, consisting of multiple superimposed flow units, the main mechanical anisotropy within the near-surface layers inhibited the along-dip fault propagation. The vertical restriction of the fault propagation produced a spread ground deformation, responding to the motion along the blind main fault. Our results provide a significant example how the laterally changing near-surface stratigraphy of an active volcano edifice can influence the ground effects due to the co-seismic displacement along strike-slip active fault. This evidence could represent new insights to be considered in predicting the susceptibility zone around active transcurrent faults in volcanic settings, prone to instabilities for future seismic events.

Controlling mine pressure by subjecting high-level hard rock strata to ground fracturing

When mining extra-thick coal seams, the main cause of strong ground pressure are the high-level thick and hard strata, but as yet there is no active and effective control technology. This paper proposes the method of subjecting hard roofs to ground fracturing, and physical simulation is used to study the control effect of ground fracturing on the strata structure and energy release. The results show that ground fracturing changes the structural characteristics of the strata and reduces the energy release intensity and the spatial extent of overburden movement, thereby exerting significant control on the ground pressure. The Datong mining area in China is selected as the engineering background. An engineering test was conducted on site by ground horizontal well fracturing, and a 20-m-thick hard rock layer located 110 m vertically above the coal seam was targeted as the fracturing layer. On-site microseismic monitoring shows that the crack propagation length is up to 216 m and the height is up to 50 m. On-site mine pressure monitoring shows that (1) the roadway deformation is reduced to 100 mm, (2) the periodic weighting characteristics of the hydraulic supports are not obvious, and (3) the ground pressure in the working face is controlled significantly, thereby showing that the ground fracturing is successful. Ground fracturing changed the breaking characteristics of the high-level hard strata, thereby helping to ameliorate the stress concentration in the stope and providing an effective control approach for hard rock.

Research and application of the underground fire detection technology based on multi-dimensional data fusion

Underground mining has been plagued by gob fires triggered via self-igniting coal, the emission of toxic fumes, particulate matter, and possibly induced explosions from the gob fires make mining extremely dangerous. The spontaneous combustion of underground coal seriously affects the mining of adjacent coal seams and the overall safety production. The key to control the shallow coal seam fire is to accurately locate its the location and scope by surface detection method. Based on the non-dimensional normalization processing of different types of data and the weight analysis of analytic hierarchy process (AHP), a multi index data fusion method of temperature, gas and radon concentration was proposed by using the practical radon measurement, borehole temperature measurement and gas measurement methods, and the index of fire zone delineation (IFZD) based on multi-dimensional data fusion was obtained. According to the content total method based on fractal theory, the anomalousthreshold of IFZD was determined by piecewise linear fitting in double logarithmic coordinates. Eventually, the multi-dimensional data fusion underground fire detection method was established completely, and the method was applied to the fire detection of shallow coal seam in typical integrated mine. The results showed that the weight coefficients of the detection indexes (CO, CO2, SO2, temperature and radon) in the fire area were 0.12, 0.03, 0.05, 0.12, 0.68, and the lower bound of the anomaly of IFZD was 0.29. According to the comprehensive isoline map, abnormal area plan and stereogram drawn through IFZD and its outlier threshold, there were eight areas with the total area of 27061 m2, which developed from the abandoned well, main well location to the southwest and northeast. The isolines of abandoned air shaft and main shaft were densest and the value was the largest, indicating that coal oxidation in this area is severest, so it is necessary to strengthen the ground fracture investigation and sealing. This method solved the problems such as poor accuracy of single index circle fire zones, and difficulty in direct fusion of multi-index data with different dimension and range, and difficulty in determining the abnormal lower boundary of the fusion index after dimensionless normalization, which provided a new technical method support for the detection of underground shallow coal seam fire area.

Effects of Ground Fracturing with Horizontal Fracture Plane on Rock Breakage Characteristics and Mine Pressure Control

Ground fracturing is a new and effective method for controlling high-level hard roofs. In underground coal-seam mining, the maximum principal stress is horizontal stress, along with the direction of hydraulic fracture propagation. In this study, the control mechanism of the horizontal fracture plane formed by ground fracturing on the strata breaking span was analyzed theoretically, and the effect of the horizontal fracture plane on the structural characteristics, stress distribution, and impact effect of the high-level thick and hard strata (hereinafter referred to as THS) were numerically investigated. To verify the results, the 8218 working face in the Tashan coal mine of the Datong mining area was selected as a case study. The fractured stratum was 20 m thick and was separated vertically from the coal seam by 110 m. After ground fracturing, the extension range of the fracture plane was 216 m in length and 30–100 m in width, covering the working face. In situ monitoring of the mine pressure revealed that the bearing strength of the supports in the working face was weakened by the ground fracturing, and that the roadway deformation was significantly reduced, indicating that ground-fracturing technology plays an important role in controlling high-level THS and improving the mining environment of the working face.

Investigating the kinematics of the unstable slope of Barberà de la Conca (Catalonia, Spain) and the effects on the exposed facilities by GBSAR and multi-source conventional monitoring

The paper presents a multi-source approach tailored for the analysis of ground movements affecting the village of Barbera de la Conca (Tarragona, Catalonia, Spain), where cracks on the ground and damage of different severity to structures and infrastructure was recorded. For this purpose, monitoring of ground displacements performed by topographic survey, geotechnical monitoring and remote sensing techniques (ground-based synthetic aperture radar, GBSAR) are combined with multi-temporal damage surveys and monitoring of cracks (crackmeters) to get an insight into the kinematics of the urban slope. The obtained results highlight the correspondence between the monitoring data and the effects on the exposed facilities induced by ground displacements, which seem to occur predominantly in the horizontal plane with diverging directions (northward and southward) from the main ground fracture crossing the centre of the village. The case study stands as a further contribution to fostering this kind of integrated approaches that via cross-validations can improve data reliability as well as enrich datasets for slope instability recognition and analysis, which are crucial to plan risk mitigation works.

Land subsidence and associated ground fracturing: study cases in central Mexico with ALOS-2 PALSAR-2 ScanSAR Interferometry

Abstract. Land subsidence affects highly developed urban areas in central Mexico, where inhabitants rely on groundwater for about 60 % of water supply and most of the cities are located in volcanic valleys filled with fine and coarse grained sediments. Compaction associated to groundwater depletion in areas with subsoil contacts sediments-rock have caused differential subsidence, ground fracturing and eventually the reactivation of pre-existing faults, depending on the local geological setting. Remote sensing monitoring methods of land deformation have proved to be useful tools to assess this geological hazard for urban planning. We used L-band ScanSAR data from the ALOS-2 PALSAR-2 mission to produce a regional land subsidence map over an area of about 350 km × 350 km over central Mexico. Our results indicate with a remarkable spatial coverage widespread land subsidence over the major cities, which is ranging from more than 30 cm yr−1 in Mexico City to 5–10 cm yr−1 in other locations.

Factors that condition physical vulnerability to ground fracturing in Mexico City

Abstract. In spite of subsidence being a well-studied geological phenomenon in Mexico City, its effects and risks for urban infrastructure and inhabitants have been neglected. Damage in the short, medium and long term implies maintenance and important mitigation costs. There are not systematic studies that address methodologies for the estimation of physical vulnerability of the geological media to fracture. In this work, factors conditioning the deformation and susceptibility to fracturing are analyzed using a deterministic approach. The identified physical variables were mapped, measured and integrated into a database that allowed for an adequate correlation of the parameters that condition fractures spatial distribution. A methodology for estimating a vulnerability index to fracturing (VIF) useful for decision making is proposed in this work.

Ground Fracturing Related to 7.8Mw Saravan Earthquake, Sistan and Baluchistan, Iran - Evidence for Brittle Deformation

Abstract The eastern parts of the Sistan and Baluchistan province, southeast Iran is a tectono-magmatically active zone that continues to witness numerous small and large earthquakes. The volcanism in this region is related to the subduction of the Oman plate below the Eurasian plate. The study of the spatial distribution of the epicenter and focus of the earthquakes suggests close association with the numerous faults related to collisional tectonics. Evidence of ground fractures and faulting related to Saravan earthquake of 16th April 2013 which is the largest (7.8 Mw) recorded earthquake in the region is documented. This earthquake occurred along a segment of the NW-SE trending Saravan normal fault and its reverberations were felt as far away as New Delhi and Dubai. En echelon, 2-km long, northwest-southeast trending surface fractures and faults are recorded in the field near Hampani village southwest of Gosht city. The epicenter is located in the remote hilly terrain east of Gosht. Many of the fractures are listric. The fault records a downthrow of about half a meter and some segments record brecciation of phyllite, liquefaction of sediments and emergence of saline springs are associated features. Despite the high magnitude only a few casualties and minor damage to civil structures were recorded in Iran due to the sparse population and its remoteness.

High-resolution imaging of hydrothermal heat flux using optical and thermal Structure-from-Motion photogrammetry

Quantifying hydrothermal heat flux at meter-scale resolution over >0.25 km2 is required to bridge in-situ heat flux and satellite-based measurements. We advance a methodology that blends ground-based daytime optical and nighttime thermal infrared (TIR) imagery using Structure-from-Motion photogrammetry to map radiant hydrothermal heat flux over these scales at sites with low signal-to-noise ratios that would otherwise be difficult to characterize using, for example, unmanned aerial systems. The improved method uses a computerized telescopic mount to relocate and align daytime optical acquisitions with nighttime TIR imagery, thereby enabling TIR acquisition from multiple camera orientations positioned throughout a study area. This facilitates mapping of thermal features at sites of varying size and complexity and helps to ameliorate topographic occlusion effects and geometric distortions that can bias radiant hydrothermal heat flux estimates derived from the resulting orthorectified thermal maps. We assessed detection thresholds of this method at three sites across central California, which range in size, topography, and heat flux conditions. We found that blending of optical and thermal acquisitions successfully detected anomalous heat flux, even in cases where temperatures were only slightly greater than background. This approach might be applied to a variety of volcanic and hydrothermal systems to quantify the spatial distribution of heat flux, and how this may relate to factors such as the distribution of ground fractures and lava flow rheology.

THE COMBINED USE OF LONG-TERM MULTI-SENSOR INSAR ANALYSIS AND FINITE ELEMENT SIMULATION TO PREDICT LAND SUBSIDENCE

Abstract. Land subsidence in Tehran Plain, Iran, for the period of 2003–2017 was measured using an InSAR time series investigation of surface displacements. In the presented study, land subsidence in the southwest of Tehran is characterized using InSAR data and numerical modelling, and the trend is predicted through future years. Over extraction of groundwater is the most common reason for the land subsidence which may cause devastating consequences for structures and infrastructures such as demolition of agricultural lands, damage from a differential settlement, flooding, or ground fractures. The environmental and economic impacts of land subsidence emphasize the importance of modelling and prediction of the trend of it in order to conduct crisis management plans to prevent its deleterious effects. In this study, land subsidence caused by the withdrawal of groundwater is modelled using finite element method software Plaxis 2D. Then, the model was verified using InSAR data. The results were in good agreement with the measurement results. The calibrated model was used to predict the land subsidence in future years. It could predict future subsidence for any assumed rate of water depletion.

Probability assessment method and application of surface rupture on main controlling fault

This paper summarizes the macro-assessment of meizoseismal ground fracture experience, based on the probabilistic assessment methods described in engineering practice and research status. Earthquake engineering probabilistic analysis is the inevitable result of scientific development, to meet the people’s understanding level. Statistics on the Chinese mainland strong ground fracture frequency; proposed a simple method of calculating the probability, and made a spreadsheet. The model uses data primarily from seismic hazard analysis commonly used data, the results are acceptable, the probability model is a simple, easy-to-application features.

Study on the spatio-temporal relationship between ground fracturing and underground drainage holes arrangement

Based on the respective technical advantages of ground fracturing and underground gas drainage, a joint drainage mode of ground wells and underground is proposed, which focuses on utilizing the large-scale advantages of ground fracturing to promote underground gas drainage. Experimental study of two kinds of ground fracturing and underground drainage connection Mode, that is “Ground fracturing lags behind drilling construction” and “drilling construction lags behind the ground fracturing”. Through the micro-seismic method and the underground hole exposure method, it is concluded that the cracks in the coal seam are mainly horizontal cracks with a small northeast opening, and the crack length is about 158~203m. According to the law of crack distribution, fracturing investigation schemes of two modes were designed. The reasonable time connection between the ground fracturing and underground drainage is preliminarily determined by the engineering practice, it is effective in increasing the permeability of the coal seam, reducing the abnormal gas emission from the coal seam and the risk of coal and gas outburst by using “ground fracturing lags behind drilling construction”; the gas drainage effect is remarkable when the underground drilling is delayed within 3 months of ground fracturing by using “drilling construction lags behind the ground fracturing”.

Research on Coal Pillar Malposition Distance Based on Coupling Control of Three-Field in Shallow Buried Closely Spaced Multi-Seam Mining, China

In order to explore the rational coal pillar malposition distance (CPMD) based on coupling control of stress field, displacement field and fracture field (three-field) in shallow buried closely spaced multi-seam (SBCSM-S) mining, and realize coupling control of underground concentrated stress and ground surface fractures, taking the No. 1–2 and No. 2–2 coal seams mining in the northward east area of Ningtiaota coal mine as background, through physical simulation and theoretical analysis, the three-field evolution in SBCSM-S mining was analysed, the effect of different CPMD on coal pillar concentrated stress, ground surface subsidence and fractures development was revealed, and the rational CPMD based on coupling control of three-field was put forward. The results show that the concentrated fractures and concentrated stress are due to the strata’s uneven subsidence by coal pillars. Rational arrangement of CPMD can avoid the superposition of vertical stress caused by upper and lower coal pillars and reduce the development of ground fractures and uneven subsidence. Two theoretical models were established: one was based on the control of a concentrated stress field, the other on the control of the displacement and fracture fields. These results will be applied in a follow-up arrangement at the Ningtiaota coal mine, and can provide a new way for safe and green mining in SBCSM-S.

Overexploitation of groundwater resources in the faulted basin of Querétaro, Mexico: A 3D deformation and stress analysis

The City of Querétaro is located on a continental basin filled since the Oligocene with lacustrine and alluvial sediments, pyroclastic deposits, and interbedded fractured basalts. The graben structure of the basin was formed by two major North-South trending normal faults, among which the thicknesses of the filling materials vary many tens of meters in close distances. Hence, important differences of hydraulic and mechanical properties characterize the various geologic units. Groundwater has been strongly withdrawn over the last three decades in the study area, with a decline of the piezometric level exceeding 100 m. Because of the high variability of the geologic deposits, the piezometric decrease and consequently the effective stress increase are characterized by a large spatial variability. Piezometric variations are also due to faults that strongly impact on groundwater flow dynamics. The deformation and effective stress variability has caused large differential subsidence causing ground fracturing that has damaged the urban infrastructure of the City of Querétaro. This complex geological setting has been properly accounted into a three-dimensional (3D) flow and geomechanical modeling approach to quantify the displacement, deformation, and stress fields caused by water withdrawal. The static geologic model was accurately defined using geological logs from extraction wells, field mapping of faults, fractures, and the integration of major structures reported in previous geophysical works. The model has been calibrated using observed groundwater levels and land settlement records. The simulations have spanned the period from 1970 to 2011. The modeling results highlight that the areas where large differential subsidence and horizontal displacements developed correspond to the portions of the city where ground fractures are observed. Normal and shear components of the stress field changes accumulate along the discontinuity surfaces at depth, providing evidence that large piezometric declines can be a key factor triggering the fault reactivation. The spatial relationship between major withdrawals, discontinuities of the geologic structure, and accumulation of large stress and strain fields clearly emerged from the outcomes of the 3D geomechanical model.

Geological Factors for the Formation of Xi’an Ground Fractures

Xi’an ground fractures are the most typical ground fractures in China. Fourteen fractures have nearly divided the historical city into several distinct sections. These fractures are parallel and distributed in NEE direction at the same interval, with all features exhibiting a down dropping southerly block which extends to connect with the underlying fault. The activities of fractures are primarily expressed as normal faults. The faulted strata are well defined and dislocation displacement increases with depth. Thus, fractures have the characteristics of syn-sedimentary faults, which constitute the hanging wall of the Lintong-Chang’an fault branch system. Crustal thinning caused by the uplifting of upper mantle provides a power source for extension and stretching along the fracture surface of the upper crust, which results in a series of extensional faults and the suitable conditions for forming massive ground fractures. The movement of tectonic blocks influences the normal dip-slipping tension of Lintong-Chang’an fault branches, and produces a series of secondary tectonic fractures adjacent to surface, which constitute the prototype of ground fractures. The recent regional tensile stress produced by modern mainland deformation, also profoundly influences the current activity of Xi’an ground fractures.

Riesgo geológico que afectará al poblado Tapacocha (Recuay ‐ Ancash)

Las construcciones civiles edificadas sobre suelos inestables son vulnerables a los procesos naturales como la geodinámica interna, externa y el cambio climático. El poblado de Tapacocha que está asentado sobre suelo deslizado es sensible a los procesos naturales. El terremoto de mayo de 1970 ocasionó fracturamiento de la planicie, destrucción de sus construcciones; las intensas lluvias de los años 1942 y 1997 ocasionaron huaycos que destruyeron algunas de sus edificaciones y terrenos de cultivo. La geodinámica interna modeló el basamento con un intenso plegamiento y fracturamiento de las rocas sedimentarias; la geodinámica externa por geoformas modeladas por los movimientos rotacionales, deslizamientos, erosión diferencial. En la actualidad el efecto del cambio climático se manifiestan por las inusuales torrenciales lluvias que erosionan periódicamente y ponen en peligro las edificaciones civiles y la agricultura. Con el presente estudio se propone alertar a las autoridades y sus pobladores para prevenir y mitigar los efectos naturales destructivos.

InSAR to support sustainable urbanization over compacting aquifers: The case of Toluca Valley, Mexico

This paper illustrates how InSAR alone can be used to delineate potential ground fractures related to aquifer system compaction. An InSAR-derived ground fracturing map of the Toluca Valley, Mexico, is produced and validated through a field campaign. The results are of great interest to support sustainable urbanization and show that InSAR processing of open-access Synthetic Aperture Radar (SAR) data from the Sentinel-1 satellites can lead to reliable and cost-effective products directly usable by cities to help decision-making.The Toluca Valley Aquifer (TVA) sustains the water needs of two million inhabitants living within the valley, a growing industry, an intensively irrigated agricultural area, and 38% of the water needs of the megalopolis of Mexico City, located 40km east of the valley. Ensuring water sustainability, infrastructure integrity, along with supporting the important economic and demographic growth of the region, is a major challenge for water managers and urban developers. This paper presents a long-term analysis of ground fracturing by interpreting 13 years of InSAR-derived ground displacement measurements. Small Baseline Subset (SBAS) and Persistent Scatterer Interferometry (PSI) techniques are applied over three SAR datasets totalling 93 acquisitions from Envisat, Radarsat-2, and Sentinel-1A satellites and covering the period from 2003 to 2016.From 2003 to 2016, groundwater level declines of up to 1.6m/yr, land subsidence up to 77mm/yr, and major infrastructure damages are observed. Groundwater level data show highly variable seasonal responses according to their connectivity to recharge areas. However, the trend of groundwater levels consistently range from −0.5 to −1.5m/yr regardless of the well location and depth. By analysing the horizontal gradients of vertical land subsidence, we provide a potential ground fracture map to assist in future urban development planning in the Toluca Valley.

Near‐Surface Electrical Resistivity Investigation of Coseismic Liquefaction‐Induced Ground Deformation Associated with the 2016Mw 5.8 Pawnee, Oklahoma, Earthquake

ABSTRACT The M w 5.8 Pawnee, Oklahoma, earthquake on 3 September 2016 produced the largest moment release associated with induced seismicity in the southcentral United States. The earthquake ruptured a previously unknown west‐northwest–east‐southeast‐trending left‐lateral strike‐slip fault, named the Sooner Lake fault (SLF). Unlike the previous earthquakes in Oklahoma, the Pawnee earthquake produced coseismic liquefaction‐induced surface deformations including fractures, sand blows, and lateral spreading. In this study, we used high‐resolution electrical resistivity tomography to image the zones of surface deformation. We also mapped the fracture orientations and compared them with the mainshock and aftershock pattern in the area of the earthquake to elucidate the relationship between the surface deformation and the causative fault. Our results reveal that (1) fractures and sand blow sites are located 2–9 km from the SLF, consistent with patterns of distributed deformation; fracture azimuths vary between 93°–116° and 110°–250° (subparallel and orthogonal to the 109° strike of the SLF); (2) sites of sand blow and ground fracture occur within the zone of maximum recorded ground shaking and are underlain by Quaternary alluvial sediments; (3) mega fractures (34 cm wide and up to 226 m long) oriented parallel to river meanders resulted from lateral spreading; and (4) liquefaction sites are underlain by low electrical resistivity (

Minor shallow gravitational component on the Mt. Vettore surface ruptures related to MW 6, 2016 Amatrice earthquake

<p>On 24th August 2016 a M<sub>L</sub> 6.0 earthquake occurred near Amatrice (central Italy) causing nearly 300 fatalities. The mainshock ruptured a NNW-SSE striking, WSW dipping normal fault. The earthquake produced several coseismic effects at ground, including landslides and ground ruptures. In particular, ground surveys identified a 5.2 km long continuous fracture along the Mt. Vettore flank, both on rock and slope deposits, along one of the active normal fault segments bounding the relief to the west. In this work, we evaluated the contribution of seismically-induced surface instabilities to the observed ground fractures by means of a permanent-displacement approach. The results of a parametric analysis show that the computed seismically-induced gravitational displacements (about 2-10 cm) are not enough to explain field observations, testifying to a mean 20-25cm vertical offset. Thus, the observed ground fractures are the result of primary faulting related to tectonics, combined with gravitational phenomena.</p>

Groundwater depletion in Central Mexico: Use of GRACE and InSAR to support water resources management

AbstractGroundwater deficits occur in several areas of Central Mexico, where water resource assessment is limited by the availability and reliability of field data. In this context, GRACE and InSAR are used to remotely assess groundwater storage loss in one of Mexico's most important watersheds in terms of size and economic activity: the Lerma‐Santiago‐Pacifico (LSP). In situ data and Land Surface Models are used to subtract soil moisture and surface water storage changes from the total water storage change measured by GRACE satellites. As a result, groundwater mass change time‐series are obtained for a 12 years period. ALOS‐PALSAR images acquired from 2007 to 2011 were processed using the SBAS‐InSAR algorithm to reveal areas subject to ground motion related to groundwater over‐exploitation. In the perspective of providing guidance for groundwater management, GRACE and InSAR observations are compared with official water budgets and field observations. InSAR‐derived subsidence mapping generally agrees well with official water budgets, and shows that deficits occur mainly in cities and irrigated agricultural areas. GRACE does not entirely detect the significant groundwater losses largely reported by official water budgets, literature and InSAR observations. The difference is interpreted as returns of wastewater to the groundwater flow systems, which limits the watershed scale groundwater depletion but suggests major impacts on groundwater quality. This phenomenon is enhanced by ground fracturing as noticed in the field. Studying the fate of the extracted groundwater is essential when comparing GRACE data with higher resolution observations, and particularly in the perspective of further InSAR/GRACE combination in hydrogeology.