The fault that moved during the 2017 Mw 5.4 Pohang earthquake in SE Korea;　implications for the EGS project and the generation of the Pohang earthquake

2020 ◽  
Author(s):  
Toshihiko Shimamoto ◽  
Shengli Ma ◽  
Lu Yao ◽  
Tetsuhiro Togo ◽  
HyunJee Lim ◽  
...  
Keyword(s):  
Large Scale ◽  
Water Pressure ◽  
Damage Zone ◽  
Fault Gouge ◽  
Granitic Rocks ◽  
Induced Earthquakes ◽  
Fault Rocks ◽  
Earthquake Fault ◽  
Mud Loss ◽  
Fault Breccia

<p>     Korean Government Commission concluded that the stimulation during the Pohang EGS project triggered the 2017 Mw 5.5 Pohang earthquake in SE Korea which propagated far beyond the stimulated zone of ~ 1 km in size in granitic basement where induced earthquakes had occurred (Ellsworth et al., 2019, SRL).  Distributions of aftershocks of the Pohang earthquakes (Kim et al., 2018, Science) and of the induced earthquakes both indicate that the Pohang earthquake fault (i.e., fault that moved during the Pohang earthquake) cuts PX-2 well at a depth of 3,800 m.  We found abundant fault gouge and fine fault breccia in forms of mud balls (round-shaped fragile fragments of fault rocks coated by thin drilling mud) in the PX-2 borehole cuttings at the depths of 3790-3816 m (26 m interval).  The fault rocks in mud balls are very similar to fault gouge and fine fault breccia constituting the fault cores of the Yangsan and Yeongdeok faults, major faults in SE Korea.  The average content of the fault rocks in the coarse cuttings is 48% and this corresponds to a fault zone of several meters in width, even wider than the fault cores (~ a few meters) of the major faults.  Thus the Pohang earthquake fault is a large fault in SE Korea.  Big mud loss occurred at depths of 3815~3850 m during the PX-2 drilling, causing induced seismicity, and the mud loss is likely to have occurred in fractured host rock in the damage zone.  The PX-2 drilling record reports 10~40 % of gouge at 3790~3805 m depths, nearly consistent with our result, but we could not find fault rocks at many other depths where the drilling record reports gouge.</p><p>     It was so unlucky for the EGS project to have a large-scale fault between PX-1 and PX-2 wells.  First, water injection during the EGS stimulation became nearly direct injection into the faut zone, causing the Pohang earthquake with a small amount of injected water (5,841 m^3; injected water minus flow back).  Second, an impermeable gouge zone could have shut down hydraulic connection between the two wells to inhibit water circulation in the EGS project.  On the other hand, the Pohang earthquake can be a prototype earthquake for studying the mechanisms of induced/triggered earthquake because the induced earthquakes occurred within about 1 km in rather homogeneous granitic rocks (simple geology) and fault-rock samples only several hundred meters away from the epicenter of the Pohang earthquake are available for physical property measurements.  Preliminary experiments on the fault rocks at a temperature of 200 degC, pore water pressure of 30 MPa, and effective normal stresses of 10, 20 and 30 MPa revealed friction coefficients of 0.55 to 0.7 with slight velocity weakening.  The frictional properties are distinctly different from those of the surface fault gouge from the Yangsan and Yeongdeok fault zones.  It is important to reproduce the Pohang earthquake by modeling with known injection history and with measured frictional and transport properties.</p>

scholarly journals Classification of fault breccias and related fault rocks

2008 ◽  
Vol 145 (3) ◽  
pp. 435-440 ◽  
Author(s):  
N. H. WOODCOCK ◽  
K. MORT
Keyword(s):  
Grain Size ◽  
Fault Gouge ◽  
Genetic Classification ◽  
Fault Rocks ◽  
Commercial Importance ◽  
Fault Breccia

AbstractDespite extensive research on fault rocks, and on their commercial importance, there is no non-genetic classification of fault breccias that can easily be applied in the field. The present criterion for recognizing fault breccia as having no ‘primary cohesion’ is often difficult to assess. Instead we propose that fault breccia should be defined, as with sedimentary breccia, primarily by grain size: with at least 30% of its volume comprising clasts at least 2 mm in diameter. To subdivide fault breccias, we advocate the use of textural terms borrowed from the cave-collapse literature – crackle, mosaic and chaotic breccia – with bounds at 75% and 60% clast content. A secondary breccia discriminant, more difficult to apply in the field, is the ratio of cement to matrix between the clasts. Clast-size issues concerning fault gouge, cataclasite and mylonite are also discussed.

scholarly journals Analysis of Pore Water Pressure and Piping of Hydraulic Well

Water ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 502
Author(s):  
Jinman Kim ◽  
Heuisoo Han ◽  
Yoonhwa Jin
Keyword(s):  
Numerical Analysis ◽  
Water Level ◽  
Pore Water ◽  
Large Scale ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Hydraulic Gradient ◽  
Water Levels ◽  
Seepage Velocity ◽  
Seepage Analysis

This paper shows the results of a field appliance study of the hydraulic well method to prevent embankment piping, which is proposed by the Japanese Matsuyama River National Highway Office. The large-scale embankment experiment and seepage analysis were conducted to examine the hydraulic well. The experimental procedure is focused on the pore water pressure. The water levels of the hydraulic well were compared with pore water pressure data, which were used to look over the seepage variations. Two different types of large-scale experiments were conducted according to the installation points of hydraulic wells. The seepage velocity results by the experiment were almost similar to those of the analyses. Further, the pore water pressure oriented from the water level variations in the hydraulic well showed similar patterns between the experiment and numerical analysis; however, deeper from the surface, the larger pore water pressure of the numerical analysis was calculated compared to the experimental values. In addition, the piping effect according to the water level and location of the hydraulic well was quantitatively examined for an embankment having a piping guide part. As a result of applying the hydraulic well to the point where piping occurred, the hydraulic well with a 1.0 m water level reduced the seepage velocity by up to 86%. This is because the difference in the water level between the riverside and the protected side is reduced, and it resulted in reducing the seepage pressure. As a result of the theoretical and numerical hydraulic gradient analysis according to the change in the water level of the hydraulic well, the hydraulic gradient decreased linearly according to the water level of the hydraulic well. From the results according to the location of the hydraulic well, installation of it at the point where piping occurred was found to be the most effective. A hydraulic well is a good device for preventing the piping of an embankment if it is installed at the piping point and the proper water level of the hydraulic well is applied.

scholarly journals Active Fault Systems in the Inner Northwest Apennines, Italy: A Reappraisal One Century after the 1920 Mw ~6.5 Fivizzano Earthquake

Geosciences ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 139
Author(s):  
Giancarlo Molli ◽  
Isabelle Manighetti ◽  
Rick Bennett ◽  
Jacques Malavieille ◽  
Enrico Serpelloni ◽  
...  
Keyword(s):  
Large Scale ◽  
Active Fault ◽  
Active Faults ◽  
Dense Network ◽  
Earthquake Fault ◽  
Slip Rates ◽  
Fault Systems ◽  
Seismological Data ◽  
Seismogenic Faults

Based on the review of the available stratigraphic, tectonic, morphological, geodetic, and seismological data, along with new structural observations, we present a reappraisal of the potential seismogenic faults and fault systems in the inner northwest Apennines, Italy, which was the site, one century ago, of the devastating Mw ~6.5, 1920 Fivizzano earthquake. Our updated fault catalog provides the fault locations, as well as the description of their architecture, large-scale segmentation, cumulative displacements, evidence for recent to present activity, and long-term slip rates. Our work documents that a dense network of active faults, and thus potential earthquake fault sources, exists in the region. We discuss the seismogenic potential of these faults, and propose a general tectonic scenario that might account for their development.

Wavelet analysis of the temporal-spatial distribution in the Eurasia seismic belt

2017 ◽  
Vol 15 (03) ◽  
pp. 1750018 ◽  
Author(s):  
Wenfeng Zheng ◽  
Xiaolu Li ◽  
Lirong Yin ◽  
Zhengtong Yin ◽  
Bo Yang ◽  
...  
Keyword(s):  
Fault Zone ◽  
Compact Support ◽  
Large Scale ◽  
Temporal Distribution ◽  
Seismic Energy ◽  
Research Area ◽  
Earthquake Activity ◽  
Seismic Zone ◽  
Seismic Belt ◽  
Earthquake Fault

Due to the growing frequency of earthquakes, safeties of human lives and properties are facing serious threats. However, the research in the field of spatial-temporal distribution of earthquake is quite a few. In this paper, we use wavelet model to analyze the spatial-temporal distribution of earthquakes. Because the spatial-temporal distribution of earthquake activity is closely related to the distribution of the earthquake fault zone, we analyze large-scale earthquake clusters by selecting the Eurasia seismic belt and the surrounding region as the research area. From the perspective of the time domain, the results show that the seismic energy of the earthquake fault zone presences compact support or similar compact support distribution, suggesting that the seismic zone exists a relatively quiet period and active stage. This indicate that the seismic zone is periodical. The period of strong earthquakes above normal and less than normal is different by time changes. The cycles of earthquakes are different due to different regions and different geological and geographical environment.

scholarly journals Large-scale integrated subglacial drainage around the former Keewatin Ice Divide, Canada reveals interaction between distributed and channelised systems

2020 ◽  
Author(s):  
Emma L. M. Lewington ◽  
Stephen J. Livingstone ◽  
Chris D. Clark ◽  
Andrew J. Sole ◽  
Robert D. Storrar
Keyword(s):  
Spatial Distribution ◽  
Dynamic Response ◽  
Large Scale ◽  
Water Pressure ◽  
Pressure Fluctuations ◽  
Drainage System ◽  
Different Types ◽  
Form Part ◽  
Subglacial Meltwater ◽  
Subglacial Drainage

Abstract. We identify and map traces of subglacial meltwater drainage around the former Keewatin Ice Divide, Canada from ArcticDEM data. Meltwater tracks, tunnel valleys and esker splays exhibit several key similarities, including width, spacing, their association with eskers and transitions to and from different types, which together suggest they form part of an integrated drainage signature. We collectively term these features 'meltwater corridors' and propose a new model for their formation, based on observations from contemporary ice masses, of pressure fluctuations surrounding a central conduit. We suggest that eskers record the imprint of a central conduit and meltwater corridors the interaction with the surrounding distributed drainage system. The widespread aerial coverage of meltwater corridors (5–36 % of the bed) provides constraints on the extent of basal uncoupling induced by basal water pressure fluctuations and variations in spatial distribution and evolution of the subglacial drainage system, which will modulate the ice dynamic response.

scholarly journals Stability Improvement Method for Embankment Dam with Respect to Conduit Cracks

2022 ◽  
Vol 12 (2) ◽  
pp. 567
Author(s):  
Young-Hak Lee ◽  
Jung-Hyun Ryu ◽  
Joon Heo ◽  
Jae-Woong Shim ◽  
Dal-Won Lee
Keyword(s):  
Large Scale ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Three Dimensional ◽  
Internal Erosion ◽  
Scale Model ◽  
Seepage Analysis ◽  
Large Scale Model ◽  
Proposed Model ◽  
Improvement Method

In recent years, as the number of reservoir embankments constructed has increased, embankment failures due to cracks in aging conduits have also increased. In this study, a crack in a conduit was modeled based on the current conduit design model, and the risk of internal erosion was analyzed using a large-scale model test and three-dimensional deformation–seepage analysis. The results show that when cracks existed in the conduit, soil erosion and cavitation occurred near the crack area, which made the conduit extremely vulnerable to internal erosion. Herein, a model is proposed that can reduce internal erosion by applying a layer of sand and geotextiles on the upper part of the conduit located close to the downstream slope. In the proposed model, only partial erosion occurred inside the conduit, and no cavitation appeared near the crack in the conduit. The results suggest that internal erosion can be suppressed when the water pressure acting intensively on the crack in the conduit is dispersed by the drainage layer. To validate these results, the pore water pressure, seepage line, and hydraulic gradient were investigated to confirm the erosion phenomenon and reinforcement effect.

scholarly journals Ice Segregation as an Origin for Lenses of Non-Glacial Ice in “Ice-Cemented” Rock Glaciers

1981 ◽  
Vol 27 (97) ◽  
pp. 506-510 ◽  
Author(s):  
William J. Wayne
Keyword(s):  
Groundwater Flow ◽  
Large Scale ◽  
Water Pressure ◽  
Snow Melt ◽  
Total Thickness ◽  
Rock Glacier ◽  
Glacial Ice ◽  
Substantial Loss ◽  
Rock Glaciers ◽  
Ice Segregation

AbstractIn order to flow with the gradients observed (10° to 15°) rock glaciers cannot be simply ice-cemented rock debris, but probably contain masses or lenses of debris-free ice. The nature and origin of the ice in rock glaciers that are in no way connected to ice glaciers has not been adequately explained. Rock glaciers and talus above them are permeable. Water from snow-melt and rain flows through the lower part of the debris on top of the bedrock floor. In the headward part of a rock glacier, where the total thickness is not great, if this groundwater flow is able to maintain water pressure against the base of an aggrading permafrost, segregation of ice lenses should take place. Ice segregation on a large scale would produce lenses of clear ice of sufficient size to permit the streams or lobes of rock debris to flow with gradients comparable to those of glaciers. It would also account for the substantial loss in volume that takes place when a rock glacier stabilizes and collapses.

scholarly journals Experimental insights into consolidation rates during one-dimensional loading with special reference to excess pore water pressure

2020 ◽  
Vol 15 (12) ◽  
pp. 3571-3591
Author(s):  
Bartłomiej Szczepan Olek
Keyword(s):  
Pore Water ◽  
Large Scale ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Small Scale ◽  
Coefficient Of Consolidation ◽  
Consolidation Process ◽  
Factors Affecting ◽  
Fine Grained ◽  
Fine Grained Soil

AbstractConsolidation rate has significant influence on the settlement of structures founded on soft fine-grained soil. This paper presents the results of a series of small-scale and large-scale Rowe cell consolidation tests with pore water pressure measurements to investigate the factors affecting the consolidation process. Permeability and creep/resistance structure factors were considered as the governing factors. Intact and reconstituted marine clay from the Polish Carpathian Foredeep basin as well as clay–sand mixtures was examined in the present study. The fundamental relationship correlating consolidation degrees based on compression and pore water pressure was assessed to indicate the nonlinear soil behaviour. It was observed that the instantaneous consolidation parameters vary as the process progresses. The instantaneous coefficient of consolidation first drastically increases or decreases with increase in the degree of consolidation and stabilises in the middle stage of the consolidation; it then decreases significantly due to viscoplastic effects occurring in the soil structure. Based on the characteristics of the relationship between coefficient of consolidation and degree of dissipation at the base, the consolidation range that complies with theoretical assumptions was established. Furthermore, the influence of coarser fraction in clay–sand mixtures in controlling the consolidation rates is discussed.

Large-Scale Resonant Fatigue Testing of Welded Tubular X-Joints for Offshore Jacket Foundations

2019 ◽  
Author(s):  
Jeroen Van Wittenberghe ◽  
Philippe Thibaux ◽  
Maarten Van Poucke
Keyword(s):  
Large Scale ◽  
Fatigue Testing ◽  
Water Pressure ◽  
Limit State ◽  
Fatigue Tests ◽  
Offshore Wind ◽  
Design Standards ◽  
Initiation Phase ◽  
Out Of Plane ◽  
Jacket Structures

Abstract Offshore wind turbines are being installed in deeper water and with more powerful generators resulting in more severe loading conditions on its foundations such as jacket structures. Because the main loading is due to wind and currents, the dominant design limit state is fatigue. The fatigue performance of the tubular joints used in jacket structures has been assessed several decades ago based on test results with limited component dimensions (diameter and wall thickness). In addition, improvements of welding methods and evolution of steel grades are not considered in the current design standards. To provide experimental fatigue-life data on large-scale structures a test program has been carried out on 4 welded tubular X-joints. Each X-joint consists of two horizontal braces with a diameter of 711 mm welded to a central vertical tubular member with 806 mm diameter. The X-joint has a total length of 7.5 m and has two identical welds that are fatigue tested. The fatigue tests are carried out on an innovative resonant bending fatigue test rig that allows to load the specimen in in- and out-of-plane direction at a different amplitude to obtain an even stress distribution over the circumference of the welds. The tests are carried out at a speed close to the resonance frequency of the X-joint. During the test, hotspot strains are measured using strain gauges and a limited amount of water pressure is used to detect through-thickness cracks. The tests are carried out in two phases. During the crack initiation phase, the sample is loaded in both the in- and out-of-plane mode. Once cracks are detected, the test is continued in the crack propagation phase with loading in the plane where cracks had been initiated until through-thickness cracking appeared. During this phase the beach marking technique has been used to mark the shape of the fracture surface at different moments during the fatigue tests. The testing program is part of the RFCS project JABACO that aims to reduce offshore wind cost by incrementing prefabrication of the jacket substructure.

scholarly journals Study on the mechanism of water inrush in the arid western mining area

2019 ◽  
Vol 118 ◽  
pp. 03008
Author(s):  
Chao Zheng ◽  
Lan Yu ◽  
Jiangyi He ◽  
Fengfeng Yang ◽  
Jufeng Zhang
Keyword(s):  
Large Scale ◽  
Water Pressure ◽  
Water Inrush ◽  
Hydrodynamic Pressure ◽  
Mining Area ◽  
Mining Areas ◽  
Isolation Layer ◽  
Working Face ◽  
Combined Action ◽  
Tension Fracture

The analysis found that the coal mining process in the western mining area has the mining loss and disaster effect of the water-rich aquifer of the coal seam roof, which is mainly manifested by the overburden water in the roof. On this basis, the formation and development of the separation water of the roof is proposed, and the mechanism of the water inrush from the layer is revealed. It is found that there is hydrostatic pressure and hydrodynamic pressure in the separated water, under the combined action of bed separation water pressure, the mining-induced fracture and water-isolation layer tension fracture are connected, which causes water inrushing in the coal working face of the mine, and provides a theoretical guarantee for the large-scale development of coal resources in western mining areas.

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