Loading transfer mechanism of a piled raft subjected to normal faulting in sand

Although different kinds of foundations have been investigated against an earthquake faulting, the interaction between pile group and dip-slip fault has not yet been fully understood. This letter investigates the interaction between piled raft and normal faulting by means of centrifuge and numerical modelling. In centrifuge test, a piled raft was simulated with a half model for a better observation of fault rupture path under the raft. The loading transfer mechanism was further examined using a three-dimensional finite difference software (FLAC3D). The measured and computed results showed that the piled raft displaced and tilted linearly with the magnitude of faulting. The fault rupture bifurcated into two and diverted towards both edges of the raft. Two types of loading transfer mechanism were identified during faulting. Working load transferred from the raft to the underneath piles, and also from the piles on the side of the hanging wall to the piles on the footwall side, resulting in compression failure of the piles on the footwall side.

Application of Cascade Forward Backpropagation Neural Networks for Selecting Mining Methods

Decision-making is very important in many fields, such as mining engineering. In addition, there has been a growth of computer applications in all fields, especially mining operations. One of these application fields is mine design and the selection of suitable mining methods, and computer applications can help mine engineers to decide upon and choose more satisfactory methods. The selection of mining methods depends on the rock-layer specification. All rock characteristics should be classified in terms of technical and economic concerns related to mining rock specifications, such as mechanical and physical properties, and evaluated according to their weights and ratings. Methodologically, in this study, the criteria considered in the University of British Columbia (UBC) method were used as references to establish general criteria. These criteria consist of general shape, ore thickness, ore plunge, and grade distribution, in addition to the rock quality designation (ore zone, hanging wall, and foot wall) and rock substance strength (ore zone, hanging wall, and foot wall). The technique for order of preference by similarity to ideal solution (TOPSIS) was adopted, and an improved TOPSIS method was developed based on experimental testing and checked by means of the application of cascade forward backpropagation neural networks in mining method selection. The results provide indicators that decision makers can use to choose between different mining methods based on the total points given to all ore properties. The best mining method is cut and fill stopping, with a rank of 0.70, and the second is top slicing, with a rank of 0.67.

Detachment-parallel recharge explains high discharge fluxes at the TAG hydrothermal field

Submarine massive sulfide deposits on slow-spreading ridges are larger and longer-lived than deposits at fast-spreading ridges1,2, likely due to more pronounced tectonic faulting creating stable preferential fluid pathways3,4. The TAG hydrothermal mound at 26°N on the Mid-Atlantic Ridge (MAR) is a typical example located on the hanging wall of a detachment fault5-7. It has formed through distinct phases of high-temperature fluid discharge lasting 10s to 100s of years throughout at least the last 50,000 years8 and is one of the largest sulfide accumulations on the MAR. Yet, the mechanisms that control the episodic behavior, keep the fluid pathways intact, and sustain the observed high heat fluxes of up to 1800 MW9 remain poorly understood. Previous concepts involved long-distance channelized high-temperature fluid upflow along the detachment5,10 but that circulation mode is thermodynamically unfavorable11 and incompatible with TAG's high discharge fluxes. Here, based on the joint interpretation of hydrothermal flow observations and 3-D flow modeling, we show that the TAG system can be explained by episodic magmatic intrusions into the footwall of a highly permeable detachment surface. These intrusions drive episodes of hydrothermal activity with sub-vertical discharge and recharge along the detachment. This revised flow regime reconciles problematic aspects of previously inferred circulation patterns and can be used as guidance to one critical combination of parameters that can generate substantive mineral systems.

Microseismicity and lithosphere thickness at a nearly amagmatic mid-ocean ridge

Successive flip-flop detachment faults in a nearly-amagmatic region of the ultraslow-spreading Southwest Indian Ridge (SWIR) at 64°30'E accommodate ~100% of plate divergence, with mostly ultramafic seafloor. As magma is the main heat carrier to the oceanic lithosphere, the nearly-amagmatic SWIR 64°30'E is expected to have a very thick lithosphere. Here, our microseismicity data shows a 15-km thick seismogenic lithosphere, actually thinner than the more magmatic SWIR Dragon Flag detachment with the same spreading rate. This challenges current models of how spreading rate and melt supply control the thermal regime of mid-ocean ridges. Microearthquakes with normal focal mechanisms are colocated with seismically imaged damage zones of the detachment and reveal hanging-wall normal faulting, which is not seen at more magmatic detachments at the SWIR or the Mid-Atlantic Ridge. We also document a two-day seismic swarm, interpret as caused by an upward-migrating melt intrusion in the detachment footwall (6-11 km), triggering a sequence of shallower (~1.5 km) tectonic earthquakes in the detachment fault plane. This points to a possible link between sparse magmatism and tectonic failure at melt-poor ultraslow ridges.

Benefits of Defining Geological Sensitive Zones in the Mitigation of Disasters Along Earthquake Fault Zones in Taiwan – The Case of Milun Fault

In Taiwan, the main purpose of earthquake fault zone legislation is to prevent earthquake-related disasters around the surface traces of active faults, particularly in urban areas. Here, the Geologically Sensitive Area (GSA) of the Milun Fault (Milun Earthquake Fault Zone) is used as an example to reveal the importance of such legislation. Field data collected along the Milun Fault before and after the 2018 Hualien Earthquake were used to reveal the reappearance of damages within the GSA. The 2018 Hualien Earthquake represents one of the shortest recurrence intervals (67 years) among all major faults in Taiwan. Most of the surface ruptures and damaged buildings in Hualien City were within the Milun Fault GSA and concentrated on the hanging wall of the fault. Moreover, 61% (91/148) of the damaged buildings and 83% (692/835) of the surface ruptures occurred within 100 m of the fault line. The results of this study demonstrate the importance of defining GSAs of active faults for mitigating earthquake hazards.

Geologic observations in the San Marcos area, Coahuila, Mexico: the case for sediment-hosted stratiform copper–silver mineralization in the Sabinas basin during the Laramide orogeny

The sediment-hosted stratiform copper–silver mineralization in the San Marcos area of Coahuila, northeastern Mexico occurs predominantly at an Early Cretaceous redox boundary between footwall siliciclastic red beds of the San Marcos Formation and hanging-wall carbonate strata of the Cupido Formation in the Sabinas basin. The hypogene mineralization is mainly present as chalcocite-group minerals, with additional bornite and chalcopyrite, and everywhere occurs in both disseminated and vein/veinlet forms. Supergene copper-bearing oxides (malachite, chalcanthite, azurite, chrysocolla) are, however, the dominant surface expression of the mineralization. Additional sediment-hosted stratiform copper–silver mineralization also occurs, albeit erratically, in lower strata of the Sabinas basin as well as in veins in basement granitoids, thus spanning ~3000 m of basin stratigraphy. Where best developed, the stratiform mineralization displays intense structural control proximal to the regional San Marcos fault system. This major bounding fault, regional in nature and with numerous periods of activity, controlled the evolution of the Sabinas basin. Structural controls on mineralization include stacked, shallow-angle, bedding-parallel, northeast-vergent thrust faults and associated drag folds, in addition to numerous, steeply-dipping, northeast-trending copper-bearing veins and veinlets. The mineralized veins and veinlets, and the bedding-parallel thrusts display mutually crosscutting relationships. These elements are all consistent and in harmony with a regional northeast-trending direction of horizontal shortening accompanying reverse motion of the San Marcos fault system. Inversion along the San Marcos fault system, and the entire Sabinas basin in the Paleogene from ~60 to 40 Ma, resulted from wholesale contractional deformation during the Laramide (Mexican) orogeny. Hence, emplacement of the sediment-hosted stratiform copper–silver mineralization at San Marcos, and elsewhere in the larger Coahuila region, is interpreted as a natural corollary of large-scale, metal-bearing fluid expulsion, migration, and precipitation resulting from orogenic shortening, lithostatic loading, and squeezing of the Sabinas basin during Mexican orogen construction. Although sedimentation of the host strata in the Sabinas basin took place in a pericratonic setting associated with the opening of the Gulf of Mexico, sediment-hosted stratiform copper-silver mineralization occurred during orogenic uplift and conversion of the original basin into an orogen-foreland pair, with similarities to some of the world´s largest sediment-hosted stratiform copper provinces.

Accuracy of Sentinel-1 PSI and SBAS InSAR Displacement Velocities against GNSS and Geodetic Leveling Monitoring Data

Correct use of multi-temporal Interferometric Synthetic Aperture Radar (InSAR) datasets to complement geodetic surveying for geo-hazard applications requires rigorous assessment of their precision and accuracy. Published inter-comparisons are mostly limited to ground displacement estimates obtained from different algorithms belonging to the same family of InSAR approaches, either Persistent Scatterer Interferometry (PSI) or Small BAseline Subset (SBAS); and accuracy assessments are mainly focused on vertical displacements or based on few Global Navigation Satellite System (GNSS) or geodetic leveling points. To fill this demonstration gap, two years of Sentinel-1 SAR ascending and descending mode data are processed with both PSI and SBAS consolidated algorithms to extract vertical and horizontal displacement velocity datasets, whose accuracy is then assessed against a wealth of contextual geodetic data. These include permanent GNSS records, static GNSS benchmark repositioning, and geodetic leveling monitoring data that the National Institute of Statistics, Geography, and Informatics (INEGI) of Mexico collected in 2014−2016 in the Aguascalientes Valley, where structurally-controlled land subsidence exhibits fast vertical rates (up to −150 mm/year) and a non-negligible east-west component (up to ±30 mm/year). Despite the temporal constraint of the data selected, the PSI-SBAS inter-comparison reveals standard deviation of 6 mm/year and 4 mm/year for the vertical and east-west rate differences, respectively, thus reassuring about the similarity between the two types of InSAR outputs. Accuracy assessment shows that the standard deviations in vertical velocity differences are 9−10 mm/year against GNSS benchmarks, and 8 mm/year against leveling data. Relative errors are below 20% for any locations subsiding faster than −15 mm/year. Differences in east-west velocity estimates against GNSS are on average −0.1 mm/year for PSI and +0.2 mm/year for SBAS, with standard deviations of 8 mm/year. When discrepancies are found between InSAR and geodetic data, these mostly occur at benchmarks located in proximity to the main normal faults, thus falling within the same SBAS ground pixel or closer to the same PSI target, regardless of whether they are in the footwall or hanging wall of the fault. Establishing new benchmarks at higher distances from the fault traces or exploiting higher resolution SAR scenes and/or InSAR datasets may improve the detection of the benchmarks and thus consolidate the statistics of the InSAR accuracy assessments.

Seismic Response of a Water Transmission Pipeline Across a Fault Zone Adopting a Large-Scale Vibration Table Test

The seismic response is generally amplified significantly near the fault zone due to the influence of discontinuous interfaces and weak-broken geotechnical structures, which imposes a severe geologic hazard risk on the engineering crossing the fault. The Hanjiang to Weihe River Project (phase II) crosses many high seismic intensity regions and intersects with eight large-scale regional active faults. Seismic fortification of the pipelines across the fault zone is significant for the design and construction of the project. A large-scale vibration table test was adopted to investigate the seismic response and fault influences. The responses of accelerations, dynamic stresses, strains, and water pressures were obtained. The results show that the dynamic responses were amplified significantly by the fault zone and the hanging wall. The influence range of fault on acceleration response is approximately four times the fault width. The acceleration amplification ratio in the fault zone generally exceeds 1.35, even reaching 1.8, and the hanging wall amplification ratio is approximately 1.2. The dynamic soil pressure primarily depends on the acceleration distribution and is apparently influenced by pipeline location and model inhomogeneity. The pipeline is bent slightly along the axial direction, accompanied by expansion and shrinkage in the radial direction. The maximum tensile and compressive strains appear at the lower and upper pipeline boundaries near the middle section, respectively. Massive y-direction cracks developed in the soil, accompanied by slight seismic subsidence. The research findings could provide reasonable parameters for the seismic design and construction of the project.

Using Structural Geology and Cosmogenic Nuclide Dating to Infer the Slip Rate and Frictional Strength of the Active Mai’iu Low-Angle Normal Fault, Eastern Papua New Guinea

<p>Low-angle normal faults (LANFs) have induced debate due to their apparent non -Andersonian behaviour and lack of significant seismicity associated with slip. Dipping 21°/N, the Mai’iu Fault, located in the Woodlark Rift, Eastern Papua New Guinea is an active LANF that occupies a position at the transition between continental extension and seafloor spreading. Surface geomorphology indicates that the Mai’iu Fault scarp is not significantly eroded despite high rainfall and ~2900 m of relief. Based on modelling of regional campaign GPS data (Wallace et al., 2014) the Mai’iu Fault is thought to accommodate rapid (7–9 mm/yr) horizontal extension; however the slip rate of the Mai’iu Fault has not been directly validated. I use a range of methodologies, including field mapping, cosmogenic exposure dating, cosmogenic burial dating, and Mohr-Coulomb modelling, in order to provide new constraints on LANF strength and slip behaviour. I analyse the structure of conglomeratic strata within a back -rotated rider block atop the Mai’iu Fault surface. The Gwoira rider block is a large fault-bounded sedimentary rock slice comprising the Gwoira Conglomerate, located within a large synformal megamullion in the Mai’iu Fault surface. The Gwoira Conglomerate was originally deposited on the Mai’iu Fault hanging wall concurrent with extension, and has since been buried to a maximum depth of ~2 km (evidenced by modelling of vitrinite reflectance data, and structural analysis), back-tilted, and synformally folded. The Mai’iu Fault is also overlain by a large fault slice (the Gwoira rider block), that has been transferred from the previous LANF hanging wall to the current footwall by the initiation of the younger Gwoira Fault. Both the Gwoira Conglomerate (former hanging wall) and mylonitic foliation (footwall) of the Mai’iu Fault have been shortened ~E-W, perpendicular to the extension direction. I show that N-S trending synformal folding of the Gwoira Conglomerate was concurrent with on-going sedimentation and extension on the Mai’iu Fault. Structurally shallower Gwoira Conglomerate strata are folded less than deeper strata, indicating that folding was progressively accrued concurrent with ~N -S extension. I also show that abandonment of the inactive strand of the Mai’iu Fault in favour of the Gwoira Fault, which resulted in formation of the Gwoira rider block, occurred in response to progressive megamullion amplification and resultant misorientation of the inactive strand of the Mai’iu Fault. I attribute N-S trending synformal folding to extension-perpendicular constriction. This is consistent with numerous observations of outcrop-scale conjugate strike-slip faults that deform the footwall and hanging wall of the Mai’iu Fault (Little et al., 2015), and accommodate E-W shortening. Constrictional folding remains active in the near-surface as evidenced by synformal tilting of inferred Late Quaternary fluvial terraces atop the Gwoira rider block. In order to date this sequence of progressive constrictional folding, I have processed ten ²⁶Al/¹⁰Be terrestrial cosmogenic nuclide burial samples obtained from the Gwoira Conglomerate; unfortunately these data were not yet available at the time of printing, due to reasons outside of my control. I also present terrestrial cosmogenic nuclide (TCN) exposure ages for ten rock samples obtained from the lowermost Mai’iu Fault scarp at Biniguni Falls, in order to determine the Holocene slip-rate and style using cosmogenic ¹⁰Be in quartz. I model exposure age data after the approach of Schlagenhauf et al. (2011), using a Monte-Carlo simulation in which fault slip rate, the period of last slip on the fault, and local erosion rate are allowed to vary. Modelling evidences that the Mai’iu Fault at Biniguni Falls is active and slipping at 13.9±4.0 mm/yr (1σ), resolved over the last 13.2±2.7 ka (1σ). Modelling constrains the time of last slip to 2.9±1.4 ka (1σ); this is consistent with a seismic event at that time, followed by non-slip on the Mai’iu Fault until the present day. Finally, because rider block formation records abandonment of the uppermost part of a LANF, Coulomb fault mechanical analysis can be applied to field observations to provide an upper limit on LANF frictional strength (µf). Calculations are made in terms of Mohr-Coulomb mechanics, after the framework of Choi and Buck (2012). The lock-up (abandonment) orientation at any particular position on the Mai’iu Fault is principally a function of fault friction (µf), crustal friction (µc), fault cohesion (Cf), crustal cohesion (Cc), depth, fault orientation, fluid pressure, and the orientation of the greatest principle stress. Model results suggest that fault friction for the active Gwoira-Mai’iu Fault surface is 0.128≤μf≤0.265 for Cf<1.8 MPa, and 0.2≤μf≤0.265 for Cf≤0.5 MPa. Modelling of abandonment of the inactive Mai’iu Fault suggests that 0.26≤μf≤0.309 for Cf<1.8 MPa. This suggests that past slip on the inactive Mai’iu Fault, and continued slip on the active Gwoira-Mai’iu Fault, were enabled by low fault frictional strength. I also model the strength of the active Mai’iu Fault at Biniguni Falls; results suggest greater LANF friction (μf≥0.32) than the Gwoira-Mai’iu Fault surface, and inactive Mai’iu Fault. In order to explain active slip on the LANF at Biniguni Falls concurrent with widespread field observations of outcrop-scale faulting of the LANF footwall, I suggest a process whereby overall the LANF remains viable and active, but locally stress conditions exceed the LANF abandonment criteria; this results in highly localised and temporary ‘footwall damage’ where the LANF footwall is locally dissected by outcrop-scale faulting.</p>