Steep Dips Research Articles

Extraction of solid sulfide ore reserves from the Second Southern Lens in Mayak Mine with regard to the ore morphology and mode of occurrence

The article presents the studies aimed to optimize and validate a mining flow chart for extraction of solid sulfide ore reserves from the Second Southern Lens with regard to the ore morphology and mode of occurrence. The geology of the Second Southern Lens is represented by the upper Devonian overburden and the lower Tunguska series cut with differentiated intrusion of gabbro-dolerite. Bed rocks are overlaid with thick and sheet-like quaternary strata, with an aquifer in boulder–chisley deposits at the bottom. The latter are overlaid with clay and loam layers 50–60 m thick. For safe and convenient mining under the old quaternary aquifer, an ore crown was left to isolate the zone of mining operations from the water-bearing body. With regard to the mode of occurrence of the ore body, the ground control assumes cemented paste backfill transported from the surface backfill preparation plant to the backfill holes by dump trucks. Full backfill ensures compete extraction of high-value ore reserves and sufficient safety of mining. The existing constraints (small thickness of the ore body in combination of its steep dip, low quality of the ore–barren rock interface, aquifer and shallow occurrence), as well as the high extraction standards govern selection of the stoping mining system with vertical slicing and horizontal blind entry cuts.

Early Results of Eastern Indonesia P-wave Tomography Study Using Regional Events

The tectonic system of Eastern Indonesia is controlled by several major and minor plates, such as Indo-Australian, Australian plate, and Pacific plates. This area is known for its complexity, and high seismic activity. This study tries to image the complex structures beneath this region by employing regional events data and seismic tomography methods. We used five years of regional events catalog provided by the Indonesian Agency of Meteorology, Climatology, and Geophysics. We have sorted 7336 events recorded between 120° – 136° longitude and 0° – 13°(-) latitude consisting of 46446 P and 15467 S wave arrival data. Relocated hypocenter map shows a better constrain location on seismicity along outer Bandar Arc. A dipping pattern of seismicity is seen that is going deeper to the Banda Sea. The seismicity map also images a steep angle pattern of seismicity that could be related to the subduction slab roll-back model at North of Wetar island. Interestingly, we spotted a seismicity gap in West Seram that could be linked with slab tear zone. The checker-board test suggests a proper resolution is still reliable to a depth of 200 km with a less interpretable model at a depth of 300 km. P-wave tomographic models image the high velocity dipping down going slab. The Banda slab is seen to subduct from south Timor Island to the north, from east Tanimbar and Aru Island to west part, and from north Seram Island to south. We observed the down-going slab meet from all directions at about 300 km beneath the Banda sea. P wave tomogram also shows the Timor Island slab has a steeper dip that agrees with the seismicity pattern. Near the Seram island, we identify a low-velocity anomaly zone infiltrate the Banda slab beneath the shallow part of West Seram, which was previously interpreted as slab tear zone. This study also noticed a higher velocity tomogram model at North of Wetar island that might indicate a back-arc thrust. Lastly, a low-velocity band is also exposed at a shallow depth close to the volcano chain along that Banda volcanic arc.

The likely Quaternary active El Arrayán fault, Santiago, Chile

Understanding the location and nature of Quaternary active crustal faults is critical to the reduction of both fault rupture and strong ground motions hazards in built environments. Recent work along the San Ramón Fault (SRF) demonstrates that crustal seismic sources are important hazards within the Santiago Metropolitan region of Chile. In this paper, we present the evidence of a second likely Quaternary active fault (the El Arrayán Fault, EAF) that runs through the northeastern part of Santiago, in the Lo Barnechea area. The EAF is a strike-slip fault zone at least 13 km-long, has a steep dip (mean dip 77º NNE), and a WNW-ESE general trend (~110º) that cuts across folded rocks of the Abanico Formation and Quaternary deposits. Sequences of meter-wide fault rocks in El Arrayán area are coincident with the tectonic geomorphology of the EAF, with fault scarps, deflected streams, saddles, “island hills”, sag ponds and linear valleys in the La Dehesa area and coincident with fault strike from the bedrock exposures. Although direct dating is not yet available, fault exposures tied to fault-related tectonic and geomorphic features that crosscut Late-Quaternary morphologies and deposits (including hillslopes, ridges, landslides and alluvial fans), provides strong evidence that the EAF is a Quaternary active and seismogenic crustal fault. Sinistral slickensides and left-lateral deflected streams indicates a left-lateral kinematics (with slight up to the north reverse motion) for the EAF. Due to the location, geometry, kinematics and likely Quaternary activity of the EAF, this structure is interpreted as an arc-oblique transfer zone of the West Andean Thrust (WATS). If the EAF has stick-slip behaviour, it is potentially an important source of fault rupture and strong ground motions and could be responsible for earthquakes up to Mw 6.4 based on earthquake scaling laws and microseismicity observations in and around Santiago. The lack of fault zone avoidance criteria (i.e., do not build in and around active faults) in Chilean law, requires immediate enhanced fault mapping, legislation and the implementation of active fault rupture avoidance areas to reduce the risk associated with active crustal structures in the built environment.

Impact of inversion tectonics on the spatial distribution of hydrocarbon traps in the NW Persian Gulf and the southern Dezful Embayment, SW Iran

Inversion tectonics has a major impact on distribution of fault-controlled hydrocarbon traps in the fold-and-thrust belts. In order to characterize the spatial distribution of several fault-controlled hydrocarbon traps adjacent to the Nourooz-Hendijan-Izeh Fault, this study describes the structural and tectono-sedimentary evolution of the fault based on the geological interpretation and tectono-sedimentary analysis of seven seismic sections in the Bahregansar, Hendijan, Tangu, and Rag-e-Sefid oilfields in the NW Persian Gulf and the southern Dezful Embayment. The results indicate that the Nourooz-Hendijan-Izeh Fault is a segmented pre-existing basement fault with steep dip, which reactivated to at least seven tectonic phases. Three-phase inversion tectonics along the Nourooz-Hendijan-Izeh Fault occurred at the Late Devonian-Carboniferous (positive inversion), Permian-Early Triassic (negative inversion), and Late Cenomanian-Early Turonian (positive inversion) boundaries and modified the evolutionary history of the sedimentary basin. Inversion affected hydrocarbon trap development at the Late Cretaceous and controlled their current conditions in the NW Persian Gulf and the southern Dezful Embayment along the northeastern margin of African-Arabian plates. Considering the hydrocarbon migration at the Late Miocene in these regions up to now, the N–S trending anticlines (Arabian trend) have a larger share of oil and gas in their hydrocarbon traps and lower hydrocarbon exploration risk than the NW-SE trending anticlines (Zagros trend). Mild to moderate inversion structures can be considered as preferred petroleum exploration targets.

A Walkaway Vertical Seismic Profiling Modeling and Imaging Study and Combining Its Results with Migrated Surface Seismic Images

This paper presents and analyzes results from a Finite Difference Modeling (FDM), processing, and imaging study of a Walkaway Vertical Seismic Profiling (WVSP) survey, and discusses how the images from WVSP enhance those from the surface seismic data. It is shown that the results from the WVSP integrate well with the image from the surface seismic performed in the same line. For the study, a seismic model with vertically and horizontally varying velocities was built and a WVSP data set was generated. The surface seismic had difficulty to show clear images from the layers with steep dips and near vertical displacements on the model due to the lack of ray coverage. The study demonstrates that the WVSP geometry can record reflections from near vertical layers facing the borehole, which help with imaging the parts of the subsurface structure which were missing in the surface seismic. With proper combination of the images from the WVSP and the surface seismic, a more complete image profile of the subsurface can be constructed around the borehole. However, while contributing to surface seismic, it is also seen that the WVSP introduces more migration artifacts related to source interval distance and interbed multiples than the surface seismic data.

Igneous genesis of the Bayan Obo REE–Nb–Fe deposit: New petrographical and structural evidence from the H1–H9 cross-section and deep-drilling exploration

Rare earth elements (REEs) are a focus of global attention because of their unique properties and high-tech applications. Bayan Obo is the world's largest REE deposit and is hosted in the Paleoproterozoic Bayan Obo Group, Inner Mongolia. The REE resources are concentrated in unit H8, “dolomite marble.” However, whether unit H8 has an igneous or sedimentary origin is debated, and relationships among units H1–H9 are unclear, hindering our understanding of the formation of such a giant REE deposit. It was previously assumed that the unit H8 orebody is located in both limbs of the Bayan syncline and unit H9 in the core, which also needs to be confirmed because it is a guide for ore exploration. Field observations and petrographic studies of units H1–H9 were undertaken to re-evaluate the petrology and structure of the Bayan Obo Group. It was found that some units (e.g., H5–H7) are missing from the studied cross-section, with the two sides of unit H9, across the hinge of the so-called syncline, not being directly comparable. Unit H8 displays petrological, mineralogical, and whole-rock REE geochemical characteristics distinct from those of the other units investigated, suggesting they are of different origin. Moreover, deep-drilling exploration indicates major differences between the two limbs of the orebodies in terms of thickness, occurrence, and spatial distribution. The East orebody has a steep dip angle of 70°–80° and continuously extends to depth without reduction of angle, suggesting the syncline is probably nonexistent. These results, combined with the reported intrusion relationship of unit H8 with surrounding rock and in situ isotopic studies previously reported, indicate that the orebody is a carbonatitic igneous conduit rather than being of sedimentary origin. SHRIMP U–Pb dating of detrital zircons from the units H2–H9 yielded ages of 2574 ± 25 to 132 ± 2 Ma, overlapping the ages of units H1–H9 and the main REE mineralization periods reported previously. These protracted and complicated ages of the orebody likely represent fluid-aided resetting ages.

3D adaptive internal multiples modeling based on globally optimised Fourier finite-difference method

Abstract Numerical methods have been widely applied to simulate seismic wave propagation. However, few studies have focused on internal multiples modeling. The formation mechanism and response of internal multiples are still unclear. Therefore, we develop a weighted-optimised-based internal multiples simulation method under 3D conditions. Using a one-way wave equation and full-wavefield method, the different-order internal multiples are computed numerically in a recursive manner. The traditional Fourier finite-difference (FFD) method has low numerical accuracy in a horizontal direction. A globally optimised FFD (OFFD) method is used to improve the lateral propagation accuracy of the seismic waves. Meanwhile, we adopt an adaptive variable-step technique to improve computational efficiency. The 3D internal multiples modeling technique is capable of calculating the different-order multiple reflections in complex structures. We use the present method to simulate internal multiples in several models. Theoretical analyses are consistent with the numerical results. Numerical examples demonstrate that the 3D internal multiples modeling technique has superior performance when adapting to lateral velocity changes and steep dip. This also implies that our method is fit for the simulation of internal multiples propagation in a 3D complex medium and can assist in identifying the internal multiples from full-wavefield data.

Reasonable Clear Spacing for Large-SpanTwin Tube Four Track Underground Metro Station in Steep Dip Rocks

Reasonable Clear Spacing for Large-SpanTwin Tube Four Track Underground Metro Station in Steep Dip Rocks

Comprehensive identification of statistical homogeneity of fractured rock masses for a candidate HLW repository site, China

Determining the statistically homogeneous regions is important for engineering geological modeling and promoting systematic research on regional rock mass characteristics and rock engineering designs. This study proposes a comprehensive framework considering multiple discontinuity geometry parameters (e.g., orientation, trace length, density, and cluster characteristics.) to distinguish statistical homogeneity of fractured rock masses. First, based on the equal-area plot method (Schmidt net), the quantitative judgment ability of the Miller method for determining the similarity between two discontinuity orientation populations was improved by optimizing block network division scheme and blank area merging principle. Then, considering the distribution characteristics of discontinuity in rock mass space and the variation features of discontinuity at different geographical locations, a three-dimensional fracture network model, established using the discontinuity geometry parameters obtained from field investigation, was combined with the fractal dimension method (called the network fractal dimension method; NFD) to further evaluate the statistical homogeneity of fractured rock mass. The proposed approaches were subsequently applied to the identification of the statistical homogeneity of several typical granite fracture outcrops in the Beishan area, which is a candidate site for high-level radioactive waste (HLW) repository of China. The case study reveals that the optimized Miller method is more flexible and applicable than the conventional orientation-based methods, especially in dealing with the complex situation of the coexistence of gentle dip angle and steep dip angle as well as clustering characteristics of discontinuity. The NFD method was used to unify the influence of the main discontinuity characteristic parameters for a logical and unbiased evaluation of the statistical homogeneity. The comprehensive framework developed herein integrates the advantages of the two methods and reduces the interference of subjective evaluation. Therefore, it can be employed to efficiently determine the statistical homogeneity of rock masses at different locations at a large scale without concern over the deviation caused by different directions and size of the compared areas.

The world unique triangular shaped Jonah High in the Levant Basin, eastern mediterranean – Tectonic setting, stratigraphy and exploration considerations

A clear magnetic anomaly is evident across the central part of the Southern Levant Basin, coinciding with prominent structural features known as the Jonah High and Jonah Ridge. Jonah High is a triangular shaped, horst-like structure, bounded at each of its three rims by segments of steep dips and is capped by a prominent seismic marker. An attempt to drill through the cap resulted in a loss of circulation in the Lower Miocene. The well was side-tracked to the east of the cap and penetrated a Lower Miocene and Upper Oligocene deep-water section, as found in other wells in the basin. Few models were suggested since the 1980's to explain the combined magnetic anomaly, gravity and oddly shaped structure; they include basement high, intrusive body and shallow volcanic edifice. The upper part of the high has been suggested to be a carbonate build-up of either Mesozoic or Cenozoic age or a shale structure. This study takes advantage of recently released 3D surveys acquired over the Jonah High and the results of the well. It is suggested that the Jonah High was intruded during the Lower to Middle Miocene by allochthonous bodies; these form an equilateral triangle, measuring 265 sq. km at 6.5 km depth, that might be world unique. The interior of the upper part of Jonah High, from about 5 km to 6.5 km, is suggested to be composed of a deep-water Oligocene and Lower Miocene section and probably contains the Tamar Sands, the main gas-bearing reservoir in the basin. The deep part exhibits folded and tilted high amplitude strata that may be partly composed of old magmatic material that upwelled during the Cenozoic by mobile sediment acting under the regional contractional regime; these might be associated with the observed magnetic and gravity anomalies. Further exploration by better imaging and drilling together with analogue cases from other basins are required in order to solve this enigmatic feature.

Seismic Velocity Structure Beneath the Tofino Forearc Basin Using Full Waveform Inversion

Given the effects of steep dips and large lateral variations in seismic velocity beneath the Vancouver Island continental shelf, seismic processing and travel time inversion are inadequate to obtain a detailed velocity model of the subsurface. Therefore, seismic full waveform inversion is applied to multichannel seismic reflection data to obtain a high-resolution velocity model beneath the Tofino fore-arc basin under the continental shelf off Vancouver Island margin. Seismic velocities obtained in this study help in understanding the shallow shelf sediment structures, as well as the deeper structures associated with accreted terranes, such as Pacific Rim and Crescent terranes. Shallow high velocities, as large as ∼5 km/s, were modeled in the mid-shelf region at ∼1.5–2.0 km depth. These coincide with an anticlinal structure in the seismic data, and possibly indicate the shallowest occurrence of the volcanic Crescent terrane. In general, seismic velocities increase landward, indicating sediment over-consolidation related to the compressional regime associated with the ongoing subduction of the Juan de Fuca plate and the emplacement of Pacific Rim and Crescent accreted terranes. Seismic velocities show a sharp increase about 10 km west of Vancouver Island, possibly indicating an underlying transition to the Pacific Rim terrane. A prominent low velocity zone extending over 10 km is observed in the velocity model at 800–900 m below the seafloor. This possibly indicates the presence of a high porosity layer associated with lithology changes. Alternatively, this may indicate fluid over-pressure or over-pressured gas in this potential hydrocarbon environment.

The 2014–2015 complex collapse of the Bárðarbunga caldera, Iceland, revealed by seismic moment tensors

Between August 2014 and February 2015, a caldera collapse process in Bárðarbunga volcano accompanied a fissure eruption at the Holuhraun lava field after magma had propagated laterally 45 km from the Bárðarbunga magma chamber to the lava field. The Icelandic Meteorological Office (IMO) reported around 30,000 earthquakes at the caldera, including more than 70 earthquakes with moment magnitude MW ≥ 5.0. We built a moment tensor catalog of around 230 seismic events at the caldera with MW between 3.7 and 5.5 using a waveform inversion method. We identified five event families based on focal mechanisms, double couple (DC) and compensated linear vector dipole (CLVD) components, epicentral distribution relative to the caldera center, and time of occurrence. The main characteristics of these families are (1) DC to CLVD normal faulting events with steep (50°–70°) to near-vertical (>70°) dip angles on the northern side of the caldera; (2) DC to CLVD normal events with predominant steep (50°–70°) dip angles on the southern side of the caldera; (3) intra-caldera oblique strike-slip events; and (4) thrust events at the eastern side of the caldera with a horizontal tension axis compensated linear vector dipole (T-CLVD) component. Each family provided new insights about the Bárðarbunga collapse mechanism such as (1) a systematic increase in the CLVD component with magnitude, corroborating that the curvature in the ring fault is the likely cause for the vertical CLVD moment tensors observed for the largest events; (2) seismic evidence of near-vertical dip angles in agreement with the vertical faults observed in many calderas worldwide, and numerical and analog models of caldera collapse structures; (3) intra-caldera oblique and strike-slip events on the western side of the caldera occurred by asymmetric collapse; (4) thrust horizontal T-CLVD events observed at the last stage of the eruption, possibly related to a viscoelastic response.

Fault‐Valve Behavior Estimated From Intensive Foreshocks and Aftershocks of the 2017 M 5.3 Kagoshima Bay Earthquake Sequence, Kyushu, Southern Japan

AbstractDetermining fluid migration and pore pressure change within the Earth is key to understand earthquake occurrences. We investigated the spatiotemporal characteristics of the intense foreshocks and aftershocks of the 2017 ML 5.3 earthquake in Kagoshima Bay, Kyushu, southern Japan, to examine the physical processes governing this earthquake sequence. Our relocated hypocenters show the foreshocks moved on a sharply defined plane with a steep dip. The mainshock rupture initiated at the edge of the foreshock seismic gap. The size of the foreshock seismic gap is comparable to that of the mainshock estimated from the source corner frequency, suggesting this seismic gap corresponds to the large slip region of the mainshock. The aftershocks migrated upward along several steeply dipped planes with a seismicity pattern that deviated from the typical mainshock–aftershock type. This deviation of seismicity pattern, together with the hypocenter migrations, suggests aseismic processes, such as pore pressure migration and aseismic slip, affected this earthquake sequence. We established the following hypothesis. First, fluids originating from the subducting slab migrated upward and intruded into the fault plane, reducing the fault strength and causing the foreshock sequence and potentially aseismic slip. Second, the mainshock rupture occurred due to the decreased fault strength and the increased shear stress in an area with relatively high strength. Third, pore pressure increase associated with post‐failure fluid discharge caused the upward aftershock migration. These observations are consistent with the fault‐valve model and show the importance of fluid movement at depth not only in earthquake swarms but also in foreshock–mainshock–aftershock sequences.

Rock magnetism of ejected basaltic boulders from Lonar crater, India: Implications for the existence of a short‐lived impact‐generated weak magnetic field

AbstractThe continuous ejecta deposit around the rim of Lonar impact crater, central India, contains angular basaltic boulders of size ≤5 m. These boulders experienced varying level of shock between 2–30 GPa due to impact, as indicated by the extreme fracturing of these basaltic boulders, fragmentation of plagioclase and titanomagnetite constituents of these ejected boulders, and the presence of maskelynite in them. We measure some rock magnetic properties, e.g., NRM/χ (natural remanent magnetization [NRM]/bulk magnetic susceptibility [χ]), REM (=NRM/saturation isothermal remanent magnetization [SIRM] ratio expressed in %), and anisotropy of magnetic susceptibility (AMS) on 53 subsamples from 18 oriented drill cores of the shocked ejected basaltic boulders from the eastern half of ejecta deposit in the present study. The measured data are similar in many respects to our previous observations on Lonar crater rim shocked basalts (Arif et al. 2012b). For example, a small population of the ejected basaltic boulder samples show very high NRM/χ (between 378 and 989 Am−1; n = 7) and REM (between 1.5 and 7%; n = 4) and the AMS axes of these ejected basaltic boulders show triaxial distributions in stereographic projections. Moreover, some of the ejected basaltic boulders show higher values of squareness ratio (Mrs/Ms) and median destructive field (MDF) suggesting permanent changes in the intrinsic magnetic properties due to impact shock pressure. In stereographic plot, the high coercivity and high temperature (HC_HT) magnetization component of these ejected basaltic boulders are distributed in discrete clusters on the periphery of a small enveloping circle whose center (D = 108.0°, I = +69.2°) lies close to the HC_HT cluster of the crater rim shocked basalts. The center of this enveloping circle and the average HC_HT component of Lonar crater rim shocked basalts have the same statistical orientation, although the former has steeper dip. This distribution suggests the possibility that the ejected basaltic boulders, which were deposited during the modification stage of Lonar crater evolution, were magnetized in an impact‐induced magnetic field that was rapidly decaying just after the impact. Our present study suggests that the ejected basaltic boulders and Lonar crater rim shocked basalts experienced high shock pressure (≥2 GPa) magnetization during impact.

Catastrophic mechanism analysis of deformation and instability of the layered rock slope

This paper is based on engineering background in the phosphate mine called Jianlinshan belonging to the Yunnan Phosphate Chemical Group limited company. In terms of the deformation and instability characteristics of stratified steep dip rock slope, the slope instability process and intrinsic controlling factor have been analyzed by using the cusp catastrophe model. The excavation open-pit slope stability has been researched with respect to the stress state of the stratified rock slope. The results show the following conclusions. (1) The increase of strata thickness can improve the flexural rigidity of rock mass, and can effectively control the occurrence of slope collapse and buckling. The risk of destabilization of the slope can be reduced by using rock-soil anchorage technology or grading bedding. (2) When the slope rock thickness is fixed, the critical slope length decreases with the increase of the dip angle, and the higher the thickness, the more obvious the decreasing trend; When the dip angle of strata is certain, the critical slope length of the slope increases with the increase of the stratum thickness, and the increasing amplitude decreases. Meanwhile, when the dip of strata is greater than 40°, critical slope length increasing amplitude caused by the thicker thickness of strata tends to coincide. The relevant research results can provide theoretical and technical guidance and advice for the open pit transportation technology of this mining area or mining area with similar conditions.

Using paleomagnetism to test rolling hinge behaviour of an active continental low angle normal fault, Papua New Guinea

Metamorphic core complexes (MCCs) have been attributed to slip on long-lived detachment faults in extensional environments. At the surface, such faults are typically shallow dipping (<30°). This is inconsistent with Andersonian faulting theory, which requires that normal faults should nucleate and slip at steeper dips. One possible solution to this mechanical problem is a “rolling hinge” evolution for the fault during its slip history. In this model, faults initiate at steep dips (e.g. 60°) and back-tilt to shallower dips due to flexure and isostatic uplift in response to unloading of the footwall during slip. The Mai'iu fault is an active, rapidly slipping (∼1 cm/yr) low-angle (dip 20-22° at the surface) normal fault. Sampling of the footwall Goropu Metabasalt revealed a consistent normal-polarity component of magnetisation with moderate inclination that we interpret to have been acquired during uplift and cooling of the footwall rocks during the Brunhes chron. Comparison of the direction of the normal component with the expected average (geocentric axial dipole) direction at the site latitude indicates 23.9° ± 2.6° (1σ) of back-tilting of the footwall about the strike of the Mai'iu fault, consistent with a rolling hinge style of rotation. This indicates an original fault dip of 41.3-48.5°, as is consistent with independent estimates of original fault dip from fault-bedding cut-off angles and microseismicity at depth. This study is the first of its kind to demonstrate, using paleomagnetism, large-scale horizontal-axis rotations consistent with a rolling hinge evolution for a continental MCC.

High mobility of the channelized ancient Linka rock avalanche within the Bangong - Nujiang suture zone, SE Tibetan Plateau

Abstract Large rock avalanches often result in loss of life and catastrophic damage to infrastructure far from their initial failure positions, predominantly due to their tremendous volumes, high velocities and long runouts. Studies of the surface morphologies and internal structures of rock avalanche deposits can reveal evidence of their movement and deposition mechanisms. Through field survey, satellite image interpretation and particle-size distribution analysis, we studied the ancient, long-runout Linka rock avalanche, which is next to the Nujiang River, southeast Tibetan Plateau. The Linka rock avalanche, with a source volume of ~310 Mm3 originated from a high, steep dip slope and then transformed into a channelized rock avalanche, showing high mobility with a superelevation back-calculated maximal velocity of 42 m/s, a travel distance of ~6200 m and a Fahrboschung of 0.24. The slope failure sequence consisted of an initial failure of an outer limestone slab and a second failure of an inner sandstone slab. The limestone avalanche had 2 or 3 surges, while the sandstone avalanche probably had only one surge. The high mobility of the Linka rock avalanche predominantly resulted from a buckling failure occurred on a high relief source, low-energy dissipation during the channelized flow, intensive rock fragmentation in the basal facies and possible water lubrication when propagating bi-directionally along the Waqu River. Our findings for the Linka rock avalanche support previous knowledge that multiple mechanisms have different roles at different stages in a long runout rock avalanche.

The application of ambient noise and reflection seismic exploration in an urban active fault survey

As the detection of urban active faults becomes increasingly important, high-resolution detection of urban blind active faults is very important for urban planning, land use, and disaster risk reduction. However, it is difficult to determine the corresponding surface positions in the city environment for noise and building restrictions. The active source reflection seismic technique is considered the best technique to image faults with a high resolution and deep penetration. However, urban geophysical exploration must often consider the complex urban environment, which includes moving vehicles, dense power grids, and irregular buildings. These features make active source reflection seismic exploration difficult for wide application due to its drawbacks of high cost and the necessary use of explosives. In contrast, ambient noise seismic surveys have the advantages of continuous ambient noise sources, low cost, and fast deployment. These advantages are good for urban exploration. Although ambient noise seismic surveys have a lower resolution than active seismic surveys, their ultrahigh-density layout can improve the resolution. We have conducted two active source seismic lines and two ambient noise seismic lines near the Huangzhuang-Gaoliying fault (HGF) in a northern suburb of Beijing. The autocorrelation and crosscorrelation results are consistent with the active source reflection seismic results. They revealed the location of the HGF, which is composed of a set of steep dip faults. The study of the combination of the two techniques demonstrates that ambient noise seismic surveys are effective for urban active fault detection, especially for larger scale area surveys, and active source reflection seismic surveys can be used for detailed surveys. The combination of the two techniques has a higher efficiency and lower costs and can be widely used in blind urban active fault surveys.

Identifying septic pollution exposure routes during a waterborne norovirus outbreak - A new application for human-associated microbial source tracking qPCR

In June 2017, the Pennsylvania Department of Health (PADOH) was notified of multiple norovirus outbreaks associated with 179 ill individuals who attended separate events held at an outdoor venue and campground over a month period. Epidemiologic investigations were unable to identify a single exposure route and therefore unable to determine whether there was a persistent contamination source to target for exposure mitigation. Norovirus was detected in a fresh recreational water designated swimming area and a drinking water well. A hydrogeological site evaluation suggested a nearby septic leach field as a potential contamination source via ground water infiltration. Geological characterization revealed a steep dip of the bedrock beneath the septic leach field toward the well, providing a viral transport pathway in a geologic medium not previously documented as high risk for viral ground water contamination. The human-associated microbial source tracking (MST) genetic marker, HF183, was used as a microbial tracer to demonstrate the hydrogeological connection between the malfunctioning septic system, drinking water well, and recreational water area. Based on environmental investigation findings, venue management and local public health officials implemented a series of outbreak prevention strategies including discontinuing the use of the contaminated well, issuing a permit for a new drinking water well, increasing portable toilet and handwashing station availability, and promoting proper hand hygiene. Despite the outbreaks at the venue and evidence of ground water contamination impacting nearby recreational water and the drinking water well, no new norovirus cases were reported during a large event one week after implementing prevention practices. This investigation highlights a new application for human-associated MST methods to trace hydrological connections between multiple fecal pollutant exposure routes in an outbreak scenario. In turn, pollutant source information can be used to develop effective intervention practices to mitigate exposure and prevent future outbreaks associated with human fecal contaminated waters.

Dynamic Stability Evaluation of Underground Caverns in Jointed Rock Mass using Friction Energy Generated by Joint Sliding

General seismic damage surrounding underground excavations of jointed rock masses is closely associated with the presence and response of discrete fracture networks. As the failure of rock masses is mainly controlled by joints, energy dissipated through slippage along joints is proposed as an evaluation index for dynamic stability analysis of underground caverns. Energy dissipated in slippage is represented as a product of the shear stress and plastic shear displacement. The method was demonstrated through dynamic analysis of an underground cavern containing joints of varying dip friction angle and location. The results show that the proposed index can record the failure history and damage of rock structures surrounding an underground cavern subjected to dynamic loading. The effects of four types of joint sets on the dynamic stability of a cavern in the DaGangshan hydropower project were assessed using the friction energy of the joints. The combination of steep and non-steep joint sets was found to be much more unfavorable to large caverns than joints sets of only steep dip angle or non-steep dip angle.