Step Faults Research Articles

Theoretical and numerical investigations of the floor failure characteristics affected by coal mining near complex fault structures

Water inrush from underlying aquifers under the synergistic action of complex faults and mining activities seriously threatens the mining of coal seams in North China. The failure characteristics of the coal seam floor under complex fault conditions are the keys to understanding the water inrush mechanism during mining. To investigate floor failure characteristics and water inrush mechanisms influenced by complex fault structures, theoretical analysis and numerical simulation were carried out. An improved theoretical model is first proposed, including complex fault structures such as horst, graben, and step fault structures. The calculation formula for waterproof coal pillars under complex fault conditions is established based on the improved theoretical model. The failure and displacement characteristics of the coal floor under complex faults are analyzed via numerical simulation. Compared with those under normal mining conditions, the theoretical and numerical simulation results reveal the following: (1) Under the horst structure, the floor failure characteristics show an increase in the compression failure area on both sides, and shear failure occurs on the large-dip fault side. The simulation results reveal that the failure width on the large-dip fault side increases by 25%, indicating a failure trend toward the large-dip fault side. The width of waterproof coal pillars needs to be increased by 20% to ensure mining safety. (2) Under the graben structure, the floor failure characteristics show an increase in the compression failure area on both sides, and shear failure occurs on the small-dip fault side. The simulation results reveal that the failure width on the small-dip fault side increases by 25%, indicating a failure trend toward the small-dip fault side. The width of waterproof coal pillars needs to be increased by 40% to ensure mining safety. (3) Under the step fault structure, the floor failure characteristics show compression failure on both sides, increasing the floor compression failure area on the large-dip fault side. The simulation results show that the failure width on the small-dip fault side increases by 15%, the large-dip fault side increases by 50%, and the floor failure depth increases by 20%. The width of waterproof coal pillars needs to be increased by 50% to ensure mining safety.

A GNSS/SINS fault detection and robust adaptive algorithm based on sliding average smooth bounded layer width

Abstract The Global Navigation Satellite System/Strapdown Inertial Navigation System (GNSS/SINS) integrated navigation system is an important technology for UAV measurement and vehicle movement measurement. But in the operational process of the GNSS/SINS integrated navigation system, the Global Navigation Satellite System (GNSS) signal is vulnerable to external interference, resulting in abnormal system measurement data, and system faults. These faults will reduce the navigation and positioning performance of the system and reduce the measurement accuracy of the system. Aiming at this problem, a GNSS/SINS fault detection and robust adaptive algorithm based on sliding average smooth bounded layer width is proposed. The algorithm evaluates the system measurement data based on the innovation residual and incorporates the sliding average filter to design the fault detection function based on the smooth bounded width layer. Accurate detection of system faults using fault detection function. The fault detection function value is used to construct the robust cofactor matrix to correct the measurement error in real-time, to improve the accuracy and robustness of the state estimation. The experimental results show that: The proposed algorithm in the paper compares with two traditional robust adaptive algorithms based on smooth bounded layer fault detection and residual chi-square fault detection. The fault detection rates for small step faults show an increase of more than 44.26% and 9.54%, respectively. Similarly, for slowly varying faults, the fault detection rates exhibit an increase of more than 29.32% and 13.56%, respectively. Throughout the fault, the filtering accuracy demonstrates an increase of more than 16.52% and 15.47%, respectively. The algorithm effectively improves the measurement accuracy of the GNSS/SINS integrated navigation system.

Unraveling the role of dextral faults in the formation of pull-apart basin structures and their implications on the genesis of ophiolites and pluto-volcanics

Rhombic structures have been observed in the Qom-Zefreh-Nayin-Dehsheir-Baft region, specifically along the direction of the dextral faults, which have caused significant changes in strike length. This study investigates the geological features and fault interactions in the region through the examination of aerial images, fault-lithology correlations, petrology, crustal thickness, and seismic studies. The analysis of aerial photos and geological correlations revealed the presence of ophiolites and pluto-volcanics associated with faults and rhombic structures. By conducting field geology and combining various geological studies, a pull-apart basin was identified in the area, contributing to the formation of three rhombic structures. This basin played a crucial role in the genesis of the region’s ophiolites and pluto-volcanics. The research suggests that the initial tensional stress leading to the pull-apart basin was caused by the right step of a dextral fault within the Urumieh-Dokhtar magmatic arc. This fault formation occurred due to the oblique Arabian subduction towards the Iranian plateau. During the Zagros orogeny, the stretched area persisted, leading to the formation of oceanic crust in this location. The subduction angle changes from subduction to super-subduction, resulting in the classification of the region into two types: C and E genes. Different types of magma, including alkaline, subalkaline, shoshonite, calcalkaline, and adakitic, were identified in this region. The study highlights the significance of tholeiitic arcs, abyssal features, crust thickness, and seismicity in understanding oblique diagonal subduction models and tensional pull-apart basins, which are crucial in the transition from subduction to super-subduction. This research offers valuable insights into the geological complexities of the region and opens up opportunities for further exploration of similar models.

Discovery and petroleum geological significance of delta in the third member of Oligocene Lingshui Formation in southern Baodao Sag, Qiongdongnan Basin, South China Sea

Based on the 3D seismic data and the analysis and test data of lithology, electricity, thin sections and chronology obtained from drilling of the Qiongdongnan Basin, the characteristics and the quantitative analysis of the source-sink system are studied of the third member of the Upper Oligocene Lingshui Formation (Ling 3 Member) in the southern fault step zone of the Baodao Sag. First, the YL10 denudation area of the Ling 3 Member mainly developed two fluvial systems in the east and west, resulting in the formation of two dominant sand transport channels and two delta lobes in southern Baodao Sag, which are generally large in the west and small in the east. The evolution of the delta has experienced four stages: initiation, prosperity, intermittence and rejuvenation. Second, the source-sink coupled quantitative calculation is performed depending on the parameters of the delta sand bodies, including development phases, distribution area, flattening thickness, area of different parent rocks, and sand-forming coefficient, showing that the study area has the material basis for the formation of large-scale reservoir. Third, the drilling reveals that the delta of the Ling 3 Member is dominated by fine sandstone, with total sandstone thickness of 109–138 m, maximum single-layer sandstone thickness of 15.5–30.0 m, and sand-to-strata ratio of 43.7%–73.0%, but the physical properties are different among the fault steps. Fourth, the large delta development model of the small source area in the step fault zone with multi-stage uplift is established. It suggests that the episodic uplift provides sufficient sediments, the fluvial system and watershed area control the scale of the sand body, the multi-step active fault steps dominate the sand body transport channel, and local fault troughs decide the lateral propulsion direction of the sand body. The delta of the Ling 3 Member is coupled with fault blocks to form diverse traps, which are critical exploration targets in southern Baodao Sag.

Study on Evolution Characteristics of Stress Field of Stepped Fault

With the development of mining to the deep, the ground stress increases correspondingly, and the geological conditions become more and more complicated. Mine dynamic disasters mainly occur near faults. Numerous studies have been conducted on single faults, but few studies have been done on stepped faults formed by double faults under complex geological conditions. Based on this, with the 3110-working face of Zhong Tai Mining in He bi as the engineering background, Single fault model a and different step fault models b, c, d, e and f were established by Flac3D numerical simulation software. The characteristics of stress field evolution of single fault and step fault under the influence of deep mining are studied. The results show that the stress distribution in the upper wall of the fault forms a stress concentration zone, and in the lower wall forms a stress weakening zone. Under the influence of excavation disturbance, the vertical fault distance and the horizontal distance between faults will affect the stress evolution characteristics of the stepped fault.

Model analysis and control of biped dynamic walker with fault steps in a gait cycle

The biped robot has two identical legs that undergo alternating stance and swing phases during walking. The robot’s motion is facilitated by actuators positioned at the ankle and hip joints. The paper investigates various fault scenarios in dynamic walker models, specifically situations where one or both actuators experience failure while the robot is in motion. The first model assumes faults in both the hip and ankle joints, while the second model assumes a fault only in the ankle joint. The dynamic walker typically undergoes two steps in each cycle. This study specifically examines the different types of faults that may occur during the second step. The goal is to identify the potential walking gaits that can result from these faults. It is observed that walking with faults at both the hip and ankle joints exhibited greater stability and a wider range of stable states compared to walking with a fault only at the ankle joint. This suggests that incorporating hip joint faults or underactuation into robotic or prosthetic gait patterns could improve their stability and overall performance. The local and global stability of the dynamic walker were analyzed using Poincare’s method and the basin of attraction plot, respectively. Additionally, a control algorithm based on kinetic energy shaping is proposed for the second model, which resulted in an increased basin of attraction. Notably, the second model exhibited the ability to walk with variable step length and speed, akin to human locomotion.

Tectonic evolution of buried hills and the main controlling factors of fractures in the fault step zone of the Pearl River Mouth Basin, northern South China Sea

Buried hills are an essential offshore oil and gas exploration direction. Based on the new three-dimensional (3D) seismic data, formation micro scanner images (FMI), and zircon chronology data, the stratigraphic structure, structural characteristics, and fracture reservoir characteristics of the buried hills in the fault step zone in the Pearl River Mouth Basin in the northern South China Sea were analyzed. Then, the tectonic evolution of buried hills and the controlling factors of fracture development were discussed. From the results, the target buried hill is composed of Mesozoic volcanic rocks, and the primary reservoir types are medium-high angle structural fractures. The buried hill underwent a multi-stage tectonic evolution during the Mesozoic-Cenozoic period. Mesozoic extrusion and Cenozoic extension processes controlled the fractures in the buried hill. Shear and extensional fractures developed against Mesozoic extrusion, while shear and tensional fractures developed during Cenozoic tensional processes and magma intrusion. Tectonic movements control the development of fractures in the interior of the buried hill. Groups and types of fractures cut into each other to form network fractures, providing good reservoir space for oil and gas.

Inhibition of spastin impairs motor function recovery after spinal cord injury

Promoting axonal regeneration is an effective strategy for recovery from traumatic spinal cord injury (SCI). Spastin, a microtubule-severing protein, modulates axonal outgrowth and branch formation by regulating microtubule dynamics. However, the exact role of spastin during recovery from SCI remains unknown. Therefore, we utilized a hemisection injury model of the mouse spinal cord and explored the effect of spastin using a spastin inhibitor, spastazoline. Results showed that spastazoline significantly suppressed the microtubule-severing activity of spastin in COS-7 cells and inhibited the promoting effect of spastin on neurite outgrowth in primarily cultured hippocampal neurons. The protein expression level of spastin was significantly upregulated in the injured spinal cord. Injured mice showed impaired motor functions, which included increased toe-off angle and foot fault steps and decreased stride length and Basso mouse scale score. Notably, these motor function impairments were aggravated by the application of spastazoline. Inhibition of spastin exacerbated neurogenesis impairment, as demonstrated by neuronal nuclei antigen staining, the inflammatory response, as shown by Iba-1 and GFAP staining, and axonal regeneration impairment, as shown by 5-hydroxytryptamine staining. Furthermore, mass spectrometry analysis revealed that the inhibition of spastin resulted in numerous dysregulated differentially expressed proteins that were closely associated with vesicle organization and transport. Taken together, our data suggest that spastin is critical for recovery from SCI and may be a potential target for the treatment of SCI.

An improved detection method of GNSS faults with fractional information divergence

Early detection of faults guarantees the integrity of navigation systems. The standard receiver autonomous integrity monitoring (RAIM) incorporated with the Kullback-Leibler divergence (KLD) has been proposed to improve detection performance. However, the KLD-RAIM cannot ensure a high detection rate in the presence of small or growing faults. This paper broadens the existing KLD-RAIM to further enhance the detection ability for satellite navigation-based aviation applications. The Cumulative residual KL information (CRKL) replaces the KLD to quantify the dissimilarity between the current and normal cumulative distribution functions for the CRKL-RAIM construction. Then CRKL is extended to fractional orders using Riemann–Louville (RL) calculus to form fractional CRKL-RAIM for detection sensitivity enhancement. Simulations using static GNSS station data were conducted to compare four methods: the standard RAIM, existing KLD-RAIM, the proposed CRKL-RAIM, and fractional CRKL-RAIM. When dealing with small step faults, the detection sensitivity increases progressively, with the fractional CRKL-RAIM capable of detecting 10-meter faults. Regarding growing faults, the standard RAIM fails to detect and KLD-RAIM barely detects faults around 600 s with 50% missed detection rate. By contrast, CRKL-RAIM and fractional CRKL-RAIM detect faults around 100 and 200 s in advance, respectively, without any missed detection events.

Geometric phase analysis for characterization of 3D morphology of carbon fiber reinforced composites

In carbon fiber-reinforced resin matrix composites, differences in the mechanical properties of carbon fibers and matrix resins can lead to differences in height, causing step faults at the interphase during grinding and polishing. Accurately and efficiently characterizing the step height at the interphase is crucial for analyzing the mechanical properties and residual stress distribution of the composite materials. In this paper, an orthogonal grating, with a frequency of 10,000 lines/mm, was prepared on the surface of the composite material using the SEM electron beam grating technique. The surface morphology of the T700 carbon fiber-reinforced epoxy resin matrix composite was analyzed using the geometric phase analysis method. The average step height between the fiber and matrix was found to be 128.6 nm. Moreover, the geometric phase analysis method can provide a morphology distribution map within the range of 155 × 100 μm2. This research will provide an effective way to quantitative characterization of three-dimensional surface morphology of composite materials.

Influence of ground shaking on the fault: numerical simulation

The paper considers a possible model of the behavior of faults under the influence of external influences. A complication in the form of a step is assumed in the structure of the fault banks. A hook on a step leads to the appearance of two local stress concentration regions. A possible mechanism for slowing down the response to external stimuli is discussed. An external influence can be a shaking of the ground from a neighboring earthquake or a deformation tidal wave. The calculation is carried out within the framework of the elastic-brittle medium model by the finite-difference method supplemented with the ability to calculate cracks with the definition of their faces as free surfaces. As a result of the simulation, the emergence of a region of stress concentration is observed, which may not immediately lead to destruction. There will be an accumulation of damage as a result of a hook on the fault step, and the reaction to external influence will slow down. Over time, the medium exhausts the possibilities for implementing all the mechanisms of accommodation to the load, which leads to a break in the vicinity of the roughness with the emission of the next portion of seismic waves.

The controlling effect of chair-shaped slope break landforms on sedimentation in continental faulted basins: A case study in the Xilinhaolai area, Baiyinchagan depression, Erlian Basin, China

To reveal the geomorphic characteristics of the gentle slope zone in a continental faulted basin and its control on sedimentary systems, we have performed the geomorphic units division and comprehensive analysis of seismic facies, well-log facies, and core facies in the Xilinhaolai area in the western area of the Baiyinchagan depression, North China. The results find that the gentle slope in the Xilinhaolai area developed a chair-shaped slope break, which includes four geomorphic segments: steep slope of the depression margin (SSDM), shallow-water gentle slope (SWGS), deepwater steep slope (DWSS), and depression center. The chair-shaped slope break controlled the distribution of the sand body by controlling the water depth and hydrodynamic type of sedimentation. The SSDM was a favorable place for the deposition of beach bars. It has become a good oil reservoir not only because of its shallow burial and good physical properties but also because of the location configured with stepped faults. On the SWGS, the active river current and lake waves caused the deposition of large-scale braided river deltas and shoal bars, which are already the main oil and gas areas discovered in the Xilinhaolai area. On the DWSS, a large-scale slump turbidite fan developed and became a very favorable oil and gas reservoir near the oil and gas source rock. The slumped turbidite fans on the DWSS and the shoal bar on the SSDM are potentially favorable reservoirs for future oil exploration.

A bran-new performance evaluation model of coal mill based on GA-IFCM-IDHGF method

Adopting a more scientific and precise assessment method to evaluate the current running performance of coal mills in practice work is essential to maintain the security and reliability of the coal-fired power plant. However, traditional assessment methods have ignored an important problem that the importance among variables varies with the current operation data of coal mill, which has a serious influence on performance evaluation of coal mill. In this paper, a bran-new GA-IFCM-IDHGF assessment method is proposed. Genetic algorithm (GA) is first applied to optimize initial parameters, which is fundamental and significant step to obtain more accurate the number of clusters. Secondly, intuitionistic fuzzy clustering model (IFCM) is adopted to identify the running modes of the coal mill. According to the Delphi, analytic hierarchy process, gray relations analysis and fuzzy integrated evaluation (DHGF), the security range of variables under the normal observed samples from different running modes is acquired, which is helpful to determine whether the current operation data is normal data. Subsequently, an improved Delphi, analytic hierarchy process, gray relations analysis and fuzzy integrated evaluation (IDHGF) method is used to assess the current running performance of coal mill under the abnormal monitoring data. The performance of the proposed performance assessment method is verified through its application in a self-defined step fault system and an actual industrial cases of coal mill. Compared with the traditional methods, the experimental results demonstrate the effectiveness of the proposed method.

Fault Location and Classification for MVDC Networks

This paper proposes a two step fault detection scheme for medium-voltage dc (MVDC) networks based on wavelet analysis. The proposed Grid Transients Classifier (GTC) is used to continuously monitor energy of wavelet packet decomposition levels (WPDL) for voltage and current signals to determine any transient disturbance like load change, pole to pole (PP) or pole to ground (PG) faults, pole to pole to ground (PPG), voltage sags, switching, etc. Subsequently, type of disturbance is identified through an artificial neural network (ANN) classifier. Then, proposed Active Grid Impedance Estimator (AGIE) injects a signal with two fundamental frequencies to evaluate grid impedance from the measurement point in new condition. Using the obtained data, fault type, location and its severity are specified. Hardware-in-the-Loop (HIL) results are provided for a shipboard grid case study to validate the real-time application of the proposed method and demonstrate its effectiveness.

СТРУКТУРНЫЕ УСЛОВИЯ ЛОКАЛИЗАЦИИ ПОЛИМЕТАЛЛИЧЕСКОГО ОРУДЕНЕНИЯ В РУДНОМ УЗЛЕ ЧО ДЬЕН (МЕТАЛЛОГЕНИЧЕСКАЯ ЗОНА ЛО ГАМ, СЕВЕРНЫЙ ВЬЕТНАМ)

Structural research in the Cho Dien ore cluster and its environs has revealed that folds and faults were formed by sublatitudinal stresses. At the Nam Lung deposit, the stratified ore-bearing strata show evidences for upward interlayer migration of ore constituents, which is associated with wide development of interstratal thrusts during the anticline formation. Migrating ore constituents constrained by step faults cutting the anticline hinge zone accumulate to form low-angle ore shoots. Such a mechanism of structural control to mineralization is probably one of the conditions for most commercially important Pb-Zn deposits to be confined to the anticline hinge zone in the Cho Dien ore cluster.

Evaluation of tight sandstone reservoir in Es<SUB align="right">4 member of Yi176, Bonan Oilfield, China

The Yi-176 block is located in the Yi-176 Boshen-4 fault step zone of the Bonan oilfield in the south of the Bonan sag. The Es4 member is considered as the target interval for this study. A systematic study of reservoir microscopic characteristics is carried out, through core observation, scanning electron microscope and other means in order to study the structure and type of conventional pores and nano-micrometer pores in the member and to determine the petrological and structural characteristics of the reservoir. Moreover, using mercury intrusion test parameters, the reservoir types in the study area are divided into four categories through cluster analysis, followed by prediction of the planar distribution of different types of reservoirs. The results show that the development of Type I reservoirs is relatively mature, while, is Type II and Type III reservoirs are considered as the main exploration and development direction in the future.[Received: May 8, 2020; Accepted: January 20, 2021]

New insights on the Alboran Sea basin extension and continental collision from magnetic anomalies related to magmatism (western Mediterranean)

In the Alboran Sea there are a few well exposed Neogene and Quaternary volcanic zones, often geographic highs, that are generally associated with magnetic anomalies. In this paper, we present a characterization of these magnetic anomalies based on a recent and accurate magnetic data compilation for the Abloran Sea area. The anomalies reveal the distribution of magmatism and shed light into the discussion about the origin and evolution of the westernmost Mediterranean. One of the most relevant magnetic anomalies is the Nador dipole, which extends from the Gourougou volcano to the Chafarinas Islands, and is related to an E-W crustal scale intrusion. However, the main NE-SW elongated continuous dipoles of the central Alboran Sea are not related to any surface structure, but they are parallel to the Alboran Ridge, which is the main volcanic high in the Alboran Sea, and are located to the north of it. These anomalies extend discontinuously eastward along the NW-SE dipoles located along the Yusuf fault zone. The results of our 2D magnetic forward modeling suggest that the causative bodies of these main magnetic dipoles are deep igneous bodies. According to the tectonic evolution of the region, and the high magnetic susceptibility values obtained, these igneous bodies probably are made of a basic igneous rocks. Their emplacement may represent the westward tip of the rift axis of the AlKaPeCa Domain, which is related to the Oligocene-Miocene NW-SE extension, and associated with the southern slab retreat stage and oceanic spreading of the Algerian basin. Afterwards, these bodies were displaced toward the west, together with the Alboran Domain, and affected by the STEP fault located at its southern limit. Since the Late Miocene, the north Alboran Ridge elongated intrusions acted as a backstop that conditioned the folding and uplift of the Alboran Ridge in a tectonic indentation setting. In this setting, the STEP fault is deformed and the eastern part of the bodies were segmented along the Yusuf transtensional fault system. Simultaneously, the E-W crustal body related to the Nador magnetic dipole was emplaced, possibly evidencing a slab tearing process. The deep seated basic igneous bodies constitute main crustal heterogeneities that reveal and drive the Alboran Sea tectonic inversion.

Stacking Fault Manifolds and Structural Configurations of Partial Dislocations in InGaN Epilayers

This cover focuses on an important mechanism proposed in article number 2100190 by George P. Dimitrakopulos and co-workers: the emanation of threading dislocations (TDs) from junctions of basal stacking fault (BSF) steps in III-nitride semiconductors. The HRTEM image in the center is a projection along [21̅1̅0] showing such an emanating TD in an InGaN epilayer, and its upper inset illustrates the partial dislocation character of a BSF single step, amounting to a disconnection between mirror-related BSF variants. The lower left schematic illustrates the mechanism, whereas the lower right illustration is a plan-view of the atomic structure on the plane of the BSF on either side of the steps.

Characteristics and origin of continental marginal fault depressions under the background of preexisting subduction continental margin, northern South China Sea, China

Based on the new seismic and drilling data and the recent related research results, this paper systematically analyzes the diversity and complexity of evolution process of crustal lithosphere structure and basin structure in the Pearl River Mouth Basin on the northern margin of the South China Sea. Three types of detachment faults of different structural levels exist: crust-mantle detachment, inter-crust detachment and upper crust detachment. It is considered that different types of extensional detachment control different subbasin structures. Many fault depressions controlled by upper crust detachment faults have been found in the Zhu I Depression located in the proximal zone. These detachment faults are usually reformed by magma emplacement or controlled by preexisting faults. Baiyun-Liwan Sag located in the hyperextension area shows different characteristics of internal structure. The Baiyun main sag with relative weak magmatism transformation is a wide-deep fault depression, which is controlled by crust-mantle detachment system. Extensive magmatism occurred in the eastern and southwest fault steps of the Baiyun Sag after Middle Eocene, and the crust ductile extensional deformation resulted in wide-shallow fault depression controlled by the upper crust detachment fault. Based on the classical lithosphere extensional breaking and basin tectonic evolution in the Atlantic margin, it is believed that the magmatic activities and pre-existing structures in the Mesozoic subduction continental margin background are important controlling factors for the diversified continental margin faulted structures in the northern South China Sea.

Classification of slope area types and hydrocarbon accumulation rules in Wuerxun-Beier Depression

After more than 50 years of exploration and development, Wuerxun-Beier depression has entered a high exploration stage. It is more and more difficult to find large-scale structural reservoirs. Therefore, structural-lithologic reservoirs in slope areas have gradually become the focus of exploration. Based on the overall study and dissection of the depression, the geological differentiation characteristics of the large-scale slope area are discussed. According to the occurrence of the slope, the intensity of tectonic activity, the intensity of source supply and the pattern of synsedimentary fault combination, the slope zone in the study area can be divided into six types, namely, the steep slope with strong source along the fault step type, the compound fault step type of medium slope with strong source, the reverse fault step type of the gentle slope with strong source, and the weak supply type. Different types of slope have different sand control mechanisms and reservoir forming characteristics, such as the source gentle slope forward fault terrace type, the weak source gentle slope reverse fault terrace type and the weak source middle slope forward fault terrace type. Source supply intensity and slope dip control the development type of sedimentary system, the combination of synsedimentary faults and valleys controls the distribution characteristics of sedimentary system. Through exploration practice, significant discoveries have been made on the southwestern, southeastern and northern slopes of Beixi, Wuerxun-Beier depression, which confirms that the slope area is the main breakthrough direction for oil and gas exploration and large-scale reservoir increase in continental fault-depression lake basins.