Table of Content

    20 December 2023, Volume 45 Issue 6
    SHEN Bai, ZHANG Zhi-liang, REN Zhi-kun, LIU Jin-rui
    2023, 45(6):  1247-1264.  DOI: 10.3969/j.issn.0253-4967.2023.06.001
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    As the NW-trending dextral strike-slip fault on the northern margin of the Tarim Basin, the Kalayu’ergun Fault defines the western boundary between the western Kuqa Depression and Wensu Bulge. It holds immense importance to understand the deformation occurring within the Kuqa Depression. However, there is still ongoing debate regarding the length, activity time and formation mechanism of the Kalayu’ergun Fault. In this study, a comprehensive investigation was conducted, incorporating sub-surface geophysical data, high-resolution remote sensing satellite images, and the findings of previous researchers. The results demonstrate that the Kalayu’ergun Fault cuts off the Awate anticline in the north, and to the south, it extends near the southern flank of the North Kalayu’ergun anticline but does not reach the Middle Kalayu’ergun anticline. The total extension of the fault is estimated to be approximately 40km. And the minimum of the fault strike-slip distance is estimated by the sum of the tectonic shortening of the North Kalayu’ergun anticline and the shortening absorbed by the strata on the northern flank of the Awate anticline through drag, which amounts to about 4.1-4.3km. Additionally, the Kalayu’ergun Fault has been active since its formation in the early Pliocene, but its activity intensity has been weakened obviously. The activity of the Kalayu’ergun Fault corresponds to the deformation time of the North Kalayu’ergun anticline, which is consistent with the deformation time determined using the same structural sedimentary constraints. This indicates that the North Kalayu’ergun anticline was formed under the combined action of near north-south compressional and horizontal shear stresses. The development of this transverse fault is synchronous with the overthrust structures on both sides and is developed in synchrony with the strong uplift of the southern Tian Shan orogenic belt since the late Cenozoic. The formation of the Kalayu’ergun Fault can be affected not only by the differences in the basement nature on both sides but also closely related to the difference in the thickness of the gypsum salt layer. The former resulted in variations in horizontal shortening on both sides of the fault, leading to the tearing of the Cenozoic sedimentary cover. The latter, which under the action of the extrusion stress, influenced the generation and evolution of salt-overlying beds, and then influenced the formation of the fault. In addition, the existence of prior salt structures, also known as salt diapirs, may have also played an important role in the formation of the fault. As the boundary fault in the western part of the Kuqa Depression, the Kalayu’ergun Fault is responsible for accommodating crustal shortening on both sides and even in the whole eastern and western parts of the Kuqa Depression. As a result, the shortening of the Kuqa Depression gradually decreased from east to west. Furthermore, the Kalayu’ergun Fault also had significant impacts on geomorphology, as it controls and modifies the landscape in the southern Tian Shan foreland basin. In the meanwhile, the Kalayu’ergun Fault creates favorable conditions for the transportation and accumulation of oil and gas resources.

    Research paper
    HUANG Wei-liang, ZHANG Jia-le, XIANG Wen, YANG Qian-hao
    2023, 45(6):  1265-1285.  DOI: 10.3969/j.issn.0253-4967.2023.06.002
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    The southeastern margin of the Tibetan plateau is one of the most intensely deformed regions in the continental crust. A series of active faults with varying lengths and mechanical properties have segmented the lithosphere into multiple active blocks, with the Sichuan-Yunnan block being one of the most tectonically active regions. Its eastern boundary is characterized by secondary fault zones such as the Xianshuihe-Anninghe-Zemuhe, Xiaojiang, and Daliangshan fault zone, forming a narrow and continuous strike-slip deformation zone with a total length exceeding 1 100km. The western boundary of the Sichuan-Yunnan Block is mainly composed of the Jinsha River and the Red River fault zone, with the Jinsha River fault zone consisting of more than 20 roughly parallel secondary faults, forming a complex fault zone with 30~200km width. Despite recent GNSS network observation revealing the current tectonic deformation rates in this region, there is still a lack of research on the deformation characteristics and rates of individual active faults. This limitation makes it difficult in the assessment and understanding of seismic hazards in the area, restricting the scientific understanding of the current deformation mode in the southeastern margin of the Tibetan plateau.

    The Batang Fault, located within the Jinsha River fault zone at the western boundary of the Sichuan-Yunnan block, is a NE-trending main fault that obliquely cuts across the Jinsha River Fault, dividing later into northern and central segments. Presently, the Batang Fault is characterized by dominant right-lateral strike-slip motion. The deformation characteristics and rates of this fault since the Late Quaternary are crucial for understanding the spatial distribution of strong earthquakes and deformation patterns in the Sichuan-Yunnan block.

    The Batang Fault has a total length of 115km and is a Holocene right-lateral strike-slip active fault. The fault extends along the margins of bedrock mountains on both sides of the Maqu river and Jinsha River valleys, trending NNE or NWW to SEE, with a steep dip. The fault exhibits linear distribution of topographic features such as slopes, ridges, triangular facets, and fault scarps, essentially controlling the boundaries of bedrock mountains. In view from the geomorphology, the Batang Fault appears continuous and straight without distinct segmentation, except for localized small-scale step-like features. The Batang Fault has preserved abundant Late Quaternary activity evidence in two areas, Huangcaoping village and Batang county. This study utilized unmanned aerial vehicle photogrammetry to establish sub-meter digital terrain data for Huangcaoping and Batang site, accurately measuring displaced features such as alluvial fans and gullies affected by faulting. In Huangcaoping site, the fault has cut through multiple mountain-front alluvial fans, causing varying degrees of horizontal displacement in features such as gullies and the margin of the alluvial fans. This provided a scale for quantifying fault displacement. In Huangcaoping, five large-angle gullies intersect with the fault, one of which is a large gully developed in the bedrock mountain area. The gully has a deep incision, a narrow valley, and a rapid downstream turn to the right after exiting the mountain. The left bank of the gully preserves two geomorphic surfaces, Qo(older)and Qi(younger)surface, with the fault cutting across both surfaces, forming linear steep terrain. The measured total right-lateral offset of this gully since exiting the bedrock mountain area is(46±9)m. To constrain the activity rate of the Batang Fault at this location, we used cosmogenic nuclide single clast dating to determine the exposure age of the oldest geomorphic surface, Qo, as(12.5±0.5)ka. Considering that the formation of the river predates the Qo geomorphic surface, the age-constrained slip rate of the fault at this location is considered a maximum value, estimated at(3.6±0.8)mm/a. At Batang county, the Batang Fault has preserved clear faulted topography when cutting through the Moqu alluvial fan. The southern edge of the Moqu alluvial fan has been displaced by the fault, providing a well-preserved geomorphic marker for determining the strike-slip displacement of the fault. The Batang Fault, when intersecting the steep edge of the Moqu River alluvial fan, caused an obvious right-lateral offset, determined by comparing the consistent morphology of the steep edge on both sides of the fault. The right-lateral strike-slip displacement along the southern edge of the alluvial fan is measured at (40±5)m. The cosmogenic nuclide depth profile dating was used to determine the age of the faulted alluvial fan. From a vertical profile excavated along a man-made road on the edge of the alluvial fan, four mixed samples of small pebbles were collected from bottom to top. The calculated exposure ages of the debris flow alluvial fan are (15.2+3.2/-5.4)ka (without consideration of erosion)and (16.4+3.9/-5.6)ka (with consideration of erosion). Combining the fault displacement along the southern edge of the alluvial fan and the cosmogenic nuclide depth profile ages, the slip rate of the Batang Fault at this location is estimated to be of(2.6±0.6)mm/a (without erosion)or(2.4±0.8)mm/a (considering erosion). We believe that the age results with consideration of erosion effects is closer to the true values, thus we take 2.4mm/a as the activity rate of the Batang Fault at this location. The two slip rate values of the Batang Fault obtained in the Huangcaoping and Batang county sites are similar, indicating a right-lateral strike-slip rate of 2~4mm/a since the Late Quaternary. This rate accounts for 50%~80% of the present GPS observation shear deformation across the western boundary of the Sichuan-Yunnan block, indicating that the Batang Fault is a major deformation absorption zone in the Jinsha River fault zone. However, this rate is lower than the predicted~10mm/a using block models. The discrepancy may be due to the different understanding of the deformation mode at the western boundary of the Sichuan-Yunnan Block. In the block model, block sliding mainly relies on the primary boundary fault to regulate, but the long-term and lower geological activity rate of the Batang Fault obtained in this study does not match the assumption of a higher activity rate for the boundary fault in this model. The continuous and diffuse deformation characteristics of crustal deformation in the southeastern margin of the Tibet plateau may corroborate the lower activity rate of the Batang Fault obtained in this study.

    LI Yuan, YANG Zhou-sheng, PANG Ya-jin, LIANG Hong-bao, LIU Xia
    2023, 45(6):  1286-1308.  DOI: 10.3969/j.issn.0253-4967.2023.06.003
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    The Menyuan MS6.9 earthquake occurred on January 8, 2022, which is the third strong MS>6 earthquake on the western part of the Lenglongling fault following two Menyuan MS6.4 earthquakes that took place in 1986 and 2016. In order to explore the fault deformation and stress states of different timescales before the MS6.9 Menyuan earthquake and the dynamic environment of frequent strong earthquakes in the area nearby the epicenter, with GPS velocities of 1991—2015 and 2017—2021 as boundary constraints, a fine three-dimensional viscoelastic finite element model was established. The model included the impacts of tectonic units, the layered structure of the crust-mantle, the inhomogeneity of the medium, the interactions of many different faults, and the shape of the faults. It also refined the key faults in the region and their geometric characteristics. The basic pattern of stress accumulation in the Qilian Mountain tectonic region under the long-term tectonic movement environment, the long-term slip rate and stress accumulation rate of faults and their change characteristics during the five years before the Menyuan MS6.9 earthquake are calculated and analyzed. Combining the results of the source mechanism solution and cross-fault level observation, the following conclusions are obtained:

    (1)According to the simulation results for a longer period of 1991—2015, the stress field in the study area gradually rotates clockwise, with NNE-SSW extrusion and NWW-SEE tension to NE-SW extrusion and NW-SE tension from west to east. The direction of the principal compressive stress is mostly perpendicular to the fault strike. The region near the epicenter of the Menyuan MS6.9 earthquake has been subjected to long-term NE-SW extrusion and NW-SE tensional stress. The maximum shear stress accumulates faster than the surrounding area. The above stress accumulation characteristics overall promote NW-oriented shear and NE-oriented extrusion movement of faults, which contribute to the generation and occurrence of strike-slip and thrust earthquakes on the NWW-oriented Lenglongling Fault.

    (2)The simulation results show that most NWW-orientated faults exhibit a left-lateral strike-slip and thrust nature. In contrast, NNW-orientated faults display a right-lateral strike-slip and extrusion nature. The fault’s stress nature corresponds with its movement nature. Spatially, the overall trend of fault movement in the study area is that the extrusion rate gradually decreases from west to east, and the slip rate gradually increases from west to east. This indicates that the Qilianshan tectonic belt plays a significant role in transforming and adjusting the tectonic deformation of the northeastern margin of the Qinghai-Tibetan plateau.

    (3)The fault movement and its stress distribution show significant segmentation, indicating the crucial role of fault geometry in fault movement. The western segment of the Lenglongling Fault has a geometric inflection pattern, causing stress accumulation variability and uncoordinated movement between different segments. Compared to the surrounding fault segments, this fault segment has a higher rate of stress accumulation yet experiences hindered movement in space which causes a lower slip rate. fault zones that exhibit motion deficits and rapid energy accumulation are more susceptible to earthquakes.

    (4)Compared to the period between 1991 and 2015, the simulation outcomes obtained during 2017—2021 demonstrated noticeable differences and irregularities in the distribution of motion and stress increment fields along the fault, which were segmental in nature. Within~5 years before the Menyuan MS6.9 earthquake, the strike-slip rate at the western segment of the Lenglongling fault is further reduced, the accumulation rate of shear stress was significantly increased; the extrusion rate was significantly weakened, and the rate of positive stress accumulation was slowed down. These recent changes in fault motion and stress are conducive to promoting left-lateral slip-strike earthquakes on this fault segment.

    (5)From a hydrostatic perspective, the above studies demonstrate that the epicenter region had accumulated high stress for a long time before the earthquake, and as the earthquake approached, the positive stress on the seismic fault surface increased slowly, and the friction increased synchronously, leading to the weakening and deficit of movement on the local fault segment.

    In conclusion, the western segment of the Lenglongling fault has a strong stress background and favorable conditions for the occurrence of strong earthquakes, and the risk of strong earthquakes is still predicted to exist in the future.

    XIONG Guo-hua, JI Ling-yun, LIU Chuan-jin
    2023, 45(6):  1309-1327.  DOI: 10.3969/j.issn.0253-4967.2023.06.004
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    The surface deformation information can effectively reflect the activity status of the magma chamber under the volcano, which is very important for understanding the evolution process of volcanic activity. By capturing deformation anomalies, the volcanic hazard can be assessed, providing insights into the supply, storage, and triggering mechanisms of volcanic magma systems.

    According to statistics, there are 14 active volcanoes in China with potential eruption risks. Among them, Tianchi volcano of Changbaishan is considered the largest and most dangerous active volcano within China’s borders. It is located on the northern edge of the Sino-Korean Plate, situated to the east of the Dunhua-Mishan fault at the outermost edge of the Northeast rift system and to the west of the back-arc basin of the Japan Sea. Multiple groups of faults in the NE-SW and NW-SE directions are widely developed in the region. Since 2002, seismic activity in the Tianchi volcano area has gradually increased, with the annual average earthquake frequency rising from dozens to over a hundred times, reaching its peak in 2003 with over a thousand occurrences. However, seismic activity has gradually decreased after 2006. Nevertheless, between 2020 and 2022, two episodes of seismic swarms occurred beneath the Tianchi volcano, with epicenters exhibiting a dispersing pattern gradually spreading from beneath the volcanic vent. This indicates that the Tianchi volcano still retains the potential for eruption.

    This study investigates the Tianchi volcano as the research area. It utilizes Sentinel-1A/B images from three orbits, namely ascending and descending passes, and employs advanced techniques including Small Baseline Subset(SBAS)InSAR and Stacking InSAR to retrieve Line of Sight(LOS)surface deformation results of the Tianchi volcano from 2015 to 2022. Additionally, InSAR observations are used as surface constraints, and the geometric distribution of the magma reservoir in Tianchi volcano is inverted using the Mogi point source model. By analyzing the inferred volume change rate of the magma reservoir and integrating it with previously published results obtained from geodetic measurements, the mechanisms underlying the variations in the magma reservoir and the temporal sequence of volcanic activity in Tianchi volcano are explored. The primary conclusions are as follows:

    (1)According to the acquired LOS InSAR average deformation rate data from 2015 to 2022, covering the Tianchi volcano, the deformation results from different orbits show good consistency in their distribution. Near the volcano crater, there is an overall trend of deformation, while in areas farther away from the crater, local deformation exists. Over the past seven years of monitoring, there has been a slow subsidence phenomenon near the volcano crater, with a deformation rate of approximately -4mm/a to -2mm/a. By extracting the profile deformation time series from one descending orbit, it is found that the maximum cumulative deformation is about -40mm. The results of the deformation time series indicate that the surface deformation of the Tianchi volcano was relatively small between 2014 and 2017, indicating relatively stable magmatic activity during this period. However, starting in 2018, there has been a certain degree of accelerated deformation, and surface deformation mainly occurs around the volcano crater.

    (2)According to the inversion results of the Mogi model, the shallow magma chamber beneath the Tianchi volcano has an estimated depth of approximately 6km, with a volume change rate of -3.3×105m3/a. The geographical location of the magma chamber is situated slightly below and to the west of the Tianchi volcano crater. The inversion results indicate that during the monitoring period, the magma chamber displayed an overall slow contraction. It is speculated that the deformation activity of the magma chamber may be attributed to magma cooling and crystallization processes.

    (3)According to the inversion of geodetic measurement data on magma chamber volume changes, during the period from 1995 to 1998, the magma chamber of the Tianchi volcano underwent progressive expansion deformation at a sluggish rate. The Tianchi volcano experienced significant surface uplift deformation from 2002 to 2005. During this period, the magma chamber exhibited a rapid expansion deformation with a fast volume change rate. Starting from 2006, the surface deformation rate weakened, and the volume change rate slowed down. From 2009 to 2011, the inversion of leveling observation data indicated a contraction of the magma chamber volume. Throughout the observation period of this study, the magma chamber continued to exhibit a contraction phenomenon. From 1995 to 2022, the Tianchi volcano underwent a process of magma activity, transitioning from a state of quiescence to perturbation and back to quiescence.

    LIU Kang, YANG Ting, LI Hong-guang, FANG Li-hua, SONG Jian
    2023, 45(6):  1328-1348.  DOI: 10.3969/j.issn.0253-4967.2023.06.005
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    From March 8th to 29th, 1966, five earthquakes(M≥6)occurred in the Xingtai area, with the MS6.8 earthquake on March 8th and the MS7.2 earthquake on March 22nd being the most severely damaged. The Xingtai earthquake resulted in over 8 000 deaths and the economic losses up to 1 billion yuan. The Xingtai earthquake has opened the scientific practice of earthquake prediction in China and is a milestone in the development of earthquake science in China.

    Based on previous research results, there is a deep fault beneath the Xingtai earthquake area, which is the energy source of earthquakes, while there is a relatively independent fault system in the shallow part, which is generally recognized by scholars. However, the divergence regarding the seismogenic structure of the Xingtai earthquake mainly focuses on the unclear coupling relationship between the deep and shallow structural systems in the seismic area. The structural relationship between deep seismic faults and the shallow Xinhe Fault system requires new evidence to determine. In addition, previous scholars have proposed the viewpoint of “Newly generated Fault”, which can better explain the rupture characteristics of the Xingtai earthquake, but it still needs to be supported by the inversion results of the seismic rupture process based on the three-dimensional crustal fine structure. There are many small earthquakes in the Xingtai area. Deep structural information can be obtained using small earthquake data. Especially after 2009, the significant improvement in earthquake positioning accuracy in North China has made it possible to obtain new insights into deep structures. By locating small earthquakes, the spatial distribution and motion characteristics of faults are characterized, and seismic travel time tomography reveals the deep crustal velocity structure characteristics of the earthquake area. Combining previous geophysical exploration results, conducting deep and shallow structural analysis is of great significance for studying the spatial distribution, motion characteristics, and coupling relationship between deep and shallow structural systems of the fault system in the study area. The continuous aftershocks after the 1966 MS7.2 earthquake in Xingtai, Hebei Province, have provided favorable conditions for conducting studies on deep tectonic structures in the region.

    In this paper, based on the observation data of the Hebei seismostation from 1991 to 2021, we obtained the precise position results of 9 644 earthquakes in Xingtai and its neighboring area using the double-difference positioning method, and depicted the spatial patterns of deep ruptures. Based on the observation data of the North China Mobile Seismic Array from 2006 to 2008, 38 578 P-wave arrivals were used to obtain high-resolution travel time tomography results in the study area. This study shows that there are strong lateral heterogeneities in the velocity structure of the crust in the study area, with obvious low-velocity anomalies in the upper crust and high-velocity anomalies in the middle and lower crusts between the Xinhe Fault and the Yuanshi Fault, and the Xingtai earthquake is located at the junction of the high- and low-velocity anomalies, which has the medium conditions for accumulating large amounts of strain energy and is prone to rupture and stress release. The general trend of the dense zone of small earthquakes in the Xingtai earthquake area is relatively consistent with that of the eastern boundary of the high- and low-velocity anomalies. It is assumed that the deep and shallow fractures spreading along the eastern boundary of the high- and low-velocity bodies have been connected up and down and that the boundary of the anomalies is also a part where velocity changes are relatively strong and easily lead to seismic rupture; the results of various seismic and geological surveys have revealed that a deep major rupture that cuts through the entire crust exists beneath the Xingtai earthquake zone, with SE tendency and the upper breakpoint located near Dongwang, and the Xingtai earthquake prompted the deep and shallow pre-existing ruptures to connect from top to bottom.

    SONG Dong-mei, ZHANG Man-yu, SHAN Xin-jian, WANG Bin
    2023, 45(6):  1349-1369.  DOI: 10.3969/j.issn.0253-4967.2023.06.006
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    MODIS land surface temperature(LST)products are of great value in the exchange of atmospheric matter and energy, climate change research, and detection of thermal anomalies as earthquake precursors. However, due to the influence of the cloud, there are a large number of missing values in the MODIS LST data products, limiting its wide application. Therefore, in this study we propose a method of surface temperature reconstruction based on mixed model: SCLSTM(SSA-CLSTM). Compared with traditional methods, this method does not need to establish a complex regression relationship model. In addition, since CNN can fully extract local features of one-dimensional time series data, and LSTM can fully learn long-term time series features of data, the combination of CNN and LSTM is capable of fully learning potential features of data.

    Firstly in this study, the trend value of LST time series is extracted by SSA model to fill the missing pixel, and the initial reconstruction of LST is realized. Then, CLSTM(that is, 1DCNN, three-layer stacked LSTM)model is used to learn the local temporal characteristics and long-term dependence of the data, and the iterative prediction of the surface temperature of the missing pixel is realized to complete the fine reconstruction of the data. Based on the experimental results in Hotan region of Xinjiang and Wenchuan region of Sichuan, it can be proved that compared with the other two existing reconstruction methods based on mixed models, the reconstructed return data error is minimum, and the consistency with the original data is the highest. The RMSE of this method can be reduced to 0.712K, the minimum is 0.695K, and the correlation between the reconstructed return data and the original data can reach more than 0.95. In addition, the reliability of the method is further verified by the measured surface temperature data of the meteorological station. In summary, the proposed method provides a new technical means and ideas for deep learn-based reconstruction work, and also provides a solid data foundation for the research of surface processes and seismic thermal anomalies.

    Using MODIS MYD11A2 remote sensing data and based on the proposed new method, the reconstruction experiments were carried out in Hotan region of Xinjiang Uygur Autonomous Region and Wenchuan region of Sichuan Province with the strategy of “remove-construction-contrast”, and the results were compared with other two mixed model methods. In addition, the reliability of the reconstruction accuracy of the proposed method is verified based on the 0cm measured surface temperature data of the weather station. The main conclusions are as follows:

    (1)Through the reconstruction experiment of LST in Hotan, Xinjiang, it is concluded that compared with the existing two hybrid model reconstruction methods, the new method can better capture the time series features of LST data, so that the reconstructed image can not only better maintain the texture features of the original image, but also improve the accuracy of data reconstruction. The reconstruction error is the smallest among the three methods, RMSE can be reduced to 0.712K, and the correlation with the original data can reach more than 0.95 after reconstruction.

    (2)In order to prove the regional applicability of the new method, a reconstruction experiment was carried out in Wenchuan region of Sichuan Province, and the missing values were reconstructed using the proposed method. Through this reconstruction experiment, we found that the reconstruction method in this paper can achieve better data reconstruction effect even in areas with more cloud and fog coverage, poor weather conditions, and complex land cover types, which proves the reliability and regional universality of the method in this paper.

    (3)To further verify the reliability of the new method, the accuracy of the new method was evaluated by using the measured 0cm surface temperature data of 6 meteorological stations in Hotan region of Xinjiang. Based on the temporal variation characteristics of the MODIS return data from 2015 to 2019, the return values of 2020 are reconstructed, and the reconstructed results are compared with the measured data. By comparing the 0cm measured data of the meteorological station and the data before and after reconstruction, it can be concluded that the correlation and average deviation of the returned data and measured data after reconstruction based on SCLSTM method are closer to the correlation and average deviation of the original data and measured data. Therefore, the reconstructed data based on the new method can maintain a good consistency with the original data.

    (4)By reconstructing the missing value regions of Hotan region of Xinjiang in 2008 and Wenchuan region of Sichuan in 2020, we found that the texture of the images after the supplementary value is fine and natural, without obvious boundary effect. Therefore, it can be proved that the method in this paper can realize the data reconstruction of a large area with missing values.

    In summary, the method proposed in this paper provides a new idea and technique for MODIS surface temperature reconstruction work based on deep learning, and also provides a solid data foundation for the ground process research and seismic thermal anomaly information extraction based on MODIS LST.

    Research paper
    XIE Tao, HAN Ying, YU Chen
    2023, 45(6):  1370-1384.  DOI: 10.3969/j.issn.0253-4967.2023.06.007
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    There have been four MS≥6.0 earthquakes, i.e. the Yangbi MS6.4, Lushan MS6.1, Maerkang MS6.0 and Luding MS6.8, occurred in Sichuan-Yunnan area from 2021 to 2022. Three borehole apparent resistivity monitoring stations of Hongge, Mianning and Garzê, normally operated within 400km away from these earthquakes. These stations recorded different types of middle-short abnormal changes before the four earthquakes. The EW and NS arrays at Hongge station began to display synchronous decline change since December 2020. According to the empirical relationship between the duration of the anomaly and the magnitude, it is predicted that there is a possibility of a magnitude 6.0 earthquake in the Sichuan-Yunnan border area. But there had been no short-term abnormal changes that can give a forecast opinion on a time scale. Short-term abnormal changes appeared at Hongge station in March 2021. The maximum decline magnitudes of the NS and EW arrays were 2.1% and 1.4%, respectively. We believed that the risk of a strong earthquake has further increased. The distance from the Yangbi earthquake to Hongge station is 232km. Data of NS array recovered to normal status after the Yangbi MS6.4 earthquake in 2021, but the data of EW array continued to decline. In the fault virtual dislocation(FVD)model, the coseismic slips are loaded in a way of equal in magnitude but opposite in direction, which provides the relative deformation around the epicenter. In a compressive tectonic region, compressive areas from the FVD model can be formed as the areas with compression enhancement. The dilatant areas cannot be distinguished between absolutely dilatant areas and compressive areas. However, they can be regarded as relatively dilatant areas where the original extensive stress is enhanced, or the original compressive stress is released to some extent. It is found that Hongge station is located in the relative expansion region generated by the Yangbi earthquake. Abnormal changes at Hongge station are not only affected by the seismogenic process of the Yangbi earthquake, but also possibly indicating the existence of another strong earthquake. The anomaly duration of the EW array was about 21 months long and the decline magnitude was 2.8%up to September 5, 2023, when the Luding MS6.8 earthquake occurred, which is about 340km far away from Hongge station. The N10°E array of Garzê station began to show abnormal decline change since April 2022 with the maximum decline magnitude of about 0.5%. Apparent resistivity curve changed to rise change since late June, and the anomaly recovered to the normal status in October. Three earthquakes of Lushan MS6.1, Maerkang MS6.0 and Luding MS6.8 occurred during the period of anomaly evolution, with a distance of 306km, 183km and 293km from the Garzê station, respectively. The regional deformation before Lushan and Maerkang earthquakes from the fault virtual dislocation model show that the seismogenic process of these two earthquakes has little influence on the abnormal changes detected from Garzê station. The abnormal changes are probably related to the preparation of another big earthquake. At the earthquake situation consultation meeting on August 26, the Electromagnetism Laboratory predicted that a magnitude 6.0 earthquake would occur in the northwest of Sichuan in the short term. After the Luding MS6.8 earthquake, the observation data of the N10°E array returned to the normal status. The N60°W array showed distortion in annual variation pattern from September to November 2022. Another MS5.6 earthquake occurred in Luding on January 26, 2023. The EW, NS and N45°W arrays of Mianning station showed synchronous rise changes since late June 2022, and anomalies recovered after the Luding MS6.8 earthquake. After the Luding earthquake, the regional deformation characteristics before the earthquake are also analyzed by the fault virtual dislocation model. The Garzê station is located in the area of compression enhancement, while Mianning station is located in the area of relative expansion. Results from petrophysical experiments have demonstrated the decline changes when water-bearing rock and soil samples are under compression, and the rise changes as samples are undergoing stress unloading. Resistivity does not recover to the initial status when the compression stress is completely released, suggesting the existence of irreversible change in the samples. Therefore, the patterns of anomalies recorded at Garzê and Mianning stations are consistent with the area deformation where the stations were located. In summary, according to the abnormal changes of three borehole apparent resistivity observation in Hongge, Mianning and Garzê station from 2020 to 2022, we have made short-term prediction for the Yangbi MS6.4 in 2021, Luding MS6.8 in 2022 and Luding MS5.6 in 2023, at the regular weekly and monthly earthquake situation consultation meetings.

    LUO Xiang-fei, LI Zhong-liang, LI Yong-jiang, WANG Ze-yuan, JI Ji-fa, HE Xin, YU Bo
    2023, 45(6):  1385-1399.  DOI: 10.3969/j.issn.0253-4967.2023.06.008
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    We examine the density structure, tectonic features, and seismic activity along the Yichuan-Tai’an profile. To do this, we use regional Bouguer gravity anomaly data and analyze the correlation between the Bouguer gravity anomaly, residual density, and density structure distribution along the profile. We also incorporate seismic detection and geological tectonic results to conduct density inversion and residual density correlation imaging studies on the profile. The results show that:

    (1)The Bouguer anomaly in the profile ranges from-(161.7~5.5)×10-5m/s2 and shows an overall upward trend from west to east. The Yichuan-Linfen-Changzhi section has a low background with a gradual upward trend, but the Bouguer anomaly is noticeably “depressed” between the Luoyunshan Fault and the Huoshan Mountain Frontal Fault. This depression could be due to the presence of low-density structures in the upper crust of the Linfen Basin and the density “loss” between the enclosing rocks.

    The Changzhi-Taihongshan-Linxian section changes from a gentle rise in a low background to a rising trend in a high background. The Bouguer gravity anomaly suddenly drops and then rises again, indicating the existence of pre-Taihang Mountains fractures and the undulations of the Moho interface. The Anyang-Nanle-Tai’an section shows a gradually rising trend of high background, with many local anomalies and small-scale gradient zones distributed in the background. These anomalies and zones are related to smaller internal depressions and uplifts.

    The background anomaly responds to the change in crustal thickness, showing a pattern of deep crust in the west and shallow crust in the east. However, the crustal uplift in the Linfen Basin and North China Fault Basin may be due to the extrusion and expansion uplift of the crust when the upper mantle material invades upward. In the uplifted areas of Luliang Mountains and Taihang Mountains, the crust is depressed, likely due to the splitting between the upper and lower crust, making the uplifted massif thicker than the basin crust.

    We observed changes in the gradient of the Bouguer gravity anomaly at the major fault zones spanned by the profile. The magnitude of the gradient change indicates the relative depth of the fractures, and the Bouguer gravity anomaly change may be controlled by the development of the fractures.

    (2)The model of profile density distribution reveals differences in the distribution of crustal density in both horizontal and vertical directions. Horizontally, the crust is divided into four blocks from west to east: Ordos fault block, Shanxi fault zone, Taihang Mountain fault block, and North China Plain fault block. The density of each block varies significantly, with the Linfen Basin showing low density and the Taihang Mountains showing high density. The low density in the Linfen Basin may be related to Cenozoic material deposition, while the high density in the Taihang Mountains may be related to contraction, extrusion, and folding movements, and may also be the remnant of refractory, high-density lithosphere of the Taiyuan continental plate remaining after demolition and sinking.

    Longitudinally, the crust can be divided into four structures: Basal, upper, middle, and lower crust. As depth increases, the density difference becomes smaller. There are clear low-density anomalies in the crust on the eastern side of the Taihang Mountains fault block and the North China Fracture Basin. These anomalies may be caused by the process of mantle uplift, the upwelling of deeper plastic material along the fracture in the crust, or the rising of deep magma along the fracture. These events can cause partial melting of material in the crust, resulting in phase change metamorphosis, and expansion. The physical properties of the medium on both sides of this low-density body are different, and historically strong earthquakes have occurred in this area, which is known as the “earthquake-prone layer.”

    Moreover, the low-density medium of the North China Plain fault block basin is connected to the eastern part of the Taihang Mountains fault block, indicating that the evolutionary tectonic movements are closer, and the deep background tends to be consistent.

    (3)Around 70% of earthquakes with a magnitude of 5 or above happen in the transition zones between high and low densities. These transition zones correspond to active fractures, which suggest that the heterogeneity of crustal material density is a factor in earthquakes.

    In this study, we investigate the relationship between crustal density structure and seismic activity by analyzing the gravity and density structure of the profile lattice. The subduction of the Pacific plate is a significant factor in the study area, and the inhomogeneity of the crustal medium is the primary cause of seismic activity. The Ordos fault block has relatively homogeneous crustal medium and low seismic activity, while the Shanxi fault zone and the North China Plain fault block have significant inhomogeneity and frequent seismic activity. Fracture zones influence the development of density anomalies, and there is a close connection between fracture activity and earthquake occurrence. Earthquakes are more likely to happen in the transition zones between high and low densities corresponding to active fractures.

    XU Zhi-ping, LIU Qiao-xia, LIU Zhi, TIAN Xiao-feng, WANG Fu-yun, DUAN Yong-hong, LIN Ji-yan, QIU Yong, TANG Lin
    2023, 45(6):  1400-1418.  DOI: 10.3969/j.issn.0253-4967.2023.06.009
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    The Longmenshan fault zone is located in the northeastern margin of the Qinghai-Tibet plateau, with an overall direction of NNE and a total length of about 500km. As we have known, the Longmenshan fault zone is the boundary fault between the Bayanqala block and Sichuan basin. Since the Cenozoic, the Longmenshan fault zone has experienced intense tectonic activity and multi-stage magmatic activity, forming a series of active faults with different scales and properties.

    And Lushan MS7.0 earthquake in 2013 and Lushan MS6.1 earthquake in 2022 occurred in the southern section of Longmenshan fault zone, and the two earthquakes were only 10km far away apart. The generation of the two strong earthquakes is closely related to the seismic tectonic environment and crustal physical structure parameters. So to study the characteristics of shallow crustal physical structure and its relationship with deep dynamic processes, is good for us to understand the seismogenic environment of this area. The wide angle inverse/refraction detection method is an effective means to obtain the physical property parameters of the crust. In this paper we extracted the first arrival travel time data of P-wave and S-wave from Jinchuan-Lushan-Leshan deep seismic sounding(DSS)profile data. The 2D ray-tracing travel-time imaging method proposed by Zelt et al.(1998)was used to obtain the 2D P-wave, S-wave and Poisson’s ratio structure of the upper crust in the source area of the Lushan strong earthquake and its adjacent area. Then based on the results of deep crust exploration, seismic distribution characteristics and other geophysical and geological studies in this area, we focus on the response of shallow tectonic environment and deep dynamic processes in the upper crust, and analyze the seismogenic environment and seismogenic mechanism of M6-7 strong earthquakes in this area. The results show that: 1)The crustal velocity and Poisson’s ratio are significantly different at different positions of the profile. In the Songpan-Ganzi block, the velocities of P- and S-waves in the upper crust are relatively high and the Poisson’s ratio is relatively low. While in the Sichuan basin, the velocities of P- and S-waves in the upper crust are relatively low and the Poisson’s ratio is relatively high. In Longmenshan tectonic belt which between the Songpan-Garze block and the Sichuan basin, the velocities of P- and S-waves and Poisson’s ratio isolines of the upper crust are controlled by regional tectonic activities, which are basically consistent with the occurrence of the strata and show a near-vertical trend. The sedimentary basement below the tectonic transition zone shows obvious structural differences, and the velocity and Poisson’s ratio contour lines form “V” shape characteristics. 2)The characteristics of high crust velocity and low Poisson ratio(<0.26) in the Songpan-Ganzi block may be the direct reflection of the strong deformation of Sinian-Paleozoic strata caused by the orogenic activities in the northeastern margin of the Qinghai-Tibet plateau in the Indosinian period, and the bi-direction contraction of the strata in the Triassic Xikang Group, the obvious thickening of the crust, and the multi-stage magmatic activities. 3)The large lateral variation gradient of velocity and Poisson’s ratio in Longmenshan tectonic belt between Songpan-Ganzi block and Sichuan basin is the direct evidence of vertical crustal deformation caused by the compression of low Poisson’s ratio crust from the eastern margin of Qinghai-Tibet plateau to the hard Yangzi platform(high Poisson’s ratio)by the remote effect of the collision between the Indian plate and the Asian plate since late Quaternary. 4)The aftershocks of the MS7.0 earthquake mainly occurred on the high-velocity and Low-Poisson’s ratio side of the velocity and Poisson’s ratio gradient belts in the crust. The seismicity in this area is not only controlled by the regional fault structure, but also closely related to the physical structure characteristics of the upper crust.

    Research paper
    ZHU Guo-jun, FENG Shao-ying, YUAN Hong-ke, HOU Li-hua, QIN Jing-jing, HAN Jian, WU Quan, ZUO Ying
    2023, 45(6):  1419-1431.  DOI: 10.3969/j.issn.0253-4967.2023.06.010
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    The Zhumadian-Huaibin depression, which is located in the southern margin of the North China block, is a NW trending faulted basin between the thrust nappe belt on the northern margin of Qinling Mountains and Xiping-Pingyu uplift and controlled by the NW trending Zhumadian-Xixian Fault and Suyahu Fault. To find out the risk base of earthquake disasters and identify the characteristics of seismotectonic in Zhumadian City, based on the analysis of deep seismic exploration results, we used high-resolution shallow seismic reflection imaging technology to complete a shallow seismic profile, about 22km long, and obtain the fine near-surface structure image and fault characteristics of Zhumadian-Huaibin depression.

    As regards seismic data acquisition, we used an observation system with 3m channel spacing, 15m shot spacing, 180 recording traces and 18 folds. The seismic wave is generated by a M18-612 vibrator, with a scanning frequency band of 20-160Hz and a scanning length of 12s. The data processing adopts the common center point stacking method, with a focus on improving the signal-to-noise ratio. The processing process mainly includes the elimination of waste traces, static correction, pre-stack filtering, predictive deconvolution, velocity analysis and NMO correction, residual static correction, common center point stacking, post-stack denoising, etc. The resulting shallow seismic profile has a high signal-to-noise ratio, clearly reflecting the near-surface structural changes and fault characteristics of the Zhumadian-Huaibin depression. Similar to the characteristics of deep seismic reflection profiles, the Zhumadian-Huaibin depression on the shallow seismic profile also exhibits a fault-controlled fault basin.

    The shallow seismic profile reveals multiple sets of distinct stratigraphic interface reflections, which are characterized by continuous horizontal and dense vertical layering on the profile, with typical sedimentary stratigraphic reflection characteristics. Taking the bottom interface of the Neogene and Paleogene as the boundary, there are three distinct sets of reflection characteristics in the upper, middle, and lower layers, reflecting the sedimentary differences of different tectonic periods. The lateral continuity of the reflection waves in the Neogene and Quaternary strata is good, and the overall performance is a tilted layer with high west and low east, reflecting the overall subsidence of the Southern North China region since the Neogene, and forming relatively stable Neogene and Quaternary systems; The bottom interface of the Neogene and the overlying Paleogene show obvious angular unconformity, reflecting the sedimentary discontinuity between the Neogene and Paleogene formed by the overall uplift and erosion of the Southern North China region in the late Oligocene; The lateral fluctuation of reflected waves in the Paleogene strata reflects that during the Paleogene period, the southern margin of the North China block entered a stage of fault basin development with the Southern North China region, and the the Paleogene strata was controlled by tectonic movements and fault activities; Under the Paleogene bottom interface, at both ends of the profile the reflected wave energy is weak and the continuity of the same phase axis is poor, it is speculated that it is early Paleozoic sedimentary rock and Archean dense metamorphic rock mass.

    The results show that the Zhumadian-Huaibin depression was formed during the development stage of the fault basin in the Southern North China Basin in the Paleogene; The Zhumadian-Xixian Fault, which controls the western boundary of the depression, is composed of four east-dipping normal faults, manifested as a set of fault step belts that fall down layer by layer from west to east, and has not staggered the bottom interface of the Neogene, is speculated to be an active fault in the late Paleogene period; The Suyahu Fault, which controls the eastern boundary of the depression, is composed of three west-dipping normal faults, and has staggered upward to the middle-upper part of the Neogene, and is speculated to be an active fault in the middle-late Neogene period.

    Suyahu Fault has a significant impact on the local changes in the near-surface strata and the trend of modern rivers and lakes, it is recommended to focus on earthquake prevention and disaster reduction work in the Zhumadian City. This study provides a geophysical basis for further understanding the near-surface structural characteristics and basin-controlling fault activity of Zhumadian-Huaibin depression, which has important scientific value and social benefits for earthquake disaster mitigation and urban planning of the Zhumadian City.

    DAI Meng-yao, WANG Ping, LI An-bo, DING Lu, LIU Pin-qin, DAI Jin-gen, ZHANG Hui-ping, LIU Shao-feng
    2023, 45(6):  1432-1451.  DOI: 10.3969/j.issn.0253-4967.2023.06.011
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    Low-temperature thermochronology is a key technology for studying neotectonics and landscape evolution. However, it is intrinsically different from the other geochronological methods in the data expression, analysis and interpretation. In recent years, with the widespread adoption of low-temperature thermochronology techniques, the size volume of data has continuously increased, giving rise to many studies on tectonic geomorphic evolution based on big data. However, these data are mostly scattered across literature from different sources, with inconsistent formats and contents, and varying data quality, which to a certain extent hampers innovative research based on big data. There is a need to construct specialized databases to cope with the growing low-temperature thermochronology data and meet the demands of innovative research using big data.

    In this paper, four conventional geochronological databases, including National Geochronological Data Base, Geochron, Petlab, DataView, and recent databases, AusGeochem and Sparrow are reviewed for comparison of their capability in data sources, data volume, data storage structure, completeness of data content, data entry methods, data retrieval methods, coverage areas, database update patterns, and data analysis tools. The conventional geochronological databases, of which the thermochronological data comprise only a small part, are generally stored in databases similar to or outside this subject, such as radioisotope chronology database, geochronology database, petrological mineral and geological analysis databases. They amplify the commonalities between different disciplines, and thus focus only on the presentation of sample units. It is not suitable for “big data” research, because all the data are managed by relational database with strictly structured tables and limited data sources. It was found that conventional geochronological databases design approaches are often suitable for absolute age data. However, low-temperature thermochronology differs from conventional geological dating methods, as its age values only record cooling time. The more geologically significant cooling history comes from numerical simulations based on elevation profiles, track lengths, and the diffusion dynamics models of the(U-Th)/He system. Additionally, the innovation in experimental techniques also imposes new requirements on the construction of thermochronology databases.

    Comparing with the conventional geochronology databases, recent databases focus more on low-temperature thermochronological data and support both the structured and unstructured data with variable data sources, which makes it more comprehensive and professional. These databases own the characteristics of flexibility and expandability, especially for the addition of new dating methods and experimental methods, the storage of big data and the linkage between laboratories and database. Using different types of database platform and associated APIs, both relational and non-relational data can be involved and managed for data query, analysis and visualization. However, the construction of these recent databases is still in the preliminary exploration stage, and ensuring the continuous growth of data remains a challenge. Moreover, establishing a flexible numbering system for sustainable and expandable unique identification of samples and data is also an important task for recent databases. Finally, in addition to raw data, numerous thermal history information is included in published paper related to fission track. These interpretations or inverted results constitute interpretive data, which are crucial for reconstructing cooling history or tectonic uplift. Therefore, how to incorporate such data into the database is also a question that must be considered during database design.

    The key to supporting the database lies in the users who it oriented. Considering the needs of users in professional field for scientific research management, experimental analysis and “big data” innovative research, as well as in view of the problems existing in the current databases, we put forward following suggestions for the future construction of low-temperature thermochronology database.

    Firstly, in order to ensure the activity of specific low-temperature thermochronology database. from a technical perspective, artificial intelligence technologies such as natural language processing or other forms of machine learning algorithms should be utilized to semi-automatically or automatically extract information from paper, assisting users in quickly extracting relevant information and understanding the content of the literature. Platforms like Semantic Scholar, GeoDeepDive, and DeepShovel have implemented interactive features in data mining, wherein data is normalized and automated into the database based on user-specified rules, significantly reducing manpower and time costs in data acquisition, providing great convenience. In terms of ideology, the open-sharing academic ecosystem has given rise to open-sharing platforms such as arXiv for preprints, data repositories like Pangaea, and the Deep-Time Digital Earth integrated online research platforms, drastically shortening the cycle from research and experimentation to publication. This facilitates the incorporation of the latest research data into databases, greatly expanding the data sources. Regarding user volume, academic social networks possess advantages in academic tracking and dissemination, breaking down academic-related hierarchies, promoting academic exchange and cooperation, and attracting more users.

    Secondly, more detailed data storage capabilities and simpler data operation behaviors help improve the expansibility of the database. Most existing geochronological databases use relational databases, which are a strictly structured way of storing data. The most typical data structure presentation form is two-dimensional table, which is very suitable for logical geological data. However, non-relational databases are not tables but databases oriented towards structured and unstructured data storage requirements, which have filled the gaps in relational databases. In practical applications, the advantages of both types of databases can be combined to comprehensively include basic geological information and interpretive information, achieving the effect of New SQL.

    Thirdly, highlight its highlight. Chronological data of sample and the single data that make up the sample chronology are significant, it will be effective in distinguishing low-temperature thermochronology from other similar disciplines if the coding style of sample and single data that are not registered on IGSN can be standardized to highlight the characteristics of subject data.

    Finally, by combining the strengths of both conventional and recent databases, incorporating the concept of open academia, leveraging advanced information mining and transmission technologies, and utilizing a storage approach that combines structured and unstructured data, it can greatly meet the comprehensive needs of users, ranging from laboratories to scientists, and further to data consumers.

    Application of new technique
    SHI Wen-fang, XU Wei, YIN Jin-hui, ZHENG Yong-gang
    2023, 45(6):  1452-1462.  DOI: 10.3969/j.issn.0253-4967.2023.06.012
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    Terrestrial in-situ cosmogenic nuclide dating(TCND)is one of the most important geochronological techniques for the paleoseismic study of bedrock fault scarps, landslides, and rock avalanches. With many target minerals, due to its uncomplicated composition, widespread occurrence, and simple chemical treatment, Quartz has emerged as an ideal dating material for terrestrial in-situ cosmogenic nuclides dating methods, such as 14C, 10Be, 21Ne, and 26A1. Prior to accelerator mass spectrometry measurement, the separation of pure quartz from field-collected rock samples was a pivotal step in TCND. However, the elevated aluminum content in quartz samples undermines the reliability of TCND results. Generally, most of the aluminum content in samples originates from impurities like feldspar. To ensure accurate dating outcomes, the content of Al in samples should be reduced to less than 200 ppm. Therefore, effective separation of feldspar and quartz in samples and obtaining pure quartz is the first step in TCN dating. The conventional HF/HNO3 etching method to separate and purify quartz is widely utilized, but it is time-consuming and low-efficiency. Particularly during the HF/HNO3 etching stage when dealing with granitic samples containing abundant feldspars and mica impurity minerals necessitates repeated treatments to eliminate feldspars completely; this not only increases etching cycles but also leads to sample loss significantly. It has a great impact on the application of in-situ cosmogenic nuclide dating in active tectonics. Consequently, physically separating quartz from samples before chemical purification can effectively shorten the chemical etching duration while the flotation separation method can effectively remove most gangue minerals in quartz and achieve preliminary purification of quartz.

    This article presents a laboratory-integrated flotation purification device and proposes enhancements to the conventional quartz etching process in order to improve its purification efficiency. The purification device uses dodecylamine as the collector, hydrofluoric acid as the feldspar activator, nitric acid as the regulator, and eucalyptus oleanol as the foaming agent. The bubbling component within the device provides sufficient carbon dioxide bubbles to float out feldspar and other minerals in the sample reversely. To evaluate its efficacy in flotation separation, enrichment, and purification, this study conducted tests on two commonly encountered bedrock samples of granitic gneiss and quartzite.

    Observation results under a stereomicroscope show that the quartz content in the quartz component after floating is more than 90%. The etching results of the whole rock and the floated quartz components show that after etching 2-3 times with HF/HNO3, the Al concentration can be reduced to less than 200ppm, which fully meets the requirement of cosmogenic nuclide dating. The quartz separated by flotation from cryptocrystalline quartzite samples can also reach the dating requirements after etching 7-8 times.

    Compared to direct etching following bulk-rock sample crushing, this approach reduces etching time by over a half, significantly minimizing reagent consumption for HF/HNO3 etching and thereby enhancing TCND efficiency. The bubbling power section of our flotation device directly introduces carbon dioxide gas into the flotation liquid to increase the bubble content in the slurry. Consequently, there is improved collision and contact between quartz and feldspar particles with bubbles, resulting in enhanced flotation effectiveness. This system can be effectively employed for separating feldspar from other impurity minerals present in gneiss samples. The proposed flotation process in this study is straightforward and user-friendly while allowing flexibility in adjusting sample quantities ranging from tens to hundreds of grams as required. Furthermore, this high-efficiency flotation separation system may offer insights into processing zircon, apatite, and other dating samples.