Fault Zone Research Articles

Interaction of pipelines with landslides: analysis of mechanical properties at different strengths

Landslides, as a common geological hazard, pose a significant threat to critical infrastructure such as pipelines. With numerous large-scale engineering projects in China crossing active fault zones, the impact of geological hazards on the safe operation of pipelines is becoming increasingly prominent. To accurately assess the impact of landslides on pipelines, this study employs the open-source DualSPHysics code and constructs a three-dimensional numerical model of landslide impact on pipelines based on the Smoothed Particle Hydrodynamics (SPH) method. The study conducts a quantitative analysis of key factors such as sliding displacement and landslide scale, thoroughly exploring the mechanisms by which landslides affect pipelines. The results indicate that as the landslide displacement increases, the rate at which the pipeline's stress increases accelerates, and the rate of stress decrease after reaching the peak also accelerates. Additionally, when the width of the landslide mass increases, its volume correspondingly increases, leading to a significant enhancement in the impact force experienced by the pipeline. Furthermore, the study analyzes the impact of different initial distances between SPH particles on the pipeline to optimize the accuracy and computational efficiency of the simulations. This research not only provides new perspectives and approaches for assessing pipeline safety but also holds significant implications for enhancing pipeline disaster resistance and guiding design and safety assessments in geological engineering and infrastructure projects.

Physical Similarity Simulation of Closely Stacked Coal Seams Mined in Faulted Geological Environments: A Comprehensive Experimental Investigation

ABSTRACTThe mining of closely stacked coal seams can be associated with complex stress fields, which makes mining difficult. In addition, closely stacked coal seams often coexist with faults and confined aquifers, further complicating mining activities. However, the study of closely stacked coal seams under complex geological conditions with faults (confined water) is very rare. In this study, an experimental approach was adopted to investigate the stress field and displacement field in rocks associated with closely stacked coal mining activity (complex geological conditions with faults and confined water). The materials used in the laboratory had similar physical properties to those present in the mining environment. The results showed that the overlying rock structure has three structural types and three caving forms. When the lower coal seam is mined, the collapse of the overlying strata is characterized by “caving with digging,” “no obvious periodic pressure step,” and “it is difficult to form a beam structure.” Faults function as a stress barrier, which makes it difficult for abutment pressure to cross a fault zone and form a stress concentration near the fault zone. When mining in faulted strata with confined water, there are three areas prone to water inrush, namely near the intersection with the fault zone and coal pillar, the boundary between the coal pillar and goaf, and the middle of the goaf. The research results are of great significance to the mining of closely stacked coal seams under complex geological conditions.

Deformation mechanisms and geometries of superposed fault zones in dolostones

Understanding how heterogeneous rock volumes deform is crucial in structural geology, and several studies have addressed this issue by focusing on the impact that the mechanical stratigraphy of a layered stratigraphic sequence has on deformation. However, mechanical layering can also develop subparallel to fault surfaces within the upper crust, and how these anisotropies affect subsequent deformation has been much less explored. This work addresses this aspect by structurally and mechanically characterizing superposed fault zones developed in Triassic dolostones that crop out in the fold-and-thrust belt of the southern Apennines. We investigate how layering associated with an early, reservoir-scale, normal fault zone (F1), inherited from Upper Triassic−Lower Jurassic pre-orogenic extension, influenced the deformation mechanisms and the geometry of younger strike-slip faults (F2) that formed at an angle to it in the early Pliocene in association with out-of-sequence tectonics during the Apennine orogeny. We combined field surveys and laboratory analyses using a multiscalar and multimethodological approach. Meso- and microstructural observations and geomechanical, laboratory, and in situ tests were employed to describe fault rock attributes. We found that the architecture of the F1 normal fault primarily consists of four tens-of-meters-thick, subparallel fault rock units. They have a cataclastic core, and are bounded in the hanging wall by cemented micromosaic breccia, and in the footwall by high-strain and low-strain fault rocks. The younger F2 strike-slip faults developed alternatively as either cataclastic shear bands or compaction bands and occur in either localized or anastomosing geometries. By combining data, we demonstrate that the particle size distribution, porosity, and rock strength of the fault rock units related to older normal faults are the main controls on the deformation mechanisms (i.e., cataclasis versus compaction) and geometry (i.e., localized anastomosed) of the subsequent strike-slip faults. Our study highlights that preexisting highly porous fault rocks favor the development of compaction deformation bands. Conversely, low rock strength facilitates the formation of discrete and diffuse slip surfaces. These results can have significant implications for assessing fluid flow in multifaulted dolomite reservoirs.

Landscape changes caused by the 2024 Noto Peninsula earthquake in Japan.

Landscapes are shaped by tectonic, climatic, and surface processes over geological timescales, but we rarely witness the events of marked landscape change. The moment magnitude 7.5 Noto Peninsula earthquake in central Japan was caused by a large thrust faulting, up to nearly 10 meters of slip, that expanded more than 150 kilometers along the fault zone. The deformation field reconstructed from satellite data and field surveys reveals up to 4.4 meters of uplift and associated coastal advance along the entire northern coast of the peninsula, meter-scale systematic movement of the mountain slopes consistent with slip on flexural faults, and activation of secondary inland faults, suggesting synchronized ruptures. The findings show excellent consistency between the coseismic deformation and geomorphic features and provide a vivid example of the role of a major earthquake in landscape formation.

Seismic Activity Along the Periadriatic and Sava Faults in the Past Two Millennia—An Archaeoseismological Assessment

Most of the Periadriatic Fault System has been active during the Oligocene and Miocene times. Its western part seems to be almost inactive ever since, while the eastern segments show limited seismic activity. We conducted a systematic archaeoseismological survey along the Periadriatic-Sava fault system, assessing buildings and archaeological sites for earthquake damage. Eleven sites, four Roman and seven Medieval, bear evidence of destructive earthquakes which occurred during the past 2000 years. These are (from east to west): Roman Siscia (Sisak) near the Sava fault in Croatia, Roman Celeia (Celje) at the Savinja/Sava faults in Slovenia, Magdalensberg (Roman) just north of the Karavanka fault, Medieval Villach, the Dobratsch landslide and Medieval Arnoldstein at the junction of Mölltal and Gailtal faults, Medieval Millstatt, Sachsenburg. and Roman Teurnia on the Mölltal Fault, Medieval Lienz (all in Austria) and San Candido on the Pustertal fault, as well as Medieval Merano and Tirol (in Italy) adjacent to the North Giudicarie fault zone. Damaged upright walls of Medieval buildings and deformed floors of Roman settlements testify to local intensity up to IX. Ongoing studies of archaeological stratigraphy and construction history allow the dating of one or more seismic events at each site, ranging from the 1st century AD to the 17th century. It is remarkable that the sites, 20 to 70 km apart, along a <400 km long segment of the Periadriatic Fault system, carry evidence for so many high-intensity destructive events, suggesting that the region is tectonically active.

Interpretation of a 3D Magnetotellurics Model of the Aceh and Seulimeum Segments of the Sumatran Fault Zone

The Sumatran Fault runs from the southeast (SE) to the northwest (NW) of Sumatra Island, with the highest slip rates reaching about 3.0 cm per year in the northwestern part. There is a seismic gap along this fault, including the northern Aceh domain, which consists of the Aceh and Seulimeum fault segments. Previous studies have used various methods to investigate the Sumatran Fault system, including seismic, geoelectric, gravity anomaly, and magnetotellurics (MT). The MT method has proven advantageous as it can non-destructively image a wide range of depths. However, previous studies using the two-dimensional (2D) MT inversion did not represent realistic information of the subsurface conditions. Therefore, a three-dimensional (3D) MT data inversion was used in this study to obtain more realistic information about the resistivity structure of the Aceh and Seulimeum segments. The results confirmed that the Sumatran Fault is a strike-slip fault, with a relatively northwest (NW)–southeast (SE) direction of conductivity strike with an angle of S 71.61° E from Groom–Bailey decomposition of MT data. The 3D resistivity distribution model from 33 stations showed that the Aceh Fault Segment is 20–30 km away, while the Seulimeum Fault Segment is 55–60 km away based on the MT data. The results also indicated a creeping zone at a depth of 2 km beneath the Aceh Fault Segment. Different rock formations were identified beneath the fault system, with the western part of the Aceh Segment dominated by high-resistivity metamorphic rocks (150–1000 Ωm) from the Triassic–Cretaceous age. The zone between the Aceh and Seulimeum fault segments exhibited low resistivity, characterized by volcanic rocks (1–15 Ωm) from the Lam Teuba Volcanic Formation and the Indrapuri Formation. Beneath the eastern part of the Seulimeum Fault Segment was found to consist of low-resistivity quaternary volcanic rocks (1–15 Ωm) and high-resistivity andesite rocks (4.5 × 104–1.7 × 105 Ωm). These findings correlated well with the geological map.

Pre‐Existing Off‐Fault Damage Can Impede Coseismic On‐Fault Slip

AbstractPrimarily due to the scarce direct field evidence along a same fault, understanding the relationship between the pre‐existing off‐fault damage and coseismic slip distribution remains challenging. This study offers the first field‐based quantitative assessments of fault damage zones along the surface rupture generated by the 2008 Mw 7.9 Wenchuan earthquake in China over eight profiles with 254 outcrops. The width and mean tectonic fracture intensity of the damage zones exhibit pronounced variations along the fault strike. We introduce the damage index as a proxy to quantify the extent of pre‐existing damage. We find a statistically significant anti‐correlation between the damage index and coseismic on‐fault slip. We thus infer that pre‐existing off‐fault damage plays a significant role in dissipating rupture energy, thereby reducing coseismic on‐fault slip. This study provides a natural case for linking the long‐term fault zone evolution and the short‐term earthquake rupture dynamics.

Exploring Similarities and Differences in Water Level Response to Earthquakes in Two Neighboring Wells Using Numerical Simulation

The seismic effect of well water level is complex and variable, and even if both wells are located in an area with similar tectonic and hydrogeological conditions, they exhibit slightly varying response characteristics to the same earthquake. Wells BB and RC, located about 100 km apart in the southwest of the Huayingshan fault zone in the Sichuan and Chongqing regions, exhibited obvious similarities and differences in their co-seismically response and sustained recovery characteristics during the Wenchuan Ms8.0 earthquake. Based on the dislocation theory and fluid–solid coupling theory, this study developed the seismic stress–strain model and the response model of pore pressure to seismic stress using Coulomb 3.3 and COMSOL 6.3, respectively. Simulation findings indicate that both BB and RC are located in the expansion zone, where their water levels show a co-seismic step-down. The amplitudes of BB and RC water levels are 83 cm and 81 cm, which are approximately 10 cm smaller than the actual values. The recovery times are 60 d for BB and 3 h for RC, closely resembling the actual values. Furthermore, the numerical results from different scenarios show that the recovery time of pore pressure is reduced by several times when the permeability of the confining layer overlying the observed aquifer increases by one order of magnitude or the thickness decreases, and this change is more sensitive to the permeability. It is clear that the confining condition has an important impact in the response time of sustained changes in well water levels, which may also help to explain the variations in the characteristics of sustained changes in wells BB and RC.

Comparison of Seismic and Structural Parameters of Settlements in the East Anatolian Fault Zone in Light of the 6 February Kahramanmaraş Earthquakes

On 6 February 2023, two very large destructive earthquakes occurred in the East Anatolian Fault Zone (EAFZ), one of Türkiye’s primary tectonic members. The fact that these earthquakes occurred on the same day and in the same region increased the extent of the destruction. Within the scope of this study, twenty different settlements affected by earthquakes and located directly on the EAFZ were taken into consideration. Significant destruction and structural failure at different levels were induced in reinforced concrete (RC) structures, the dominant urban building stock in these regions. To determine whether the earthquake hazard is adequately represented, the PGA values predicted in the last two earthquake hazard maps used in Türkiye for these settlements were compared with the measured PGAs from actual earthquakes. Subsequently, the damage to reinforced concrete structures in these settlements was evaluated within the scope of construction and earthquake engineering. In the final part of the study, static pushover analyses were performed on a selected example of a reinforced concrete building model, and target displacement values for different performance levels were determined separately for each earthquake. For the 20 different settlements considered, the displacements were also derived based on the values predicted in the last two earthquake hazard maps, and comparisons were made. While the target displacements were exceeded in some settlements, there was no exceedance in the other settlements. The realistic presentation of earthquake hazards will enable the mentioned displacements predicted for different performance levels of structures to be determined in a much more realistic manner. As a result, the performance grades predicted for the structures will be estimated more accurately.

Enrichment and sources of major and trace elements in the Qinghai-Tibetan Plateau: a case study of the Golog Prefecture.

The Qinghai-Tibet Plateau (QTP) is a vital region for global atmospheric circulation and biodiversity. This study aims to evaluate the contents and enrichment status of 25 soil elements, namely Al, As, Ca, Cd, Co, Cr, Cu, K, Mg, Mn, Mo, N, Na, Ni, P, Pb, S, Sc, Si, Sn, Sr, Fe, Ti, V, and Zn, in the plateau region. Specifically, our analysis revealed that As exhibited significant enrichment near fault zones and intrusive rocks, while Ca was mainly enriched due to the dissolution of carbonate rocks. Additionally, Principal Component Analysis and Multiple Linear Regression (PCA-MLR) were used to examine the origins of these elements. The potential ecological risk posed by Cd and Pb was evaluated and found to be negligible. Soil element enrichment in the QTP was mainly influenced by lithology, and high spatial variability was observed in As, Ca, and S, which were mainly affected by geological processes and grazing activities. Six sources of elements in the plateau region were identified, namely geological mixed sources, grazing activities, alkaline granite, ultrabasic rocks, fault zones and intrusive rocks, as well as atmospheric deposition. Among these, geological mixed sources and grazing activities were determined to be the priority contributors. Although grazing activities on the QTP as well as atmospheric deposition at long distances caused the enrichment of elements in the area, the ecological risk was negligible. The outcomes of this work can be used as a theoretical basis for prospective investigation on the stability of high-altitude ecosystems, species diversity, and geochemical background.

Evaluation of CO2 Leakage Potential through Fault Instability in CO2 Geological Sequestration by Coupled THMC Modelling

A faulted saline aquifer system was simulated in a coupled thermal-hydraulic-mechanical-chemical (THMC) framework to examine the potential breaching of the caprock seal from long-term CO2 sequestration. The pH of the brines steadily dropped from 7.5 to 4.7 due to the continuous injection of scCO2 (supercritical CO2), which was caused by the rapid dissolution of calcite in the reservoir and associated fault zones, alongside alterations in the concentrations of primary and secondary minerals within the formation. The increase in pore pressure with the continuous injection of scCO2 triggered fault reactivation at 6y with the resultant leakage of CO2 along the fault. This builds CO2 saturation inside the fault at 7y to six-fold higher than pre-slip. Continuing shear reactivation and creation of reactive surface area following the initial CO2 leakage accelerates dissolution/precipitation reactions, in turn further increasing porosity and permeability of the reservoir and fault. In particular, the permeability and porosity in the fault zone were increased by only 2% and 6%, respectively – staunched by competitive feedbacks in dissolution countered by precipitation that are individually much larger. Comparison of mineral concentrations adjacent to the fault before-and-after instability revealed that the development of shear failure also promotes the transport of reactivated minerals into the fault zone. Among them, feldspar changes most significantly in later stages, dominated by dissolution with the volume fraction decreasing by 80% and increasing the aqueous concentration of K+ by approximately an order of magnitude. However, secondary minerals counter this dissolution through precipitation with the volume fraction of kaolinite increasing by an order of magnitude compared with the original fraction. Finally, the evolution of the fault sealing coefficient (FS) demonstrates that the porosity and permeability exert a pivotal influence in controlling the self-sealing behavior in the basal of the fault, while the upper fault layer exhibits self-enhancing response. A notable observation is that changes in mineral ion concentrations in fault zones could be applied as a significant diagnostic signal to monitor fault stability and the potential for progress of self-sealing behavior.

Ferrous Iron (Fe+2) Released From Iron‐Rich Chlorite as a Reductant for Unconformity‐Related Uranium Mineralization: Insights From Reactive Fluid Flow Modeling

AbstractDebate continues over the reducing mechanisms for the formation of unconformity‐related uranium (URU) deposits. This paper evaluates, for the first time, the potential of iron‐rich chlorite as a reductant for uranium mineralization using reactive fluid flow modeling method. Our results confirm that Fe2+, released from the breakdown of iron‐rich chlorite, can reduce aqueous hexavalent uranium to precipitate economically significant URU deposits similar in size and grade to those formed with CH4 as the reducing agent. The resulting uranium mineralization tends to occur in the basement and below the downwelling parts of overlying basinal fluid circulation cells, where oxidizing basinal fluid percolates across the unconformity and reacts with upward flowing reducing basement brine. Therefore, the basinal fluid circulation pattern controlled by the permeability of the sandstone aquifer is critical in determining the formation and distribution of URU deposits. When the sandstone layer is more permeable, the simulated uranium deposits become larger in size, and vice versa. If the sandstone permeability is <5 × 10−14 m2, no obvious uranium deposits can be formed. In contrast, the permeability of fault zones does not have a significant effect on uranium mineralization, although it does affect fluid flow behaviors within the fault zone itself. We also demonstrate that fault zones do not appear to be a prerequisite for the formation of URU deposits when Fe+2 serves as a reductant, which highlights important exploration implications. Uranium exploration should, in addition to continuing to target graphitic fault zones, also consider areas where faults and/or graphite units do not exist.

A Study of Lineament Density and Correlation Residual Gravity Anomalies to Identify Pacul Fault in Mount Pandan, East Java

Abstract This study analyzes the identified Pacul Fault using lineament density and residual gravity anomalies in Mount Pandan, East Java. The study utilizes DEMNAS data, geological data, and gravity satellites. The research process includes creating hill shades from DEM data, extracting lineaments using PCI Geomatica software, and interpolating data to create a lineament density map. Further analysis correlates lineament density and residual anomaly with the fault zone around the Pacul Fault. The results show that fault zones are located in areas with moderate to high lineament density and at anomaly contrast from residual anomaly. The complete Bouguer anomaly map indicates low anomalies likely representing fault planes. This study confirms a positive correlation between lineament density and contrast anomaly according to the pacul fault presence of Mount Pandan.

A novel reverse and forward directional relaying scheme in six phase overhead transmission lines using adaptive neuro-fuzzy inference system

Recent power system is structurally difficult and is vulnerable to undesirable conditions like transmission faults. In this event of transmission line faults, exact fault zone detection enhances the restoration process, thus improving reliability of the complete power system. In order to solve the above problem, this paper presents an adaptive neuro-fuzzy inference system (ANFIS) based fault zone detector, which combines artificial neural network (ANN) and fuzzy logic technique (FLT) in six phase overhead transmission lines (SPOTL). To overcome the limitation of ANN and fuzzy expert system (FES) architectures and, the selection work has been formulated as an optimization method and solved using ANFIS. The inputs are the zero sequence component currents at the middle bus of the transmission line. The training data are extracted using discrete Fourier transform and collected, and then ANFIS is trained to identify the fault zone. The ANFIS based scheme reach setting has been checked for various types of faults, with a wide range of faults and transmission line parameters. Simulation study ensure that this method has a high reach setting, does not require the design of communication channel. Further, the ANFIS study shows that ANFIS is suitable for all type of faults. The ANFIS significantly outperforms other techniques proposed in the literature in terms of various evaluation metrics.

Optimization of GGMplus Gravity Data to Identify Sumatran Faults Segments in Kaba Stratovolcano, Bengkulu, Revealed by FHD and SVD Techniques

Abstract Kaba volcano is a perilous and currently active volcanic site located near the Sumatran fault, specifically within the Kepahiyang region of Bengkulu. Given the intricate nature of its location, it is crucial to monitor the local fault zone activity in the vicinity of the Kaba volcano. meanwhile, these fault zones are typically associated with high permeability areas and are characterized by high-density contrasts. Therefore, we applied First Horizontal Derivative (FHD) and Second Vertical Derivative (SVD) methods to identify the presence of the Musi Kepahiyang segment in Bengkulu, using GGMplus high resolution gravity data. Based on the results of the FHD analysis, clear gravity anomalies are observed along the northwest (NW) and southeast (SE) regions of Kepahiyang, with Bouguer anomaly values reaching 800 mGal. The discernible patterns unveiled through FHD analysis distinctly delineate the Musi fault (NW), Kepahiyang fault (SW), and Garba fault, unveiling a rich tapestry of tectonic activity surrounding the Kepahiyang area in Bengkulu. Complementing these findings, SVD analysis reveals a consistent anomaly distribution, albeit with marginally diminished Bouguer anomaly values, affirming the robustness of the detected features. Through the fusion of FHD and SVD methodologies, our study offers an understanding of the structural complexities pervading the segment in Kaba Stratovolcano, shedding light on its dynamic geological evolution, and fortifying our comprehension of fault dynamics in the Sumatra region.

Luwuk Banggai Geoheritage: A Story about the Collision and Obduction of the Banggai Microcontinent

Abstract Various publications have discussed the geological uniqueness of Banggai-Sula in numerous scientific papers. This interest increased particularly after the discovery of petroleum in the area, making it the only oil field operating on Sulawesi Island. In this region, a rather rare geological phenomenon occurs: obduction, which has brought ophiolite rocks from the eastern arm of Sulawesi (East Sulawesi Ophiolite belt) into collision with the Banggai-Sula microcontinent. This obduction process has resulted in various rock exposures related to the formation of the Luwuk landmass, the presence of nickel minerals, and the emergence of petroleum. The local government of Luwuk Regency then proposed to designate this area as a geopark with the aim of conserving its various rock exposures, developing earth science-based education, and empowering the community through tourism enhancement. Based on field observations, there are three geosites related to ophiolites, two geosites related to the Banggai-Sula microcontinent, two geosites related to post-collision sedimentation, and two geosites related to obduction and fault zones that will be proposed as geoheritage sites. All of these sites are located in areas with good access, beautiful views, and highly unique exposures. They could all become attractive locations for conservation, study, and development into tourist destinations.

Evaluating karst features and geological fault leakage risks based on geophysical method in Dongzhuang reservoir area, Shaanxi

Leakage along faults, particularly in karst area faults, is a critical concern that can prevent impounding a reservoir. The Laolong Mountain fault in the Dongzhuang Reservoir Project Area in Shaanxi Province, China, is a large fault that may impede the project. To assess whether concentrated leakage can occur along this fault, we used a comprehensive approach involving footrill exploration, an electromagnetic method, optical imaging techniques, water pressure testing, and large-scale groundwater tracer tests. Footrill exploration results revealed that the karst features predominantly comprise karst cavities with some fissures and karst caves. These formations are typically clustered along fractures with a linear joint density of 0.4–1.5 joints/m. The linear karst rate was 0.39 %, and the karst cavities have small diameters of only a few centimeters and depths not exceeding 15 cm. A geophysical exploration indicated that low resistivity values (approximately 200 Ω·m) on the north side of the fault zone's hanging wall, with the lowest values being approximately 100 Ω·m. The fault's footwall was noted to have higher resistivity (approximately 2000 Ω·m). The rock properties on either side of the fault zone differ considerably. The upper plate of the fault (downstream of the river) has high-resistance carbonate rock formations with a well-preserved structure, whereas the lower plate (upstream of the river) comprises low-resistance sandstone and mudstone formations with notable fragmentation at the fault's surface compression zone. Tracer tests indicated an eastward groundwater flow from Zuantian Ridge toward the Jing River in the west. The results suggest that eastward leakage along the Laolong Mountain fault and its influence zone is unlikely upon reservoir impoundment. The geophysical exploration method in this study integrated and cross-validated the footrill exploration, hydrological test, groundwater tracing, optical imaging, and other methods; it can thus serve as a reference for future research.

A three-dimensional visualization experimental apparatus for seepage failure of filling medium in the fault zone: Development and application

A three-dimensional visualization experimental apparatus for seepage failure of filling medium in the fault zone: Development and application

Imaging the Devene fault system beneath the Iskar floodplain in Bulgaria through shallow electrical resistivity profiling

We studied the Nivyanin fault segment from the Devene fault system in NW Bulgaria, using shallow electrical resistivity profiling. The measured profile was located on the Iskar floodplain near Chomakovtsi village and crossed a lineament that connects the northernmost exposures of Upper Cretaceous limestone and Miocene conglomerate on elevated surfaces in which the Iskar valley was incised. The results suggest that the studied fault segment was a strike-slip fault that was active after the deposition during the Miocene. The fault zone is broad over 100 m and consists of sub-vertical fractures and breccia. Vertical fault displacement did not affect the Quaternary fluvial deposit.

Source Analysis of April 2, 2023, Magnitude 5.6 Flores Sea Earthquake North of Bima, Sumbawa, Indonesia

Abstract The seismotectonic setting and the potential of significant earthquakes from the Flores Sea region in eastern Indonesia are not well understood. On April 2, 2023, a magnitude 5.6 earthquake occurred north of Bima (Sumbawa), specifically under the Flores Sea. This area has a complex tectonic setting with a Flores back-arc thrust and some local active faults. Our study aims to analyze the source mechanism of this earthquake using moment tensor inversion and hypocenter relocation methods. We utilized five (5) three-component regional BMKG seismic stations for the moment tensor inversion and analyzed aftershocks within one month following the main event for hypocenter relocation purposes. Our findings indicate that the earthquake was generated by an unidentified fault segment with a strike-slip mechanism, either an N/NW-S/SE west-dipping fault segment or an E-W north-dipping fault segment. Through hypocenter relocation, we found that aftershocks were oriented directly to the N/NW-S/SW north of the Flores Thrust fault zone. We interpreted that this earthquake was not directly associated with the activity of the Flores Thrust system. This study can help update our understanding of the active fault system around the Flores Sea and as a constraint to support seismic hazard mitigation.