Tectonic Faults Research Articles

Geologic structure and origin of the Zadlog karst polje

In the wider Idrija area in western Slovenia, several large plains formed along the thrusts within the dolomite and at the contact of dolomite and limestone. The purpose of this paper is to present the detailed structural-geological background of one such plain, namely the Zadlog plain, and based on these findings, to provide new starting points for analyzing the genetic conditions of other karst poljes in Notranjska. The Zadloško polje was formed in a wider near-fault crushed zone at the contact of two structural units within the Upper Triassic Norian-Rhaetian dolomite, with the thrust crossing the polje in its central part. The initially lowered area at the thrust represented a morphological basis, and the crushed zones in the dolomite played a hydrological retention role inducing the stagnation of surface water and, as a result, the formation of the karst polje. Younger fault tectonics then established efficient drainage of surface water and the erosion of sediments to the karst underground. Besdies this, slope equilibration leads us to conclude that the karst polje capability of hydrologic retention is recently decreased. The example of Zadloško polje shows that the thrust structures and associated hydrological conditions are the key elements for the formation of karst poljes in the dissected karst surface. Further detailed structural-geological mapping will reveal whether similar structural-geological conditions are the basis for the formation of other karst poljes in the region.

Optimal Routing of Gas Pipelines in Seismic Regions Using an Efficient Decision-Support Tool: A Case Study in Northern Greece

High-pressure gas pipelines are significantly vulnerable to earthquake-related geohazards (tectonic faulting, slope instabilities, and/or soil liquefaction phenomena). Avoiding geohazardous areas is not always techno-economically feasible, as it would increase the length and cost of the infrastructure. Conversely, crossing these areas may adversely affect the structural performance of the pipeline, leading to unfeasible mitigation measures. Thus, selecting cost-effective, safe, and resilient routing is crucial. This study presents a GIS-based decision-support tool for optimal routing, taking into account, among other criteria, earthquake-related geohazards. The proposed tool considers not only the aforementioned but also more complex earthquake-related geohazards, such as secondary fault ruptures that are non-parallel or even perpendicular to the main fault, which might have been overlooked during the design of existing pipelines. To validate its effectiveness, the present tool is applied in a real case study in northern Greece, where the aforementioned earthquake-related geohazards coexist. Through a GIS-based multi-criteria decision method, various scenarios are examined by assigning different weights to the adopted criteria, and several cost-minimized routes are derived. This tool could be highly beneficial for the pipeline industry since it can assist operators and stakeholders in selecting the optimal pipeline route in geohazardous areas.

Modeling of Stress-Strain State and Coseismic Effects of Epicentral Zone of Tangshan Earthquake (Southeastern China)

The paper presents the results of numerical modeling and analysis of stress-strain state of the epicentral zone of the strong earthquake in the north-east of China, which occurred on 27.07.1976 with Ms=7.8. Many present-day works continue to discuss the reasons for such a strong earthquake, which occurred in tectonic conditions ‒ far from interplate boundaries, inside the Tangshan tectonic block bounded by tectonic faults. However, published new geodynamic, seismological, geophysical and geodetic data provide confidence in the determining role of fault tectonics in this region. Based on the analysis of the results of modeling of the stress-strain state preceding the Tangshan earthquake with coseismic geophysical and geodetic data, we propose a model of earthquake rupture formation. The results of comparison of independent estimates of shear stresses with the results of modeling in the sources of strong earthquakes suggest that the areas of tectonic stress concentration are localized in the interfault rupture of the Tangshan fault, reaching maximum values at the termination of fault ruptures σi ≈ 50 MPa и τxy ≈ 20 MPa. The hypocenter of the main seismic event (taking into account the error of coordinate determination) is located in the region of stress intensity 35‒50 MPa and the ratio of main stresses σxx/σyy ≈ 8–10. It should be expected that these zones are the starting site of rupture, the extent of which depends on the amount of accumulated elastic potential energy of tectonic stresses in the adjacent region. For the Tangshan earthquake, this area corresponds to a high intensity of stresses exceeding 30 MPa in a band with a length more than 30 km and a width reaching 4.5 km.

Research on the Influence of Fault Structure on Physical and Chemical Structure of Coking Coal During Spontaneous Combustion

ABSTRACT The spontaneous combustion tendency and oxidation combustion properties of coking coal in fault fracture zone and primary coking coal are different. Accordingly, this study uses Thermogravimetric analysis, in-situ Fourier transform infrared spectroscopy, Scanning electron microscope, low-temperature N2 adsorption and Electron spin resonance techniques were used to study the difference of macroscopic and microscopic structural characteristics between coking coal and primary coking coal in fault fracture zone. The results show that: The oxygen absorption capacity of coking coal in fault fracture zone is enhanced and the thermogravimetric characteristic temperature is advanced, and the ignition point temperature is advanced by 5.36°C; the maximum weight loss temperature of coking coal in fault fracture zone is 3.32°C lower than that of primary coking coal. The apparent activation energy of coking coal in oxidation stage and pyrolytic combustion stage decreased by 4.88 and 5.03 kJ/mol, respectively. Compared with primary coking coal, the pore structure of coking coal in fault fracture zone is more complex, which increases the roughness of coal surface and is conducive to oxygen adsorption. In addition, fault tectonics promotes the separation and cracking of oxygen-containing functional groups into small molecules, and the polycondensation of aliphatic hydrocarbon structure promotes the formation of active free radicals, thus promoting spontaneous combustion. This study provides an important reference and theoretical support for further understanding of the structural evolution and oxidation kinetics of highly metamorphic coking coal induced by fault tectonics, which is helpful for fire prevention and control in fault structure-developed mining areas and safe production of coal industry.

Tectonic Control of Aseismic Creep and Potential for Induced Seismicity Along the West Valley Fault in Southeastern Metro Manila, Philippines

Vertical creep along 15 ground ruptures within a 15 km long and 1.5 km wide zone has been occurring along the southeastern part of Metro Manila. Though the unusually high rates of vertical slip point to excessive groundwater withdrawal as the trigger, the evidence presented herein indicates that these may not be simple irregular subsidence fissures. Tectonic control of creep along these traces is suggested by the following: the occurrence of some of these ground ruptures along pre-existing scarps that coincide with topographic and lithologic boundaries, the left-stepping en echelon pattern of surface rupturing, and the distribution of the creeping zone within the dilational gap of the dextral strike-slip West Valley Fault (WVF). Furthermore, interpretation of an exposure across one of the creeping faults indicates reactivation by creep of a pre-existing tectonic fault zone. The paleoseismic evidence also suggests that the pre-creep slips are coseismic and dominantly strike-slip. Recognizing the occurrence of coseismic slip preceding aseismic creep is a primary consideration in assessing the potential of the WVF’s creeping segment and its adjacent segments in generating earthquakes. Tighter groundwater extraction regulations may be necessary to avoid exacerbating the effects of vertical ground deformation and the occurrence of induced seismicity.

საქართველოს რელიეფის მორფოსტრუქტურული ანალიზი

As a result of the morphostructural analysis of the relief of Georgia, a scheme of tectonic faults has been compiled, the validity of which has been reinforced by the study of space materials. The faults represent straight-line structures and create an orthogonal diagonal system grid. The scheme explains the morphology of many geological structures and geological outcrops, as well as the peculiarities of the location of mineral deposits.

Seasonal slow slip in landslides as a window into the frictional rheology of creeping shear zones.

Whether Earth materials exhibit frictional creep or catastrophic failure is a crucial but unresolved problem in predicting landslide and earthquake hazards. Here, we show that field-scale observations of sliding velocity and pore water pressure at two creeping landslides are explained by velocity-strengthening friction, in close agreement with laboratory measurements on similar materials. This suggests that the rate-strengthening friction commonly measured in clay-rich materials may govern episodic slow slip in landslides, in addition to tectonic faults. Further, our results show more generally that transient slow slip can arise in velocity-strengthening materials from modulation of effective normal stress through pore pressure fluctuations. This challenges the idea that episodic slow slip requires a narrow range of transitional frictional properties near the stability threshold, or pore pressure feedbacks operating on initially unstable frictional slip.

Topographic metrics for unveiling fault segmentation and tectono-geomorphic evolution with insights into the impact of inherited topography, Ulsan Fault Zone, South Korea

Abstract. Quantifying today's topography can provide insights into landscape evolution and its controls, since present topography represents a cumulative expression of past and present surface processes. The Ulsan Fault Zone (UFZ) is an active fault zone on the southeastern Korean Peninsula that was reactivated as a reverse fault around 5 Ma. The UFZ strikes NNW–SSE and dips eastward. This study investigates the relative tectonic activity along the UFZ and the landscape evolution of the hanging-wall side of the UFZ, focusing on neotectonic perturbations using 10Be-derived catchment-averaged denudation rates and bedrock incision rates, topographic metrics, and a landscape evolution model. Five geological segments were identified along the fault, based on their relative tectonic activity and fault geometry. We simulated four cases of landscape evolution to investigate the geomorphic processes and accompanying topographic changes in the study area in response to fault movement. Model results reveal that the geomorphic processes and the patterns of topographic metrics (e.g., χ anomalies) depend on inherited topography (i.e., the topography that existed prior to reverse fault reactivation of the UFZ). On the basis of this important model finding and additional topographic metrics, we interpret the tectono-geomorphic history of the study area as follows: (1) the northern part of the UFZ has been in a transient state and is in topographic and geometric disequilibrium, so this segment underwent asymmetric uplift (westward tilting) prior to reverse faulting on the UFZ around 5 Ma, and (2) its southern part was negligibly influenced by the asymmetric uplift before reverse faulting. Our study demonstrates the utility of topographic metrics as reliable criteria for resolving fault segments. Together with landscape evolution modeling, topographic metrics provide powerful tools for examining the influence of inherited topography on present topography and for the elucidation of tectono-geomorphic histories.

Fractal Characterization on Three-Dimensional Tortuosity of Fault Tectonic

Faults, as a kind of fracture tectonics, play a role in reservoir closure or provide oil and gas transportation channels. The accurate understanding of the distribution characteristics of faults is significant for oil and gas exploration. The traditional fractal dimension for fault number (Df3) cannot comprehensively characterize the complexity and heterogeneity of fault network distribution. In this paper, a fractal characterization method on three-dimensional (3D) tortuosity of fault tectonics is proposed based on 3D seismic exploration. The methodology is described in detail to establish the model on the fractal dimension for the 3D tortuosity of fault tectonics. The results show the proposed method of estimation of the DT3 displaying high accuracy and rationality. Compared with the traditional fractal dimension Df3, the proposed DT3 can comprehensively characterize the fractal characteristics of faults network systems in the 3D space. This study achieves a breakthrough in the fractal characterization of the 3D tortuosity of fault tectonics. It is worth further study for establishing an analytical fractal equation based on the DT3 and oil or gas transfer, which can provide the theoretical foundation and technical support for oil and gas exploration.

Disaster Mitigation Training for Disaster Preparedness Groups in Batang Arau Village, South Padang Sub-District, Padang City

Indonesia is a disaster-prone region because it is located in the Ring of Fire and at the confluence of four tectonic plate faults: the Eurasian, Indo-Australian, Philippine Sea, and Pacific plates. A disaster is an event that cannot be predicted in terms of its arrival and impact but can be reduced in terms of risk. Community preparedness related to disasters needs to be improved because of the risk of disasters that can threaten the lives and livelihoods of people affected by disasters. Padang City is one of the coastal areas in West Sumatra Province with the risk of disasters such as earthquakes, tsunamis, and landslides because one of the factors is its geographical condition, which is located in a potential natural disaster area. Therefore, preparedness training is needed to help people who live in disaster-prone areas cope with and reduce disaster risks. This disaster preparedness and mitigation training was held on 8 November 2023 at the Batang Arau Village Office, Padang Selatan District, Padang City. The conclusion obtained after the implementation of this activity is the community's insight into the importance of being prepared and mitigating disasters that have the potential to occur in residential areas.

Event classification, seismicity, and eruption forecasting at Great Sitkin Volcano, Alaska: 1999–2023

The frequency content of volcanogenic seismicity is often used to classify events and their spatial and temporal progression is then used to map subsurface volcanic processes. The progression of volcano-seismic events and associated source processes also plays a critical role in eruption forecasting. Here we develop and evaluate a computerized methodology for characterizing volcano-seismic event types using Frequency Index and Average Peak Frequency. We apply and test this technique at Great Sitkin Volcano, Alaska, classifying over 9000 hypocenters between 1999 and 2023. This 24-year time span covers periods of seismic quiescence, earthquake activity on nearby tectonic (bookshelf) faults, precursory unrest from 2016 to 2021, and the explosive onset in May 2021 of the ongoing effusive eruption. We use the spatial and temporal evolution of classified event types to map the active volcanic and tectonic processes, develop a conceptual model of the subsurface magmatic system, and perform a retrospective analysis of eruption forecasts at Great Sitkin Volcano between 2016 and the present. The classification and progression of hypocenters suggests the subsurface Great Sitkin Volcano magmatic system consists of a mid- to lower- crustal source zone between 10 and 40 km depth and an upper crustal magma storage area between −1 and 10 km depth (hypocenter depth is referenced to sea level and negative depths reflect height above sea level). The earliest precursors occurred in July 2016 and consisted of deep long-period and volcano-tectonic earthquakes at mid-crustal depths suggesting the subsequent unrest and eruption were triggered by a deeper intrusion of magma. This mid-crustal seismic activity was immediately followed by the onset upper-crustal long-period events and volcano-tectonic earthquakes VTs suggesting a strong linkage between the shallow and deeper portions of the magmatic system. The upper crustal area was likely capped by the 1974 lava dome until the magmatic explosion on May 26, 2021.

Research on the prevention and manage of rockburst in deep‐seam mining roadways

AbstractThis study presents a strategy for preventing and controlling rockbursts in deep and vast seams during the mining operation. We analyzed the main factors influencing rockburst by combining the geological structure of the rock mass with field‐collected microseismic monitoring data. Determined the disturbance strain sensitive threshold through mechanical experiments on coal's antidisturbance characteristics, the indoor pull‐out test of the supporting bolt was carried out. Studied the rockburst support technology and the antirockburst capability of the support system based on the energy method. The key governing variables of regional impact risk in the big buried deep coal seam operating face include high tectonic stress, goaf effect, fault, and fault protection coal pillar. The uniaxial compressive strength of the coal sample in the 3308 working face is 15.11 MPa, the antidisturbance strength is 10 MPa. When the extreme stress is 86.03%, the specimen fails; the ultimate failure strength under disturbance is 13 MPa. The support system's antishock ability is analyzed based on its energy absorption, under the premise of ensuring the support quality and support strength, the antiscour ability of 3308 Tailentry support meets the anti‐impact requirements. It is believed that the system offers adequate lateral confining pressure for the internal creep disturbance‐sensitive area, enhancing the area's resistance to disturbance. This is crucial in preventing and managing rockburst incidents.

Unraveling the link between magma and deformation during slow seafloor spreading

Detachment faulting related to oceanic core complexes (OCCs) has been suggested to be a manifestation of slow seafloor spreading. Although numerical models suggest OCCs form under low magma supply, the specific interaction between magmatism and tectonic faulting remains elusive. This paper examines seismic observations detailing the spatiotemporal interactions between magmatism, high-angle faulting, and detachment faulting at a slow-spreading mid-ocean ridge in the West Philippine Basin. We identified a magma-rich spreading phase, indicated by a magmatic top basement and oceanic crust with shallow-penetrating high-angle normal faults. An axial valley reveals an along-strike transition from magmatically-dominated to highly tectonized oceanic crust over a distance of 70 km. Two older OCCs with concave-down fault geometries and a younger OCC with steep-dipping faulting suggest sequential detachments with the same polarity. Our findings suggest: (1) slow seafloor spreading alternates between high-angle faulting with a relatively high magma supply and detachment faulting with a limited magma supply; (2) sequential development of younger detachments in the footwall of its predecessor leads to an asymmetric split in the newly accreted crust; and (3) the life cycle of OCC ends with high-angle faults that overprint the detachment and act as magma pathways, sealing the OCC. Our study captures the dynamic interaction between high-angle and detachment faults and their concurrent and subsequent relationship to magmatic systems. This reveals that strain distribution along strike is critical to OCC formation, thus enriching our understanding beyond conventional considerations such as spreading rates and melt budgets at mid-ocean ridges.

Research advances on the mechanisms of reservoir formation and hydrocarbon accumulation and the oil and gas development methods of deep and ultra-deep marine carbonates

Based on the new data of drilling, seismic, logging, test and experiments, the key scientific problems in reservoir formation, hydrocarbon accumulation and efficient oil and gas development methods of deep and ultra-deep marine carbonate strata in the central and western superimposed basin in China have been continuously studied. (1) The fault-controlled carbonate reservoir and the ancient dolomite reservoir are two important types of reservoirs in the deep and ultra-deep marine carbonates. According to the formation origin, the large-scale fault-controlled reservoir can be further divided into three types: fracture-cavity reservoir formed by tectonic rupture, fault and fluid-controlled reservoir, and shoal and mound reservoir modified by fault and fluid. The Sinian microbial dolomites are developed in the aragonite-dolomite sea. The predominant mound-shoal facies, early dolomitization and dissolution, acidic fluid environment, anhydrite capping and overpressure are the key factors for the formation and preservation of high-quality dolomite reservoirs. (2) The organic-rich shale of the marine carbonate strata in the superimposed basins of central and western China are mainly developed in the sedimentary environments of deep-water shelf of passive continental margin and carbonate ramp. The tectonic-thermal system is the important factor controlling the hydrocarbon phase in deep and ultra-deep reservoirs, and the reformed dynamic field controls oil and gas accumulation and distribution in deep and ultra-deep marine carbonates. (3) During the development of high-sulfur gas fields such as Puguang, sulfur precipitation blocks the wellbore. The application of sulfur solvent combined with coiled tubing has a significant effect on removing sulfur blockage. The integrated technology of dual-medium modeling and numerical simulation based on sedimentary simulation can accurately characterize the spatial distribution and changes of the water invasion front. Afterward, water control strategies for the entire life cycle of gas wells are proposed, including flow rate management, water drainage and plugging. (4) In the development of ultra-deep fault-controlled fractured-cavity reservoirs, well production declines rapidly due to the permeability reduction, which is a consequence of reservoir stress-sensitivity. The rapid phase change in condensate gas reservoir and pressure decline significantly affect the recovery of condensate oil. Innovative development methods such as gravity drive through water and natural gas injection, and natural gas drive through top injection and bottom production for ultra-deep fault-controlled condensate gas reservoirs are proposed. By adopting the hierarchical geological modeling and the fluid-solid-thermal coupled numerical simulation, the accuracy of producing performance prediction in oil and gas reservoirs has been effectively improved.

Spatial variation of the source mechanisms in the Egyptian continental margin

The spatial variability of the focal mechanism solutions in the NW Egypt Cyrenaica and Levant-north Egypt domains of the Egyptian Continental margin is investigated based on the polarity of the P-wave first motions of eleven earthquakes with local magnitudes ML ranging from 4.2 to 6.2. The identified focal mechanism solutions in the Levant-north Egypt domain are evaluated in two sub-provinces with different geological settings. The first sub-province shows strike-slip faulting mechanisms with right-lateral motion along the NE-trending Rosetta-Qattara fault zone, while the NW-trending Temsah fault zone produces left-lateral strike-slip motion. The inland extension of the Rosetta-Qattara fault zone towards the Western Desert reflects the same sense of motion. Strike-slip faulting with thrust components dominates the focal mechanisms in the second sub-province but with a different stress orientation. A single thrust faulting mechanism event which occurred on the periphery of the continental shelf shows the same common orientation of the stress field at the Hellenic Arc. This type of mechanism in this locality can be explained by the mean of compressional stress transfer towards the coast generated by the accelerated southwest retreat of the Hellenic Trench. The complex regional stress along the Cyprian and Hellenic arcs, the current local structure features, and the dominant orientation of the pre-existing fault are the factors that contribute to the changeable stress pattern field in the Levant-north Egypt domain. A single event in the second domain, the NW Egypt Cyrenaica, is a strike-slip with a right-lateral sense of motion on a WNW-oriented plane, consistent with motion along the WNW tectonic fault which separates the continental shelf from the oceanic crust.

Geomechanical risk assessment for CO2 storage in deep saline aquifers

We study CO2 injection into a saline aquifer intersected by a tectonic fault using a coupled modeling approach to evaluate potential geomechanical risks. The simulation approach integrates the reservoir and mechanical simulators through a data transfer algorithm. MUFITS simulates non-isothermal multiphase flow in the reservoir, while FLAC3D calculates its mechanical equilibrium state. We accurately describe the tectonic fault, which consists of damage and core zones, and derive novel analytical closure relations governing the permeability alteration in the fault zone. We estimate the permeability of the activated fracture network in the damage zone and calculate the permeability of the main crack in the fault core, which opens on asperities due to slip. The coupled model is applied to simulate CO2 injection into synthetic and realistic reservoirs. In the synthetic reservoir model, we examine the impact of formation depth and initial tectonic stresses on geomechanical risks. Pronounced tectonic stresses lead to inelastic deformations in the fault zone. Regardless of the magnitude of tectonic stress, slip along the fault plane occurs, and the main crack in the fault core opens on asperities, causing CO2 leakage out of the storage aquifer. In the realistic reservoir model, we demonstrate that sufficiently high bottomhole pressure induces plastic deformations in the near-wellbore zone, interpreted as rock fracturing, without slippage along the fault plane. We perform a sensitivity analysis of the coupled model, varying the mechanical and flow properties of the storage layers and fault zone to assess fault stability and associated geomechanical risks.

Populations of the stygobiotic amphipod Palearcticarellus pusillus (Martynov, 1930) maintain genetic connectivity between the mountain springs and the deep bottom habitats of Lake Teletskoye (Altai Mountains, Russia)

The diversity of underground fauna is often associated with the presence of karst areas, which have extensive underground cavities and connecting channels. Non-karst areas, however, make up a larger portion of the planet’ surface, and our understanding of the distribution and dispersal abilities of underground fauna in these areas currently remains limited. During a recent study of the diversity of stygobiotic crustaceans in the mountain streams of the Kurai Mountain Range (Altai, Russia), a small-sized species of crangonyctid amphipod, Palearcticarellus pusillus (Crustacea, Amphipoda, Crangonyctidae) was found in high-altitude springs. This species has been previously known only from deep-water habitats in Lake Teletskoye, and molecular genetic analysis revealed that these amphipods maintain genetic connections between the springs and bottom lake habitats. We assume that individuals of this certainly stygobiotic species fall to the bottom of the lake as a result of leaching from tectonic faults connecting these habitats and are not permanent inhabitants of the lake bottom. This hypothesis also suggests that the very small body size of these animals may be related to the narrow crevices and pores of the tectonic faults, rather than neoteny, as it has been previously suggested. The estimated divergence time calculation has also revealed that P. pusillus obviously diverged from its sister species, Palearcticarellus mikhaili from valley springs in Kurai Steppe, ~5 Ma, at the beginning of the Pliocene, possibly due to the uplifting of the Kurai Mountain Range. Subsequent speciation occurred as a result of secondary tectonic activity and changes in groundwater flow, likely during the Pleistocene, approximately 2.7–0.7 Ma. Populations that were isolated for a long time continue to live near mountain springs in the study area.

PROSPECTS FOR THE DEVELOPMENT OF THE SHEBELYN GAS CONDENSATE FIELD

The paper provides a brief geological and industrial characterization of the Shebelinsky gas-condensate field, including the height of the gas-bearing layer, the area of gas occurrence, porosity, permeability of collectors, effective gas-saturated thickness of the coppery sandstones, and araucarite strata. The peculiarity of the deposits lies in the low permeability and gas saturation, deterioration of collector properties of productive reservoirs from the lower to the upper and from the central to the peripheral part of the deposit. A structural map of the cover of coppery sandstones and a map of water saturation of all productive horizons are presented. The dynamics of gas reserves and reservoir pressures of the field over the years are shown, along with the authors; forecasts for their future dynamics. Calculations of the volumes of water saturation of horizons and the total volume of reservoir water that has invaded the gas-bearing part of the field have been conducted. An analysis of water saturation and its future prospects has been carried out. Statistical calculations of the dependence of water saturation volumes on time and reservoir pressure have been performed, indicating a decrease in the rates of water saturation at the late stage of field development. A geological section of the Shebelinsky field is presented, indicating the possibility of gas migration through tectonic faults. All factors influencing the maintenance of reservoir pressure within the deposit have been analyzed, including: contour water flooding; surface subsidence; internal waterdrive regime; the elasticity of rock formations, gas, and It is shown that drilling 12 deep wells within the Shebelinsky field did not reveal new deposits or caps but confirmed the presence of gas saturation to a depth of 5.5 thousand meters. The analysis of field development indicates a balance between gas production and its migration from deep horizons as of the year 2023. Approved development indicators and author’s options are provided, supported by actual field development. The conclusion is drawn that, due to migration with a volume of production of 1700– 1900 million m3, the field will operate for another 100 years.

Strong controlling effect of stress evolution on the 2022 Ms5.0 Honghe earthquake sequence

Understanding stress evolution patterns as a response to earthquake ruptures at geologically complex tectonic faults is vital because of the role of fault geometry as a source for the stress evolutionary constraints. Here, we analyze the 2022 Ms5.0 Honghe earthquake sequence and calculate the tectonic stress distribution of the two Ms. ≥ 3.5 earthquakes in this sequence. Results indicate that the focal mechanism type of the sequence obtained corresponds to strike-slip motion with an ESE-oriented strike and a steeply dipping NE-oriented nodal plane. The focal region is subjected to NNW-oriented horizontal compression and ENE-oriented horizontal tension. We find that the adjacent Ailaoshan fault constituted the major seismogenic fault of the mainshock and the regional stress field exerted a strong controlling effect on the associated postseismic events. Our results suggest that the stabilization of tectonic faults may help to enhance the effects of stress accumulation on the occurrence of medium-to-strong earthquakes.

A strainmeter array as the fulcrum of novel observatory sites along the Alto Tiberina Near Fault Observatory

Abstract. Fault slip is a complex natural phenomenon involving multiple spatiotemporal scales from seconds to days to weeks. To understand the physical and chemical processes responsible for the full fault slip spectrum, a multidisciplinary approach is highly recommended. The Near Fault Observatories (NFOs) aim at providing high-precision and spatiotemporally dense multidisciplinary near-fault data, enabling the generation of new original observations and innovative scientific products. The Alto Tiberina Near Fault Observatory is a permanent monitoring infrastructure established around the Alto Tiberina fault (ATF), a 60 km long low-angle normal fault (mean dip 20°), located along a sector of the Northern Apennines (central Italy) undergoing an extension at a rate of about 3 mm yr−1. The presence of repeating earthquakes on the ATF and a steep gradient in crustal velocities measured across the ATF by GNSS stations suggest large and deep (5–12 km) portions of the ATF undergoing aseismic creep. Both laboratory and theoretical studies indicate that any given patch of a fault can creep, nucleate slow earthquakes, and host large earthquakes, as also documented in nature for certain ruptures (e.g., Iquique in 2014, Tōhoku in 2011, and Parkfield in 2004). Nonetheless, how a fault patch switches from one mode of slip to another, as well as the interaction between creep, slow slip, and regular earthquakes, is still poorly documented by near-field observation. With the strainmeter array along the Alto Tiberina fault system (STAR) project, we build a series of six geophysical observatory sites consisting of 80–160 m deep vertical boreholes instrumented with strainmeters and seismometers as well as meteorological and GNSS antennas and additional seismometers at the surface. By covering the portions of the ATF that exhibits repeated earthquakes at shallow depth (above 4 km) with these new observatory sites, we aim to collect unique open-access data to answer fundamental questions about the relationship between creep, slow slip, dynamic earthquake rupture, and tectonic faulting.