Inactive Fault Research Articles

Stratigraphic and Structural Features of The Sinop Basin Close to The Mid Black Sea Ridge Using Multi-Channel Seismic and Multi-Beam Bathymetric Data

Focal mechanism solutions of the earthquakes that occurred in the Black Sea in the last 100 years show that thrust and strike-slip faults are predominantly active in the region. One of these clusters is developing off the coast of Samsun where the submarine Sinop basin is located. In order to investigate the seismic sources of earthquakes in this area, high-resolution multi-channel seismic sections and multi-beam bathymetric data were processed and evaluated. The oldest seismic stratigrafic units (U4) is referred to as acoustic basement with wavy reflectors, while its top is marked by high amplitude reflection indicating an unconformity. This uniconformity is overlain by parallel or less parallel Unit 3 deposits. Upper surface of Unit 2 is marked by an erosional surface which is overlain by the parallel reflector of Unit 1. Unit 1 is the youngest sediments and truncated by Yeşilırmak canyon. Three fault types of different ages were determined. The oldest fault could reach only top of unit 4 has been interpreted as inactive fault. Faults that border the Sinop basin and reach the sea floor by cutting all seismic units are considered in the active fault class. However, the faults that remain within Unit 1 and do not reach the seafloor are considered as faults that are coeval with sedimentation. According to these data, faulting in the Central/Eastern Pontide structural block should be reconsidered in the context of the seismic activity of the region and re-evaluated as an earthquake hazard that will pose a risk in the future.

Unveiling the transtensional geodynamics of Cenozoic depocenter changes in the Andaman sea: Seismic evidence for the existence of the East Sagaing Fault and the Andaman Basin Central Fault Zone in the Tanintharyi region

The Andaman Sea, situated at the highly oblique convergent boundary of the Indian and the Sunda Plates in the eastern Indian Ocean, has been shaped by transtensional geodynamics throughout the Cenozoic and has given rise to the formation of fault systems in the Andaman back-arc region. Out of these faults, the Sagaing Fault system exists as the active transform boundary between the Burmese and Eurasian Plates. The East Sagaing Fault, which runs through the Gulf of Martaban in the Andaman Sea, is a critical component of this Sagaing Fault system in fostering the transtensional regime and contributing to the opening of the Andaman Sea as a pull-apart basin. In contrast, the Andaman Basin Central Fault Zone, previously misinterpreted as the South Sagaing Fault, is an inactive fault system that experienced deformation until the Middle Miocene and is currently concealed beneath the East Andaman Basin. This temporal disparity in the Andaman Basin Central Fault Zone and East Sagaing Fault activity patterns has led to uncertainty regarding their existence within the Tanintharyi region of the Andaman Sea. To address this uncertainty, 2D and 3D seismic data interpretations were used to explore the distribution of faults, including the presence and extent of these two faults in the Tanintharyi region. Through a comparative analysis of the structural characteristics of the East Sagaing Fault in the northern part, and the Andaman Basin Central Fault Zone in the southern part of the Andaman Sea, this study presents compelling evidence confirming the existence of both faults in the Tanintharyi region with their structural implications. The innovative discoveries in this article contribute to a deeper understanding of Cenozoic depocenter changes in the Tanintharyi region, substantiating the significance of these two faults in transtensional geodynamics and allowing for a comprehensive examination of geodynamic evolution in the Andaman Sea region.

2023 Earthquake Doublet in Türkiye Reveals the Complexities of the East Anatolian Fault Zone: Insights from Aftershock Patterns and Moment Tensor Solutions

Abstract The East Anatolian Fault Zone (EAFZ) is a 700-km-long left-lateral transform fault system along the boundary between the Anatolian and Arabian plates. In the interseismic period, the eastern segments of the EAFZ display relatively uniform seismic activity, whereas the western segments exhibit seismic gaps, localized clusters, and extensive diffuse zones. Hence, our understanding of the geometry and kinematics of the western and northern segments remain limited. The occurrences of the 6 February 2023 Mw 7.8 Kahramanmaraş on the main branch and Mw 7.6 Elbistan earthquakes on the northern branch have led to complex aftershock activity shedding light on the nature of these relatively silent segments. In this study, to better understand the complexities of the fault, we constructed a comprehensive catalog of ∼32,000 earthquakes that occurred between 6 February 2023 and 30 March 2023, using a deep-neural-network-based picker. In addition, 170 earthquake source mechanisms with Mw 3.5+ were obtained from regional moment tensor inversion. The spatial distribution of the aftershocks shows that most of the activity clusters around the fault bends and major depressions. Previously unmapped and inactive secondary faults of varying lengths are identified within these geometrical complexities. The new seismological observations provide compelling evidence of extension along the Karasu valley, compression occurring along the Erkenek segment, reactivation of basin faults near the Narlı fault zone and the persistent shallow seismic creep of the Pütürge segment. The analysis of seismicity and earthquake source mechanisms along the northern branch reveals the structures of previously inactive faults, both near the extensional Göksun bend in the west and the compressional Nurhak fault complex in the east. In summary, we illustrate the intricacies of previously quiet segments of the EAFZ and aim to gain a deeper understanding of how secondary faults and geometrical discontinuities along the EAFZ played a role in shaping the 2023 Türkiye doublet earthquakes.

Microstructural comparison in fault gouges and slip surfaces of active and inactive faults: A case study at Watarigawa area in northeastern Yamaguchi Prefecture, SW Japan

Microstructural comparison in fault gouges and slip surfaces of active and inactive faults: A case study at Watarigawa area in northeastern Yamaguchi Prefecture, SW Japan

High-resolution seismic velocity structure using induced inter-event interferometry at the geothermal sites, Geysers, Eastern California

The possibility of retrieving Rayleigh wave empirical Green's functions (EGFs) using virtual seismometers provides an opportunity to calculate high-resolution velocity models without a set of dense stations and/or expensive seismic imaging/monitoring. The high-resolution tomographic map can give an overview of the fracturing within the saturated rock. Theoretically, the cross-correlations of earthquakes contain significant information about the EGFs between event-pairs. In this work, we developed an application of virtual seismometers on a very small scale in superficial layers where anthropogenic seismicity occurred. To test this method's capabilities, we applied it to investigate the NW-part of The Geysers (TG) geothermal field. We used 1276 micro-earthquakes, occurred in a cuboid with the horizontal side of ∼1 × ∼2 km and the vertical edge at a depth from 0.9 to 2.2 km, to obtain the high-resolution (100 × 100 m) velocity structure. A group of strict criteria was imposed separately for single event waveform and event pairs to stabilize the tomographic results. After retrieving the inter-event EGF signal and calculating the Rayleigh wave group velocity dispersion curves, we obtained the group velocity maps for each horizontal layer. The tomographic maps as a function of depth indicated a low-velocity anomaly related to existing inactive faults, topography variation of the top of the steam zone, and low-velocity anomalies possibly stimulated by fluid injection. The topography of the top of the steam varies from ∼1.0 km to 1.3 km of maps, and also anomalies connected with fluid migration appear at the depth of injection wells (1.5–1.9 km).

New Insight on the Active Fault System in the Halmahera Volcanic Arc, Indonesia, Derived from the 2022 Tobelo Earthquakes

Abstract On 9 January 2022, two shallow earthquakes occurred in the east arm of Halmahera, Indonesia, with magnitudes of Mw 5.2 and 5.4 felt at III–V modified Mercalli intensity. The existence of the causative fault for the earthquakes was unknown. One possible explanation is that the earthquakes were caused by the activity of an inactive fault striking in the southeast–northwest direction, and possibly linked to the volcanic activities in Halmahera. Thus, further analysis of their characteristics is crucial to identify the previously an inactive fault. In this study, we relocated the associated earthquake hypocenters using the double-difference method with an updated velocity model, and determined the focal mechanisms by employing full waveform inversion using moment tensor analysis. The focal parameters were used to analyze the static stress changes. The relocated hypocenters show specific hypocenter clusters, aligning in the north–south direction, associated with left-lateral faulting mechanisms. This north–south alignment differs from the northeast–southwest trend of some other active faults in Halmahera. We propose that the newly found Tobelo fault dips at an angle of around 80° to the west. The seismic stress change from the mainshock and the foreshock of the Tobelo earthquakes corresponds with the distribution of the aftershocks. A detailed analysis of unidentified faults in the high seismicity area is essential to comprehend the tectonic study of Halmahera Island and its seismic hazard assessments.

Cost Estimation of Structural Work for Residential Building with Seismic Design Consideration

The Sumatra-Andaman earthquakes had triggered local earthquakes in Malaysia by reactivation of ancient inactive faults. Previously on 5thJune 2015, Ranau, a region located in Sabah, Malaysia, had experienced a moderate earthquake of Mw6.1. The structural failures occurred because all existing buildings only designed for gravity load without any seismic provision. Recent research work exhibits the seismic designs’ impact on the cost of material and its parameters thatimpact the cost. There are two types reinforced concrete residential buildings called Type 1 and Type 2 for two storey and four storeywhich had been used as models. This research applied four seismicity levels to the reference peak ground acceleration value, αgR= 0.07g, 0.10g, 0.13g & 0.16g, and two soil types: Soil Types B and D. The result shows that for twostorey reinforced concreteresidential buildings on soil types B and D, seismic design increases structural work costs, which is around 0.62% to 1.31% and 0.61% to 2.16%, respectively,for Type 1 modelcompared to non-seismic design. Besides,model Type 2, the increment is around 0.24% to 1.22% and 0.20% to 1.71%, respectively.Otherwise, for reinforced concreteresidential building with four storeyon soil types B and D,the result shows that seismic design tends to have a higher structural work’s costaround 0.41% to 2.48% and 0.98% to 11.23%, respectively, for Type 1 model. Besides, for model Type 2 the increment is around 1.80% to 2.05% and 2.34% to 8.53%, respectively, compared to non-seismicdesign.

Surface and subsurface structural mapping for delineating the active emergency spillway fault, Aswan, Egypt, using integrated geophysical data

The High Dam is one of the world’s biggest embankments dams. Moreover, the new city of Aswan, which locates on the western side of the Nile River, is one of the cities that was established to overcome the growing population problem. Therefore, the detailed geophysical studies for the active faults are of more importance for assessing the seismic stability for both of them. Indeed, the emergency spillway fault was documented as a normal and inactive fault. While, a moderate earthquake (ML = 4.6) was recorded along this fault in 2010, about 4.5 km away from the Dam. Hence, its activity must be re-evaluated. The seismic activity along the fault and its extension has been studied. The seismicity distributions and the fault plane solution indicate normal faulting with a strike-slip component and shallow focal depth. Moreover, pore pressure and fluid diffusion play an essential role in fault activation process. On the other hand, the magnetic data for the research area was subjected to a detailed analysis. 2D spectrum analysis and 3D Euler deconvolution methods, were used to analyze and interpret the aeromagnetic anomaly data so as to better understand the tectonic framework of the study region. Finally, the integrated geophysical data delineate the trend of the emergency spillway fault which extends NW–SE. This fault could assist in updating the current seismic source model around the High Dam and new Aswan city for evaluating the seismic hazard for both of them.

Capacity Analysis and Understanding of Pilot Test Well in Gas Storage A

There is a relatively simple gas reservoir structure in gas storage A, with good trap sealing, large cap rock thickness, relatively inactive fault activity, good overall reservoir connectivity, large storage capacity, water invasion occurs in only a few wells in the low part of the structure, so there are the geological conditions for building gas storage reservoir. This paper analyzed the capacity and maximum recovery capacity of horizontal wells in this block, and the pressure influence range during the recovery process of high-speed pilot production through the pilot test of reservoir construction; moreover, it got the following understanding: the horizontal wells with good development effect, high recovery capacity, and the pressure influence range in this block are mainly within 400m from the well distance; there are differences in the gas production capacity of different types of reservoirs, and the capacity contribution of Class I reservoirs is large, while the capacity contribution of Class II and III reservoirs is small, together these believe that Shengping gas storage has the capacity conditions for building reservoir.

Geodetic Strain of the Baribis Fault Zone in West Java, Indonesia

The Baribis Fault’s status, which is located in the northern part of Java, as an active or inactive fault is a matter of considerable debate. In this study, we investigate the strain rate of the Baribis fault zone’s segment in northeastern West Java, Indonesia, as revealed by a dense network of GPS stations. We analyzed 17 surveyed GPS stations combined with continuous GPS sites over West Java from 2017 to 2021, then we estimate the GPS velocities fields. We calculated the strain rate and estimated it from the GPS velocities. In general, the Baribis fault zone experiences a significant strain rate (> 50 nano-strain/yr) with the compressional dilatation strain associated with the ongoing deformation in that area. The dilatation strain suggest that the northeastern Baribis fault in the West Java is an active thrust fault system. This information is essential to supporting a disaster mitigation program.

Displacement/Length Scaling Relationships for Normal Faults; a Review, Critique, and Revised Compilation

The relationship between normal fault displacement (D) and length (L) varies due to numerous factors, including fault size, maturity, basin tectonic history, and host rock lithology. Understanding how fault D and L relate is useful, given related scaling laws are often used to help refine interpretations of often incomplete, subsurface datasets, which has implications for hydrocarbon and low-carbon energy applications. Here we provide a review of D/L scaling laws for normal faults, discuss factors that could influence these relationships, including both geological factors and errors in measurement, and provide a critique of previously published D/L databases. We then present our newly assembled database of 4059 normal faults from 66 sources that include explicit information on: 1) fault length and displacement, 2) host rock lithology, 3) host basin tectonic history, and 4) maturity, as well as fault D and L through time when these data are available. We find an overall scaling law of D = 0.3L0.92, which is similar to previously published scaling equations and that varies in response to the aforementioned geological factors. Our data show that small faults (<1 m length) tend to be over-displaced compared to larger faults, active faults tend to be under-displaced compared to inactive faults, and faults with stiffer host rock lithologies, like igneous and carbonate rocks, tend to be under-displaced with respect to faults within softer, more compliant host rocks, like clastic sedimentary rocks. Our dynamic D/L through time data show that faults follow the hybrid fault growth model, i.e., they initially lengthen, during which time they will appear under-displaced, before accumulating displacement. To the best of our knowledge, this is the first comprehensive, integrated, critical study of D/L scaling laws for normal faults and the factors influencing their growth. These revised relationships can now be utilized for predicting fault length or displacement when only one variable is available and provide the basis for general understanding D/L scaling laws in the context of normal fault growth. This underpinning database is open-access and is available for analysis and manipulation by the broader structural geology community.

Shaking table tests on fault-crossing tunnels and aseismic effect of grouting

Tunnels crossing inactive faults may experience large differential deformations along their lengths during earthquakes, resulting in damage. Faults always have inferior material properties for historical geological reasons. Grouting is an auxiliary construction measure in fault-crossing tunnels and has the potential to be an economical and effective aseismic measure. However, the feasibility and seismic mitigation mechanisms of grouting in fault-crossing tunnels have not been sufficiently studied. In this study, large-scale shaking table tests were conducted to verify the aseismic effect of grouting in a tunnel crossing an inactive fault and to explore the seismic mitigation mechanism behind it. On this basis, verified numerical models were developed to determine the optimized design parameters. The test results indicate that grouting reduces the acceleration response of the tunnel within the fault and reduces the differences in the acceleration responses in the longitudinal direction of the tunnel induced by the fault. As grouting increases the shear strength and stiffness of the strata around the tunnel within the fault, the strain of the tunnel invert is effectively reduced by over 80%, and the potential damage of the invert uplift is reduced simultaneously. Meanwhile, grouting effectively reduces the diameter deformation of the tunnel within the fault and reduces the differences in tunnel deformation in different areas of the fault site. By reducing the resonance caused by the frequency components of the input seismic wave that is close to the natural frequency of the strata, which contributes most to the tunnel response, grouting effectively reduces the seismic responses of the fault-crossing tunnels. Increasing the stiffness of the grouting zone is an effective approach to improve its seismic mitigation performance. In the example of this study, adjusting the relative stiffness ratio to approximately 100 between the grouting zone and the fault resulted in a favorable condition for aseismic effects, which could be deemed to be a suitable parameter for grouting. The above results can provide a reference for the seismic design of mountain tunnels crossing inactive faults.

Assessing active and capable faulting as best practice for post-earthquake reconstruction activities: the Sant’Eutizio Abbey case study, in the epicentral area of the 2016 central Italy seismic sequence

Surface faulting is, together with strong ground shaking, a hazard associated with major earthquake faults. Assessing surface faulting potential of a given active tectonic structure is a fundamental prerequisite to adequately plan the use of territories and to perform new constructions, in order to act practices aimed to mitigate the associated risk. Assessing the surface faulting potential represents also ground for correctly performing re-construction and retrofitting of buildings and infrastructures during post-earthquake activities. We investigated a branch of a major seismogenic normal fault in the central Apennines of Italy, the Campi-Preci fault, along which the monumental Sant’Eutizio Abbey is located. The medieval Abbey is one of the most important cultural/religious edifices of the central Apennines, heavily damaged by the MW 6.5 October 30, 2016, earthquake, focused a few km to the south. Our study, based on field geological, geomorphological and structural survey and trenching investigations revealed that I) the trace of the Campi-Preci active fault branch is not actually located where presently reported in the available literature, II) the supposed morpho-tectonic features (basically, some km-long scarp carved on the Meso-Cenozoic carbonate bedrock), that suggested the presence of the fault segment in the area of the Sant’Eutizio Abbey, are not related to the active fault but are probably associated to a presently inactive reverse fault and III) the Sant’Eutizio Abbey is likely not potentially affected by primary surface faulting. Our work highlights that only a comprehensive multidisciplinary approach allows to correctly assess surface faulting potential in both seismotectonic and engineering perspectives.

Tectonic Geomorphic of Sulawesi Island and Its Implication for Future Large Earthquake

This paper analyzes how resource of past and prospective great earthquake on the Central Sulawesi Arm, adhere on topography analysis from several space-based source. To answer the question, we analysis the tectonic geomorphic, stream pattern, exhumed fault, geological mapping and seismicity data. Detailed tectonic geomorphic studies in Sulawesi still lacking due to tectonic and fault obscures. For instance, Palu Koro Fault (PKF) was unpredictable, because the historical seismic records inevitably remain poorly documented and unrecognized fault strand, which was buried beneath abundant Quaternary alluvium subsequently obscured the fault trace. In other hand, the faults have been active during Quaternary must take into account because potentially dangerous, also the inactive faults during instrumental period must be re-evaluated in order to have awareness for large future large earthquake. Surprisingly, recent seismic activity of PKF generate super shear rupture a Mw 7.5 earthquake on 28th September 2018 with average slip 41 mm/year, which over the past two decade quiet from any seismic activity. The seismic potential for large fault is essential, since it has been silent during the instrumental period. Therefore, our motivation in this study to produce detail tectonic geomorphic map of the region in local scale, which is currently not available to prepare better knowledge and awareness for the large future earthquake. We have use Shuttle Radar Topography Mission (SRTM) with resolution ~30m, which run by ArcGIS software to observed tectonic geomorphic evidence of fault system and supplement with structural, geological and bathymetric data’s as ware available to us. We relate this analysis with seismicity data from Centroid Moment Tensor Solution (CMT) to recognize the seismic source. Our results show the tectonic geomorphic of Central Sulawesi Arm due to nature extension of NNW-SSE left-lateral slip curving to WNW-ESE of Palu-Koro Fault (PKF), then transcript to N-S circular normal fault of Poso Fault (PF). The PF indicate replica of PKF curving, where has not been mapped previously. We have mapped 60 major onshore fault systems, 10 faults showed evidence maximal to rapid rate tectonic activity along instrumental periods. Based on our CMT analysis, Sulawesi Island is greatly dominated by oblique fault.

Seismic Response of Tunnel across Inactive Fault: Numerical Analysis

Earthquake damage investigations in recent years have revealed that fault zone is one of the most dangerous areas of tunnels in earthquakes, leading scholars to investigate the mechanisms of seismic response of fault-crossing tunnels and the aseismic measures. However, due to the complex fault-rock-tunnel interaction, the seismic response mechanism of tunnels crossing inactive faults is not yet complete and the suitability of different aseismic measure has not been evaluated. In this paper, a series of 3D numerical models of fault-crossing tunnels were established to study the seismic response of tunnels crossing inactive faults with different widths. On this basis, the suitability of grouting and flexible joints for fault-crossing tunnels were discussed. Due to the difference of physical property between the fault and the surrounding rock, the differential deformation will be produced at the interface, and resulting in a shear damage of the tunnel. The tunnel crossing wide fault is more vulnerable in earthquake than that crossing narrow fault. For the tunnel crossing inactive faults, especially those with wide widths, grouting reinforcement is a desirable aseismic measure. It can reduce the acceleration response of the tunnel within the fault and significantly reduce the tensile damage, while flexible joints have little effect on the acceleration response and the damage reduction of the tunnel within the fault. The present study can contribute to a better understanding of the seismic response of tunnels crossing inactive faults and provide some guidance to the seismic design.

Nonlinear Seismic Response of Rock Tunnels Crossing Inactive Fault under Obliquely Incident Seismic P Waves

Nonlinear Seismic Response of Rock Tunnels Crossing Inactive Fault under Obliquely Incident Seismic P Waves

Quantitative determination of the lowest density domain in major fault zones via medical X-ray computed tomography

Determination of the youngest active domains in fault zones that are not overlain by Quaternary sedimentary cover is critical for evaluating recent fault activity, determining the current local stress field, and mitigating the impacts of future earthquakes. Considering the exhumation of a fault zone, the youngest active domain in a fault zone is supposed to correspond to the activity at the minimum fault depth of a buried fault, such that the most vulnerable area, which possesses the lowest rock/protolith density ratio, is assumed to be indicative of this recent fault activity. However, it is difficult to measure the density of fault rocks and map the rock/protolith density ratio across a given fault zone. Here, we utilize medical X-ray computed tomography (CT), a non-destructive technique for observing and analyzing materials, to investigate the fault characteristics of several fault zones and their surrounding regions in Japan, and attempt to determine the lowest density domain of a given fault zone based on its CT numbers, which are a function of the density and effective atomic number of the fault rock and protolith. We first investigate the density, void ratio, and effective atomic number of active and inactive fault rocks, and their respective protoliths. We then calculate the CT numbers after reducing the beam-hardening effects on the rock samples and study the relationships among the CT number, density, and effective atomic number. We demonstrate that the density, effective atomic number, and CT number of the fault rock decrease as the youngest active zone, identified by outcrop observation, are approached, such that the region with the lowest CT number and rock/protolith density ratio defines the lowest density domain of a given fault zone. We also discuss the relationship between the lowest density domain and the youngest active domain in major fault zones and investigate the points to be considered when the youngest active domain is identified from the lowest density domain determined by the CT number.

Evolution of normal fault displacement and length as continental lithosphere stretches

AbstractContinental rifting is accommodated by the development of normal fault networks. Fault growth patterns control their related seismic hazards, and the tectonostratigraphic evolution and resource and CO2 storage potential of rifts. Our understanding of fault evolution is largely derived by observing the final geometry and displacement (D)‐length (L) characteristics of active and inactive fault arrays, and by subsequently inferring their kinematics. We can rarely determine how these geometric properties change through time, and how the growth of individual fault arrays relate to the temporal evolution of their host networks. Here we use 3D seismic reflection and borehole data from the Exmouth Plateau, NW Shelf, Australia to determine the growth of rift‐related, crustal‐scale fault arrays and networks over geological timescales (>106 Ma). The excellent‐quality seismic data allows us to reconstruct the entire Jurassic‐to‐Early Cretaceous fault network over a relatively large area (ca. 1,200 km2). We find that fault trace lengths were established early, within the first ca. 7.2 Myr of rifting, and that along‐strike migration of throw maxima towards the centre of individual fault arrays occurred after ca. 28.5 Myr of rifting. Faults located in stress shadows become inactive and appear under‐displaced relative to adjacent larger faults, onto which strain localises as rifting proceeds. This implies that the scatter frequently observed in D‐L plots can simply reflect fault growth and network maturity. We show that by studying complete rift‐related normal networks, rather than just individual fault arrays, we can better understand how faults grow and more generally how continental lithosphere deforms as it stretches.

Joint interpretation of geophysical data: Applying machine learning to the modeling of an evaporitic sequence in Villar de Cañas (Spain)

An optimal strategy for building realistic geological models must combine different geophysical techniques, each with its advantages and limitations. However, dealing with multiple geophysical datasets to derive a geological interpretation is not straightforward since geophysical parameters are not always functionally related. In this work, we propose an innovative approach consisting of using machine learning techniques to jointly interpret three geophysical datasets (a pseudo-3D resistivity model, a 3D velocity model, and 4 well-logs). These datasets, among others, were acquired to characterize the suitability of an evaporitic sequence for hosting a temporary storage facility of hazardous radioactive waste, which was planned in Villar de Cañas (Spain). Our strategy consisted of integrating both models in a single 3D bi-parametric grid that nested the velocity and resistivity values in each node. We then used a supervised learning algorithm to lithologically classify each node according to a training set based on the borehole data, which acts as ground truth. The training set is composed of classifiers that lithologically label resistivity-velocity pairs. However, the very shallow nodes lack classifiers due to the poor well-log coverage at the top part of the evaporitic sequence. To fill this gap, we computed an unsupervised cluster analysis that provided new classes to complete the training set. Finally, the supervised classification was applied, providing a new 3D lithology model that is far more consistent with the geology than the models derived from each parameter independently. The 3D model also revealed geological features previously unknown, notably the existence of an inactive fault. The proposed method can be applied to integrate and jointly interpret any kind of multidisciplinary datasets in a wide range of geoscientific problems, including natural resource exploration, geological storage, environmental monitoring, civil engineering practice, and hazard assessment. • The joint interpretation of geophysical data improves subsurface characterization. • Machine learning makes the interpreter's job easier while reducing bias. • Combined supervised and unsupervised learning makes the most of data. • Machine learning to enhance geological interpretation of historic datasets. • Geophysical surveys should be planned anticipating their subsequent integration.

Coulomb stress change in the neighboring region and faults imparted by Anchorage Mw7.0 earthquake in Alaska

The Anchorage Mw7.0 earthquake on November 30, 2018, was the most extensively felt event in the region since the 1964 Alaska Mw9.2 earthquake. Based on published data of source fault model, we performed a preliminary analysis on the Coulomb stress change produced by Anchorage earthquake in the neighboring region and faults. The results show that the mainshock has triggered subsequent aftershocks, most of which are located in stress-increased region. The Anchorage earthquake also imparts Coulomb stress change on the Castle Mountain fault, with different fault segment ranging from − 2 × 105 to 3.27 bar. Similarly, on the Border Range fault, this stress ranges from − 0.71 to 3.31 bar despite being inactive fault on present knowledge. Furthermore, on nodal planes I and II of the Anchorage Mw7.0 earthquake, the Coulomb stress change imparted by the 1964 Mw9.2 earthquake ranges from 2.490 to 3.968 bar and from 3.283 to 5.140 bar, respectively. These results indicate that the 1964 Mw9.2 earthquake produces a large amount of Coulomb stress on the seismogenic fault plane of the Anchorage Mw7.0 earthquake and promote it more closer to failure. These results contribute to our understanding of the seismic hazard in the region and on fault segments where the Coulomb stress has been sharply changed.