Seismic Potential Research Articles

Dam impoundment near active faults in areas with high seismic potential: Case studies from Bisri and Mseilha dams, Lebanon

Reservoir induced seismicity is caused by stress changes due to the impoundment of water behind dams. In seismically active areas, the presence of critically located active faults makes the impoundment of water behind dams a seismic safety risk. Dam projects in Lebanon have become a soaring example of complacency and negligence that has overlooked the concerns for seismic safety raised over the projects and their high potential of inducing seismicity. In this paper, we use 2D and 3D fully coupled poroelastic modeling to assess the risk of dam impoundment on seismogenic faults located near dam sites in Lebanon. The coulomb failure stresses are calculated along the faults, and their variations are observed in relation to changes in pore pressures and normal stresses. In addition, the expected maximum earthquake magnitudes are computed along those faults. Our results show a high risk for reservoir induced seismicity on faults that are either underneath the reservoir or hydraulically connected to a fault beneath the reservoir. Consequently, the studied dams would present a serious hazard of induced seismicity in time where the region is already at high risk of destructive earthquakes after the catastrophic seismic events that struck Turkey and Syria on 6 February 2023 on the Eastern Anatolian Fault, which is connected to the Dead Sea Transform Fault that passes through Lebanon.

Postseismic deformation due to the 2021 MW 7.4 Maduo (China) earthquake and implications for regional rheology and seismic hazards around the Bayan Har block

GPS and InSAR observations of the first ∼1.5 years of postseismic deformation caused by the 2021 MW 7.4 Maduo earthquake provide a valuable opportunity to investigate fault interactions and regional rheological structure, as well as the future seismic potential around the Bayan Har block, northeastern Tibetan Plateau. We develop an integrated model to simulate the afterslip and viscoelastic relaxation contributions to the observed postseismic displacements, and found that afterslip driven by the coseismic stress is concentrated downdip of rupture, and dominates the postseismic deformation in the early stage (∼0.4 year after the event). Because afterslip decays quickly over time, viscoelastic relaxation should become the main postseismic mechanism as time goes on. The two mechanisms produce similar displacements during 0.4–1.5 years after the earthquake, but at 1.5 years after the earthquake the velocity caused by viscoelastic relaxation is larger than that caused by afterslip. Viscoelastic models assuming either a Burgers body or power-law rheology produce very similar predictions, with the Burgers body model having a slightly lower overall misfit. The rheological structure constrained by the postseismic observations supports the 35-km thick elastic upper crust overlying a Burgers body viscoelastic lower curst with a Maxwell viscosity of 3 × 1019 Pa s (5 - 50 × 1018 Pa s at 95% confidence), assuming the Kelvin viscosity is equal to 10% of that value. This is different from the regional rheology inferred by the postseismic investigations on the 2001 MW 7.8 Kokoxili and the 2008 MW 7.8 Wenchuan events, and the preferred thickness of the elastic crust is also different from that inferred from magnetotelluric profiles deployed in previous studies. We thus infer that the rheological structure within the Bayan Har block is possibly heterogeneous from west to east. Finally, the normal stress changes triggered by the coseismic rupture and postseismic process are estimated to be negative, but the shear stress changes to be positive on the western Kunlun fault, the eastern Dari fault and Bayan-Har Mountain fault. However, the current observations and studies are quite insufficient on those fault segments, therefore, we need to focus on their faulting behavior and seismic risk in the future.

Quantitative Assessments of the Liquefaction Hazard of Soils considering Possible Strong Earthquakes in Seismically Active Regions of Russia

Introduction The seismogenic liquefaction of the soil poses a great hazard to society and the environment. Therefore, it is actively studied in many countries. In Russian engineering and seismological practice, this area is not sufficiently developed. The deterministic approach still prevails in Russian research on this topic. More modern probabilistic estimates are very rare. Methods This paper describes examples of both deterministic and probabilistic assessments of the seismogenic liquefaction hazard performed in certain areas of the Russian territory with different seismogeological conditions. Deterministic estimates were made using the Iwasaki-Seed-Finn methods and their modifications. Probability distribution functions of a random variable, the “seismic potential of liquefaction” (SPL), were developed for probabilistic estimates. These functions are regional in nature and take into account two types of uncertainties. The first is the uncertainty in achieving “critical” values by the SPL value in the event of potentially dangerous earthquake sources for a given location. The second is the uncertainty in the very occurrence of these sources in a given place for a given period of time. The “critical” SPL values are determined by the strength properties of the site soils. All estimates are based on multivariate calculations using various models of strong ground motions and seismicity. In all cases, the probability of liquefaction of water-saturated sandy and sandy-loam deposits was estimated which were found near the seabed and at depths of up to 80 m in the waters of Pogibi cape (the coast of Sakhalin island), in the districts of Sochi and Novorossiysk, as well as in land conditions (Stavropol, Krasnodar). Results The results of the research made it possible to correctly (at the quantitative level) take into account this component of the seismic hazard of the studied territories. Conclusion The variants of practical use of the obtained data are offered. An assessment of the possibilities and limitations of the developed methodology is made, and ways to improve it are outlined.

Rupture behaviors of the southern Xianshuihe fault and seismicity around Mt. Gongga: Insights from the 2022 MW 6.6 Luding (China) earthquake sequence

The 2022 MW 6.6 Luding earthquake occurred on the Moxi segment of the Xianshuihe fault at the southeast margin of Tibetan Plateau, China. To assess the seismic potential of the Moxi segment, we examine the rupture process of the mainshock and aftershock sequence, along with historical seismicity. Our preferred slip model inverted from teleseismic body waves and regional GNSS static displacements shows a dominant southeastward rupture consisting of two distinct, prominent slip patches along strike extending by ∼15 km, with a peak slip of ∼2.8 m, approximately balancing the slip deficit since the last major earthquake in 1786. The northern section of the Moxi segment experienced minor coseismic slip, which, together with the significant slip deficits and positive Coulomb failure stress change induced by the 2022 mainshock indicates a high seismic potential. Several aftershock clusters are distributed along or near the Moxi segment, with strike-slip focal mechanisms around the downdip edge of the coseismic slip area at ∼8‐12 km. At the eastern flank of Mt. Gongga, another cluster of normal faulting aftershocks is located at shallower depths of ∼3‐7 km, with high seismicity rate over ∼9 months including two other M5 sequences in January and February 2023. Similar intense shallow normal faulting activity had occurred after the impoundment of the nearby Dagangshan reservoir in 2015. We speculate that some NW-SE trending normal faults were initially developed by the gravitational collapse of Mt. Gongga underneath the eastern flank, further weakened by fluid flow, as supported by the existence of hot springs and water impoundment, and reactivated by the tensional stress change induced by the 2022 mainshock. These results have important implications for assessing the seismic hazard in and around the Moxi segment, and the potential interplay between strike-slip fault and nearby mountain areas.

Normal fault architecture, evolution, and deformation mechanisms in basalts, Húsavik, Iceland: Impact on fluid flow in geothermal reservoirs and seismicity

Faults within layered basaltic sequences significantly influence hydrothermal fluid flow in shallow geothermal reservoirs and potentially during CO2 sequestration and storage. Nevertheless, their characterization regarding fault zone architecture, fluid flow, deformation mechanisms, and seismic potential remains underdeveloped. This study addresses this gap by integrating structural and microstructural observations with X-ray diffraction analyses of exposed normal-transtensional faults associated with the seismically active Húsavík-Flatey Fault in the Tjörnes Fracture Zone, Northern Iceland. Our findings demonstrate that the evolution of basalt-hosted normal-transtensional faults progresses through distinct stages: (1) low-displacement fault propagation from pre-existing cooling joints; (2) fault linkage via dilational jogs; (3) damage zone/fault core growth through brecciation and cataclastic processes; (4) shear localization along sharp slip surfaces; and (5) smearing of volcaniclastic interbeds along the principal fault plane. Evidence of shear localization, truncated clasts, and hydrothermal breccias/veins suggests repeated seismic slip events facilitated by overpressured fluids. Conversely, the presence of clay-rich foliated cataclasite indicates aseismic slips during interseismic periods. Slip along fault jogs, bends, geometric irregularities, and orientation changes causes the dilatant opening of the fault planes and extensional horsetail fractures at fault tips. These structures create main tabular zones for lateral movement of hydrothermal fluids parallel to the fault strike in shallow geothermal reservoirs situated in active extensional-transtensional tectonic settings. In addition, the dilational jogs and the intersection of horsetail veins with the hosting faults may define linear zones of high structural permeability and intense localized fluid flow parallel to the σ2 paleostress orientation and finally mineral precipitation. The results of this study can be utilized to improve models of geothermal fluid flow for enhanced recovery in basaltic reservoirs and assess seismic risk in basaltic faults.

Structural inheritance, morphotectonics and Holocene activity of the Cucalón-Pancrudo extensional fault (Iberian Chain, Spain)

A large active extensional fault is characterized, which will contribute to improve seismic hazard assessment in an intraplate region of the Mediterranean domain whose seismic potential until today has been underestimated. The Cucalón-Pancrudo fault (CPF) is a NNW-SSE striking extensional fault that represents the negative (extensional) inversion of a previous, Late Variscan and Paleogene, transpressional fault. It is part of the Río Grío-Pancrudo fault zone, the largest active structure in the intraplate central-eastern Iberian Chain. This study focuses on characterizing the CPF structure, morphotectonics and paleoseismology. The fault offsets a well-known regional planation surface (lower level of the Fundamental Erosion Surface, FES3, 3.5 Ma), providing a basis for calculating the maximum fault throw (c. 280–300 m, including the contribution of a minor synthetic fault and a gentle accommodation monocline), and hence estimating the net slip (c. 305–325 m) and the long-term slip rate (0.09 mm/a). A trench dug in a Holocene fluvial terrace reveals an ensemble of listric, domino-style ruptures synthetic to the main fault. They were activated during at least two paleoseismic events (X, Z), 14.9 ± 1.4 ka and 6.9 ± 0.4 ka in age. An intermediate event (Y), dated to 11.0 ± 1.0 ka, as an uncertainty because the attribution of their ruptures to event Z cannot be ruled out. The total net slip accumulated during these events (1.15–1.25 m) provides an apparent short-term slip rate of 0.07–0.09 mm/a, very similar to the long-term slip rate. Nevertheless, it is very likely that the faults exposed in the surveyed trench do not represent a complete paleoseismic record. Therefore, the actual slip rate during Late Pleistocene-Holocene times could be significantly higher, approaching that reported for most of the recent extensional faults in the central Iberian Chain. The inclusion of CPF in the map of Active Faults of Iberia (QAFI database) will result in improving seismic hazard assessment in Spain.

RANKING OF SEISMIC INTENSITY ATTENUATION LAWS AND MODELING OF SEISMIC SOURCES FOR SEISMIC HAZARD ASSESSMENT IN UZBEKISTAN

Quantitative assessments of seismic hazard in seismically active areas depend to a large extent on the intensity-distance attenuation laws which are used in calculations. To account for epistemic uncertainty in the nature of seismic effects, it is recommended to perform probabilistic seismic hazard analysis using several different attenuation relationships. The most effective tool for their selection is the ranking procedure which consists in attributing a weight to one or another equation depending on the degree of compliance between the equation-based seismic effects and the real experimental data available for the region under study. The article presents the results of ranking intensity attenuation laws derived for Central Asia. Ranking was carried out by LH and LLH methods. Based on the ranking results, these has been made a generalized attenuation model used subsequently in PSHA for Uzbekistan. Consideration was given to three alternative models of seismic sources: area sources, active faults, and seismogenic zones. Parameterization of the models considered involved determining seismic potential, frequency of recurrence of earthquakes of different energy levels, and the predominant type of motions in each earthquake source. Seismic zoning maps of Uzbekistan in points of the MSK-64 intensity scale have been compiled for different probabilities of occurrence of non-exceedance level earthquakes in the next 50 years.

Determination of individual disaster resilience levels of hospital staff: A case study of Kartal Dr. Lütfi Kirdar City Hospital

Istanbul is one of Turkey's most important financial and industrial centers, and it is located in a region with a high potential for seismicity. Due to its historical architecture and high level of urbanization, the city has a large population and is particularly vulnerable due to the building stock that will be affected by earthquakes. In the event of a possible earthquake in Istanbul, it is crucial that the hospital staff have high levels of disaster resilience/resilience. This is particularly important given the seismically isolated and earthquake-resistant structure of Istanbul Kartal Dr. Lütfi Kırdar City Hospital and its capacity to serve those injured by the earthquake. This study examines the resilience levels of hospital staff at Kartal Dr. Lütfi Kırdar City Hospital in the face of earthquake disasters and the various factors that affect these resilience levels. The data for this study were collected using a 13-question personal information form and the ‘Individual Disaster Resilience Assessment (IDRA)’ scale developed by DiTirro (2018). Descriptive statistics, Pearson Chi-square tests, Independent Samples T-tests, and One-Way ANOVA were used to analyze the data. The research found that the hospital staff's IDRA scores averaged 3.27. It was concluded that the mean resilience score of the participants was above the medium level. The research findings show that receiving disaster training or being prepared for disasters in advance significantly influences individual resistance/resilience. In this context, it is essential to determine the earthquake resistance levels of all healthcare workers in Istanbul, especially those at the city hospital where the study was conducted. Necessary training should be provided, and simulation-based disaster drills should be planned and integrated into in-service training programs. Additionally, projects should be developed to ensure that healthcare workers can reach their hospitals safely during disaster situations.

Preliminary Results on Deformations of the Central North Anatolian Fault Zone

The North Anatolian Fault Zone (NAFZ) in the north of Türkiye is considered one of the most active faults on earth and have caused many major earthquakes in the last century. Surface ruptures by those earthquakes indicate that this tectonic feature consists of many segments, which reveal different characteristics in terms of geometry and mechanism. NAFZ lies along between Bingöl in the eastern Turkey and Saros Gulf in the west. This study focuses on the central part of the NAFZ between Niksar and Ilgaz provinces. In addition to the main branch, the central section of the NAFZ also contains two sub-branches extending southward: Merzifon-Esençay and Sungurlu Faults. In the literature, there are several studies for the region, however a comprehensive study mainly focusing on the main branch of the NAFZ and its sub-branches along the central NAFZ has not been conducted yet, which would fully reveal the fault mechanism and seismic potential in the region. The aim of this study is to derive an up-to-date high-spa-tial-resolution Global Navigation Satellite Systems (GNSS) velocity field for the central NAFZ and to correlate with the strain accumulations along the faults. Based on this, a high-spatial-resolution GNSS network consisting of 60 sites was established enclosing the central NAFZ. The previously archived GNSS data for the same observation sites were collected from the different studies in the region and a new GNSS campaign measurement was conducted between October 2023 and February 2024. All GNSS data were processed using GAMIT/GLOBK software, and the results indicate the GNSS velocities ranging from 3-30 mm/year and their associated uncertainties of maximum ± 1.5 mm/year with respect to the Eurasian tectonic plate.

Variations of Whole–Adria Microplate Motion During the Interseismic Phase Preceding the MW 6.3, 6 April 2009 L’Aquila (Italy) Earthquake

AbstractTectonic plate motions feed the earthquake cycle—a process whereby stress along crustal faults slowly increases over decade– or century–long periods, to then suddenly drop during earthquakes. Steadiness of plate motions during such cycles has long been a central tenet in models of earthquake genesis and of faults seismic potential, and can be tested against measurements of contemporary plate motions available from Global Navigation Satellite Systems (GNSS). Here we present analyses of GNSS data from Central and Northern Italy that illuminate the motion of the Adria microplate over a period of 6 years preceding the MW 6.3, 6 April 2009 L’Aquila (Italy) earthquake. We show that the motion of the whole Adria microplate changed before the 2009 earthquake, and slowed down by around 20%. We demonstrate with quantitative models that the torque required upon Adria in order to drive such a kinematic change is consistent with what is imparted to Adria by temporal stress variations occurring during the late interseismic phase of the 2009 L’Aquila earthquake cycle. The inference that plate motions can be influenced by, and thus sensitive to, earthquake cycles offers an additional perspective to assessing the seismic potential of tectonic margins.

Geodetic plate coupling and seismic potential on the main Himalayan thrust in Nepal

We model interseismic plate coupling distribution on the Main Himalayan Thrust (MHT) in Nepal through the inversion of secular GNSS velocity data. To complement previously published data, we compile velocity data from ten additional continuous stations to improve spatial resolution in central and mid-western Nepal. A regional non-planar structural model is adopted to reproduce the MHT fault plane. In general, the coupling pattern seems nearly binary, indicating that transition from full coupling to decoupling is occurring sharply in very narrow zones. In eastern Nepal (> 84.5ºE), plate coupling is very strong from the surface to intermediate depths, including the source region of the 2015 Mw 7.8 Gorkha earthquake. Geodetically estimated slip deficit rates are consistent with the rupture history of great earthquakes in the east revealed by geomorphological observations. In the west (< 83.0ºE), a weakly coupled zone extends laterally at intermediate depths, whereas the coupling in the shallower part remains very strong. Although the slip deficit rate in the west is significantly smaller than that in the east, seismic moment accumulated, since the last complete rupture in 1505 may be capable of generating a future great event. In central Nepal, estimated slip deficit rates are comparable with those in the east, and no great event has been documented over the past several centuries. Thus, the seismic risk may be most urgent in central Nepal. The development of local seismicity and crustal deformation should be carefully monitored.Graphical

Earthquake-induced paleo-landslides in the Tehran Region and its role in assessing the seismic hazard, Iran

In the central portion of the Arabia-Eurasia collision zone, the Tehran domain is positioned at a transitional boundary between seismotectonic zones of the Central Iranian lowland (to the south) and the Alborz highland (to the north). Consequently, numerous destructive seismic events have occurred in this active tectonic domain. This study delves into the tectonic geomorphology of the region within its northern highland domain, specifically focusing on the hanging wall of the E-striking north-dipping North Tehran fault (NTF) zone. Our findings in this northern domain emphasize several prominent topographic scars as significant co-seismic features. These include huge landslides, rockfalls, rock avalanches, and offset geomorphic surfaces and could be present as the main indirect co-seismic morphological features. Within this seismically active region, the extensive dimensions of these geomorphic pieces of evidence reveal the seismic potential of the Tehran Region to experience really strong earthquakes (i.e. M&gt;7.5). These results contrast with the previous Maximum Credible Earthquake (MCE) magnitude estimated for the Tehran Region (i.e. M~7.2) through different approaches in Seismic Hazard Assessments (SHAs). Consequently, the previous SHAs of the Tehran Region might have underestimated the seismic risk, and therefore, it is necessary to conduct an updated and complementary deterministic SHA based on the more detailed seismogenic geological features in this crucial area.

Possible Maximum Earthquake Tsunami Along the South Coast of China Inferred From GPS‐Derived Surface Velocities

AbstractThis study aims to assess the tsunami hazard of the maximum possible earthquake along the south coast of China. GPS‐derived surface velocities around the Manila Trench have been used to clarify the active tectonics and estimate the seismic potential of Manila subduction, where catastrophic tsunamis may originate and cause devastating damage to the surrounding area of the South China Sea. Based on the maximum potential earthquake magnitude estimated from the accumulated seismic moment, more than 100,000 possible tsunami scenarios with varying epicenters have been simulated considering the slip heterogeneity. The impact of several uncertain parameters including the release period and release ratio of accumulated seismic moment are investigated, as well as some assumptions in the model of tsunami generation. Although different release conditions for accumulated seismic moment result in a significant impact on the value of tsunami height, similar trend in spatial distribution has been shown. The results show that the tsunami wave height along the south coast of China has an increasing trend from west to east, with the maximum tsunami wave height exceeding 10 m corresponding to the potential earthquake Mw = 9.1 with a 1,000‐year release period. The impact of fault slip heterogeneity on tsunami wave height is significant. Compared to uniform slip, considering stochastic slip will increase the average tsunami wave height by about 15%. Considering locking distribution will increase the average tsunami wave height by about 20%–30% and also increase the maximum tsunami wave height by about 60%–70%.

Double-Vergent Plate Boundary Faults and Triggered Coseismic Rupture of the 2022 Chihshang Doublet Earthquake Occurred in Eastern Taiwan

Abstract The earthquake doublet of Mw 6.5 and 6.9 occurred along the west-dipping Central Range fault (CRF) adjacent to the east-dipping creep segment of the Longitudinal Valley fault in eastern Taiwan on 17–18 September 2022. The faulting model derived from the Interferometric Synthetic Aperture Radar and Global Positioning System observation suggests that the west-dipping CRF rupture is responsible for the two mainshocks. Meanwhile, the two major earthquakes resulted in ∼100 km of fault slip along the double-convergent plate boundary faults near the Longitudinal Valley in eastern Taiwan. The 2022 Chihshang earthquake sequence filled the seismic gap of the CRF located between the 2006 ML 6.1 Taitung earthquake and the 2013 ML 6.1 Ruisui earthquake. Finally, the 2022 Chihshang earthquake sequence increased the Coulomb failure stress in the southernmost segment of the CRF, which may cause a higher seismic potential in the future.

Study examining active buried faults using shallow seismic reflection and joint multi-drilling: A case from the Xinding Basin, Shanxi Graben system

Active buried faults are a type of potential seismic source that are typically very difficult to explore and study in detail due to their undetectability using traditional geological survey methods. A ring of active basins has currently formed around the stable Ordos Block. However, few studies have been conducted to determine the activity of buried faults in these basins. This study utilized the Xinding Basin of the northern Shanxi Rift System as the target area. Based on comprehensive evidence from shallow seismic exploration, joint geological multi-drilling, and Quaternary dating methods, a new buried active fault named the Xinzhou Fault (XF) was identified in the Dingxiang Graben, a subbasin of the Xinding Basin. The youngest faulted layer was dated to earlier than 144.84 ± 16.92ka and is likely at approximately 118.94 ± 15.2ka. The slip rate of the newly observed Xinzhou Fault could be limited to 0.08–0.12 mm/a since the Late Pleistocene. This fault that was the first NW-striking active fault in the Shanxi Rift System is likely a secondary tension fracture of the main NE-striking Holocene basin-controlling faults. Currently, a strong earthquake at M7.2 can be considered as the maximum seismic potential of the XF, thus posing a significant seismic hazard to the area of the Xinding Basin. The discovery of this NW-striking active fault likely presents a low seismic risk. However, the occurrence of a strong earthquake should not be ignored due to its high seismic hazard.

Custody in the age of digital assets : The path to building market infrastructure fit for a tokenised economy

This paper charts the dynamic evolution of finance and capital markets amid the digital asset surge. Tracing the historical trajectory from conventional banking to the current digital era, the paper underscores the intertwined narrative of finance and technology. Distributed ledger technology (DLT) and digital assets take centre stage, driving continuous financial operations and reshaping market dynamics. Custody emerges as a pivotal factor in this digital transformation. Established financial institutions strategically invest in digital asset infrastructure, recognising the seismic potential of tokenisation. Research from major companies projects significant tokenisation of assets, prompting global banks to align their strategies accordingly. The paper explores diverse use cases, from custody and trading services for cryptocurrencies to tokenising financial securities and real-world assets. Navigating the regulatory landscape proves crucial, with varying regulations across jurisdictions posing challenges. A unified regulatory framework is advocated for fostering global adoption. The paper delves into the technological nuances of safeguarding digital assets, exploring key management solutions such as multiparty computation (MPC) and hardware security modules (HSMs). The paper anticipates a shift towards recentralisation as the digital asset market matures, with established financial institutions and custodians poised to leverage trust, balance sheets and regulatory compliance to open up commercial opportunities in the digital asset space. In essence, the paper provides a sweeping overview of the current digital asset landscape, offering insights into challenges, opportunities and technological considerations shaping the digital asset custody value chain.

Incorporating seismic risk assessment into the determination of the optimal route for gas pipelines

ABSTRACT Earthquake-induced damage to gas pipelines can have severe economic, social, and environmental consequences. To mitigate these risks, one effective way is to carefully design the route of gas pipelines, considering the seismic hazard of the region. This paper proposes a methodology that incorporates seismic risk assessment into the process of designing gas pipeline routes. Conventional gas pipeline design methods consider only minimum distances from faults and fail to account for seismic potential. The methodology is applied to three gas pipeline routing problems in the high seismic region of southern Iran. Seismic risk is evaluated using the HAZUS method, and routing is performed through a GIS-based approach. Results are compared with conventional approaches in terms of length, seismic risks, and damage costs, showing the proposed method’s effectiveness in reducing immediate consequences like leaks and breaks in gas transportation. The proposed method reduces seismic damage by 3 to 68% for routing problems.

3D mechanical analysis of geothermal reservoir operations in faulted sedimentary aquifers using MACRIS

Accurate and efficient predictions of three-dimensional subsurface stress changes are required for the assessment of geothermal operations with respect to fault stability and the potential risk for induced seismicity. This work extends the model capabilities of Mechanical Analysis of Complex Reservoirs for Induced Seismicity (MACRIS) to account for high-resolution thermo-elastic stress evaluations in structurally complex (i.e. faulted) and matrix permeability dominated geothermal systems. By adopting a mesh-free approach suitable to industry standard flow simulation models, MACRIS is capable of preserving the complex 3D hydraulic development of the injected cold-water volume and the 3D geometrical complexities of the reservoir model. The workflow has been applied to three-dimensional models with clastic reservoir characteristics representative for low enthalpy geothermal exploitation in the Netherlands. The models are marked by a single fault, subject to no and normal offset. Comparison of simulated stress evolutions in MACRIS with alternative analytical solutions highlight the effects of stress arching involved in the poro- and thermo-elastic stress developments on complex faults intersected by or in direct contact with the cold-water volume. Results are in agreement with previous studies and show the effect of thermal stressing to be dominant, arching of stresses to occur at the rim of the cold-water volume, and in cooling reservoirs, the intersection area of the cold-water volume in direct contact with the fault plane to be the main driver for fault reactivation and subsequent seismic potential. Moreover, results show the effects of stress arching (i) to be enhanced in the case of reservoir throw and flow compartmentalization, and (ii) to be reduced by a relative increase in conductive heat transfer between the reservoir and surrounding formations.

The Te Puninga Fault, Hauraki Plains: a new seismic source in the low seismicity northern region of New Zealand

ABSTRACT In this study, we provide the first field-based assessment of the seismic potential of the Te Puninga Fault, Hauraki Plains, Waikato region. Initially considered to be part of the nearby Kerepehi Fault, our new mapping and field data suggest the Te Puninga Fault is independent. A new net slip rate value of 0.25 mm/yr, based on geomorphic data and evaluations from two paleoseismic trenches, is slightly higher than previously considered. Comparisons of geomorphic expression between the two faults suggest that the slip rate currently assigned to the Kerepehi Fault could be underestimated. The earthquake magnitude estimated here for the Te Puninga Fault (Mw 6.9 ± 0.35) is based on a characteristic earthquake model. New PGA and MMI estimates here are only slightly larger than those published prior to this study. Although ruptures of the Te Puninga Fault are infrequent (derived recurrence range of 3000–11,500 years), and thus its hazard is low, with this paper we wish to enhance the community awareness to prepare for the rare large earthquake in the region. We also recommend that this new information is added to fault databases used for seismic assessment.

Sedimentary Records in the Lesser Antilles Fore‐Arc Basins Provide Evidence of Large Late Quaternary Megathrust Earthquakes

AbstractThe seismic potential of the Lesser Antilles subduction zone is poorly known and highly debated. Only two damaging earthquakes have been reported in the historical period, in 1839 and 1843, but their sources and magnitude are still uncertain. Global Navigation Satellite Systems and coral data contradict each other, and no conclusion has been reached on the coupling ratio of the plate interface. Given the threat posed by the possible occurrence of a large megathrust earthquake, it is crucial to gain information on prehistorical events. We present the results of a submarine paleoseismological study that covers an exceptional ∼120 Kyr‐long period. We studied the sediments sampled in six up to 26 m‐long piston cores collected in deep fore‐arc basins located over the epicentral region of the 1843 earthquake. Using a multiproxy approach combining geophysical, geochemical, and sedimentological analysis, biostratigraphy and radiocarbon dating, we identified, characterized, and dated numerous event deposits that we then correlated with the sampled basins over an up to 160 km‐long area. We show that at least 33 earthquakes likely triggered these sediment remobilizations in the last 120 Kyr. Four of these events promoted exceptional deposits of turbidites + homogenites. From peak ground acceleration calculated for potential earthquakes occurring on various faults, and the absence of deposits linked to the historical earthquakes, we propose that the sources are likely megathrust earthquakes. Over the last 60 Kyr, we inferred at least three 15–25 Kyr‐long seismic cycles in which the recurrence times of earthquakes shortens from ∼5 to ∼2 Kyr.