Pub Date : 2025-01-25DOI: 10.1016/j.tecto.2025.230638
Alison Kirkby , Rob Funnell , Phil Scadden , Anya Seward , Conny Tschritter , Katie Jones
<div><div>Geothermal heat provides a low-carbon energy source, which can be used directly or to produce electricity. It is an important part of New Zealand's energy mix, but to date geothermal use in New Zealand has been focused in known hot regions, particularly the Taupō Volcanic Zone (TVZ), above the subducting Pacific Plate. This study examines the complexity of New Zealand's heat flow and crustal temperature distribution, using borehole temperature measurements and conductive heat flow modelling, with a focus outside the TVZ. The modelling includes the transient heat flow effects of exhumation, basin subsidence and changes in crustal thickness, allowing gaps between sparse direct subsurface temperature measurements to be filled. Variations in New Zealand's heat flow largely reflect its position on a major plate boundary. The forearc region of the Hikurangi Subduction Margin has broadly low heat flow (30–50 mWm<sup>−2</sup>), associated with the down-going Pacific Plate, consistent with evidence from geophysical models and fluid chemistry. Heat flow is elevated in the Coromandel Volcanic Zone (100–140 mWm<sup>−2</sup>), north of the TVZ, which may be associated with volcanism from 18 to 4 Ma. High heat flow in Northland (100–220 mWm<sup>−2</sup>) is associated with more recent igneous activity. High heat flow along the Alpine Fault collisional plate boundary (150–250 mWm<sup>−2</sup>) is largely a result of rock advection (exhumation), which has been occurring at up to 6 mm yr<sup>−1</sup> over the last 2 Ma. These results demonstrate the importance of including transient processes in modelling heat flow in active areas.</div></div><div><h3>Plain language summary</h3><div>Understanding the temperatures in the upper 5–10 km of the Earth is important for many reasons. These include a growing drive to expand the use of geothermal energy, or heat energy in the earth, as a low-carbon way of producing electricity or direct use of heat for processes that would otherwise use electricity or fossil fuels. Knowing the temperature distribution is also important in understanding processes such as earthquake rupture. Subsurface temperatures have been measured in boreholes in some locations, but there are also large areas without any measurements. This paper uses our knowledge of geological processes occurring in New Zealand to predict underground temperatures between measurement locations. The underground temperatures of the Earth generally increase with depth, but the rate of increase varies greatly in different places. This variation is largely due to New Zealand's location on the boundary between two tectonic plates, the Pacific and Australian Plate. In the North Island, the Pacific Plate is subducting beneath the Australian Plate. This causes low crustal temperatures along the southeastern margin of the North Island but high temperatures in the central North Island (Taupō Volcanic Zone). In the South Island, the Pacific and Australian Plates are collid
{"title":"Heat flow in an active plate margin: New Zealand's crustal thermal regime from borehole temperatures and numerical modelling","authors":"Alison Kirkby , Rob Funnell , Phil Scadden , Anya Seward , Conny Tschritter , Katie Jones","doi":"10.1016/j.tecto.2025.230638","DOIUrl":"10.1016/j.tecto.2025.230638","url":null,"abstract":"<div><div>Geothermal heat provides a low-carbon energy source, which can be used directly or to produce electricity. It is an important part of New Zealand's energy mix, but to date geothermal use in New Zealand has been focused in known hot regions, particularly the Taupō Volcanic Zone (TVZ), above the subducting Pacific Plate. This study examines the complexity of New Zealand's heat flow and crustal temperature distribution, using borehole temperature measurements and conductive heat flow modelling, with a focus outside the TVZ. The modelling includes the transient heat flow effects of exhumation, basin subsidence and changes in crustal thickness, allowing gaps between sparse direct subsurface temperature measurements to be filled. Variations in New Zealand's heat flow largely reflect its position on a major plate boundary. The forearc region of the Hikurangi Subduction Margin has broadly low heat flow (30–50 mWm<sup>−2</sup>), associated with the down-going Pacific Plate, consistent with evidence from geophysical models and fluid chemistry. Heat flow is elevated in the Coromandel Volcanic Zone (100–140 mWm<sup>−2</sup>), north of the TVZ, which may be associated with volcanism from 18 to 4 Ma. High heat flow in Northland (100–220 mWm<sup>−2</sup>) is associated with more recent igneous activity. High heat flow along the Alpine Fault collisional plate boundary (150–250 mWm<sup>−2</sup>) is largely a result of rock advection (exhumation), which has been occurring at up to 6 mm yr<sup>−1</sup> over the last 2 Ma. These results demonstrate the importance of including transient processes in modelling heat flow in active areas.</div></div><div><h3>Plain language summary</h3><div>Understanding the temperatures in the upper 5–10 km of the Earth is important for many reasons. These include a growing drive to expand the use of geothermal energy, or heat energy in the earth, as a low-carbon way of producing electricity or direct use of heat for processes that would otherwise use electricity or fossil fuels. Knowing the temperature distribution is also important in understanding processes such as earthquake rupture. Subsurface temperatures have been measured in boreholes in some locations, but there are also large areas without any measurements. This paper uses our knowledge of geological processes occurring in New Zealand to predict underground temperatures between measurement locations. The underground temperatures of the Earth generally increase with depth, but the rate of increase varies greatly in different places. This variation is largely due to New Zealand's location on the boundary between two tectonic plates, the Pacific and Australian Plate. In the North Island, the Pacific Plate is subducting beneath the Australian Plate. This causes low crustal temperatures along the southeastern margin of the North Island but high temperatures in the central North Island (Taupō Volcanic Zone). In the South Island, the Pacific and Australian Plates are collid","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"899 ","pages":"Article 230638"},"PeriodicalIF":2.7,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143204528","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
As one of the most renowned continental rifts on Earth, the East African Rift System (EARS) is characterized by intense rifting and active volcanic activity, creating a favorable geological setting for the development of crustal discontinuity and ground fissures. In this study, crustal discontinuities are defined as regions of weakness resulting from fault activity and crust-mantle interaction. This study investigates the crustal discontinuity in the Central Kenyan Rift (CKR) through a multidisciplinary approach that includes mapping, trenching, gas geochemical testing, magnetotellurics, surface deformation analysis, correlation analysis and geodynamic modelling. A total of 83 ground fissures were identified, mostly distributed along the eastern side of the rift zone and are primarily characterized by opening and uplifting of the flank. Helium isotope values (RC/RA) of gases escaping the fissures were generally greater than 0.2. Compared to the volcanic gases, those from the fissure is more indicative of mantle origin. Fissured areas are located above two crustal discontinuities identified by low-resistivity zones. These discontinuities (weakness) are located at depths of approximately 1 km and 5–20 km, with thicknesses of 200–600 m and 2–14 km, respectively. In the areas with deep discontinuities, the thicknesses of the anomaly zone increase with the RC/RA values, while the opposite is observed in the areas with shallow discontinuities. The spatial distribution of fissures suggests the westward-dipping mantle plume in the EARS is the main cause of the crustal discontinuity. This research not only enhances the understanding of the crust-mantle interaction in EARS but also aids in evaluating the fracture network in the crust.
{"title":"Mantle influence on crustal discontinuity revealed by He isotopes and resistivity in the East African Rift System","authors":"Zhijie Jia , Jianbing Peng , Pietro Sternai , Quanzhong Lu , Weiliang Huang , Lingqiang Zhao , Jiewei Zhan , Qiang Xu","doi":"10.1016/j.tecto.2025.230637","DOIUrl":"10.1016/j.tecto.2025.230637","url":null,"abstract":"<div><div>As one of the most renowned continental rifts on Earth, the East African Rift System (EARS) is characterized by intense rifting and active volcanic activity, creating a favorable geological setting for the development of crustal discontinuity and ground fissures. In this study, crustal discontinuities are defined as regions of weakness resulting from fault activity and crust-mantle interaction. This study investigates the crustal discontinuity in the Central Kenyan Rift (CKR) through a multidisciplinary approach that includes mapping, trenching, gas geochemical testing, magnetotellurics, surface deformation analysis, correlation analysis and geodynamic modelling. A total of 83 ground fissures were identified, mostly distributed along the eastern side of the rift zone and are primarily characterized by opening and uplifting of the flank. Helium isotope values (R<sub>C</sub>/R<sub>A</sub>) of gases escaping the fissures were generally greater than 0.2. Compared to the volcanic gases, those from the fissure is more indicative of mantle origin. Fissured areas are located above two crustal discontinuities identified by low-resistivity zones. These discontinuities (weakness) are located at depths of approximately 1 km and 5–20 km, with thicknesses of 200–600 m and 2–14 km, respectively. In the areas with deep discontinuities, the thicknesses of the anomaly zone increase with the R<sub>C</sub>/R<sub>A</sub> values, while the opposite is observed in the areas with shallow discontinuities. The spatial distribution of fissures suggests the westward-dipping mantle plume in the EARS is the main cause of the crustal discontinuity. This research not only enhances the understanding of the crust-mantle interaction in EARS but also aids in evaluating the fracture network in the crust.</div></div>","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"898 ","pages":"Article 230637"},"PeriodicalIF":2.7,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143072469","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-25DOI: 10.1016/j.tecto.2025.230639
Briant García , César J. Guevara-Pillaca , Martyn Unsworth , Patrizia Pereyra , Carlos Benavente , Andy Combey , Daniel Palacios , Anderson Palomino , Rafael Ponce , Lorena Rosell , Alonso Muñoz
This study presents a novel approach to identifying and characterizing active faults in urban areas, using an example from the city of Cusco in Peru, by combining magnetotelluric (MT) exploration and radon gas monitoring. The research aims to improve understanding of the active faults in the Cusco Valley by using the MT method to provide subsurface electrical resistivity data, enabling the mapping of fault structures and determination of fault properties. A 2-D inversion of the MT data resulted in resistivity models that revealed critical information about fault geometry, such as dip and depth. Radon gas measurements complement the MT data by being able to distinguish between active and inactive faults. This is because active faults can exhibit higher permeability due to ongoing tectonic activity. This increased permeability facilitates the migration of radon from deeper rock formations to the surface, leading to detectable anomalies. Active faults are particularly significant as their continued deformation enhances permeability, making radon anomalies a valuable indicator for locating these structures. A clear correlation was found between elevated radon concentrations (>5.9 kBq m−3) and the locations of faults identified through the MT resistivity model, and additional gas sample analyses ruled out the possibility that these anomalies were caused by lithological variations. This integrated approach holds significant potential for detecting active faults in urban areas such as Cusco. In these locations faults such as the Cusco and Alto Qosqo faults may be obscured by construction. The findings uncovered previously unmapped fault lineaments and advanced the understanding of fault kinematics in Cusco, emphasizing the importance of combining MT and radon monitoring for earthquake hazard assessment in urban environments.
{"title":"Locating active faults in the Cusco Valley using magnetotelluric and radon gas data","authors":"Briant García , César J. Guevara-Pillaca , Martyn Unsworth , Patrizia Pereyra , Carlos Benavente , Andy Combey , Daniel Palacios , Anderson Palomino , Rafael Ponce , Lorena Rosell , Alonso Muñoz","doi":"10.1016/j.tecto.2025.230639","DOIUrl":"10.1016/j.tecto.2025.230639","url":null,"abstract":"<div><div>This study presents a novel approach to identifying and characterizing active faults in urban areas, using an example from the city of Cusco in Peru, by combining magnetotelluric (MT) exploration and radon gas monitoring. The research aims to improve understanding of the active faults in the Cusco Valley by using the MT method to provide subsurface electrical resistivity data, enabling the mapping of fault structures and determination of fault properties. A 2-D inversion of the MT data resulted in resistivity models that revealed critical information about fault geometry, such as dip and depth. Radon gas measurements complement the MT data by being able to distinguish between active and inactive faults. This is because active faults can exhibit higher permeability due to ongoing tectonic activity. This increased permeability facilitates the migration of radon from deeper rock formations to the surface, leading to detectable anomalies. Active faults are particularly significant as their continued deformation enhances permeability, making radon anomalies a valuable indicator for locating these structures. A clear correlation was found between elevated radon concentrations (>5.9 kBq m<sup>−3</sup>) and the locations of faults identified through the MT resistivity model, and additional gas sample analyses ruled out the possibility that these anomalies were caused by lithological variations. This integrated approach holds significant potential for detecting active faults in urban areas such as Cusco. In these locations faults such as the Cusco and Alto Qosqo faults may be obscured by construction. The findings uncovered previously unmapped fault lineaments and advanced the understanding of fault kinematics in Cusco, emphasizing the importance of combining MT and radon monitoring for earthquake hazard assessment in urban environments.</div></div>","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"898 ","pages":"Article 230639"},"PeriodicalIF":2.7,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143072466","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-25DOI: 10.1016/j.tecto.2025.230636
Haiyan Li , Juqing Chen , Zhengbo Li , Xiaofei Chen , Huiteng Cai , Xuping Feng , Gongheng Zhang , Zhen Jin
Southeastern Coastal China, located at the southeastern margin of the Eurasian continent, is an essential part of the South China Block. It is characterized by extensive Mesozoic magmatism and polymetallic mineralization. To explore the potential impact of Mesozoic magmatic events on the crust, we analyzed inter-station cross-correlation functions from 878 seismic stations. Utilizing the recently developed frequency-Bessel transform method, we extracted multimodal Rayleigh wave dispersion curves and constructed an updated 3D shear-wave velocity model. Our model reveals prominent and widespread mid-crustal low-velocity zones (MCLVZs) across the study area, likely attributable to the alpha-beta quartz phase transition. Additionally, a strong correlation is observed between MCLVZs characteristics and Jurassic-Cretaceous magmatic activities, with a southwest-to-northeast variation in MCLVZs continuity and intensity, reflecting the spatiotemporal migration of magmatism. These findings offer new constraints on the tectonic evolution of Southeastern Coastal China.
{"title":"Mid-crustal low-velocity zones beneath Southeastern Coastal China revealed by multimodal ambient noise tomography: Insights into Mesozoic magmatic activities","authors":"Haiyan Li , Juqing Chen , Zhengbo Li , Xiaofei Chen , Huiteng Cai , Xuping Feng , Gongheng Zhang , Zhen Jin","doi":"10.1016/j.tecto.2025.230636","DOIUrl":"10.1016/j.tecto.2025.230636","url":null,"abstract":"<div><div>Southeastern Coastal China, located at the southeastern margin of the Eurasian continent, is an essential part of the South China Block. It is characterized by extensive Mesozoic magmatism and polymetallic mineralization. To explore the potential impact of Mesozoic magmatic events on the crust, we analyzed inter-station cross-correlation functions from 878 seismic stations. Utilizing the recently developed frequency-Bessel transform method, we extracted multimodal Rayleigh wave dispersion curves and constructed an updated 3D shear-wave velocity model. Our model reveals prominent and widespread mid-crustal low-velocity zones (MCLVZs) across the study area, likely attributable to the alpha-beta quartz phase transition. Additionally, a strong correlation is observed between MCLVZs characteristics and Jurassic-Cretaceous magmatic activities, with a southwest-to-northeast variation in MCLVZs continuity and intensity, reflecting the spatiotemporal migration of magmatism. These findings offer new constraints on the tectonic evolution of Southeastern Coastal China.</div></div>","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"898 ","pages":"Article 230636"},"PeriodicalIF":2.7,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143072467","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-24DOI: 10.1016/j.tecto.2024.230600
Hsin Tung , Horng-Yue Chen , Ya-Ju Hsu , Chi-Hsien Tang , Jian-Cheng Lee , Yu Wang , Hung Kyu Lee
We characterize the spatiotemporal patterns of ground deformation caused by an earthquake doublet: the September 17, 2022, ML 6.6 Guanshan and the September 18, 2022, ML 6.8 Chihshang earthquakes occurred on the Central Range fault, eastern Taiwan. We use geodetic data collected from continuous and campaign-mode GNSS stations, as well as two precise leveling routes to estimate coseismic displacements and invert for fault slip distributions. The ML 6.6 foreshock caused northwestward horizontal displacements and uplift reaching 200 mm and 170 mm, respectively, in the region between Chihshang and Taitung. Seventeen hours later, the ML 6.8 mainshock generated coseismic displacements about four times larger than the foreshock, with horizontal displacements exceeding 900 mm and vertical displacements of 800 mm in the area between Guanshan and Ruisui. The maximum horizontal and vertical coseismic displacements of the entire earthquake sequence exceed one meter. The epoch-by-epoch high-rate GNSS data reveal significant seismic shaking, with maximum displacement exceeding 600 mm and 1100 mm during the foreshock and mainshock ruptures, respectively, correlating with severe infrastructure damage near surface ruptures. The dense spatial coverage of networks allows us to map the largest surface deformation along the Yuli fault, a branch of the steeply west-dipping Central Range fault, as well as the associated pop-ups along the east-dipping Longitudinal Valley fault. This observation suggests a likely coseismic and/or postseismic slip along the Longitudinal Valley fault. Our slip model indicates a maximum slip of approximately 3 m at a depth of 4.5 km to the west of Yuli, primarily on the Central Range fault. The coseismic slip extends over 50 km along the fault with two asperities near the hypocenter and Yuli. In addition, the Longitudinal Valley fault is characterized by shallow slip, with a maximum of 0.85 m at depths of 0–3 km.
{"title":"Geodetic constraints on the September 2022 Guanshan and Chihshang earthquakes, eastern Taiwan","authors":"Hsin Tung , Horng-Yue Chen , Ya-Ju Hsu , Chi-Hsien Tang , Jian-Cheng Lee , Yu Wang , Hung Kyu Lee","doi":"10.1016/j.tecto.2024.230600","DOIUrl":"10.1016/j.tecto.2024.230600","url":null,"abstract":"<div><div>We characterize the spatiotemporal patterns of ground deformation caused by an earthquake doublet: the September 17, 2022, M<sub>L</sub> 6.6 Guanshan and the September 18, 2022, M<sub>L</sub> 6.8 Chihshang earthquakes occurred on the Central Range fault, eastern Taiwan. We use geodetic data collected from continuous and campaign-mode GNSS stations, as well as two precise leveling routes to estimate coseismic displacements and invert for fault slip distributions. The M<sub>L</sub> 6.6 foreshock caused northwestward horizontal displacements and uplift reaching 200 mm and 170 mm, respectively, in the region between Chihshang and Taitung. Seventeen hours later, the M<sub>L</sub> 6.8 mainshock generated coseismic displacements about four times larger than the foreshock, with horizontal displacements exceeding 900 mm and vertical displacements of 800 mm in the area between Guanshan and Ruisui. The maximum horizontal and vertical coseismic displacements of the entire earthquake sequence exceed one meter. The epoch-by-epoch high-rate GNSS data reveal significant seismic shaking, with maximum displacement exceeding 600 mm and 1100 mm during the foreshock and mainshock ruptures, respectively, correlating with severe infrastructure damage near surface ruptures. The dense spatial coverage of networks allows us to map the largest surface deformation along the Yuli fault, a branch of the steeply west-dipping Central Range fault, as well as the associated pop-ups along the east-dipping Longitudinal Valley fault. This observation suggests a likely coseismic and/or postseismic slip along the Longitudinal Valley fault. Our slip model indicates a maximum slip of approximately 3 m at a depth of 4.5 km to the west of Yuli, primarily on the Central Range fault. The coseismic slip extends over 50 km along the fault with two asperities near the hypocenter and Yuli. In addition, the Longitudinal Valley fault is characterized by shallow slip, with a maximum of 0.85 m at depths of 0–3 km.</div></div>","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"895 ","pages":"Article 230600"},"PeriodicalIF":2.7,"publicationDate":"2025-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142821058","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-24DOI: 10.1016/j.tecto.2024.230576
Yanqiang Wu , Changyun Chen , Zaisen Jiang , Jingwei Li , Mikhail Vladimir Rodkin , Valeri Grigorevich Gitis , Yajin Pang , Yuan Li
Strain accumulation is closely related to the occurrence of strong earthquakes. To investigate the pre-seismic deformation status of strong earthquakes, the correlation between the GNSS (Global Navigation Satellite System) strain rates and earthquakes subsequent to the GNSS observation period in Western China was studied. The primary results show that a large part of MW ≥ 6.0 earthquakes occurred in the medium and low value regions (MLVR) of the second invariant of strain rate (SR). Meanwhile, about 81 % of strike-slip earthquakes occurred in the MLVR of the maximum shear strain rate, and the ratios are 72 % and 100.0 % for the reverse-faulting and normal-faulting earthquakes in the MLVR of principal compressive and tensile strain rates, respectively. The sustained slow fault slip rates, complex faults in different stages of inter-seismic period, and historical earthquakes, may possibly cause the typical strain rate patterns for the pre-seismic stage. Therefore, Mw ≥ 6.0 earthquakes possibly occur in MLVR of strain rates, and low strain rate is not an indicative of low-potential of strong earthquakes.
{"title":"Are strain rate lows proxies of low-potential of strong earthquakes? A case study in Western China","authors":"Yanqiang Wu , Changyun Chen , Zaisen Jiang , Jingwei Li , Mikhail Vladimir Rodkin , Valeri Grigorevich Gitis , Yajin Pang , Yuan Li","doi":"10.1016/j.tecto.2024.230576","DOIUrl":"10.1016/j.tecto.2024.230576","url":null,"abstract":"<div><div>Strain accumulation is closely related to the occurrence of strong earthquakes. To investigate the pre-seismic deformation status of strong earthquakes, the correlation between the GNSS (Global Navigation Satellite System) strain rates and earthquakes subsequent to the GNSS observation period in Western China was studied. The primary results show that a large part of <em>M</em><sub>W</sub> ≥ 6.0 earthquakes occurred in the medium and low value regions (MLVR) of the second invariant of strain rate (SR). Meanwhile, about 81 % of strike-slip earthquakes occurred in the MLVR of the maximum shear strain rate, and the ratios are 72 % and 100.0 % for the reverse-faulting and normal-faulting earthquakes in the MLVR of principal compressive and tensile strain rates, respectively. The sustained slow fault slip rates, complex faults in different stages of inter-seismic period, and historical earthquakes, may possibly cause the typical strain rate patterns for the pre-seismic stage. Therefore, <em>M</em>w ≥ 6.0 earthquakes possibly occur in MLVR of strain rates, and low strain rate is not an indicative of low-potential of strong earthquakes.</div></div>","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"895 ","pages":"Article 230576"},"PeriodicalIF":2.7,"publicationDate":"2025-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143181520","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-24DOI: 10.1016/j.tecto.2024.230580
Julian Lozos , Sinan Akçiz , Holland Ladage
Following the July 2019 Ridgecrest, California earthquakes, multiple field investigators noted that pebble- to boulder-sized rocks had been displaced from their position in the desert pavement within a stepover along the right-lateral strike-slip M7.1 rupture trace, without evidence of dragging or shearing. This implies localized ground motions in excess of 1 g, in contrast to the instrumentally recorded peak of 0.57 g. Similar rock displacement occurred in a stepover in the predominantly strike-slip 2010 M7.2 El Mayor-Cucapah earthquake. Together, these examples suggest that some aspect of how earthquake rupture negotiates a strike-slip fault stepover produces extremely localized strong ground acceleration. Here, we use the 3D finite element method to investigate how rupture through a variety of strike-slip stepover geometries influences strong ground acceleration. For subshear ruptures, we find that the presence of a stepover in general matters more than its dimensions; the strongest ground acceleration always occurs at the end of the first fault. For supershear ruptures, the stepover is effectively irrelevant, since the strongest particle acceleration occurs at the point of the supershear transition on the first fault. Our model subshear and supershear ruptures alike do produce horizontal particle acceleration above 1 g, but over a region so close to the fault (< 1 km) that a seismic network may not catch it. We suggest that the physics of rupture through a fault stepover could have been responsible for the displaced rocks in the Ridgecrest and El Mayor-Cucapah earthquakes, and that stepover regions may have particularly high ground motion hazard. Our study suggests that ground motion predictions and local hazard assessments should account for much stronger accelerations in the immediate near field of active faults, especially around stepovers and other geometrical discontinuities.
{"title":"Modeling the rupture dynamics of strong ground motion (> 1 g) in fault stepovers","authors":"Julian Lozos , Sinan Akçiz , Holland Ladage","doi":"10.1016/j.tecto.2024.230580","DOIUrl":"10.1016/j.tecto.2024.230580","url":null,"abstract":"<div><div>Following the July 2019 Ridgecrest, California earthquakes, multiple field investigators noted that pebble- to boulder-sized rocks had been displaced from their position in the desert pavement within a stepover along the right-lateral strike-slip M7.1 rupture trace, without evidence of dragging or shearing. This implies localized ground motions in excess of 1 g, in contrast to the instrumentally recorded peak of 0.57 g. Similar rock displacement occurred in a stepover in the predominantly strike-slip 2010 M7.2 El Mayor-Cucapah earthquake. Together, these examples suggest that some aspect of how earthquake rupture negotiates a strike-slip fault stepover produces extremely localized strong ground acceleration. Here, we use the 3D finite element method to investigate how rupture through a variety of strike-slip stepover geometries influences strong ground acceleration. For subshear ruptures, we find that the presence of a stepover in general matters more than its dimensions; the strongest ground acceleration always occurs at the end of the first fault. For supershear ruptures, the stepover is effectively irrelevant, since the strongest particle acceleration occurs at the point of the supershear transition on the first fault. Our model subshear and supershear ruptures alike do produce horizontal particle acceleration above 1 g, but over a region so close to the fault (< 1 km) that a seismic network may not catch it. We suggest that the physics of rupture through a fault stepover could have been responsible for the displaced rocks in the Ridgecrest and El Mayor-Cucapah earthquakes, and that stepover regions may have particularly high ground motion hazard. Our study suggests that ground motion predictions and local hazard assessments should account for much stronger accelerations in the immediate near field of active faults, especially around stepovers and other geometrical discontinuities.</div></div>","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"895 ","pages":"Article 230580"},"PeriodicalIF":2.7,"publicationDate":"2025-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143181956","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A central goal of laboratory seismology is to infer large-scale seismic processes from small-scale experiments, with acoustic emissions (AE) being a common observable. These signals, indicative of microfracturing, slip localization, and damage evolution, are often paralleled with earthquakes to understand seismic behaviors. This study challenges traditional perspectives by applying Coulomb rate-and-state seismicity theory, originally developed for earthquake clustering, to AE experiments. This theory maps stressing history to seismicity rates using rate-and-state friction, however, its validity under controlled experimental conditions remains an open question. We conducted four experiments on a sawcut sample of red felser sandstone, representing a fault under variable stress conditions. Adjustments in loading rates and initial conditions revealed that, while a single free parameter —related to the direct effect—should suffice, a rescaling of the model by 1.5 to 2.2 was necessary for fitting the data. Differences in values across experiments appeared mostly non-systematic, and partial data usage did not yield consistently systematic parameter migrations. These findings suggest that fault microstructure may complexly alter parameter values during loading beyond what is accounted for in the Coulomb rate-and-state theory. Nonetheless, with the introduction of the scaling parameter, the Coulomb rate-and-state theory effectively captures the fundamental aspects of AE responses to complex controlled loading histories.
{"title":"Applying and validating Coulomb rate-and-state seismicity models in acoustic emission experiments","authors":"Elías Rafn Heimisson , Milad Naderloo , Debanjan Chandra , Auke Barnhoorn","doi":"10.1016/j.tecto.2024.230574","DOIUrl":"10.1016/j.tecto.2024.230574","url":null,"abstract":"<div><div>A central goal of laboratory seismology is to infer large-scale seismic processes from small-scale experiments, with acoustic emissions (AE) being a common observable. These signals, indicative of microfracturing, slip localization, and damage evolution, are often paralleled with earthquakes to understand seismic behaviors. This study challenges traditional perspectives by applying Coulomb rate-and-state seismicity theory, originally developed for earthquake clustering, to AE experiments. This theory maps stressing history to seismicity rates using rate-and-state friction, however, its validity under controlled experimental conditions remains an open question. We conducted four experiments on a sawcut sample of red felser sandstone, representing a fault under variable stress conditions. Adjustments in loading rates and initial conditions revealed that, while a single free parameter <span><math><mi>A</mi></math></span>—related to the direct effect—should suffice, a rescaling of the model by 1.5 to 2.2 was necessary for fitting the data. Differences in values across experiments appeared mostly non-systematic, and partial data usage did not yield consistently systematic parameter migrations. These findings suggest that fault microstructure may complexly alter parameter values during loading beyond what is accounted for in the Coulomb rate-and-state theory. Nonetheless, with the introduction of the scaling parameter, the Coulomb rate-and-state theory effectively captures the fundamental aspects of AE responses to complex controlled loading histories.</div></div>","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"895 ","pages":"Article 230574"},"PeriodicalIF":2.7,"publicationDate":"2025-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143181521","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-24DOI: 10.1016/j.tecto.2024.230579
Motoya Suzuki, Dapeng Zhao, Genti Toyokuni, Ryota Takagi
We measure and analyze 4381 P-wave and 4307 S-wave arrival times of 48 teleseismic events recorded at 150 stations of a permanent seafloor seismic network (S-net) installed in the outer-rise and forearc region off East Japan. The obtained relative travel-time residuals amounting to ∼3 s at the S-net stations are generally negative on the incoming Pacific and Philippine Sea plates and positive on the continental Okhotsk plate, which reflect high and low seismic velocities, respectively. This pattern is generally consistent with previous results on the seismic velocity structure of the crust and upper mantle beneath the East Japan forearc and the outer-rise area. Large early arrivals (∼2.0 s) appear in the southern part of the S-net for the teleseismic events in the southwestern direction, which are mainly due to southwestward steepening of the subducting Pacific slab beneath Kanto. In the study region, the Pacific slab is the most significant anomaly with a thickness of ∼90 km and a seismic velocity of 5–6 % higher than that of the surrounding mantle. Early arrivals (∼1.5 s) also appear at the S-net stations off South Hokkaido, which are caused by northwestward steepening of the Pacific slab beneath the Tohoku-Hokkaido junction area. These results shed new light on the structural heterogeneity and subduction dynamics of the East Japan arc.
{"title":"Teleseismic evidence for structural heterogeneity in East Japan forearc from seafloor S-net data","authors":"Motoya Suzuki, Dapeng Zhao, Genti Toyokuni, Ryota Takagi","doi":"10.1016/j.tecto.2024.230579","DOIUrl":"10.1016/j.tecto.2024.230579","url":null,"abstract":"<div><div>We measure and analyze 4381 P-wave and 4307 S-wave arrival times of 48 teleseismic events recorded at 150 stations of a permanent seafloor seismic network (S-net) installed in the outer-rise and forearc region off East Japan. The obtained relative travel-time residuals amounting to ∼3 s at the S-net stations are generally negative on the incoming Pacific and Philippine Sea plates and positive on the continental Okhotsk plate, which reflect high and low seismic velocities, respectively. This pattern is generally consistent with previous results on the seismic velocity structure of the crust and upper mantle beneath the East Japan forearc and the outer-rise area. Large early arrivals (∼2.0 s) appear in the southern part of the S-net for the teleseismic events in the southwestern direction, which are mainly due to southwestward steepening of the subducting Pacific slab beneath Kanto. In the study region, the Pacific slab is the most significant anomaly with a thickness of ∼90 km and a seismic velocity of 5–6 % higher than that of the surrounding mantle. Early arrivals (∼1.5 s) also appear at the S-net stations off South Hokkaido, which are caused by northwestward steepening of the Pacific slab beneath the Tohoku-Hokkaido junction area. These results shed new light on the structural heterogeneity and subduction dynamics of the East Japan arc.</div></div>","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"895 ","pages":"Article 230579"},"PeriodicalIF":2.7,"publicationDate":"2025-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142788825","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-24DOI: 10.1016/j.tecto.2024.230582
Kyle Homman, Andrew Nyblade
Focal mechanisms for small magnitude earthquakes (M ∼ 1.3–4.1) in the mid-Atlantic region of the United States have been determined using a double-couple moment tensor inversion procedure. The 26 new focal mechanisms obtained, when combined with previously published mechanisms, show a pattern of reverse faulting in the easternmost portion of the study area and strike-slip faulting in the west, consistent with previous studies. The change in focal mechanisms from east to west helps to constrain the geographic location of the east-west transition in the stress regime to a NE-SW area within central Pennsylvania within proximity of the Allegheny Front. Stress inversions performed to constrain variations in the stress state across the region show that the maximum compressive stress varies only slightly, but that the near-vertical stress is the minimum compressive stress in the east and transitions to the intermediate compressive stress in the west, as expected for an east-west transition in reverse to strike-slip faulting. Analysis of driving forces causing the stress change suggests that tectonic terrane structure, glacial isostatic adjustment, and changes in gravitational potential energy have little effect on the stress field in this region, leaving the interaction of sublithospheric mantle flow with the eastern edge of the Laurentian cratonic lithosphere beneath central Pennsylvania as a primary explanation. The cratonic lithospheric keel may cause a deflection in mantle flow, thereby changing the stress field enough so that the magnitude of the vertical stress in relation to the minimum horizontal stress results in strike-slip as opposed to reverse faulting.
{"title":"Moment tensors for small earthquakes and the stress regime in the mid-Atlantic United States","authors":"Kyle Homman, Andrew Nyblade","doi":"10.1016/j.tecto.2024.230582","DOIUrl":"10.1016/j.tecto.2024.230582","url":null,"abstract":"<div><div>Focal mechanisms for small magnitude earthquakes (M ∼ 1.3–4.1) in the mid-Atlantic region of the United States have been determined using a double-couple moment tensor inversion procedure. The 26 new focal mechanisms obtained, when combined with previously published mechanisms, show a pattern of reverse faulting in the easternmost portion of the study area and strike-slip faulting in the west, consistent with previous studies. The change in focal mechanisms from east to west helps to constrain the geographic location of the east-west transition in the stress regime to a NE-SW area within central Pennsylvania within proximity of the Allegheny Front. Stress inversions performed to constrain variations in the stress state across the region show that the maximum compressive stress varies only slightly, but that the near-vertical stress is the minimum compressive stress in the east and transitions to the intermediate compressive stress in the west, as expected for an east-west transition in reverse to strike-slip faulting. Analysis of driving forces causing the stress change suggests that tectonic terrane structure, glacial isostatic adjustment, and changes in gravitational potential energy have little effect on the stress field in this region, leaving the interaction of sublithospheric mantle flow with the eastern edge of the Laurentian cratonic lithosphere beneath central Pennsylvania as a primary explanation. The cratonic lithospheric keel may cause a deflection in mantle flow, thereby changing the stress field enough so that the magnitude of the vertical stress in relation to the minimum horizontal stress results in strike-slip as opposed to reverse faulting.</div></div>","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"895 ","pages":"Article 230582"},"PeriodicalIF":2.7,"publicationDate":"2025-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142788826","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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