The tectonic setting of the Oligo-Miocene Cura Mallín Basin in the southern Central Andes has been a topic of debate in recent years. Proposed models include extensional, compressional, and a hybrid-sequential model with an initial extension (∼20 Ma) followed by contraction (∼19 Ma). We conducted a detailed structural analysis to understand the tectonic evolution of the Cura Mallín Basin at the eastern Andean slope in the Guañacos Fold and Thrust Belt (FTB) (37°-38°S). This tectonic element provides exceptional exposure of the upper sedimentary infill of the Cura Mallín Basin. Despite detailed studies about composition, the structural configuration of this basin remains poorly understood. This study refines the age of the upper Cura Mallín Formation on the eastern Andean slope with a new detrital U/Pb date of 15.47 ± 0.28 Ma from the basal portion of the sedimentary sequence, indicating a maximum Middle Miocene deposition, in contrasts with the previous Oligo-Miocene age. This work presents the first balanced cross-sections for the Guañacos FTB. Structural analysis reveals a thin-skinned deformation style, contrasting with previous interpretations of thick-skinned deformation, with shortenings of 9.6 km (29 %) and 8.5 km (24 %). Therefore, significant Andean contraction at these latitudes was absorbed by the Guañacos FTB. Our model assumes that all deformation in the Cura Mallín Formation postdates deposition. Contractional deformation began on the Chilean Andean slope by ∼18.7 Ma, jumped to the Argentinean side at ∼12.5 Ma, and persisted beyond 6.5 Ma, with progressively diminishing intensity. Combined evidence from the Guañacos FTB and the eastern Chos Malal FTB, suggests synchronous deformation throughout the entire orogen during the Late Miocene. Additionally, these two belts record the reactivation of Miocene thrust faults during the Quaternary. This reactivation is potentially linked to the apparent persistence of the regional stress field since the Late Miocene.
{"title":"Structural style of the Guañacos Fold and Thrust Belt (southern Central Andes): A tectonic setting for the Cura Mallín Basin revisited","authors":"Lucía Jagoe, Martín Turienzo, Lucía Sagripanti, Natalia Sánchez, Andrés Folguera","doi":"10.1016/j.tecto.2024.230611","DOIUrl":"https://doi.org/10.1016/j.tecto.2024.230611","url":null,"abstract":"The tectonic setting of the Oligo-Miocene Cura Mallín Basin in the southern Central Andes has been a topic of debate in recent years. Proposed models include extensional, compressional, and a hybrid-sequential model with an initial extension (∼20 Ma) followed by contraction (∼19 Ma). We conducted a detailed structural analysis to understand the tectonic evolution of the Cura Mallín Basin at the eastern Andean slope in the Guañacos Fold and Thrust Belt (FTB) (37°-38°S). This tectonic element provides exceptional exposure of the upper sedimentary infill of the Cura Mallín Basin. Despite detailed studies about composition, the structural configuration of this basin remains poorly understood. This study refines the age of the upper Cura Mallín Formation on the eastern Andean slope with a new detrital U/Pb date of 15.47 ± 0.28 Ma from the basal portion of the sedimentary sequence, indicating a maximum Middle Miocene deposition, in contrasts with the previous Oligo-Miocene age. This work presents the first balanced cross-sections for the Guañacos FTB. Structural analysis reveals a thin-skinned deformation style, contrasting with previous interpretations of thick-skinned deformation, with shortenings of 9.6 km (29 %) and 8.5 km (24 %). Therefore, significant Andean contraction at these latitudes was absorbed by the Guañacos FTB. Our model assumes that all deformation in the Cura Mallín Formation postdates deposition. Contractional deformation began on the Chilean Andean slope by ∼18.7 Ma, jumped to the Argentinean side at ∼12.5 Ma, and persisted beyond 6.5 Ma, with progressively diminishing intensity. Combined evidence from the Guañacos FTB and the eastern Chos Malal FTB, suggests synchronous deformation throughout the entire orogen during the Late Miocene. Additionally, these two belts record the reactivation of Miocene thrust faults during the Quaternary. This reactivation is potentially linked to the apparent persistence of the regional stress field since the Late Miocene.","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"2 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142967739","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 : 2025-01-07DOI: 10.1016/j.tecto.2025.230622
Salma Zerouali Masror, Ahmed Ntarmouchant, Mustapha Elabouyi, Telmo M. Bento dos Santos, Ahmed Manar, My Hachem Smaili, Brahim Mali, Nahla Ntarmouchant, Badr El Mahrad, Youssef Driouch, Pedro Cachapuz, Tiago Catita, El Mehdi Jeddi
Located in NW Morocco, Gharb Basin (GB) is a part of the foreland basin that was formed at the front of the Rif cordillera. It stands as a transition zone between the Maamora Plateau, to the South, and the Rif Belt, to the North. The first features of this basin began to appear in the Middle Miocene due to the compression caused by the convergence of Eurasia and Africa. The correlation of drilling data with gravity and aeromagnetic data, as well as the use of seismic data, has made it possible to reconstruct the architecture of this basin and to identify new structures responsible for the Neogene evolution of this region.
{"title":"Subsurface structure of a foreland basin from analysis of gravity and aeromagnetic data: Revealing the basement structure of Gharb Basin, NW Morocco","authors":"Salma Zerouali Masror, Ahmed Ntarmouchant, Mustapha Elabouyi, Telmo M. Bento dos Santos, Ahmed Manar, My Hachem Smaili, Brahim Mali, Nahla Ntarmouchant, Badr El Mahrad, Youssef Driouch, Pedro Cachapuz, Tiago Catita, El Mehdi Jeddi","doi":"10.1016/j.tecto.2025.230622","DOIUrl":"https://doi.org/10.1016/j.tecto.2025.230622","url":null,"abstract":"Located in NW Morocco, Gharb Basin (GB) is a part of the foreland basin that was formed at the front of the Rif cordillera. It stands as a transition zone between the Maamora Plateau, to the South, and the Rif Belt, to the North. The first features of this basin began to appear in the Middle Miocene due to the compression caused by the convergence of Eurasia and Africa. The correlation of drilling data with gravity and aeromagnetic data, as well as the use of seismic data, has made it possible to reconstruct the architecture of this basin and to identify new structures responsible for the Neogene evolution of this region.","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"49 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142967740","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 : 2025-01-03DOI: 10.1016/j.tecto.2024.230612
Kamil A. Qureshi PhD, Shuhab D. Khan PhD, Ozzy Tirmizi PhD, Zaid Khan
This research evaluated the current rate of surface deformation in the Western Himalayas, focusing on the western Salt Range and the Trans Indus Ranges. The study focused on identifying the presence of a ductile detachment and its correlation with seismic activity. We utilized the InSAR-SBAS (small baseline subset) method and 2D reflection seismic interpretation to analyze 2937 Sentinel-1 A interferograms collected from 2017 to 2023. The findings indicate that the western Salt Range, Kalabagh Fault, and Marwat-Khisor Ranges (Bannu Basin) are currently experiencing aseismic creep, with average surface deformation rates of 6 mm/year, 5.5 mm/year, and 7.6 mm/year, respectively. Interestingly, no surface deformation was observed in the Surghar Range front, although seismicity is mainly concentrated in the Kohat Fold-Thrust Belt. Despite experiencing a 5.2 Mw earthquake in 2018, the Kurram thrust does not show any surface deformation. The Global Navigation Satellite Systems (GNSS)-derived movement rates for the Salt Range and Kalabagh Fault align with the InSAR results. We also found that the presence of a single regional detachment (Precambrian Salt Range Formation) facilitates the aseismic movement of the Potwar and Bannu thrust sheet over the Punjab Foreland region, in contrast to the multiple detachments in the Kohat Fold-Thrust Belt.
{"title":"Surface deformation and geometry of the Himalayan frontal thrust system in Pakistan: An insight from InSAR and seismic interpretation","authors":"Kamil A. Qureshi PhD, Shuhab D. Khan PhD, Ozzy Tirmizi PhD, Zaid Khan","doi":"10.1016/j.tecto.2024.230612","DOIUrl":"https://doi.org/10.1016/j.tecto.2024.230612","url":null,"abstract":"This research evaluated the current rate of surface deformation in the Western Himalayas, focusing on the western Salt Range and the Trans Indus Ranges. The study focused on identifying the presence of a ductile detachment and its correlation with seismic activity. We utilized the InSAR-SBAS (small baseline subset) method and 2D reflection seismic interpretation to analyze 2937 Sentinel-1 A interferograms collected from 2017 to 2023. The findings indicate that the western Salt Range, Kalabagh Fault, and Marwat-Khisor Ranges (Bannu Basin) are currently experiencing aseismic creep, with average surface deformation rates of 6 mm/year, 5.5 mm/year, and 7.6 mm/year, respectively. Interestingly, no surface deformation was observed in the Surghar Range front, although seismicity is mainly concentrated in the Kohat Fold-Thrust Belt. Despite experiencing a 5.2 Mw earthquake in 2018, the Kurram thrust does not show any surface deformation. The Global Navigation Satellite Systems (GNSS)-derived movement rates for the Salt Range and Kalabagh Fault align with the InSAR results. We also found that the presence of a single regional detachment (Precambrian Salt Range Formation) facilitates the aseismic movement of the Potwar and Bannu thrust sheet over the Punjab Foreland region, in contrast to the multiple detachments in the Kohat Fold-Thrust Belt.","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"82 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142967738","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 : 2025-01-03DOI: 10.1016/j.tecto.2024.230613
Chandong Chang, Tae-Seob Kang, Dabeen Heo
We present a method to identify fault planes from earthquake focal mechanisms using stress field constraints to determine subsurface seismogenic fault geometry. Fault-plane ambiguity in focal mechanisms is resolved by applying two-step stress constraints. First, fault planes are inferred from the two nodal planes in each case by selecting those with the higher fault instability parameter, a function defined by plane orientations and stress state, using a commonly employed iterative linear stress inversion method. Second, the inferred fault planes are further screened by extracting those with a sufficiently high fault instability relative to the respective corresponding auxiliary planes, which is quantified by the instability ratio (IR) between the fault and auxiliary planes. Synthetic tests show that the threshold IR value, above which the inferred faults are all actual faults, varies with the degree of dispersion in fault instability. We apply the fault plane identification method to the 2016 Gyeongju earthquake sequence, which includes the largest instrumentally recorded event (ML 5.8) on the Korean Peninsula. For the Gyeongju earthquake sequence, faults having IR values greater than either ∼1.2 or ∼1.3, depending on the variability in stress state, are considered actual faults. The orientations and locations of individual faults provide better constraints for modeling the fault network than using hypocentral locations only. The constructed fault network consists of several fault structures that display four distinct orientations and constitute two conjugate fault systems. Our method can contribute to fault modeling at depth by providing independent clues for seismogenic fault geometry.
{"title":"Identification of seismogenic fault network using earthquake focal mechanisms and stress constraints: A case of the 2016 Gyeongju earthquake sequence, South Korea","authors":"Chandong Chang, Tae-Seob Kang, Dabeen Heo","doi":"10.1016/j.tecto.2024.230613","DOIUrl":"https://doi.org/10.1016/j.tecto.2024.230613","url":null,"abstract":"We present a method to identify fault planes from earthquake focal mechanisms using stress field constraints to determine subsurface seismogenic fault geometry. Fault-plane ambiguity in focal mechanisms is resolved by applying two-step stress constraints. First, fault planes are inferred from the two nodal planes in each case by selecting those with the higher fault instability parameter, a function defined by plane orientations and stress state, using a commonly employed iterative linear stress inversion method. Second, the inferred fault planes are further screened by extracting those with a sufficiently high fault instability relative to the respective corresponding auxiliary planes, which is quantified by the instability ratio (<ce:italic>IR</ce:italic>) between the fault and auxiliary planes. Synthetic tests show that the threshold <ce:italic>IR</ce:italic> value, above which the inferred faults are all actual faults, varies with the degree of dispersion in fault instability. We apply the fault plane identification method to the 2016 Gyeongju earthquake sequence, which includes the largest instrumentally recorded event (M<ce:inf loc=\"post\">L</ce:inf> 5.8) on the Korean Peninsula. For the Gyeongju earthquake sequence, faults having <ce:italic>IR</ce:italic> values greater than either ∼1.2 or ∼1.3, depending on the variability in stress state, are considered actual faults. The orientations and locations of individual faults provide better constraints for modeling the fault network than using hypocentral locations only. The constructed fault network consists of several fault structures that display four distinct orientations and constitute two conjugate fault systems. Our method can contribute to fault modeling at depth by providing independent clues for seismogenic fault geometry.","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"45 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142967774","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 : 2024-12-20DOI: 10.1016/j.tecto.2024.230609
Masume Akbari, Hojjat Kabirzadeh, Chang Hwan Kim, Chan Hong Park, Youn Soo Lee, Jeong Woo Kim
To estimate a non-uniform effective elastic thickness (Te) of lithosphere across Korean Peninsula and the Surrounding Seas (KPSS), we employ gravitational coherence analysis between gravity anomalies and topography/bathymetry data in the Fourier domain. Exploring crustal flexure and effective elastic thickness variations can offer insights into flexural strength, and evolutionary mechanics of the lithosphere under Ulleung Basin (UB). Our approach involves two scenarios: a large study area spanning the KPSS, and a more targeted investigation focused on UB. Dividing the study area into overlapping windows enables us to recover non-uniform Te values over the targeted regions. The UB study area is divide to 200 km by 200 km windows, and KPSS is divided to 400 km, 600 km, and 800 km windows to recover both short wavelengths and long wavelengths of Te. Our results reveal a Te range of 843 km for KPSS and recovered Te range from 1 to 10 km for UB. The estimated elastic thickness values in southern part of this basin are smaller compared to central and northern parts. These findings are consistent with prior estimations and comparative studies within the region, improving the understanding of UB's lithospheric properties. The recovered Te values for UB (Te<6km) suggests a young and weak oceanic lithosphere under this region. The alignment between recovered Te configuration and tectonic features in KPSS displays a large-scale lithospheric structure.
{"title":"Lithospheric flexure and effective elastic thickness under the Ulleung Basin in the East Sea using gravitational coherence","authors":"Masume Akbari, Hojjat Kabirzadeh, Chang Hwan Kim, Chan Hong Park, Youn Soo Lee, Jeong Woo Kim","doi":"10.1016/j.tecto.2024.230609","DOIUrl":"https://doi.org/10.1016/j.tecto.2024.230609","url":null,"abstract":"To estimate a non-uniform effective elastic thickness (<mml:math altimg=\"si1.svg\"><mml:msub><mml:mi>T</mml:mi><mml:mi>e</mml:mi></mml:msub></mml:math>) of lithosphere across Korean Peninsula and the Surrounding Seas (KPSS), we employ gravitational coherence analysis between gravity anomalies and topography/bathymetry data in the Fourier domain. Exploring crustal flexure and effective elastic thickness variations can offer insights into flexural strength, and evolutionary mechanics of the lithosphere under Ulleung Basin (UB). Our approach involves two scenarios: a large study area spanning the KPSS, and a more targeted investigation focused on UB. Dividing the study area into overlapping windows enables us to recover non-uniform <mml:math altimg=\"si1.svg\"><mml:msub><mml:mi>T</mml:mi><mml:mi>e</mml:mi></mml:msub></mml:math> values over the targeted regions. The UB study area is divide to 200 km by 200 km windows, and KPSS is divided to 400 km, 600 km, and 800 km windows to recover both short wavelengths and long wavelengths of <mml:math altimg=\"si1.svg\"><mml:msub><mml:mi>T</mml:mi><mml:mi>e</mml:mi></mml:msub></mml:math>. Our results reveal a <mml:math altimg=\"si1.svg\"><mml:msub><mml:mi>T</mml:mi><mml:mi>e</mml:mi></mml:msub></mml:math> range of 843 km for KPSS and recovered <mml:math altimg=\"si1.svg\"><mml:msub><mml:mi>T</mml:mi><mml:mi>e</mml:mi></mml:msub></mml:math> range from 1 to 10 km for UB. The estimated elastic thickness values in southern part of this basin are smaller compared to central and northern parts. These findings are consistent with prior estimations and comparative studies within the region, improving the understanding of UB's lithospheric properties. The recovered <mml:math altimg=\"si1.svg\"><mml:msub><mml:mi>T</mml:mi><mml:mi>e</mml:mi></mml:msub></mml:math> values for UB (<mml:math altimg=\"si34.svg\"><mml:msub><mml:mi>T</mml:mi><mml:mi>e</mml:mi></mml:msub><mml:mo><</mml:mo><mml:mn>6</mml:mn><mml:mspace width=\"0.25em\"></mml:mspace><mml:mi>km</mml:mi></mml:math>) suggests a young and weak oceanic lithosphere under this region. The alignment between recovered <mml:math altimg=\"si1.svg\"><mml:msub><mml:mi>T</mml:mi><mml:mi>e</mml:mi></mml:msub></mml:math> configuration and tectonic features in KPSS displays a large-scale lithospheric structure.","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"14 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142889087","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 : 2024-12-19DOI: 10.1016/j.tecto.2024.230608
Liguo Jiao, Jiyao Tu, Yu Lei, Junhao Zhao, Weinan Wang
The Eastern Himalayan Syntaxis (EHS) is located at the forefront of the collision between the Indian and Asian plates, representing the region with the most rugged terrain and intricate structural deformations along the southeastern margin of the Tibetan Plateau. A long-standing debate has revolved around two modes of tectonic evolution: “flat slab indentation” and “tectonic aneurysm”. This study, employing analysis and inversion of the EMAG2-v3 crustal magnetic anomalies, has obtained a 3D crustal magnetic structure. By integrating magnetic structures with rock susceptibilities, the rough crustal lithological structure is determined, and a simplified two-stage evolution model is established. The results reveal the presence of a strong magnetic body in the core of the EHS, particularly in the region of Namche Barwa Peak and Gyala Peri Peak. The 3D spatial characteristics of this strong magnetic body indicate that deep-seated materials beneath the EHS are uplifting from the plateau interior to the southeast. Both crustal magnetic and lithological structures support the “tectonic aneurysm” evolution model. The seismic hazard zone is identified as the region surrounding the boundary of strong magnetic body, particularly on the side adjacent to the strong magnetic body, with Namche Barwa Peak and Gyala Peri Peak as its center.
{"title":"Crustal magnetic structure and implications for the Eastern Himalayan Syntaxis revealed by EMAG2-v3","authors":"Liguo Jiao, Jiyao Tu, Yu Lei, Junhao Zhao, Weinan Wang","doi":"10.1016/j.tecto.2024.230608","DOIUrl":"https://doi.org/10.1016/j.tecto.2024.230608","url":null,"abstract":"The Eastern Himalayan Syntaxis (EHS) is located at the forefront of the collision between the Indian and Asian plates, representing the region with the most rugged terrain and intricate structural deformations along the southeastern margin of the Tibetan Plateau. A long-standing debate has revolved around two modes of tectonic evolution: “flat slab indentation” and “tectonic aneurysm”. This study, employing analysis and inversion of the EMAG2-v3 crustal magnetic anomalies, has obtained a 3D crustal magnetic structure. By integrating magnetic structures with rock susceptibilities, the rough crustal lithological structure is determined, and a simplified two-stage evolution model is established. The results reveal the presence of a strong magnetic body in the core of the EHS, particularly in the region of Namche Barwa Peak and Gyala Peri Peak. The 3D spatial characteristics of this strong magnetic body indicate that deep-seated materials beneath the EHS are uplifting from the plateau interior to the southeast. Both crustal magnetic and lithological structures support the “tectonic aneurysm” evolution model. The seismic hazard zone is identified as the region surrounding the boundary of strong magnetic body, particularly on the side adjacent to the strong magnetic body, with Namche Barwa Peak and Gyala Peri Peak as its center.","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"22 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142867475","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 : 2024-12-19DOI: 10.1016/j.tecto.2024.230605
Ting Liu, Xiaohui He, Yipeng Zhang, Zhiliang Liu, Wenjun Zheng, Peizhen Zhang, Yi Wang
Three strong aftershocks (MS6+) occurred in the northeastern rupture zone of the 2008 MW7.9 Wenchuan earthquake within three months. No surface ruptures were observed, and the seismogenic faults remain unclear. Resolving the source parameters and seismogenic structures of these strong aftershocks is essential for clarifying the rupture termination mechanism of the mainshock and for future seismic hazard assessment. In this study, we determined the point source parameters of eight moderate to strong aftershocks and the rupture directivity of three strong aftershocks through regional and teleseismic waveform modeling. The focal mechanisms of these aftershocks are diverse, including both strike-slip and thrust-slip types, with centroid depths ranging from the middle crust (12–19 km) to the shallow part (3–5 km), highlighting the complexity in the rupture termination zone. The rupture directivity analysis shows that the strike-slip May 25 event (Mw6.0) ruptured from SW to NE along the right-lateral plane (60°/81°/173°) for ∼7 km, the strike-slip July 24 event (Mw5.5) on ruptured from NNE to SSW along the right-lateral plane (16°/67°/147°) for ∼6 km, and the thrust-slip August 5 event (Mw5.9) ruptured upwards along the northeast dipping plane (339°/56°/83°) for 6–8 km. The strike of ruptured faults changes from NE to NNE, differing from the Qingchuan fault. The estimated stress drop of the event in the middle crust (∼19 km, 9.3 MPa) is larger than that of the shallower event (∼4 km, 1.9 MPa), possibly due to the low strength of the shallow crust. Moreover, the rupture direction of the July 24 event is opposite to that of the mainshock, potentially due to the Bikou block's differing bi-material contrast, which may have hindered the northeastward extension of the mainshock's rupture.
{"title":"Rupture directivity and seismogenic structures of strong aftershocks in the northeastern rupture zone of the 2008 Wenchuan earthquake","authors":"Ting Liu, Xiaohui He, Yipeng Zhang, Zhiliang Liu, Wenjun Zheng, Peizhen Zhang, Yi Wang","doi":"10.1016/j.tecto.2024.230605","DOIUrl":"https://doi.org/10.1016/j.tecto.2024.230605","url":null,"abstract":"Three strong aftershocks (M<ce:inf loc=\"post\">S</ce:inf>6+) occurred in the northeastern rupture zone of the 2008 M<ce:inf loc=\"post\">W</ce:inf>7.9 Wenchuan earthquake within three months. No surface ruptures were observed, and the seismogenic faults remain unclear. Resolving the source parameters and seismogenic structures of these strong aftershocks is essential for clarifying the rupture termination mechanism of the mainshock and for future seismic hazard assessment. In this study, we determined the point source parameters of eight moderate to strong aftershocks and the rupture directivity of three strong aftershocks through regional and teleseismic waveform modeling. The focal mechanisms of these aftershocks are diverse, including both strike-slip and thrust-slip types, with centroid depths ranging from the middle crust (12–19 km) to the shallow part (3–5 km), highlighting the complexity in the rupture termination zone. The rupture directivity analysis shows that the strike-slip May 25 event (Mw6.0) ruptured from SW to NE along the right-lateral plane (60°/81°/173°) for ∼7 km, the strike-slip July 24 event (Mw5.5) on ruptured from NNE to SSW along the right-lateral plane (16°/67°/147°) for ∼6 km, and the thrust-slip August 5 event (Mw5.9) ruptured upwards along the northeast dipping plane (339°/56°/83°) for 6–8 km. The strike of ruptured faults changes from NE to NNE, differing from the Qingchuan fault. The estimated stress drop of the event in the middle crust (∼19 km, 9.3 MPa) is larger than that of the shallower event (∼4 km, 1.9 MPa), possibly due to the low strength of the shallow crust. Moreover, the rupture direction of the July 24 event is opposite to that of the mainshock, potentially due to the Bikou block's differing bi-material contrast, which may have hindered the northeastward extension of the mainshock's rupture.","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"52 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142867446","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}
Natural geological systems contain porosity structures of various scales that play different roles in geophysical properties, fluid flow, and geodynamics. To understand seismic activity associated with high pore-fluid pressure and fluid migration in subduction zones, it is necessary to explore the scale dependence of geophysical properties such as seismic velocity and permeability. Here, we compare laboratory-measured ultrasonic velocity measured on core samples from the Susaki area in the Shimanto accretionary complex, SW Japan, with sonic velocity measured by borehole logging experiments. Results show that P-wave velocity decreases from the laboratory (∼6 km/s) to the borehole scales (∼5 km/s). This scale-variant effect can be explained by a differential effective medium model whereby mesoscale porosity that is undetectable at the ultrasonic wavelength is introduced into the matrix phase with microscale porosity. Assuming typical apertures for micro- and mesoscale fractures, we estimate that the effective permeability can increase to 10−12–10−11 m2 with increasing in the mesoscale porosity and decreasing P-wave velocity down to 4–5 km/s. These results indicate that seismic velocity anomalies and related seismic activity are associated with the presence of mesoscale fractures in subduction zones.
{"title":"Mesoscale fractures control the scale dependences of seismic velocity and fluid flow in subduction zones","authors":"Yuya Akamatsu, Hanaya Okuda, Manami Kitamura, Michiyo Sawai","doi":"10.1016/j.tecto.2024.230606","DOIUrl":"https://doi.org/10.1016/j.tecto.2024.230606","url":null,"abstract":"Natural geological systems contain porosity structures of various scales that play different roles in geophysical properties, fluid flow, and geodynamics. To understand seismic activity associated with high pore-fluid pressure and fluid migration in subduction zones, it is necessary to explore the scale dependence of geophysical properties such as seismic velocity and permeability. Here, we compare laboratory-measured ultrasonic velocity measured on core samples from the Susaki area in the Shimanto accretionary complex, SW Japan, with sonic velocity measured by borehole logging experiments. Results show that P-wave velocity decreases from the laboratory (∼6 km/s) to the borehole scales (∼5 km/s). This scale-variant effect can be explained by a differential effective medium model whereby mesoscale porosity that is undetectable at the ultrasonic wavelength is introduced into the matrix phase with microscale porosity. Assuming typical apertures for micro- and mesoscale fractures, we estimate that the effective permeability can increase to 10<ce:sup loc=\"post\">−12</ce:sup>–10<ce:sup loc=\"post\">−11</ce:sup> m<ce:sup loc=\"post\">2</ce:sup> with increasing in the mesoscale porosity and decreasing P-wave velocity down to 4–5 km/s. These results indicate that seismic velocity anomalies and related seismic activity are associated with the presence of mesoscale fractures in subduction zones.","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"76 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142867474","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}
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":"https://doi.org/10.1016/j.tecto.2024.230600","url":null,"abstract":"We characterize the spatiotemporal patterns of ground deformation caused by an earthquake doublet: the September 17, 2022, M<ce:inf loc=\"post\">L</ce:inf> 6.6 Guanshan and the September 18, 2022, M<ce:inf loc=\"post\">L</ce:inf> 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<ce:inf loc=\"post\">L</ce:inf> 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<ce:inf loc=\"post\">L</ce:inf> 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.","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"51 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-08","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 : 2024-12-05DOI: 10.1016/j.tecto.2024.230598
Cheng Mei
The mechanisms of slip instabilities of dilatant and fluid-saturated faults remain controversial, particularly in low-permeability environments. Using a rate and state friction model including the effects of dilatancy, we conduct a linearized stability analysis of a one-dimensional spring-slider model and reexamine the critical stiffness (kc) of the fault zone as a function of fluid diffusivity and dilatancy factor. Our analytical results indicate that under fully-drained conditions, kc is independent of dilatancy factor, while under poorly-drained conditions, kc depends on dilatancy factor and fluid diffusivity. Both analytical and numerical results show that a non-negative kc always exists, even for highly-dilatant and poorly-drained faults where kc is proportional to fluid diffusivity. This implies that dilatancy does not alter the inherent (in)stability of fault slip, and that a sufficiently low system stiffness can always produce unstable fault slips without a critical pore pressure or critical dilatancy factor. These findings may provide new insights into effects of dilatancy on fault instability. The numerical results further illustrate that the fault slip acceleration tends to be significantly suppressed by increasing dilatancy factor and decreasing fluid diffusivity. These results may explain ubiquitous slow-slip events on natural faults that vary in length.
{"title":"Slip instability of dilatant and fluid-saturated faults","authors":"Cheng Mei","doi":"10.1016/j.tecto.2024.230598","DOIUrl":"https://doi.org/10.1016/j.tecto.2024.230598","url":null,"abstract":"The mechanisms of slip instabilities of dilatant and fluid-saturated faults remain controversial, particularly in low-permeability environments. Using a rate and state friction model including the effects of dilatancy, we conduct a linearized stability analysis of a one-dimensional spring-slider model and reexamine the critical stiffness (<mml:math altimg=\"si7.svg\"><mml:msub><mml:mi>k</mml:mi><mml:mi>c</mml:mi></mml:msub></mml:math>) of the fault zone as a function of fluid diffusivity and dilatancy factor. Our analytical results indicate that under fully-drained conditions, <mml:math altimg=\"si7.svg\"><mml:msub><mml:mi>k</mml:mi><mml:mi>c</mml:mi></mml:msub></mml:math> is independent of dilatancy factor, while under poorly-drained conditions, <mml:math altimg=\"si7.svg\"><mml:msub><mml:mi>k</mml:mi><mml:mi>c</mml:mi></mml:msub></mml:math> depends on dilatancy factor and fluid diffusivity. Both analytical and numerical results show that a non-negative <mml:math altimg=\"si7.svg\"><mml:msub><mml:mi>k</mml:mi><mml:mi>c</mml:mi></mml:msub></mml:math> always exists, even for highly-dilatant and poorly-drained faults where <mml:math altimg=\"si7.svg\"><mml:msub><mml:mi>k</mml:mi><mml:mi>c</mml:mi></mml:msub></mml:math> is proportional to fluid diffusivity. This implies that dilatancy does not alter the inherent (in)stability of fault slip, and that a sufficiently low system stiffness can always produce unstable fault slips without a critical pore pressure or critical dilatancy factor. These findings may provide new insights into effects of dilatancy on fault instability. The numerical results further illustrate that the fault slip acceleration tends to be significantly suppressed by increasing dilatancy factor and decreasing fluid diffusivity. These results may explain ubiquitous slow-slip events on natural faults that vary in length.","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"10 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142788824","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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