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}
Pub Date : 2024-12-03DOI: 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":"https://doi.org/10.1016/j.tecto.2024.230579","url":null,"abstract":"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.","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"22 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-03","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":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-02DOI: 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":"https://doi.org/10.1016/j.tecto.2024.230582","url":null,"abstract":"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.","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"37 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-02","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}
Pub Date : 2024-12-02DOI: 10.1016/j.tecto.2024.230577
Diogo Farrapo Albuquerque, Marcelo Peres Rocha, George Sand França, Marcelo Bianchi, Reinhardt A. Fuck
We analyzed the influence of seismometer misorientation on crustal thickness and Vp/Vs estimated with teleseismic P-wave receiver functions simulating orientation errors during the rotation procedure of the horizontal components from true NS-EW (North-South, East-West) to RT (Radial-Tangential) coordinate system. During this procedure, we incrementally added 5° to the azimuth of the NS and EW components. The influence of the misorientation on P-wave teleseismic receiver functions was confirmed by the analysis of different parameters, such as normalized amplitude of P, Ps and multiple phases, reproduction of the radial component and crustal thickness and Vp/Vs estimates. This analysis indicated |45°| as the maximum misorientation allowed to consider crustal thickness, Vp/Vs, and geophysical interpretation reliable. For misorientations larger than |75°|, the reliability is low, and the data could be considered inappropriate for receiver function technique and crustal studies. We also identified some signs of misorientation: P-wave polarity inversion in radial RF trace combined with strong P-wave troughs in the tangential one, low Ps-wave normalized amplitude, reproduction of the radial lower than 90 % for most receiver function traces, and large standard deviations in crustal thickness and Vp/Vs estimates. Since most of the seismometers deployed at Brazilian Seismographic Network were well oriented (only three have orientation errors larger than 45°), in general, previous studies that used data from those stations for estimating crustal thickness and Vp/Vs using the H-k method are reliable. However, in future versions of Brazilian crustal models, the estimates using stations with misorientation larger than |45°| must be recalculated applying an azimuth correction. Finally, since normalized amplitudes are very sensitive to misorientation, the analysis of P and Ps amplitudes in radial receiver functions can be used as a tool to estimate seismometer orientation error and other issues affecting station gain.
{"title":"Influence of seismometer misorientation on crustal thickness and Vp/Vs estimated with teleseismic P-wave receiver functions","authors":"Diogo Farrapo Albuquerque, Marcelo Peres Rocha, George Sand França, Marcelo Bianchi, Reinhardt A. Fuck","doi":"10.1016/j.tecto.2024.230577","DOIUrl":"https://doi.org/10.1016/j.tecto.2024.230577","url":null,"abstract":"We analyzed the influence of seismometer misorientation on crustal thickness and Vp/Vs estimated with teleseismic P-wave receiver functions simulating orientation errors during the rotation procedure of the horizontal components from true NS-EW (North-South, East-West) to RT (Radial-Tangential) coordinate system. During this procedure, we incrementally added 5° to the azimuth of the NS and EW components. The influence of the misorientation on P-wave teleseismic receiver functions was confirmed by the analysis of different parameters, such as normalized amplitude of P, Ps and multiple phases, reproduction of the radial component and crustal thickness and Vp/Vs estimates. This analysis indicated |45°| as the maximum misorientation allowed to consider crustal thickness, Vp/Vs, and geophysical interpretation reliable. For misorientations larger than |75°|, the reliability is low, and the data could be considered inappropriate for receiver function technique and crustal studies. We also identified some signs of misorientation: P-wave polarity inversion in radial RF trace combined with strong P-wave troughs in the tangential one, low Ps-wave normalized amplitude, reproduction of the radial lower than 90 % for most receiver function traces, and large standard deviations in crustal thickness and Vp/Vs estimates. Since most of the seismometers deployed at Brazilian Seismographic Network were well oriented (only three have orientation errors larger than 45°), in general, previous studies that used data from those stations for estimating crustal thickness and Vp/Vs using the H-k method are reliable. However, in future versions of Brazilian crustal models, the estimates using stations with misorientation larger than |45°| must be recalculated applying an azimuth correction. Finally, since normalized amplitudes are very sensitive to misorientation, the analysis of P and Ps amplitudes in radial receiver functions can be used as a tool to estimate seismometer orientation error and other issues affecting station gain.","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"18 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142788827","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 : 2024-11-29DOI: 10.1016/j.tecto.2024.230578
Yuhan Xiong , Zhikun Liu , Xiaoxia Liu , Yi Meng , Zhi Chen , Shaopeng Yan , Chuantao Geng , Jinli Huang
On 8 July 2020, an ML 4.2 earthquake occurred in the Xiaojiang fault zone along the eastern margin of the Tibetan Plateau. Applied ambient noise monitoring technique to the continuous waveforms from a near-fault small-aperture array, we obtain daily high-resolution variations in seismic velocity before and after the earthquake. When compared with environmental observations, we exclude these factors such as groundwater level, precipitation, temperature, and atmospheric pressure that might significantly influence the seismic velocity changes. We propose that the observed ∼10-day transitional phase from relatively high velocity to low velocity following the ML 4.2 earthquake, signifies a transition within the fault zone from a relatively compressional state to an extensional one. This transition could be an indicator of transient dilatation deformation during the long-term strike-slip process of the Xiaojiang fault, which is not easily detected by space geodetic measurements. When the fault zone is in extensional state, there is stronger strain-velocity sensitivity, which is verified by local long-period tidal strain.
{"title":"Transient seismic velocity variation accompanying an ML 4.2 earthquake on SE margin of the Tibetan Plateau and its implication for fault slip processes","authors":"Yuhan Xiong , Zhikun Liu , Xiaoxia Liu , Yi Meng , Zhi Chen , Shaopeng Yan , Chuantao Geng , Jinli Huang","doi":"10.1016/j.tecto.2024.230578","DOIUrl":"10.1016/j.tecto.2024.230578","url":null,"abstract":"<div><div>On 8 July 2020, an M<sub>L</sub> 4.2 earthquake occurred in the Xiaojiang fault zone along the eastern margin of the Tibetan Plateau. Applied ambient noise monitoring technique to the continuous waveforms from a near-fault small-aperture array, we obtain daily high-resolution variations in seismic velocity before and after the earthquake. When compared with environmental observations, we exclude these factors such as groundwater level, precipitation, temperature, and atmospheric pressure that might significantly influence the seismic velocity changes. We propose that the observed ∼10-day transitional phase from relatively high velocity to low velocity following the M<sub>L</sub> 4.2 earthquake, signifies a transition within the fault zone from a relatively compressional state to an extensional one. This transition could be an indicator of transient dilatation deformation during the long-term strike-slip process of the Xiaojiang fault, which is not easily detected by space geodetic measurements. When the fault zone is in extensional state, there is stronger strain-velocity sensitivity, which is verified by local long-period tidal strain.</div></div>","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"895 ","pages":"Article 230578"},"PeriodicalIF":2.7,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142743596","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 : 2024-11-27DOI: 10.1016/j.tecto.2024.230575
Yujun Sun , Shuwen Dong , Mian Liu , Huai Zhang , Yaolin Shi
The rheological structure of the East Asia continent is the key to understanding its broad, heterogeneous, and intense Cenozoic deformation. Based on a refined three-dimensional thermal structure of the lithosphere in this region and the latest strain rate data, we derived a model of the rheological structure of the East Asian continental lithosphere. The strength envelopes, defined by the yield strength of frictional, fractural, and plastic creep, are constrained by the lithological stratification based on previous studies and the depth distribution of earthquakes. The results show large vertical and lateral variations of lithospheric strength in the East Asian continent. A weak lower crust with low effective viscosity is ubiquitous. The rheological structure agrees with the jelly sandwich model in cratons, where the mantle lithosphere is relatively strong. The Tibetan Plateau has the weakest lower crust, with its effective viscosity ranging from 1019 to 1020 Pa∙s. Its mantle lithosphere is weakened by relatively high temperature; hence, its rheological structure can be described by the crème brûlée model. The lithospheric scale faults and suture zones in and around the Tibetan Plateau, with low strength or viscosity, correspond to the banana split model. The strength of the lithosphere in the Tibetan Plateau and other zones of active Cenozoic tectonics mainly derive from the crust, while the strength of the cratonic lithosphere is dominated by that of the mantle lithosphere. The rheological heterogeneity controls the lateral growth of the Tibetan Plateau and the widespread and differential deformation in the East Asian continent.
{"title":"The rheological structure of East Asian continental lithosphere","authors":"Yujun Sun , Shuwen Dong , Mian Liu , Huai Zhang , Yaolin Shi","doi":"10.1016/j.tecto.2024.230575","DOIUrl":"10.1016/j.tecto.2024.230575","url":null,"abstract":"<div><div>The rheological structure of the East Asia continent is the key to understanding its broad, heterogeneous, and intense Cenozoic deformation. Based on a refined three-dimensional thermal structure of the lithosphere in this region and the latest strain rate data, we derived a model of the rheological structure of the East Asian continental lithosphere. The strength envelopes, defined by the yield strength of frictional, fractural, and plastic creep, are constrained by the lithological stratification based on previous studies and the depth distribution of earthquakes. The results show large vertical and lateral variations of lithospheric strength in the East Asian continent. A weak lower crust with low effective viscosity is ubiquitous. The rheological structure agrees with the jelly sandwich model in cratons, where the mantle lithosphere is relatively strong. The Tibetan Plateau has the weakest lower crust, with its effective viscosity ranging from 10<sup>19</sup> to 10<sup>20</sup> Pa∙s. Its mantle lithosphere is weakened by relatively high temperature; hence, its rheological structure can be described by the crème brûlée model. The lithospheric scale faults and suture zones in and around the Tibetan Plateau, with low strength or viscosity, correspond to the banana split model. The strength of the lithosphere in the Tibetan Plateau and other zones of active Cenozoic tectonics mainly derive from the crust, while the strength of the cratonic lithosphere is dominated by that of the mantle lithosphere. The rheological heterogeneity controls the lateral growth of the Tibetan Plateau and the widespread and differential deformation in the East Asian continent.</div></div>","PeriodicalId":22257,"journal":{"name":"Tectonophysics","volume":"895 ","pages":"Article 230575"},"PeriodicalIF":2.7,"publicationDate":"2024-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142743595","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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