Geosphere最新文献_第3页

Storm-driven sedimentation and dynamics of a sediment slug in an ephemeral stream: Influence on sediment-routing systems within source 暴风雨驱动的沉积和短时溪流中泥沙蛞蝓的动力学：对源头泥沙淤积系统的影响

Geosphere Pub Date : 2023-12-29 DOI: 10.1130/ges02683.1

Antonio F. García, Shannon A. Mahan

{"title":"Storm-driven sedimentation and dynamics of a sediment slug in an ephemeral stream: Influence on sediment-routing systems within source","authors":"Antonio F. García, Shannon A. Mahan","doi":"10.1130/ges02683.1","DOIUrl":"https://doi.org/10.1130/ges02683.1","url":null,"abstract":"Stream-terrace morphostratigraphy and optically stimulated luminescence (OSL) geochronology indicate that storm-driven sedimentation has caused down-system decoupling of the uppermost reaches of McMillan Creek (south- ern California, USA) from the lower reaches of McMillan Creek since 1960 ± 190 yr B.P. This is significant because source-to-sink studies report high degrees of sediment transport connectivity over millennial time scales during periods of high fluvial discharge in sediment routing systems. The most recent relatively large-magnitude episode of sedimentation emplaced a sediment slug in the ephemeral channel of McMillan Creek. The sediment slug is correlated to the “California Storm of January 1862” via OSL dating. In this paper, a conceptual model of sediment slug dynamics in an ephemeral stream over 16 decades is developed based on fluvial sedimentation events that in most instances included reworking slug-derived sediment. Due to the episodic nature of streamflow in ephemeral streams and the dearth of sediment transport between streamflow events, sediment slug coherency is sustained over longer periods of time in ephemeral streams than in perennial streams having steady or variable flow regimes. The longevity of sediment-slug coherency in ephemeral streams leads to more prolonged down-system decoupling in sediment routing systems than down-system decoupling caused by ordinary fluvial sedimentation. In McMillan Creek, it is possible that up-system decoupling driven by sedimentation has been contemporaneous with down-system decoupling, but factors other than sedimentation may have a more significant role in up-system decoupling. Source-to-sink studies completed in areas having a Mediterranean climate cannot assume that sediment flux out of upland source areas includes the total amount of sediment available for transport.","PeriodicalId":507979,"journal":{"name":"Geosphere","volume":" 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139144355","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Evolution of an earthquake-induced landslide complex in the South Island of New Zealand: How fault damage zones and seismicity contribute to slope failures 新西兰南岛由地震引发的滑坡综合体的演变：断层破坏带和地震如何导致斜坡崩塌

Geosphere Pub Date : 2023-12-20 DOI: 10.1130/ges02668.1

C. Singeisen, Chris Massey, Andrea Wolter, T. Stahl, Richard Kellett, Zane Bruce, Colin Bloom, Dougal Mason

{"title":"Evolution of an earthquake-induced landslide complex in the South Island of New Zealand: How fault damage zones and seismicity contribute to slope failures","authors":"C. Singeisen, Chris Massey, Andrea Wolter, T. Stahl, Richard Kellett, Zane Bruce, Colin Bloom, Dougal Mason","doi":"10.1130/ges02668.1","DOIUrl":"https://doi.org/10.1130/ges02668.1","url":null,"abstract":"Tectonic deformation within fault damage zones can influence slope stability and landslide failure mechanisms due to rock mass strength effects and the presence of tectonic structures. Here, we used detailed site investigations to evaluate controls on deformation within the Half Moon Bay landslide complex, located ~1 km from the surface trace of the Hope fault in the South Island of New Zealand. During the 2016 Mw 7.8 Kaikōura earthquake, the slope experienced up to ~13 m of displacement and partially transitioned into a rock avalanche (with a volume of ~350,000 m3). Deep-seated deformation of the entire slope predated the 2016 earthquake. Results of geomorphological analysis, field mapping, geophysical surveys, slope displacement, and a 60-m-deep borehole in the incipient portion of the landslide indicated the presence of a subvertical tectonic fabric and intense fracturing and weathering of the rock mass, which gradually decrease with depth. Based on these results, we established a conceptual model wherein the landslide failure mechanism is a combination of flexural toppling along the subvertical structures coupled with joint-step-path sliding along preexisting, closely spaced discontinuities within the graywacke rock mass. Coseismic slope displacements revealed a large area of incipient failure behind the headscarp of the 2016 rock avalanche, which will likely result in further avalanching at the site. This case study demonstrates that inherited tectonic structures (combined with seismicity and weathering in an oversteepened coastal slope) play an important role in the evolution of hillslopes near active faults.","PeriodicalId":507979,"journal":{"name":"Geosphere","volume":"68 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139169470","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

The missing ridge Enigma: A new model for the Tuamotu Plateau conjugate and Peruvian flat slab 缺失的山脊之谜：图阿莫图高原共轭和秘鲁平板的新模型

Geosphere Pub Date : 2023-11-30 DOI: 10.1130/ges02679.1

Michael Fletcher, Derek Wyman

{"title":"The missing ridge Enigma: A new model for the Tuamotu Plateau conjugate and Peruvian flat slab","authors":"Michael Fletcher, Derek Wyman","doi":"10.1130/ges02679.1","DOIUrl":"https://doi.org/10.1130/ges02679.1","url":null,"abstract":"We present a new tectonic plate reconstruction that suggests substantial revisions to events associated with development of the Peruvian flat slab and resolves several long-standing issues regarding the subduction of bathymetric highs in the region. The Tuamotu Plateau is widely considered to be the product of Easter Plume magmatism, and plate reconstructions suggest it formed following initial plume ascent at ca. 55 Ma. The Nazca Ridge is also linked to the Easter Plume and is an obvious candidate to be the spreading ridge conjugate to the Tuamotu Plateau. Models for the paired evolution of the two ridges, however, generally stop at ca. 33 Ma because of the inability of plate reconstructions to associate the two ridges across a spreading center prior to this time. In addition, seafloor magnetic data demonstrate that the Tuamotu Plateau developed at a complexly shaped and evolving mid-oceanic ridge that precluded development of a simple mirror image conjugate of the type commonly employed in Nazca Ridge reconstructions. Seafloor isochrons also suggest that a ridge jump separated the Tuamotu Plateau from its conjugate at ca. 42 Ma. Global plate models offer an alternative approach to assessing conjugate development, by showing how a hypothetical conjugate to the Tuamotu Plateau is built up over time. Using such a model, we found that the conjugate that developed during the main stage of Tuamotu growth (55 Ma to 42 Ma) cannot be the Nazca Ridge, which appears to have initiated at ca. 42 Ma, when the Easter Plume diverted volcanism southward. We named the newly recognized conjugate the Enigma Ridge. Importantly, subduction of this ridge starting from ca. 17 Ma on the north Peruvian trench can account for the missing slab buoyancy previously attributed to the hypothesized, but controversial, Inca Plateau. The Enigma Ridge must still be providing far more buoyancy over a much greater area than the Nazca Ridge, which only began to subduct rather recently.","PeriodicalId":507979,"journal":{"name":"Geosphere","volume":"395 ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139203929","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Integrated geologic and geophysical modeling across the Bartlett Springs fault zone, northern California (USA): Implications for fault creep and regional structure 美国加利福尼亚州北部巴特利泉断层带的综合地质和地球物理模型：对断层蠕变和区域结构的影响

Geosphere Pub Date : 2023-11-30 DOI: 10.1130/ges02684.1

V. Langenheim, R. McLaughlin, B. Melosh

{"title":"Integrated geologic and geophysical modeling across the Bartlett Springs fault zone, northern California (USA): Implications for fault creep and regional structure","authors":"V. Langenheim, R. McLaughlin, B. Melosh","doi":"10.1130/ges02684.1","DOIUrl":"https://doi.org/10.1130/ges02684.1","url":null,"abstract":"The rate and location at depth of fault creep are important, but difficult to characterize, parameters needed to assess seismic hazard. Here we take advantage of the magnetic properties of serpentinite, a rock type commonly associated with fault creep, to model its depth extent along the Bartlett Springs fault zone, an important part of the San Andreas fault system north of the San Francisco Bay, California (western United States). We model aeromagnetic and gravity anomalies using geologic constraints along 14 cross sections over a distance of 120 km along the fault zone. Our results predict that the fault zone has more serpentinite at depth than inferred by geologic relationships at the surface. Existing geodetic models are inconsistent and predict different patterns of creep along the fault. Our results favor models with more extensive creep at depth. The source of the serpentinite appears to be ophiolite thrust westward and beneath the Franciscan Complex, an interpretation supported by the presence of antigorite, a high-temperature serpentine mineral stable at depth, in fault gouge near Lake Pillsbury.","PeriodicalId":507979,"journal":{"name":"Geosphere","volume":"149 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139206888","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Three-dimensional finite-element modeling of Coulomb stress changes on normal and thrust faults caused by pore fluid pressure changes and postseismic viscoelastic relaxation 由孔隙流体压力变化和震后粘弹性松弛引起的正断层和推力断层库仑应力变化的三维有限元建模

Geosphere Pub Date : 2023-11-30 DOI: 10.1130/ges02672.1

Jill Peikert, Andrea Hampel, M. Bagge

{"title":"Three-dimensional finite-element modeling of Coulomb stress changes on normal and thrust faults caused by pore fluid pressure changes and postseismic viscoelastic relaxation","authors":"Jill Peikert, Andrea Hampel, M. Bagge","doi":"10.1130/ges02672.1","DOIUrl":"https://doi.org/10.1130/ges02672.1","url":null,"abstract":"The analysis of Coulomb stress changes has become an important tool for seismic hazard evaluation because such stress changes may trigger or delay subsequent earthquakes. Processes that can cause significant Coulomb stress changes include coseismic slip and transient postseismic processes such as poroelastic effects and viscoelastic relaxation. However, the combined influence of poroelastic effects and viscoelastic relaxation on co- and postseismic Coulomb stress changes has not been systematically studied so far. Here, we use three-dimensional finite-element models with arrays of normal and thrust faults to investigate how pore fluid pressure changes and viscoelastic relaxation overlap during the postseismic phase. In different experiments, we vary the permeability of the upper crust and the viscosity of the lower crust or lithospheric mantle while keeping the other parameters constant. In addition, we perform experiments in which we combine a high (low) permeability of the upper crust with a low (high) viscosity of the lower crust. Our results show that the coseismic (i.e., static) Coulomb stress changes are altered by the signal from poroelastic effects and viscoelastic relaxation during the first month after the earthquake. For sufficiently low viscosities, the Coulomb stress change patterns show a combined signal from poroelastic and viscoelastic effects already during the first postseismic year. For sufficiently low permeabilities, Coulomb stress changes induced by poroelastic effects overlap with the signals from viscoelastic relaxation and interseismic stress accumulation for decades. Our results imply that poroelastic and viscoelastic effects have a strong impact on postseismic Coulomb stress changes and should therefore be considered together when analyzing Coulomb stress transfer between faults.","PeriodicalId":507979,"journal":{"name":"Geosphere","volume":"409 ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139203900","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0