Tectonic Boundary Research Articles

Recent Uplift Characteristics of the Southeast Tibetan Plateau, an Analysis Based on Fluvial Indices

The southeastern Tibetan Plateau (SETP) is well known for its large strike–slip faults with high slip rates and a high potential for seismic hazards. However, little is known about its thrust faults and associated seismic hazards, even though they can produce devastating earthquakes despite their relatively low slip rate. Here we investigated the thrust faults and the recent tectonic uplift pattern in the SETP on a regional scale by combining geomorphic analysis and geodetic data. We quantify the potential differential uplift in the SETP recorded in the long-term landscape evolution with geomorphic indices and compare them with differential uplift derived from decadal leveling data and millennial-scale fluvial terrace incision rates. The results show that the northwest of the SETP underwent higher uplift rates compared to its southeast areas, which is in agreement with the GPS-based leveling. Essentially, the geomorphic indices build two value ranges that are spatially clustered and separated by the Muli thrust fault system, a transverse fault system, which is orientated oblique/perpendicular to the large strike–slip fault. The geomorphic indices indicating rapid uplift rates spatially correspond with high rates derived from leveling data on the northwest side of the Muli thrust fault. The Muli thrust fault, therefore, acted as an important topographic and tectonic boundary absorbing partial southeast crustal movement. Hence, further detailed studies, such as seismological investigations, are suggested to be conducted on the Muli fault for seismic hazards evaluation.

Punctuated propagation of a corrugated extensional detachment offshore Ireland

AbstractLow‐angle detachments are fundamental crustal structures found in many extensional systems and plate tectonic boundaries, including onshore extensional basins, rifted margins and mid‐oceanic ridges. Direct observations of the complete geometry of extensional detachments are rare so that aspects of our understanding of their development and evolution rely mainly on proxy observations and numerical simulations. A high‐resolution 3D seismic reflection survey Offshore West of Ireland images a complete corrugated extensional detachment, from its steep oceanward breakaway faults to its back‐rotated domal crest. The detachment surface, the P reflector, developed during the Jurassic hyperextension of the Porcupine Basin and is preserved in its slip position. It covers 95 × 35 km area and has a N‐S elongate domal shape, at right angles to the prevailing extension direction, with a crest at ca. 6.3 s two‐way travel time. It is overlain by a syn‐rift sequence offset by steep frontal faults that pass eastward into shallower, predominantly west‐dipping highly listric faults that merge downwards with the detachment. The detachment has pronounced E‐W corrugations parallel to the basin opening direction, and N‐S lineaments that correspond with the footwall cutoff lines of overlying Jurassic faults. The most significant N‐S lineaments correspond with changes in dip of the detachment. We propose that the geometry of P can be explained by a conceptual model in which the detachment was assembled from initially steep faults that developed at the front of P and back‐rotated to form listric faults during extension, with punctuated oceanward propagation of the segments of the detachment. Comparisons with 2D profiles and 3D surfaces of published detachments suggest that our conceptual model may be applicable to other detachments that accommodate extreme extension at other rifted margins and at mid‐oceanic slow and ultra‐slow spreading ridges.

Thermal variation across collisional orogens: Insights from the hinterland–foreland transition zone of the Sardinian Variscan belt

AbstractUnravelling the architecture and evolution of orogenic wedges are often hampered by the presence of strongly deformed large‐scale nappes made by homogeneous metasedimentary rocks lacking diagnostic metamorphic phases. Involving nappes or tectonic units which occupy most of the chain, reconstructing the thermal architecture of the hinterland–foreland transition zone of collisional belts represents a key point to comprehend the orogenic wedge tectonics. This work provides new thermal data from Raman Spectroscopy on Carbonaceous Material (RSCM) carried out in the low‐grade metamorphic rocks of the hinterland–foreland transition zone in the Variscan belt of Sardinia. The obtained TRSCM highlighted a temperature difference, from ~470–440°C down to ~440–380°C, for the internal and external nappes, respectively. We propose that both nappes experienced syn‐nappe greenschist‐facies metamorphism with different TRSCM, further heating localized along the tectonic boundary in between, that is the Barbagia Thrust (BT), and finally, post‐nappe stacking regional‐scale folding, that deformed the TRSCM spatial distribution and drove the present‐day thermal architecture.

Mantellic degassing of helium in an extensional active tectonic setting at the front of a magmatic arc (central Mexico)

Abstract The physicochemical and isotopic characteristics of groundwater and dissolved gas of central Mexico provide valuable information about the geologic and tectonic context of the area. Low–high-enthalpy manifestations (up to 98 °C in springs and more than 100 °C in geothermal wells) are distributed within the San Juan del Río, Querétaro, and Celaya hydrologic basins, located at the boundary between the current Mexican magmatic arc and an extensional continental area with intraplate volcanism called Mesa Central Province. Groundwaters in the study area represent a mixture between the cold water end-member with a Ca2+-Mg2+-HCO3-composition and a hydrothermal end-member enriched in Na+, K+, SO42−, and Cl-. Cold and hot groundwaters δ2H and δ18O plot along the same evaporation lines and do not exhibit a magmatic input. Dissolved and free gas do not show a typical volcanic composition signature. He and Ne isotope composition provide evidence of an important contribution of non-atmospheric noble gases. Although helium composition mainly has a crustal origin (21–83%), the mantellic contribution (1–39%) is higher than expected for an area lacking recent volcanism. A volatilerich magma aging at depth was discarded as the source of this mantellic helium signature but points out a recent mantellic contribution. Thus, we propose that mantellic helium comes from the sublithospheric mantle into the shallow crust through the highly permeable tectonic boundaries between the geologic provinces, namely the N−S Taxco−San Miguel de Allende and Chapala-Tula fault systems. Mantellic helium flow rates through these fault systems were estimated to have values ranging from 0.1 m/yr to 2.9 m/yr. This He flux range implies that aside from subduction, mantle volatile degassing enhanced by crustal fault systems is the main degassing process in the region studied.

Crustal Deformation in the Sierra Nevada and Walker Lane Region Inferred From P‐Wave Azimuthal Anisotropy

AbstractCrustal deformation in the Sierra Nevada and Walker Lane is mainly investigated by geologic and geodetic constraints which suffer from a lack of depth information. In this study, we construct a new depth‐dependent azimuthally anisotropic P‐wave velocity (Vp) model of this area to investigate regional deformation regimes in the upper and middle crust. The model is built based on adjoint‐state traveltime tomography of ∼650,000 local direct P arrivals collected from 1967 to 2021. The average Vp structure agrees well with previous tomographic models with refined velocity features benefiting from the ray‐free adjoint‐state tomography and more arrival time data. The azimuthal anisotropy of Vp reveals distinct differences between the rigid Sierra Nevada block and the Walker Lane shear zone: (a) The western Sierra Nevada shows weak anisotropy (<2%) and NW‐SE oriented fast velocity directions that are parallel to the Pacific‐North American plate boundary, mainly reflecting preserved paleofabrics developed in past subduction processes. (b) In the shallow Walker Lane (<4 km), the orientation of fast‐velocity directions is NNE controlled by regional compressive stress, and changes to NNW at greater depths in the north under shear deformation regimes. (c) In the central Walker Lane, strong anisotropy with ENE‐oriented P fast axes is imaged at 6–16 km from the area south of Lake Tahoe (2%–4%) to the Long Valley volcanic area (4%–8%) because of clockwise crustal block rotations and crustal fluids. The proposed anisotropic Vp model provides new insight into how past and present‐day deformation is accommodated in this tectonic complex plate boundary region.

Some problems with the tectonic subdivision schemes application in field work – an example of the Western Sredna Gora subzone

The tectonic subdivision is a regional method for correlation, very subjective and not always applicable during the field work. Usually, more detailed field investigations do not confirm the regional tectonic schemes, main characteristics of the tectonic units and boundaries. The given example for the Western Srednogorie subzone represents the handicaps of tectonic schemes fields application.

The Mesozoic Tectonic Transition from Compression to Extension in the South China Block: Insight from Structural Deformation of the Lushan Massif, SE China

The Lushan Massif has been considered an extensional dome which represents a typical extensional structure in South China. However, the composition and structure of the Lushan Massif are still unclear. In this study, we identified the eastern detachment fault (EDF) for the first time. In addition, many sinistral strike-slip structures have also been recognized in the Lushan area, such as the Xingzi shear zone (XZSZ) and Lianhua shear zone (LHSZ). Detailed field observation and structural analysis revealed that the former sinistral faults are tectonic boundaries of the later Lushan extensional dome (LSED). The tectonic evolution sequence was established after the structural analysis combined with zircon U-Pb dating and mica 40Ar-39Ar dating of metamorphic rocks, veins, and intrusive rocks from the strike-slip fault and detachment fault. The Lushan Massif has undergone sinistral ductile shearing within 162–150 Ma. The LSED was then formed in an extensional tectonic setting from 140 to 114 Ma. Together with the regional geological setting, we believe that the sinistral strike-slip structures, represented by the XZSZ and LHSZ, are coeval with the Tanlu fault system and could be controlled by a transpressional stress field resulting from the subduction of the Pacific Plate. The LSED was formed in a back-arc extension setting resulting from the rollback of a subducted slab. The tectonic transition from compression to extension in the South China Block took place at 150–140 Ma.

Cluster analysis of velocity models around the Hudson Bay region, Eastern Canada

SUMMARYUnderstanding deep crustal structure can provide us with insights into tectonic processes and how they affect the geological record. The deep crustal structure can be studied using a suite of seismological techniques such as receiver function analysis, body and surface wave tomography. Using models of crustal structure derived from these methods, it is possible to delineate tectonic boundaries and regions that may have been affected by similar processes. However, often velocity models are grouped in a somewhat subjective manner, potentially meaning that some geological insight may be missed. Cluster analysis, based on unsupervised machine learning, can be used to more objectively group similar velocity profiles and, thus, put additional constraints on the deep crustal structure. In this study, we apply hierarchical agglomerative clustering to the shear wave velocity profiles obtained by previous studies focused on the region from the joint inversion of receiver functions and surface wave dispersion data at 59 sites surrounding the Hudson Bay. This location provides an ideal natural laboratory to study the Precambrian tectonic processes, including the 1.8Ga Trans-Hudson Orogen. We use Ward linkage to define the distance between clusters, as it gives the most physically realistic results, and after testing the number of clusters from 2 to 10, we find there are 5 main stable clusters of velocity models. We then compare our results with different inversion parameters, clustering schemes (K-means and GMM), as well as results obtained for profiles from receiver functions in different azimuths and find that, overall, the clustering results are consistent. The clusters that form correlate well with the surface geology, crustal thickness, regional tectonics and previous geophysical studies concentrated on specific regions. The profiles in the Archean domains (Rae, Hearne and Superior) are clearly distinguished from the profiles in regions influenced by Proterozoic orogenic events (Southern Baffin Island and Ungava Peninsula). Further, the crust of Melville Peninsula is found to be in the same cluster as the crust of the western coast of Ungava Peninsula, suggesting a similar crustal structure. Our study shows the promising use of unsupervised machine learning in interpreting deep crustal structures to gain new geological insights.

Key factors controlling deep Carboniferous volcanic reservoirs in the east slope of Mahu Sag, Junggar Basin, NW China

Considering the complex factors controlling volcanic reservoirs, the Carboniferous strata in the eastern slope area of the Mahu Sag (ESMS) in the northwestern Junggar Basin (NJB) were investigated using rock cores, thin sections, scanning electron microscope (SEM), physical properties, major elements, X-ray fluorescence (XRF), well logging, and seismic data. The volcanic rocks revealed by drilling are mostly weathering crust reservoirs (WCRs), the formation of which in and around the study area is significantly controlled by weathering and leaching (WL). Most types of volcanic rock can be improved by long-term weathering. Favorable reservoirs in the ESMS are often developed within 150 m below the tectonic unconformity boundary at the top of the Carboniferous. The longer the weathering duration, the better are the overall quality of the WCRs. Weathering duration of about 40 Ma is probably an important threshold in the NJB. Ultra-long leaching of atmospheric water and strong late dissolution of acidic fluids before oil and gas accumulations are important for reservoir development and petroleum accumulation in volcanic strata filled with authigenic minerals, especially calcite. The early regional tectonic movement affected the volcanic eruption and controlled the lithofacies distribution. The linear density of fractures was negatively correlated with the distance from the main controlling fault. Owing to the relatively weak filling, high-angle fractures contribute significantly to the reservoir permeability. The physical properties of volcanic breccia are better than those of tuff, and the porosity, permeability, and fracture density of andesite are higher than those of basalt. The physical properties of near-source facies belts of a volcanic edifice are better than those of far-source facies ones. Favorable exploration areas are the structural highs and fault zones where the duration of WL is more than 40 Ma, explosive facies and effusive facies near the crater are developed, or the inherited ancient buried hills transformed by faults and fractures near excellent source rocks, where the dissolution of atmospheric water and organic acidic fluids are strong.

Cenozoic intraplate volcanism in central Asia: Mantle upwelling induced by India-Eurasia collision

Most of Earth’s volcanism occurs at tectonic plate boundaries associated with subduction or rifting processes. The mantle plume hypothesis is an important supplement to plate tectonics for explaining some high-volume intraplate volcanic fields. However, many intraplate magmatic provinces occur as low-volume, monogenetic basaltic-suite fields that are neither associated with plate-boundary processes nor attributable to mantle plumes, and the origin of such magmatism has long been debated. Identification of their source characteristics and possible mechanisms that trigger mantle melting will provide essential insights into Earth’s mantle heterogeneity and also develop our knowledge of tectonic plate movement through time. Here, we report new geochronology, mineral chemistry (especially olivine), and whole-rock chemical and Sr-Nd-Pb-Hf isotopic compositions on Cenozoic intracontinental alkaline basalts from the northwestern Tarim craton (central Asia), aiming to better assess the origin of Earth’s low-volume effusive intraplate volcanic fields. The basalts (ca. 42 Ma) have olivine (e.g., mean Ni abundances of ∼2250 ppm, mean Mn/Zn ratios of 13.7) and whole-rock chemistry consistent with their derivation from a mixed peridotite-pyroxenite source. Moderately depleted Sr-Nd-Pb-Hf isotopes (87Sr/86Sr = 0.7039−0.7053; εNd = +4.0 to +5.5; 206Pb/204Pb = 18.247−18.535; εHf = +8.1 to +8.7) require a young (ca. 500 Ma) oceanic crust recycled into the source, possibly related to subduction events during the assembly of Pangea. Estimated thermal-chemical conditions indicate that the original melting occurred in a relatively dry (H2O = 1.4 ± 0.9 wt%) and reduced (logfO2 ΔFMQ = −0.97 ± 0.21, where FMQ is fayalite-magnetite-quartz) asthenosphere under a mantle potential temperature of ∼1420 °C and a pressure of ∼3.7 GPa (corresponding to a depth of ∼120 km). Combining these data with regional tectonic history and geophysical data (high-resolution P-wave tomography), we propose that the long-lasting India-Eurasia collision triggered asthenospheric upwelling, focusing melts along translithospheric zones of weakness; this model provides a robust explanation for the observed Cenozoic intracontinental volcanism in central Asia. The integrated geochemical and geophysical evidence reveals that plate subduction−induced mantle upwelling represents a likely mechanism for the generation of many regions of plume-absent intraplate magmatism within continents.

Metamorphic Evolution and Orogenic Process Related to the Eastern Paleo-Tethyan Warm Subduction and Indochina–South China Collision

Abstract The eastern Paleo-Tethyan Jinshajiang–Ailaoshan–Song Ma orogenic belt in the Southeast Tibetan Plateau represents the tectonic boundary between the Indochina and South China blocks. Regional Cenozoic lithospheric strike-slip movements caused by the India–Asia collision have modified many of the pristine geological records associated with the Indosinian orogeny. The lack of reliable petrological evidences, particularly of high-pressure (HP) metamorphism, has hindered the tracing of the evolutionary history of the Paleo-Tethyan orogenic belt. We report the mineralogy, geochemistry, geochronology and thermodynamic modelling of eclogite lenses/blocks and their host garnet–phengite schists from the Song Ma Suture Zone of Northwest Vietnam and reveal their protolith origins and metamorphic evolution. The eclogites are geochemically similar to mid-ocean ridge basalt, showing weak depletions in high field-strength elements, positive to slightly negative whole-rock ɛNd(t) ratios (−1.69 to +5.15) and slightly high 87Sr/86Sr(t) ratios (0.70466–0.70834). The igneous protolith of the eclogites formed in the late Silurian (425.4 ± 3.6 Ma; igneous zircon dating, 638–459 Ma TDM dating), which makes them the oldest known mid-ocean ridge mafic rocks in an ancient Paleo-Tethyan Ocean. Various eclogites preserve similar peak mineral assemblages (garnet + omphacite + phengite + rutile + quartz ± epidote/clinozoisite ± kyanite ± winchite) under indistinguishable peak conditions. Their prograde P–T trajectories show a uniform pattern of progressive heating and weak compression along a geothermal gradient of 8°C–10°C/km, indicating a warm subduction setting at a low angle that contrasts with the cold oceanic subduction recorded in the adjacent Paleo-Tethyan suture zones. Combined with detrital U–Pb ages from previous studies, our geochronological data indicate that the host schists originated from continental crust within the South China Block and underwent a pervasive Triassic HP metamorphism related to the Indosinian orogeny. The eclogites and host schists yielded HP metamorphic ages of 239–234 Ma and retrogressive amphibolite-facies metamorphic ages of 231–229 Ma, suggesting rapid cooling (14.0°C–21.6°C/Myr) and exhumation (6.4 km/Myr) from the mantle to the crust. The Song Ma eclogites and their host schists formed when the final ocean closure transitioned to the initial Indochina–South China collision. The Song Ma eclogites and their host schists provide essential information on the opening and closure of the eastern Paleo-Tethys and the subsequent amalgamation of Southeast Asian continental fragments.

Provenance and sedimentation age of the Proterozoic clastic succession of the Garhwal‐Kumaon Lesser Himalaya, NW‐India: Clues from U–Pb zircon and Sr–Nd isotopes

The paper presents data on the U–Pb chronology of detrital zircon grains and radiogenic isotopic composition (87Sr/86Sr, ɛNd) from the Proterozoic clastic successions of the Garhwal‐Kumaon Lesser Himalaya representing the extended northern Indian cratonic margin, NW India. The Proterozoic Lesser Himalayan Basin in Garhwal‐Kumaon Himalaya is divided into two sectors, namely, Inner Lesser Himalaya (ILH) and Outer Lesser Himalaya (OLH) by a tectonic boundary, namely the Tons Thrust (TT). Age distribution from inner and outer sectors of the Lesser Himalaya shows that the U–Pb chronology of most of these zircons provides Palaeoproterozoic (between 1.6 and 1.8 Ga) to Neoproterozoic (800 Ma) ages. The age data suggest sedimentation of the Rautgara Formation (Damtha Group) of ILH continued till the Neoproterozoic (~850 Ma), which was earlier regarded as ≤1.6 Ga. Tracking the detrital U–Pb zircon ages in the near adjacent cratonic parts point towards Aravalli Orogen as the major source region. Whole‐rock ƐNd(0) values for ILH rocks range from −37.6 to −14.6 and for OLH it ranges from −19.6 to −6.7. More negative ƐNd values along with dominance of Neoarchean‐Palaeoproterozoic ages in ILH indicates supply from more evolved protolith or recycled sources and less negative ƐNd values with major Neoproterozic zircon ages from OLH supports for less evolved source rock. The change from more negative ƐNd to less negative ƐNd values progressively upward the stratigraphy can be due to a shift in source with time. Both U–Pb zircon and ƐNd supports for a continuous sedimentation model, rule out the presence of ~500 Ma unconformity within the LH and argues for separate evolution of the Lesser Himalayan Basin on the trailing edge of the extended north Indian craton in “Columbia” configuration.

Earthquake Cycle Deformation Associated With the 2021 MW 7.4 Maduo (Eastern Tibet) Earthquake: An Intrablock Rupture Event on a Slow‐Slipping Fault From Sentinel‐1 InSAR and Teleseismic Data

AbstractIn the continents, the importance of earthquakes that occur away from major block‐bounding faults is still debated. The 21 May 2021 MW ∼ 7.4 Maduo earthquake occurred on a secondary fault away from previously‐identified major block boundaries. Here we use 7 years of Sentinel‐1 Interferometric Synthetic Aperture Radar (InSAR) time series (between October 2014 and November 2021) to determine the distribution of coseismic slip and early postseismic afterslip following the Maduo earthquake, and the preceding interseismic strain accumulation. We devised a 13‐segment 3‐D fault geometry constrained by the SAR range offsets and the distribution of relocated aftershocks and used a Bayesian method incorporating von Karman regularization to solve for coseismic slip and afterslip models. We also used teleseismic waveforms as a standalone inversion to show the rupture evolution in space and time during the earthquake, finding that it propagates bilaterally with three notable rupture episodes. Our preferred coseismic self‐similar slip model shows a moderate shallow slip deficit, with the majority of moment release occurring in the depth interval of 1–10 km. The coseismic slip deficit is taken up in part by afterslip at shallow (<4 km) depths that grows linearly with time during the first ∼6 months, and at >10 km depths where afterslip grows logarithmically with time. We suggest that this heterogeneity is likely controlled by spatial variations in fault friction related to lithology. We discuss the implications for seismic hazard away from major tectonic block boundaries in light of our observations of the earthquake cycle on this intrablock fault.

Cluster Analysis of Dense GNSS Velocity Field Reveals Characteristics Associated With Regional Tectonics in New Zealand

AbstractNew Zealand is located in the converging zone between the Australian and Pacific Plates. The Pacific Plate is descending beneath the Australian Plate in the north of New Zealand, while the Australian Plate is descending beneath the Pacific Plate in the south. The contrastive tectonics is connected by the Alpine Fault, the transform fault with NE‐SW strike along most of the length of New Zealand. Recently, previous studies showed that a cluster analysis of dense Global Navigation Satellite System (GNSS) velocity field objectively yields major velocity discontinuities, which may reflect an important tectonic boundary. We applied two different types of clustering algorithms: hierarchical agglomerative clustering (HAC) and Euler pole clustering (EPC), to the dense GNSS horizontal velocity data in New Zealand. Both methods agree that the primary kinematic boundary lies from the northern Wairarapa region to the southwestern end of the Alpine Fault. The HAC introduces a cluster boundary along the North Island Dextral Fault Belt whereas EPC emphasizes the importance of the Taupo Volcanic Zone (TVZ). Since EPC fits the data reasonably well, it indicates the TVZ is an important boundary. This result displays the limitation of the flat earth assumption. The Chatham Islands is identified as an independent cluster by the HAC, but not by the EPC. Further cluster splits illustrate that the relative motion between the two plates is accommodated by distributed deformation in the Marlborough Fault Zone in the South Island whereas the North Island is characterized by local block rotations.

A coupled model for phase mixing, grain damage and shear localization in the lithosphere: comparison to lab experiments

SUMMARYThe occurrence of plate tectonics on Earth is rooted in the physics of lithospheric ductile weakening and shear-localization. The pervasiveness of mylonites at lithospheric shear zones is a key piece of evidence that localization correlates with reduction in mineral grain size. Most lithospheric mylonites are polymineralic and the interaction between mineral phases, such as olivine and pyroxene, especially through Zener pinning, impedes normal grain growth while possibly enhancing grain damage, both of which facilitate grain size reduction and weakening, as evident in lab experiments and field observations. The efficacy of pinning, however, relies on the mineral phases being mixed and dispersed at the grain scale, where well-mixed states lead to greater mylonitization. To model grain mixing between different phases at the continuum scale, we previously developed a theory treating grain-scale processes as diffusion between phases, but driven by imposed compressive stresses acting on the boundary between phases. Here we present a new model for shearing rock that combines our theory for diffusive grain mixing, 2-D non-Newtonian flow and two-phase grain damage. The model geometry is designed specifically for comparison to torsional shear-deformation experiments. Deformation is either forced by constant velocity or constant stress boundary conditions. As the layer is deformed, mixing zones between different mineralogical units undergo enhanced grain size reduction and weakening, especially at high strains. For constant velocity boundary experiments, stress drops towards an initial piezometric plateau by a strain of around 4; this is also typical of monophase experiments for which this initial plateau is the final steady state stress. However, polyphase experiments can undergo a second large stress drop at strains of 10–20, and which is associated with enhanced phase mixing and resultant grain size reduction and weakening. Model calculations for polyphase media with grain mixing and damage capture the experimental behaviour when damage to the interface between phases is moderately slower or less efficient than damage to the grain boundaries. Other factors such as distribution and bulk fraction of the secondary phase, as well as grain-mixing diffusivity also influence the timing of the second stress drop. For constant stress boundary conditions, the strain rate increases during weakening and localization. For a monophase medium, there is theoretically one increase in strain rate to a piezometric steady state. But for the polyphase model, the strain rate undergoes a second abrupt increase, the timing for which is again controlled by interface damage and grain mixing. The evolution of heterogeneity through mixing and deformation, and that of grain size distributions also compare well to experimental observations. In total, the comparison of theory to deformation experiments provides a framework for guiding future experiments, scaling microstructural physics to geodynamic applications and demonstrates the importance of grain mixing and damage for the formation of plate tectonic boundaries.

Applying lead (Pb) isotopes to explore mobility in humans and animals.

Lead (Pb) isotopes provide a complementary method to other provenance tools for tracking the origin and movement of humans and animals. The method is founded in the geographic distribution of Pb isotope ratios. However, unlike the Sr isotope method that is closely linked to the lithology of underlying rocks, Pb more closely reflects the tectonic regimes. This makes it particularly pertinent to use in Britain as there is major tectonic boundary (the Iapetus Suture) that runs between Berwick-upon-Tweed and the Solway Firth providing a compositional boundary in Pb isotope domains that approximates to the geographic areas of Scotland versus England and Wales. Modern pollution makes it difficult to use modern floral or faunal samples to characterize biosphere variation, and so we use geological datasets to define isoscape variation and present the first Pb isotope map of Britain. We have validated the use of these data form biosphere studies using well provenanced samples. Reference fields of diagnostic compositions, are created in μ-T space and these have been used in a test case to assess the geographic origins of Neolithic animals in Great Britain.

The Development Planning of the InaCORS BIG for Disaster Climate Environment and Hazard Mitigation

In the last decades, the development of the Indonesian Continuous Reference System (InaCORS) that installed by Geospatial Information Agency (Badan Informasi Geospasial/BIG) and National Land Agency (Badan Pertanahan Nasional/BPN) have been increasingly very rapidly. With the increasing development of InaCORS, it will be useful for purposes in various fields such as environmental disaster climate and hazard mitigation. The InaCORS sites should be installed in the selected area which services of positioning application can be maximized. There are several parameters that used to determine the location of InaCORS, such as existing location of InaCORS (BIG and BPN), tectonic plate boundaries, volcanoes, and land use system. By overlaying all parameters, We analyze using 50 km buffer for each site to determined which location that does not have service from InaCORS sites (blank are). The result shows that the distribution of InaCORS stations in the Papua island, Kalimatan island, small area in Sulawesi island and Sumatra island should be improved more. This information is very useful to analyzing the needs of InaCORS stations for Indonesia region, exspecially for as monitoring of environmental disaster climate and hazard mitigation

Evidence of Active Quaternary Deformation on the Great Valley Fault System near Winters, Northern California

Abstract The Great Valley fault system defines the tectonic boundary between the Coast Ranges and the Central Valley in California, is active throughout the Quaternary, and has been the source of several significant (M > 6) historic earthquakes, including the 1983 M 6.5 Coalinga earthquake and the 1892 Vacaville–Winters earthquake sequence. However, the locations and geometries of individual faults in the Great Valley fault system are poorly constrained, and fault slip rates and paleoearthquake chronology are largely unknown. Here, we report geomorphic and subsurface geophysical evidence of surface-deforming displacement on a strand of the Great Valley fault system west of Winters, California. Detailed geomorphic mapping and a high-resolution seismic reflection and tomography survey along an ∼800 m profile across the Bigelow Hills document a fault, which we call the West Winters strand of the Great Valley fault system, with apparent east side-up displacement of surficial geologic units. These data together suggest that the West Winters strand is active in the latest Quaternary. Together with local reports from the time, this raises the possibility that the West Winters strand may have ruptured and deformed the surface during the 1892 M 6 Vacaville–Winters earthquake sequence. Future earthquakes with vertical displacement on this and Great Valley fault system structures could have significant hazard implications, given the region’s low relief and the presence of major water conveyance infrastructure.

An energy-based theory of rock faulting

Faulting of rocks is a dominant earth process that governs small-scale fracturing, formation of tectonic plate boundaries, and earthquakes occurrence. Since the 18th century, the mechanics of rock faulting was commonly analyzed with the Coulomb criterion that offers empirical, useful tools for scientific and engineering applications. Here we revisit the processes of rock faulting by an alternative approach that incorporates elastic energy, strain-state, and three-dimensional deformation; these mechanical fundamentals are missing in Coulomb criterion. We propose that a stressed rock-body fails as two conditions are met: (A) The elastic energy generated by the loading system equals or exceeds a critical energy intensity that is required for the faulting process; (B) To maintain physical continuity, the internal strain of the stressed rock-body due to slip and dilation along the developing faults equals the strain-state created by the loading system. Our simulations reveal that meeting these energy and strain conditions requires an orthorhombic, polymodal fault geometry that is comparable to natural and experimental fault systems. The application of our formulation to hundreds of rock-mechanics experiments provides a new, comprehensive benchmark for rock-faulting.

Assessment of strong earthquake risk in the Chinese mainland from 2021 to 2030

The long-term earthquake prediction from 2021 to 2030 is carried out by researching the active tectonic block boundary zones in the Chinese mainland. Based on the strong earthquake recurrence model, the cumulative probability of each target fault in the next 10 years is given by the recurrence period and elapsed time of each fault, which are adopted from relevant studies such as seismological geology, geodesy, and historical earthquake records. Based on the long-term predictions of large earthquakes throughout the world, this paper proposes a comprehensive judgment scheme based on the fault segments with the seismic gap, motion strongly locked, sparse small-moderate earthquakes, and apparent Coulomb stress increase. This paper presents a comprehensive analysis of the relative risk for strong earthquakes that may occur in the coming 10 years on the major faults in the active tectonic block boundary zones in the Chinese mainland. The present loading rate of each fault is first constrained by geodetic observations; the cumulative displacement of each fault is then estimated by the elapsed time since the most recent strong earthquake.