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Journal of geophysical research
American Geophysical Union
Journal of geophysical research

American Geophysical Union

2169-9313

Journal of geophysical research/Journal Journal of geophysical research
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    Spatio-Temporal Complexity of Aftershocks in the Apennines Controlled by Permeability Dynamics and Decarbonization

    Gunatilake, ThanushikaMiller, Stephen A.
    11页
    查看更多>>摘要：In 2016, a series of large normal faulting earthquakes in the Apennines filled the seismic gap between the 1997 Colfiorito and 2009 L'Aquila earthquakes. These earthquakes, known as the Amatrice-Visso-Norcia (AVN) sequence, spawned hundreds of thousand of aftershocks in the first year, extending about 60 km along strike. The Colfiorito and L'Aquila aftershocks showed a significant high fluid-pressure component in their aftershock genesis, and here we show evidence that the AVN aftershocks also include a significant high pressure CO2 component. This CO2 is both deeply-derived, and internally generated by thermal decomposition. Using a simple model of non-linear diffusion with a source term, we compare model results with the observed cumulative number of aftershocks, and also spatial comparisons between the calculated fluid pressure and the hypocenters of about 35,000 well-located events. The good comparisons between model and observations provide evidence that the AVN sequence includes a contribution (additional fluid source) from co-seismic decarbonization. Our results suggest that internal fluid generation through devolitization or decarbonization is responsible for non-Omori type aftershock behavior such as observed for the AVN sequence and for the 2011 M-w 9.1 Tohoku (Japan) and the 2014 Iquique (Chile) M-w 8.2 megathrust subduction zone earthquakes.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    The Subducting Slab as a Chromatographic Column: Regimes of Sub-Solidus Mass Transport as a Function of Lithospheric Hydration State, With Special Reference to the Fate of Carbonate

    Zhong, XinGalvez, Matthieu E.
    28页
    查看更多>>摘要：We investigate the chemical budget of subduction zones at sub-solidus conditions using a thermodynamic-numerical simulation in which all major rock components are treated as soluble and potentially mobile in aqueous fluids. This new strategy significantly improves the accuracy of predicted fluid-rock equilibrium compositions in open petrological systems. We show that all slabs release volatiles and nonvolatiles to the mantle wedge, contributing to its refertilization. But some mobile constituents, such as alkali and alumina, may be trapped along layer boundaries or traverse without interaction depending on chemical contrasts between adjacent lithologies. The accumulation of igneous alumina and silica in the limestones of the central-eastern Pacific slabs drives their decarbonation and is marked by metasomatic garnet growth. Those slabs are also predicted to lose much of their alkalis before sub-arc depth. Even when they are produced in the altered mafic and ultramafic layers, fluids reach the slab/mantle wedge interface with distinct compositional signatures that are typical of the sedimentary cover. We distinguished supply and transport limited regimes of element subduction by testing the sensitivity of our mass balance to changes in slab hydration state (HS). Transport limited slabs sensitive to HS include notably a hotspot of carbon release to the mantle wedge (e.g., Costa Rica). Finally, we show that the quantitative budgets do depend on the geometry of fluid flows, and on assuming that slabs are mechanically continuous structures, which is questionable. Taken together, these insights will help better constrain the long-term chemical evolution of the shallow planetary interior, and the thermomechanical behavior of the subduction interface.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    Understanding the Role of Biogenic Magnetite in Geomagnetic Paleointensity Recording: Insights From Ontong Java Plateau Sediments

    Li, JiaxiYamazaki, ToshitsuguUsui, YoichiSagawa, Takuya...
    21页
    查看更多>>摘要：Marine sediments can preserve continuous paleomagnetic intensity records. Different magnetic minerals may acquire remanent magnetizations differently, so that compositional variations of magnetic mineral assemblages in sediments may hinder extraction of reliable relative paleointensity (RPI) records. To better understand this issue, we conducted a paleo- and rock magnetic study of a sediment core from the Ontong Java Plateau, western equatorial Pacific Ocean. RPI estimated by normalizing natural remanent magnetization (NRM) with anhysteretic remanent magnetization (ARM) decreases downcore with an inverse correlation with the ratio of ARM susceptibility to saturation isothermal remanent magnetization. This relationship indicates that the RPI signal weakens as the proportion of biogenic magnetite increases. The NRM-ARM demagnetization diagrams obtained have concave-down curvature. These observations indicate that the RPI recording efficiency of the biogenic component is lower than that of the terrigenous component if we assume that the magnetizations of the high- and low-coercivity windows are carried dominantly by biogenic and terrigenous components, respectively. This assumption is supported by first-order reversal curve measurements, transmission electron microscope observations, low-temperature measurements, and extraction of silicate-hosted magnetic inclusions from the sediments. Previous studies have suggested that the RPI recording efficiency of biogenic magnetite is higher than that of the terrigenous component, which disagrees with our results. Different concentrations of silicate-hosted magnetic inclusions in different sedimentary environments might explain this contradiction. We conclude that biogenic magnetite contributes to RPI records with lower efficiency than unprotected terrigenous magnetic minerals in the studied sediments. Changing biogenic magnetite proportions distort ARM-normalized RPI estimations.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    Age and Rate of Accumulation of Metal-Rich Hydrothermal Deposits on the Seafloor: The Lucky strike Vent Field, Mid-Atlantic Ridge

    Sanchez-Mora, DennisJamieson, JohnCannat, MathildeEscartin, Javier...
    16页
    查看更多>>摘要：Hydrothermal venting at the Lucky Strike hydrothermal field, located on the Mid-Atlantic Ridge, is associated with faulting linked to the tectonic dismemberment of a central axial volcano. Radium-226/Ba dating of hydrothermal barite indicates that hydrothermal venting is at least 6,600 years old, and that Lucky Strike is one of the youngest known vent fields on the Mid-Atlantic Ridge, which typically have ages exceeding 20 ka. Deposit volume calculations indicate that the total accumulated mass of the hydrothermal deposits on the seafloor at Lucky Strike is similar to 1.3 +/- 0.2 Mt, and that this mass accumulated at a maximum average rate of 194 +/- 28 t/yr. This accumulation rate is comparable to other well characterized mid-ocean ridge hydrothermal sites, such as TAG and Endeavor, but at Lucky Strike is concentrated within a relatively small area of <2.5 km(2). Plain Language Summary In this contribution we determine the age (>6,600 years) and mass (similar to 1.3 Mt) of metal-rich deposits that formed at a cluster of high-temperature seafloor hot springs called Lucky Strike, which is situated on the Mid-Atlantic Ridge. With this information we calculate the average rate of formation (194 t/yr) of these deposits. Our results indicate that the Lucky Strike vent field is much younger than other vent fields that also occur along the Mid-Atlantic Ridge, but the deposits form at similar rates, which are high when compared to other types of geological processes that produce metal-rich deposits.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    Estimation of Resolution and Covariance of Ambient Seismic Source Distributions: Full Waveform Inversion and Matched Field Processing

    Xu, ZongboMikesell, T. Dylan
    17页
    查看更多>>摘要：Both natural and anthropogenic seismic sources generate so-called ambient seismic waves. One in turn can use ambient seismic waves to estimate these source distributions and study source characteristics, for instance the source mechanism. A commonly used estimation method is called matched field processing (MFP), and the MFP results are inherently smeared by the array geometry. Another approach to estimate ambient seismic sources is to apply full waveform inversion (FWI) to the crosscorrelations of ambient seismic wave recordings. Both methods have pros and cons, but the model resolution and uncertainty in these two methods are important for the interpretation. Unfortunately, this topic has attracted little attention in the past. We propose to estimate both the model resolution matrix and model covariance matrix of the inversion using singular value decomposition. We demonstrate our estimates using two examples, one of which is an actual field array geometry. We quantitatively compare the model resolution of the two methods and discuss the model null space. We demonstrate that FWI has superior resolution with enough independent data and should be used when computational resources permit.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    Performance of a Rotational Sensor to Decipher Volcano Seismic Signals on Etna, Italy

    Di Grazia, GiuseppeJousset, PhilippeKrueger, FrankWeber, Michael...
    22页
    查看更多>>摘要：Volcano-seismic signals such as long-period events and tremor are important indicators for volcanic activity and unrest. However, their wavefield is complex and characterization and location using traditional seismological instrumentation is often difficult. In 2019 we recorded the full seismic wavefield using a newly developed 3C rotational sensor co-located with a 3C traditional seismometer on Etna, Italy. We compare the performance of the rotational sensor, the seismometer and the Istituto Nazionale di Geofisica e Vulcanologia-Osservatorio Etneo (INGV-OE) seismic network with respect to the analysis of complex volcano-seismic signals. We create event catalogs for volcano-tectonic (VT) and long-period (LP) events combining a STA/LTA algorithm and cross-correlations. The event detection based on the rotational sensor is as reliable as the seismometer-based detection. The LP events are dominated by SH-type waves. Derived SH phase velocities range from 500 to 1,000 m/s for LP events and 300-400 m/s for volcanic tremor. SH-waves compose the tremor during weak volcanic activity and SH- and SV-waves during sustained strombolian activity. We derive back azimuths using (a) horizontal rotational components and (b) vertical rotation rate and transverse acceleration. The estimated back azimuths are consistent with the INGV-OE event location for (a) VT events with an epicentral distance larger than 3 km and some closer events, (b) LP events and tremor in the main crater area. Measuring the full wavefield we can reliably analyze the back azimuths, phase velocities and wavefield composition for VT, LP events and tremor in regions that are difficult to access such as volcanoes.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    Crustal and Uppermost Mantle Heterogeneities Across the Ailaoshan Red River Shear Zone, SE Tibet: Implications for Cenozoic Magmatic Activity

    Xu, MijianYu, DayongHuang, ZhouchuanTong, Ping...
    14页
    查看更多>>摘要：The Ailaoshan Red River shear zone (ARSZ) was formed in the Mesozoic as a suture zone between the Indochina block and the Yangtze craton. Since the Cenozoic, block extrusion due to the Indo-Asian collision has reactivated the fault zone and caused large-scale shearing. Affected by the Cenozoic orogeny, a large volume of magmatic and metamorphic rocks developed in the ARSZ, forming many orogenic gold deposits. However, the source and the geodynamic process of these magmatic activities are still unclear. To gain a basic understanding of the subsurface magmatic activity, we deployed a dense array of 24 broadband seismic stations across the Daping and Chang'an gold deposits at the southern end of the ARSZ. Receiver function analysis, common conversion point stacking, and a joint inversion of receiver functions and surface wave dispersions are performed to image the detailed structure of the crust and uppermost mantle. Low-velocity zones in the mid-lower crust and thinned lithosphere (similar to 70 km) are imaged under the ARSZ. The observed subsurface structures are verified by 3D numerical modeling with the SEM-FK method. We speculate that the mantle upwelling caused by lithospheric delamination has provided the main source of the mantle component in the magmatic rocks since similar to 35 Ma; afterward, high temperatures produced partial melting in the lower crust, which was emplaced along active shear zones.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    3D GNSS Velocity Field Sheds Light on the Deformation Mechanisms in Europe: Effects of the Vertical Crustal Motion on the Distribution of Seismicity

    Pina-Valdes, JesusSocquet, AnneBeauval, CelineDoin, Marie-Pierre...
    25页
    查看更多>>摘要：Crustal deformation and seismicity in Europe are still poorly understood. Seismic activity is classically ascribed to crustal strain rates generated by edge-driven tectonic forces. However, crustal deformation is not only due to tectonic loading, but can also be related to isostatic and mantellic processes that induce additional stress and strain on the crust by flexure. The influence that those processes have on seismic activity, as well their interaction, is still controversial. The main limitation to study it is because the deformation and its causal mechanisms are usually analyzed separately in small regions. We present here a 3D secular velocity field that covers Eurasia and its plate boundaries including 4,863 Global Navigation Satellite System stations obtained by combining 10 different datasets. We have developed a method based on spatial filtering to identify outliers and smooth the velocity field, and have computed both strain and uplift rate maps that are interpreted in the light of the different driving processes that contribute to the 3D deformation in Europe. The vertical and horizontal deformation features are compared with seismic rates obtained from the spatial and temporal distribution of the seismicity in Europe. Our results suggest that is not possible to explain the seismicity in Europe with edge-driven horizontal tectonic forces only. In some areas markers of the crustal flexure such as the vertical velocity field and its derivative, resulting from buoyancy-driven processes, may help to interpret earthquake distribution.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    Rate and State Friction as a Spatially Regularized Transient Viscous Flow Law

    Pranger, CasperSanan, PatrickMay, Dave A.Le Pourhiet, Laetitia...
    33页
    查看更多>>摘要：The theory of rate and state friction unifies field, laboratory, and theoretical analysis of the evolution of slip on natural faults. While the observational study of earthquakes and aseismic fault slip is hampered by its strong multi-scale character in space and time, numerical simulations are well-positioned to link the laboratory study of grain-scale processes to the scale at which rock masses move. However, challenges remain in accurately representing the complex and permanently evolving sub-surface fault networks that exist in nature. Additionally, the common representation of faults as interfaces may miss important physical aspects governing volumetric fault system behavior. In response, we propose a transient viscous rheology that produces shear bands that closely mimic the rate- and state-dependent sliding behavior of equivalent fault interfaces. Critically, we show that the expected tendency of the continuum rheology for runaway localization and mesh dependence can be halted by including an artificial diffusion-type regularization of anelastic strain rate in the softening law. We demonstrate analytically and numerically using a simplified fault transect that important aspects of the frictional behavior are not significantly affected by the introduced regularization. Any discrepancies with respect to the interfacial description of fault behavior are critically evaluated using one dimensional numerical velocity stepping and spring-slider experiments. Since no new physical parameters are introduced, our model may be straightforwardly used to extend the existing modeling techniques. The model predicts the emergence of complex patterns of shear localization and delocalization that may inform the interpretation of complex damage distributions observed around faults in nature.
      原文链接:
    • NSTL
    • Amer Geophysical Union

    Large-Scale Interseismic Strain Mapping of the NE Tibetan Plateau From Sentinel-1 Interferometry

    Ou, Q.Daout, S.Weiss, J. R.Shen, L....
    29页
    查看更多>>摘要：The launches of the Sentinel-1 synthetic aperture radar satellites in 2014 and 2016 started a new era of high-resolution velocity and strain rate mapping for the continents. However, multiple challenges exist in tying independently processed velocity data sets to a common reference frame and producing high-resolution strain rate fields. We analyze Sentinel-1 data acquired between 2014 and 2019 over the northeast Tibetan Plateau, and develop new methods to derive east and vertical velocities with similar to 100 m resolution and similar to 1 mm/yr accuracy across an area of 440,000 km(2). By implementing a new method of combining horizontal gradients of filtered east and interpolated north velocities, we derive the first similar to 1 km resolution strain rate field for this tectonically active region. The strain rate fields show concentrated shear strain along the Haiyuan and East Kunlun Faults, and local contractional strain on fault junctions, within the Qilianshan thrusts, and around the Longyangxia Reservoir. The Laohushan-Jingtai creeping section of the Haiyuan Fault is highlighted in our data set by extremely rapid strain rates. Strain across unknown portions of the Haiyuan Fault system, including shear on the eastern extension of the Dabanshan Fault and contraction at the western flank of the Quwushan, highlight unmapped tectonic structures. In addition to the uplift across most of the lowlands, the vertical velocities also contain climatic, hydrological or anthropogenic-related deformation signals. We demonstrate the enhanced view of large-scale active tectonic processes provided by high-resolution velocities and strain rates derived from Sentinel-1 data and highlight associated wide-ranging research applications.
      原文链接:
    • NSTL
    • Amer Geophysical Union