Journal of Geodynamics最新文献

We investigate the seismic structure of the mantle wedge of the Apennines subduction zone (Central Mediterranean) using teleseismic receiver function (RF). We inverted RF for both isotropic and anisotropic properties of the mantle wedge, from below the overriding Moho to the “plate boundary”, i.e. the interface that separate the slab from the mantle wedge. Given the distribution of the seismic network, we are able to map out the change in the elastic properties at the transition between southern apennines and the Calabrian arc, given by the change in the subduction style (i.e from the subduction of continental materials to oceanic plate). We found that the anisotropy in the mantle wedge is similar between all seismic stations, generally highly anisotropic (> 10%), with a direction of the symmetry axis that rotates clockwise from North to South, following the Calabrian arc geometry and likely indicating the mantle flow driven by the slab retreat. The elastic properties of the subducted crust are more heterogeneous. To the North, the subducted crust shows a highly anisotropic (> 10%) behavior, and it occurs at larger depth (around 70 km depth), where to the South anisotropy is less intense (around 7%) and the subducted crust is shallower (around 60 km depth). These results point out a change in the subduction style that can be given by either a change in the metamorphic phase (more evolved blueschist facies stage to the North, initial greenschist facies stage to the South) or a different origin for the subducted materials (continental to the North and oceanic to the South). The differences in the anisotropic behavior of the subducted crust are reflected in the topography of the plate boundary, which becomes shallower from North to South, suggesting the existence of either a step in the slab topography or a more gentle ramp.

Conventional seismic tomography studies consider the Earth’s interior as mechanically isotropic, despite seismic anisotropy being widely observed. This current standard approach to seismic imaging is likely to lead to significant artefacts in tomographic images with first-order effects on interpretations and hinders the quantitative integration of seismology with geodynamic flow models. Although a few methodologies have been proposed for carrying out anisotropic tomography, their ability in simultaneously recovering isotropic and anisotropic structures has not been rigorously tested. In this contribution we use geodynamic and seismological modeling to predict the elastic properties and synthetic teleseismic P- and S-wave travel-time datasets for three different tectonic settings: a plume rising in an intraplate setting, a divergent margin, and a subduction zone. Subsequently, we perform seismic anisotropy tomography testing a recently developed methodology that allows for the inversion of an arbitrarily oriented weakly anisotropic hexagonally symmetric medium using multiple body-wave datasets. The tomography experiments indicate that anisotropic inversions of separate and joint P- and S-wave travel-times are capable of recovering the first order isotropic velocity anomalies and anisotropic patterns. In particular, joint P- and S-wave anisotropic inversions show that by leveraging both phases it is possible to greatly mitigate issues related to imperfect data coverage common in seismology and reduce parameter trade-offs. In contrast, by neglecting seismic anisotropy, isotropic tomographic models provide no information on the mantle fabrics and in all cases are contaminated by strong velocity artifacts. In the inversions the magnitude of anisotropy (as well as that of seismic anomalies) is always underestimated owing to regularization procedures and smearing effects. It follows that the true seismic anisotropy of mantle rocks is likely higher than estimated from anisotropic tomographies, and more consistent with predictions from laboratory and numerical micro-mechanical experiments. Altogether, these results suggest that anisotropic body-wave tomography could provide unprecedented information about the Earth’s deep geological structure, and that the latter could be better recovered by complementing teleseismic body-wave travel-times with other geophysical datasets.

The anisotropy of elastic properties, including seismic velocities, has already been investigated in the lab over past seven decades. Here, we present a review related to the development of a unique apparatus for the detailed measurement of seismic velocity anisotropy. Its originality lies in measuring velocities on spherical specimens, which allows for determination of the velocity anisotropy as a function of confining pressure loading with high resolution. The 132 directions, covering the sphere in a regular 15° net of meridians and parallels, have proven to be optimal with respect to common heterogeneities of investigated rocks. The device was designed and the first measurements were performed by a research team of the Institute of Geophysics in Prague (Babuška, Pros and Klíma) in 1968, shortly following many pioneer velocity anisotropy studies. Since then, almost 100 papers have been published using the velocity anisotropy measured with this unique device. The review consists of three separate but mutually interconnected parts: (i) historical development; (ii) microstructural insights from an ultrasonic velocity measurement perspective; (iii) macroscale applications to practical problems in geophysics, structural geology and rock mechanics.

The plate boundary between the Pacific-Caroline and Australian plates in northwestern New Guinea is associated with a geographic concentration of earthquakes developed in the Ransiki region of the northeastern Bird’s Head Peninsula (West Papua, northwestern New Guinea) at the intersection of the Ransiki and Yapen faults. We examine these earthquakes based on regional geomorphological and lithostratigraphical frameworks, field observations of surface ruptures and liquefaction phenomena, and focal mechanisms of historical earthquakes. The Ransiki earthquakes are a set of 29 earthquakes from the Global Centroid Moment Tensor catalogue in the period 1977–2019 (magnitudes of Mw4.9 to Mw7.5). In the east, focal mechanisms show sinistral movement along the east-west trending Yapen Fault including the Mw6.7 earthquake on 21 April 2012. The largest earthquake was on 10 October 2002 (Mw7.5) and along with other earthquakes mainly in the southwest were associated with dextral movement indicated by focal mechanism solutions on the northwest trending Ransiki Fault south of its intersection with the Yapen Fault. The southern part of the Ransiki Fault therefore indicates local north-northeast compression that is also evident in the newly recognised Wainoei Fault south of Yapen Island. The two largest earthquakes (10 October 2002, 21 April 2012) show ground effects associated with liquefaction, indicated by surface offsets, open fissures, and sand blows, that all occurred in saturated sediments of the Ransiki delta. Earthquakes in the Ransiki region show that west-southwest oblique plate convergence between the Australian and Pacific-Caroline plates is partitioned into east-west sinistral strike-slip motion along the Yapen Fault and north-northeast compression associated with the Ransiki Fault.

The elastic properties of nineteen samples of crystalline rocks – amphibolites from different areas/boreholes were studied in order to elucidate possible depth effect on the elastic properties of these mineralogically relatively homogenous rocks. The samples were taken from three different crustal levels – shallow (tens of meters) Stařechov (Czech Republic), medium (first thousands of meters) KTB (Germany), and extreme crustal depths (up to 12 km) KSDB3 (Russia). The elastic properties were first determined experimentally using a high-pressure apparatus allowing for multidirectional (3D) ultrasonic sounding at various levels of confining pressure. The effect of main rock fabric components was evaluated using the method of inverse calculation from experimental data. The observed increase of elastic wave velocity and elastic constants with depth could be explained by the stress memory effect.

We have investigated the local shear wave splitting of 30–300 km depth earthquakes from 38 BMKG stations between 2009 and 2020 to determine upper mantle dynamics beneath the Central and East Java (CEJ) region, Indonesia. A total of 2338 measurements is obtained and divided the analysis into two focal depths, i.e., shallow (≤ 100 km) and deep (100 – 300 km) events. (1) Both individual station measurements and spatially averaged data using shallow events (≤ 100 km) show the trench-perpendicular fast direction in the northern CEJ region. Thus, anisotropy in this domain may be associated with the downdip subduction-induced 2-D corner flow in the mantle wedge allowing A-type olivine fabric to develop. Meanwhile, the trench-parallel fast directions in the southern CEJ region may reflect some possible causes of anisotropy: the presence of a serpentinized mantle wedge that promotes the development of B-type olivine fabric and anisotropy through alignment of the melt pockets. We also suggest a change in the hydration state of the subducting slab can cause the predominant trench-perpendicular fast directions in the eastern CEJ region. (2) For deep events (100 – 300 km), fast directions are relatively trench-parallel in the eastern CEJ region and trench-perpendicular in the western CEJ region, suggesting the presence of fossilized anisotropy and 2-D mantle flow-induced anisotropy, respectively.

Previous tectonic studies have indicated that the peri-cratonic lithosphere, located away from continental margins, is sensitive to far-field stresses propagating from active plate margins, which induce variable deformation. In order to gain a better understanding of potential intraplate tectonic events associated with the geodynamic evolution of the active margin of southwestern Gondwana, we conducted a tectono-sedimentary study of the Permian-Jurassic volcano-sedimentary record in the Deseado Massif, located in southern Patagonia. Our multidisciplinary analysis includes detailed geological mapping of an area of approximately 150 km², structural analysis, geoelectric tomography, 2D seismic data, new geochronological dating, petrographic studies, and stratigraphic loggings of the volcano-sedimentary basin record. This comprehensive data set has allowed us to establish the tectonic, sedimentary, and magmatic evolution of the eastern Deseado Massif. Specifically, we have identified major normal faults associated with the syn-extensional deposition of late Permian and Jurassic sedimentary and volcanic rocks, as well as the Late Triassic emplacement of intermediate and felsic intrusive bodies. Additionally, interspersed large-scale shortening events were recognized, which induced positive tectonic inversion events in the region, recording contrasting stress fields during the analyzed lapse. Based on this, six major intraplate tectonomagmatic events were defined: (i) a potential post-Devonian pre-late Permian exhumation of the Neoproterozoic-early Paleozoic igneous-metamorphic basement, which we tentatively link to the Gondwanide orogeny; (ii) intraplate extension in the Late Permian (255 ± 4 Ma) related to the deposition of the Dos Hermanos Member of the La Golondrina Formation; (iii) Late Triassic (231 ± 3 Ma) intrusion of andesitic bodies, tentatively linked to the inland migration of arc magmatism associated with the South Gondwana flat slab; (iv) subsequent Late Triassic positive tectonic inversion of Permian extensional faults caused by a large-scale contractional event linked to the South Gondwana flat slab; (v) the extension-related emplacement and deposition of Early-Middle Jurassic (176 ± 3 Ma; 172 ± 4 Ma) sedimentary (lacustrine and fan deltas-related deposits), pyroclastic rocks (ignimbrites and ash tuffs), and lavas (lava domes and dykes) related to the Chon Aike silicic large igneous province; and (vi) poorly-constrained post-Middle Jurassic positive tectonic inversion of Jurassic faults. Therefore, we suggest that the geological events preserved in the Deseado Massif provide a key deformational record of the distal effects associated with ancient geodynamic processes that occurred along the southwestern active margin of Gondwana.

On 14 August 2021, a large earthquake struck the southern region of Haiti. The epicenter of this earthquake is located relatively close to the Enriquillo–Plantain Garden Fault (EPGF) zone, a major active fault with a strike-slip mechanism in the southern part of Hispaniola. Since the epicenter of this earthquake is located relatively close to the Enriquillo–Plantain Garden Fault zone, one might think that the EPGF is the causative fault. Using a Bayesian approach, the Sentinel-1 data is then utilized to investigate the seismogenic fault responsible for the 2021 Haiti earthquake. The Bayesian inversion indicated that the mainshock ruptured a north-dipping fault with a strike and a dip of 270.9° and 69.2°, respectively, and buried at a depth of 10.3 km from the earth’s surface. The preferred slip model showed that the rupture did not reach the surface and was confined at a depth of ∼6 km to ∼32 km. The preferred fault geometry is in good agreement with the relocated aftershock distribution and is inconsistent with the EPGF system configuration. It indicates that the EPGF is probably not the seismogenic fault responsible for the 2021 Haiti earthquake. Instead, results suggested that the 2021 Haiti earthquake ruptured an unmapped blind fault.

Land subsidence monitoring in Bandung, Indonesia, was initiated in the 2000 s. However, the monitoring has been limited to geometric observations only, which may restrict the further physical interpretation of the cause of the subsidence. In this study, we combine geometric and gravity observation methods to monitor surface subsidence in Bandung. 63 Synthetic Aperture Radar (SAR) images from Sentinel-1A covering the period of 2014–2020 were used to estimate the mean surface geometric changes. For the gravity observations, a hybrid gravity configuration that incorporates absolute (2008–2014) and relative (2011–2016) gravity observations were used to estimate the gravity changes. We estimated geometric changes of up to − 160 mm/yr, indicating rapid subsidence in the greater Bandung area. We obtained gravity changes ranging between − 56.7 and 40.1 μGal/yr. Upon subtracting the deformation-induced gravity field from the observed field, we produced a residual gravity field that was presumed to be dominated by the groundwater signal, which was then investigated further. We found that the gravity-derived groundwater signal was mainly negative, indicating subsurface mass loss. We further compared the signal with the modeled gravity effect from deep groundwater observations (1996–2008). The median difference between the observed and modeled groundwater gravity signal was estimated to be 2.8 ± 18.0 μGal/yr or equivalent to 0.08 ± 0.55 m/yr in terms of water height if we set the integration cap and groundwater depth to 1.4 km and 150 m, respectively. The discrepancy can be attributed to modeling (simple geohydrological assumption) and measurement (different observation periods and noise) factors. Nevertheless, both measurements indicate that the mass is decreasing due to groundwater depletion, demonstrating the potential of geometric-gravimetric observations to infer sub-surface mass loss.