Journal of Geophysical Research: Solid Earth

Journal: Journal of Geophysical Research: Solid Earth

Abbreviation

J. Geophys. Res. Solid Earth

Publisher

American Geophysical Union

ISSN

2169-9313
0148-0227
2169-9356

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Publications 1 - 10 of 313

Full Waveform Inversion Beneath the Central Andes: Insight Into the Dehydration of the Nazca Slab and Delamination of the Back-Arc Lithosphere
Gao, Yajian; Tilmann, Frederik; van Herwaarden, Dirk-Philip; et al. (2021)
Journal of Geophysical Research: Solid Earth
We present a new seismic tomography model for the crust and upper mantle beneath the Central Andes based on multi-scale full seismic waveform inversion, proceeding from long periods (40–80 s) over several steps down to 12–60 s. The spatial resolution and trade-offs among parameters are estimated through the multi-parameter point-spread functions. P- and S-wave velocity structures with spatial resolution of 30–40 km for the upper mantle and 20–25 km for the crust could be resolved in the central study region. In our study, the subducting Nazca slab is clearly imaged in the upper mantle, with dip-angle variations from the north to the south. Bands of low velocities in the crust and mantle wedge indicate intense crustal partial melting and hydration of the mantle wedge beneath the frontal volcanic arc, respectively, and they are linked to the vigorous dehydration from the subducting Nazca plate and intermediate depth seismicity within the slab. These low-velocity bands are interrupted at 19.8°–21°S, both in the crust and uppermost mantle, hinting at the lower extent of crustal partial melting and hydration of the mantle wedge. The variation of lithospheric high-velocity anomalies below the back-arc from north to south allows insight into the evolutionary foundering stages of the Central Andean margin. A high-velocity layer beneath the southern Altiplano suggests underthrusting of the leading edge of the Brazilian Shield. In contrast, a steeply westward dipping high-velocity block and low-velocity lithospheric uppermost mantle beneath the southern Puna plateau hint at the ongoing lithospheric delamination.
Geophysically Informed Machine Learning for Improving Rapid Estimation and Short‐Term Prediction of Earth Orientation Parameters
Kiani Shahvandi, Mostafa; Dill, Robert; Dobslaw, Henryk; et al. (2023)
Journal of Geophysical Research: Solid Earth
Rapid provision of Earth orientation parameters (EOPs, here polar motion and dUT1) is indispensable in many geodetic applications and also for spacecraft navigation. There are, however, discrepancies between the rapid EOPs and the final EOPs that have a higher latency but the highest accuracy. To reduce these discrepancies, we focus on a data-driven approach, present a novel method named ResLearner, and use it in the context of deep ensemble learning. Furthermore, we introduce a geophysically constrained approach for ResLearner. We show that the most important geophysical information to improve the rapid EOPs is the effective angular momentum functions of atmosphere, ocean, land hydrology, and sea level. In addition, semidiurnal, diurnal, and long-period tides coupled with prograde and retrograde tidal excitations are important features. The influence of some climatic indices on the prediction accuracy of dUT1 is discussed, and El Niño Southern Oscillation is found to be influential. We developed an operational framework, providing the improved EOPs on a daily basis with a prediction window of 63 days to fully cover the latency of final EOPs. We show that under the operational conditions and using the rapid EOPs of the International Earth Rotation and Reference Systems Service (IERS), we achieve improvements as high as 60%, thus significantly reducing the differences between rapid and final EOPs. Furthermore, we discuss how the new final series IERS 20 C04 is preferred over 14 C04. Finally, we compare against EOP hindcast experiments of the European Space Agency, on which ResLearner presents comparable improvements.
Reducing nonuniqueness in finite source inversion using rotational ground motions
Bernauer, Moritz; Fichtner, Andreas; Igel, Heiner (2014)
Journal of Geophysical Research: Solid Earth
We assess the potential of rotational ground motion recordings to reduce nonuniqueness in kinematic source inversions, with emphasis on the required measurement accuracy of currently developed rotation sensors. Our analysis is based on synthetic Bayesian finite source inversions that avoid linearizations and provide a comprehensive quantification of uncertainties and trade-offs. Using the fault and receiver geometry of the Tottori 2000 earthquake as a test bed, we perform inversions for two scenarios: In scenario I, we use translational velocity recordings only. In scenario II, we randomly replace half of the velocity recordings by rotation recordings, thus keeping the total amount of data constant. To quantify the noise-dependent impact of rotation recordings, we perform a sequence of inversions with varying noise levels of rotations relative to translations. Our results indicate that the incorporation of rotational ground motion recordings can significantly reduce nonuniqueness in finite source inversions, provided that measurement uncertainties are similar to or below the uncertainties of translational velocity recordings. When this condition is met, rupture velocity and rise time benefit most from rotation data. The trade-offs between both parameters are then strongly reduced, and the information gain nearly doubles. This suggests that rotational ground motion recordings may improve secondary inferences that rely on accurate information about rise time and rupture velocity. These include frictional properties of the fault, radiation directivity, and ground motion in general.
Structural Evolution of Basaltic Melts in the Deep Earth: Insights From High‐Pressure Sound Velocity of Glass
Trubowitz, Charlotte; Murakami, Motohiko; Petitgirard, Sylvain; et al. (2024)
Journal of Geophysical Research: Solid Earth
The densification mechanisms of silicate melts under high pressure are of key interest in understanding the evolution of the early Earth and its present-day internal structure. Here, we report Brillouin spectroscopy-derived transverse acoustic wave velocities (Vₛ) from a basaltic glass at high pressures up to 163 GPa and ambient temperature to provide insight into pressure-induced changes in its elasticity and, by extension, its density. We find that the pressure dependence of Vₛ below 110–140 GPa follows a trend nearly tantamount to those of pyrolite and Fe- and (Fe,Al)-bearing MgSiO₃ glasses, indicating that the large compositional differences among these glasses do not exert variable acoustic wave velocity trends. However, at higher pressures we observe a small departure from the Vₛ profiles of the Al-poor compositions toward higher acoustic wave velocities to eventually become stiffer. This pressure-induced steepening in Vₛ is comparable to that of (Mg, Fe, Al)(Si, Al)O₃ glass, and suggests a possible structural change toward a denser state caused by more rapidly changing Al–O coordination in network-forming Al. Coupled with the high Fe content in basalt, this may render basaltic melt denser than surrounding minerals in the deep lower mantle, and may provide an additional mechanism for the existence of ultralow-velocity zones.
Mapping the Earth's thermochemical and anisotropic structure using global surface wave data
Khan, Amir; Boschi, Lapo; Connolly, James (2011)
Journal of Geophysical Research: Solid Earth
We have inverted global fundamental mode and higher-order Love and Rayleigh wave dispersion data jointly, to find global maps of temperature, composition, and radial seismic anisotropy of the Earth's mantle as well as their uncertainties via a stochastic sampling-based approach. We apply a self-consistent thermodynamic method to systematically compute phase equilibria and physical properties (P and S wave velocity, density) that depend only on composition (in the Na2-CaO-FeO-MgO-Al2O3-SiO2 model system), pressure, and temperature. Our 3-D maps are defined horizontally by 27 different tectonic regions and vertically by a number of layers. We find thermochemical differences between oceans and continents to extend down to ∼250 km depth, with continents and cratons appearing chemically depleted (high magnesium number (Mg #) and Mg/Si ratio) and colder (>100°C) relative to oceans, while young oceanic lithosphere is hotter than its intermediate age and old counterparts. We find what appears to be strong radial S wave anisotropy in the upper mantle down to ∼200 km, while there seems to be little evidence for shear anisotropy at greater depths. At and beneath the transition zone, 3-D heterogeneity is likely uncorrelated with surface tectonics; as a result, our tectonics-based parameterization is tenuous. Despite this weakness, constraints on the gross average thermochemical and anisotropic structure to ∼1300 km depth can be inferred, which appear to indicate that the compositions of the upper (low Mg# and high Mg/Si ratio) and lower mantle (high Mg# and low Mg/Si ratio) might possibly be distinct.
Savani: A variable resolution whole-mantle model of anisotropic shear velocity variations based on multiple data sets
Auer, Ludwig; Boschi, Lapo; Becker, Thorsten W.; et al. (2014)
Journal of Geophysical Research: Solid Earth
We present a tomographic model of radially anisotropic shear velocity variations in the Earth's mantle based on a new compilation of previously published data sets and a variable block parameterization, adapted to local raypath density. We employ ray-theoretical sensitivity functions to relate surface wave and body wave data with radially anisotropic velocity perturbations. Our database includes surface wave phase delays from fundamental modes up to the sixth overtone, measured at periods between 25 and 350 s, as well as cross-correlation traveltimes of major body wave phases. Before inversion, we apply crustal corrections using the crustal model CRUST2.0, and we account for azimuthal anisotropy in the upper mantle using ray-theoretical corrections based on a global model of azimuthal anisotropy. While being well correlated with earlier models at long spatial wavelength, our preferred solution, savani, additionally delineates a number of previously unidentified structures due to its improved resolution in areas of dense coverage. This is because the density of the inverse grid ranges between 1.25° in well-sampled and 5° in poorly sampled regions, allowing us to resolve regional structure better than it is typically the case in global S wave tomography. Our model highlights (i) a distinct ocean-continent anisotropic signature in the uppermost mantle, (ii) an oceanic peak in above average ξ<1 which is shallower than in previous models and thus in better agreement with estimates of lithosphere thickness, and (iii) a long-wavelength pattern of ξ<1 associated with the large low-shear velocity provinces in the lowermost mantle.
Deterministic earthquake scenario for the Basel area: Simulating strong motions and site effects for Basel, Switzerland
Opršal, Ivo; Fäh, Donat; Mai, P. Martin; et al. (2005)
Journal of Geophysical Research: Solid Earth
The Basel earthquake of 18 October 1356 is considered one of the most serious earthquakes in Europe in recent centuries (I0 = IX, M ≈ 6.5–6.9). In this paper we present ground motion simulations for earthquake scenarios for the city of Basel and its vicinity. The numerical modeling combines the finite extent pseudodynamic and kinematic source models with complex local structure in a two-step hybrid three-dimensional (3-D) finite difference (FD) method. The synthetic seismograms are accurate in the frequency band 0–2.2 Hz. The 3-D FD is a linear explicit displacement formulation using an irregular rectangular grid including topography. The finite extent rupture model is adjacent to the free surface because the fault has been recognized through trenching on the Reinach fault. We test two source models reminiscent of past earthquakes (the 1999 Athens and the 1989 Loma Prieta earthquake) to represent Mw ≈ 5.9 and Mw ≈ 6.5 events that occur approximately to the south of Basel. To compare the effect of the same wave field arriving at the site from other directions, we considered the same sources placed east and west of the city. The local structural model is determined from the area's recently established P and S wave velocity structure and includes topography. The selected earthquake scenarios show strong ground motion amplification with respect to a bedrock site, which is in contrast to previous 2-D simulations for the same area. In particular, we found that the edge effects from the 3-D structural model depend strongly on the position of the earthquake source within the modeling domain.
Non‐Precursory Accelerating Aseismic Slip During Rupture Nucleation
Wang, Xiaoyu; Dal Zilio, Luca; Morgan, Julia K.; et al. (2023)
Journal of Geophysical Research: Solid Earth
Accelerating aseismic slip events have been commonly observed during the rupture nucleation processes of the earthquake. While that accelerating aseismic slip is usually considered strong evidence for precursory activity, it remains unclear whether all accelerating aseismic slip events are precursory to an incoming earthquake. Two contrasting nucleation models have been introduced to explain the observations associated with the nucleation of unstable slip: the pre-slip and cascade nucleation models. Each of these two-end members, however, has its own limitations. In this study, we employ Discrete Element Method simulations of a 2-D strike-slip fault to simulate various rupture nucleation and triggering processes. Our simulation results manifest that the final seismic event is a product contributed by multiple pre-slip nucleation sites, which may interact, causing clock advance or cascade nucleation rupture processes. We also introduce a strengthening perturbation zone to investigate the role of a single nucleation site in an imminent seismic event. The simulation results reveal a new type of non-precursory aseismic slip, representing the region favoring the generation of the precursory slip process but not correlating to the incoming main event, which differs from the previous interpretation of precursory slip. Furthermore, we include weakening perturbation zones in some simulations to demonstrate how small earthquakes may or may not trigger a nucleation site depending on spatial and temporal conditions. Our simulation results imply that such non-precursory but accelerating aseismic slip events may suggest a fault segment that appears weakly coupled but possesses the potential to be triggered seismically.
Three-dimensional S velocity of the mantle in the Africa-Eurasia plate boundary region from phase arrival times and regional waveforms
Schmid, C.; Lee, S. van der; Decar, J. C. van; et al. (2008)
Journal of Geophysical Research: Solid Earth
A new model of the three-dimensional shear velocity structure of the Africa-Eurasia plate boundary is presented. The new model is derived by jointly inverting different types of seismic data. The two main sources of information are regional waveforms and teleseismic S wave arrival times. We show that it is possible to find a model that fit the different data types nearly as well as when inverting solely one type of data. The main improvement in resolving power is achieved between depths of 300 and 700 km, though the improvements are not limited to this depth range. Our model reflects the complicated evolution of this plate boundary area. The transition zone is dominated by high-velocity anomalies which we infer to represent a mix of lithosphere that subducted relatively recently or is not sufficiently cold and dense to traverse the 660-km discontinuity. The only low-velocity zone in the transition zone is beneath the Ionian Sea. The high-velocity Hellenic slab is continuous throughout the upper mantle and into the lower mantle to about 1200 km, most likely representing subducted Neo-Tethys lithosphere. The uppermost mantle is dominated by low velocities, consistent with the high level of tectonic activity. Low-velocity regions are relatively strong beneath the Mid-Atlantic Ridge, Turkey, and the Dead Sea region. The region's current lithosphere is relatively thin, except beneath the Adriatic and Ionian seas and the easternmost Atlantic Ocean.
Stochastic inversion of geomagnetic observatory data including rigorous treatment of the ocean induction effect with implications for transition zone water content and thermal structure
Munch, Federico D.; Grayver, Alexander; Kuvshinov, Alexey; et al. (2018)
Journal of Geophysical Research: Solid Earth

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