We present the first continental‐scale seismic model of the lithosphere and underlying mantle beneath Southeast Asia obtained from adjoint waveform tomography (often referred to as full‐waveform inversion or FWI), using seismic data filtered at periods from 20 to 150 s. Based on >3,000 hr of analyzed waveform data gathered from ∼13,000 unique source‐receiver pairs, we image isotropic
We present a new 3‐D seismic structural model of the eastern Indonesian region and its surroundings from full‐waveform inversion (FWI) that exploits seismic data filtered at periods between 15–150 s.
- NSF-PAR ID:
- 10382377
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geochemistry, Geophysics, Geosystems
- Volume:
- 23
- Issue:
- 11
- ISSN:
- 1525-2027
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract P ‐wave velocity, radially anisotropicS ‐wave velocity and density via an iterative non‐linear inversion that begins from a 1‐D reference model. At each iteration, the full 3‐D wavefield is determined through an anelastic Earth, accommodating effects of topography, bathymetry and ocean load. Our data selection aims to maximize sensitivity to deep structure by accounting for body wave arrivals separately.SASSY21 , our final model after 87 iterations across seven period bands, is able to explain true‐amplitude data from events and receivers not included in the inversion. The trade‐off between inversion parameters is estimated through an analysis of the Hessian‐vector product.SASSY21 reveals detailed anomalies down to the mantle transition zone, including multiple subduction zones. The most prominent feature is the (Indo‐)Australian plate descending beneath Indonesia, which is imaged as one continuous slab along the 180° curvature of the Banda Arc. The tomography confirms the existence of a hole in the slab beneath Mount Tambora and locates a highS ‐wave velocity zone beneath northern Borneo that may be associated with subduction termination in the mid‐late Miocene. A previously undiscovered feature beneath the east coast of Borneo is also revealed, which may be a signature of post‐subduction processes, delamination or underthrusting from the formation of Sulawesi. -
SUMMARY The detailed structure near the 410-km discontinuity provides key constraints of the dynamic interactions between the upper mantle and the lower mantle through the mantle transition zone (MTZ) via mass and heat exchange. Meanwhile, the temperature of the subducting slab, which can be derived from its fast wave speed perturbation, is critical for understanding the mantle dynamics in subduction zones where the slab enters the MTZ. Multipathing, i.e. triplicated, body waves that bottom near the MTZ carry rich information of the 410-km discontinuity structure and can be used to constrain the discontinuity depth and radial variations of wave speeds across it. In this study, we systematically analysed the trade-off between model parameters in triplication studies using synthetic examples. Specifically, we illustrated the necessity of using array-normalized amplitude. Two 1-D depth profiles of the wave speed below the Tatar Strait of Russia in the Kuril subduction zone are obtained. We have observed triplications due to both the 410-km discontinuity and the slab upper surface. And, seismic structures for these two interfaces are simultaneously inverted. Our derived 410-km discontinuity depths for the northern and southern regions are at 420$\pm $15 and 425$\pm $15 km, respectively, with no observable uplift. The slab upper surface is inverted to be located about 50–70 km below the 410-km discontinuity. This location is between the depths of the 1 and 2 per cent P-wave speed perturbation contours of a regional 3-D full-waveform inversion (FWI) model, but we found twice the wave speed perturbation amplitude. A wave speed increase of 3.9–4.6 per cent within the slab, compared to 2.0–2.4 per cent from the 3-D FWI model, is necessary to fit the waveforms with the shortest period of 2 s, indicating that high-frequency waves are required to accurately resolve the detailed structures near the MTZ.more » « less
-
SUMMARY Türkiye poses a complex crustal structure and tectonic settings owing to the northward convergence of the Arabian and African plates with respect to the Anatolian and Eurasian plates. A reliable 3-D crustal structure of the unruptured segment of the North Anatolian Fault Zone (NAFZ) in the Sea of Marmara is thus of utmost importance for seismic hazard assessments considering that the megacity Istanbul—with more than 15 million habitants—is close to this seismic gap. This study provides high-resolution shear wave velocity images of northwestern Türkiye, including the NAFZ, revealed from ambient seismic noise tomography. We extract over 20 000 Green’s functions from seismic ambient noise cross-correlations and then construct group velocity perturbation maps from the measured group delays with a transdimensional Bayesian tomographic method. We further perform an S-wave velocity inversion to image depth-varying velocity structures. Our high-resolution data allowed us to image S-wave velocities down to 15 km depth and reveal weak crustal zones along the NAFZ, as indicated by low shear wave velocities. We find a low-velocity zone along the Main Marmara Fault, linked with aseismic slip and a deep creep mode. Furthermore, we identify a high-velocity anomaly associated with the unruptured section that defines the boundaries of the locked zone in the crust, which can potentially trigger a destructive earthquake in the future.
-
Abstract An oceanic plateau, the Yakutat terrane, has entered the subduction system across southcentral Alaska. Its down‐dip fate and relationship to overlying volcanism is still debated. Broadband seismometers from the Wrangell Volcanism and Lithospheric Fate (WVLF) temporary experiment were deployed with <20 km spacing across southcentral Alaska to study this region. An array‐based deconvolution procedure is used to isolate the scattered
P andS coda of teleseismicP waves for imaging discontinuity structure. This procedure is applied to WVLF and other dense seismic arrays across southcentral Alaska in a manner that accounts for near‐surface wavespeed variations. Two imaging techniques are employed: two‐dimensional migration and three‐dimensional common‐conversion‐point (CCP) stacking. Migrating the scattered phases along WVLF stations shows the ∼18 ± 4 km thick Yakutat crust subducting beneath the Wrangell Volcanic field to the NNE. It is offset from the Alaska‐Aleutian seismic zone laterally by 250 km to the southeast at 100 km depth, and dips more steeply (45°). At depths <45 km, CCP stacking reveals that the Yakutat crust is continuous for over 450 km along strike. This shallow continuity and deeper offset suggest a tear in the subducting Yakutat slab at depths >45 km, around 146°W. CCP stacking also reveals a continuous thin low‐velocity layer atop the underthrust Yakutat crust for >450 km along strike, at all depths <35 km. The uniform low‐velocity thrust zone indicates consistent properties through multiple rupture‐zone segments, showing that low‐velocity channels generally correspond with subduction megathrusts. -
Abstract Laboratory experiments and geodynamic simulations demonstrate that poloidal- and toroidal-mode mantle flows develop around subduction zones. Here, we use a new 3-D azimuthal anisotropy model constructed by full waveform inversion, to infer deep subduction-induced mantle flows underneath Middle America. At depths shallower than 150 km, poloidal-mode flow is perpendicular to the trajectory of the Middle American Trench. From 300 to 450 km depth, return flows surround the edges of the Rivera and Atlantic slabs, while escape flows are inferred through slab windows beneath Panama and central Mexico. Furthermore, at 700 km depth, the study region is dominated by the Farallon anomaly, with fast axes perpendicular to its strike, suggesting the development of lattice-preferred orientations by substantial stress. These observations provide depth-dependent seismic anisotropy for future mantle flow simulations, and call for further investigations about the deformation mechanisms and elasticity of minerals in the transition zone and uppermost lower mantle.